The coatings were formed on cylindrical Ti6Al4V specimens ground to 1200 grit and chemically activated before immersion in acidic zinc-based phosphating solutions containing different concentrations of Zr4+ and Sr2+. Scanning electron microscopy revealed dendritic, acicular and lamellar phosphate crystals arranged through overlapping and staged growth. S1 produced a rough, broadly continuous layer with relatively few extensive intercrystalline areas. Its crystals had flat faces and well-defined edges, and their orientation suggested a combination of primary and secondary nucleation. S2 developed thicker and longer lamellar crystals with more visible gaps between them. S3 contained more numerous, smaller crystals and had the most compact appearance at low magnification. At higher magnification, however, its structure appeared immature, with fragmented crystals and incomplete cohesion between neighboring grains. Thus, the visual compactness of a coating did not necessarily mean that it was chemically uniform or free of local pathways for electrolyte penetration.

Energy-dispersive X-ray spectroscopy showed zinc, phosphorus and oxygen across all three coatings, together with smaller quantities of zirconium, strontium and iron. The measured zinc-to-phosphorus atomic ratios were approximately 1.34 for S1, 1.60 for S2 and 1.19 for S3. Titanium detected within the coating signals indicated that the analytical beam reached the substrate in some areas, consistent with the thin, heterogeneous layers observed by microscopy. X-ray diffraction identified hopeite, Zn3(PO4)2·4H2O, as the dominant phase in every sample. Phosphophyllite was also detected, as were strontium-zinc phosphate and hydrated zinc-zirconium phosphate phases associated with the added ions. The coatings were therefore multiphase systems rather than pure zinc phosphate layers. Their formation was interpreted as a sequence in which hopeite developed first, phosphophyllite coprecipitated, and strontium- and zirconium-containing phases formed as zinc levels fell, local pH stabilized and the layer entered a slower-growth stage.

Fourier-transform infrared spectroscopy supported the presence of phosphate groups and showed that the three coatings differed in hydration and network structure. Hydroxyl stretching bands between 3600 and 3000 inverse centimetres were strongest and broadest for S3, indicating greater hydration. S2 produced a weaker, narrower band in this region and a shift of the phosphate deformation band from about 602 to 614 inverse centimetres. The researchers associated this shift with stronger Zr-O-P interactions and a stiffer phosphate network, consistent with S2’s relatively compact and less hydrated surface. At the same time, the coating’s chemical properties could not be separated from its morphology. Zirconium concentration promoted larger phosphate crystals, whereas increasing strontium encouraged more nucleation centers and denser growth. The data support a role for both ions in coating formation, but they do not establish that either ion improves biological performance directly.

Potentiodynamic polarization tests showed that coating superiority could change with the surrounding medium. In Ringer solution, S1 had a corrosion current density of 24.7 nanamperes per square centimetre and a corrosion rate of 0.22 micrometres per year. S2 and S3 produced rates of 0.38 and 0.34 micrometres per year, respectively, still below the alloy’s 2.94 micrometres per year. S3 recorded the highest polarization resistance, 764.8 kilohm square centimetres, but that barrier measure did not translate into the lowest corrosion rate. The investigators distinguished these outcomes: S1 provided the strongest kinetic suppression of electrochemical reactions, whereas S3 offered the greatest barrier resistance and S2 the most positive corrosion potential in Ringer solution. Local penetration through intercrystalline areas could sustain corrosion even when the coating as a whole displayed a substantial overall resistance.

The same medium-dependent pattern appeared in Dulbecco’s Phosphate-Buffered Saline and Earle’s Balanced Salt Solution. In DPBS, S2 had the lowest corrosion current density, at 18.6 nanamperes per square centimetre, and the lowest corrosion rate, at 0.16 micrometres per year. S1 had the highest polarization resistance in this medium, while S3 showed more pronounced local activity and a corrosion rate of 0.74 micrometres per year. In EBSS, S3 produced the lowest rate, 0.21 micrometres per year, and the most positive corrosion potential; S2 retained the highest polarization resistance, 662.4 kilohm square centimetres. The study attributed the variation to electrolyte composition: chloride-containing Ringer solution could expose defective regions, phosphate-containing DPBS could promote passivation and pore blocking, and the chemically complex EBSS could promote hydration, ion exchange and reorganization of the coating. A formulation that ranked first under one set of conditions therefore did not necessarily rank first under another.

Electrochemical impedance spectroscopy reinforced the distinction between barrier performance and localized reactions. Fitted equivalent circuits associated the coated systems with a phosphate-layer resistance, an interfacial or pore resistance, and a charge-transfer resistance at the metal-electrolyte interface. S1 in Ringer solution had a charge-transfer resistance approximately 300 times that of uncoated Ti6Al4V, while S2’s phosphate-layer resistance reached 1.83 million ohm square centimetres. In DPBS, S2 combined a high external-layer resistance with a low current density, consistent with effective suppression of ion transfer. In EBSS, the S3 system required a Warburg diffusion element, indicating that ionic transport through hydrated or intergranular regions contributed to its response. Even with substantial impedance, low-resistance pathways remained detectable. The data therefore support a barrier mechanism while showing that coating continuity, phase stability, hydration and electrolyte-driven changes must be considered together rather than treating density or total surface coverage as sufficient measures of protection.

Wettability measurements showed that phosphating shifted Ti6Al4V from a largely hydrophobic state toward greater affinity for aqueous liquids. The water contact angle of the uncoated alloy was 89.1 degrees, whereas the initial values for S1, S2 and S3 were 43.2, 53.2 and 57.4 degrees, respectively. The coatings’ polar surface-energy components increased to roughly 19–22 millinewtons per metre, compared with 7.7 for the bare alloy. S1 had the greatest initial hydrophilicity, consistent with a lamellar surface that allowed liquid to enter intercrystalline spaces. S2 combined high roughness with a less hydrated and more strongly bonded phosphate network, while S3’s dense fine-grained structure limited capillary spreading despite its greater chemical hydration. These measurements show that contact angle depends on both surface chemistry and physical topography. They do not, by themselves, establish improved cell attachment, tissue integration or implant performance.

Exposure to the test solutions also changed the wettability of the coated surfaces. S1’s Ringer contact angle rose from 50.8 to 62.0 degrees as its polar surface-energy component fell to 16.5 millinewtons per metre. In EBSS, by contrast, its contact angle decreased from 65.2 to 56.3 degrees and its polar component rose to 27.7 millinewtons per metre, behavior consistent with hydration and chemical reorganization in the complex medium. S2’s contact angle in EBSS fell to 47 degrees while the polar component increased to 26.04 millinewtons per metre, even though its electrochemical resistance remained high. S3 retained nearly unchanged wettability in Ringer and DPBS but developed a lower polar component after EBSS exposure, consistent with reaction products that may seal local pathways. Overall, S2 provided the most consistently stable barrier response, S3 was especially effective in EBSS and maintained more predictable wetting, and S1 performed best in Ringer solution. Because the study used electrochemical and surface measurements without direct biological testing, claims about osseointegration, antibacterial activity, osteogenic response or clinical benefit remain unverified.

Subject of Research: Effects of zirconium and strontium on zinc-based phosphate conversion coatings for Ti6Al4V alloy

Article Title: Effect of Zr4+ and Sr2+ addition on morphology, surface characteristics, and corrosion behavior of a new functional Zn-based phosphate conversion coating deposited on Ti6Al4V

Article References: Burduhos Nergis, D. P., Istrate, B., Epure, E.-L., Cazac, A., Bejinariu, C., Sandu, A.-V., & Burduhos-Nergis, D.-D. (2026). Effect of Zr4+ and Sr2+ addition on morphology, surface characteristics, and corrosion behavior of a new functional Zn-based phosphate conversion coating deposited on Ti6Al4V. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13824-3

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13824-3

Keywords: Ti6Al4V, phosphate conversion coating, zirconium, strontium, corrosion resistance, electrochemical impedance, surface chemistry, wettability, biomaterials, Effect, addition, morphology

Organosilanes occupy a unique position in biosensor engineering because they spontaneously organize into ordered, bifunctional molecular assemblies—what the authors call adlayers—on hydroxylated surfaces of inorganic and organic materials. The architecture is elegantly modular. A silyl tail function, typically a trialkoxysilyl or trichlorosilyl group, anchors to the substrate. A distal head function dictates the surface’s chemical properties and provides the reactive handle for covalently attaching a probe of choice. Between them sits an organic backbone that spaces the head group away from the surface and reinforces the assembly through intermolecular forces. In theory, this modularity offers countless chemical permutations; in practice, the authors note, the availability of head functions compatible with the highly reactive silyl tail is severely limited, since nucleophilic groups such as alcohols, carboxylic acids, and amines interfere with adlayer formation and must be protected or introduced after assembly.

The mechanism by which these adlayers form remains an active area of debate, but a broad consensus has emerged around a multi-step process. Surface-adsorbed water molecules first hydrolyze the trichlorosilyl or trialkoxysilyl moiety into a trisilanol anchoring group. This cross-linker then diffuses to the surface-solution interface, where it undergoes reversible adsorption and desorption punctuated by multiple condensation reactions with surface hydroxyl groups. Islands nucleate across the surface, expand during a reorganization phase, and aggregate into a coherent adlayer that is further strengthened by covalent cross-linking between neighboring silanols. Van der Waals forces between adjacent organic backbones add rigidity, order, and stability to the finished film.

The commercial backbone of the field remains the bifunctional propyltrialkoxysilanes. (3-Aminopropyl)trimethoxysilane (APTMS) and (3-aminopropyl)triethoxysilane (APTES) terminate in amino head groups that can be coupled to carboxylic acid functions on probe molecules via EDC-NHS chemistry or to amino groups after pre-activation with glutaraldehyde. This flexibility has made them staples for immobilizing proteins and peptides on silicon dioxide, alumina, and aluminum nitride. Related linkers include the mercapto compounds MPTMS and MPTES, whose sulfhydryl heads form disulfide bonds with thiol-bearing probes, and the glycidoxy compounds GPTMS and GPTES, whose strained three-membered epoxide rings open readily when attacked by nucleophilic atoms on the probe, forging a new covalent bond in the process.

Yet these commercial workhorses carry significant liabilities that the review does not shy away from. The amino-terminated linkers demand costly pre-activating or coupling agents. The thiol-bearing variants suffer from cross-reactivity, in which the sulfhydryl group of one immobilized linker forms a disulfide bond with that of a neighbor, effectively shutting down the very chemistry needed to anchor thiol-bearing probes. The glycidoxy counterparts react promiscuously with a wide range of nucleophilic groups, restricting their use largely to simple organic molecules rather than complex biological probes.

These shortcomings have driven interest in functionalizable alkyltrichlorosilanes, a class of linkers synthesized by converting terminal alkene precursors into trichlorosilyl anchoring groups via the classical catalytic hydrosilylation reaction using trichlorosilane and chloroplatinic acid hexahydrate. Among the most prominent examples, developed in the Thompson laboratory, are linkers bearing pentafluorophenyl ester (PFP) and benzenethiosulfonate (BTS) head functions. The PFP moiety reacts potently with primary amine residues to form strong amide bonds, while the BTS head function exhibits regioselectivity for sulfhydryl groups, forming disulfide bonds without cross-reacting with itself. In one demonstration, PFP-modified AT-cut quartz surfaces were functionalized with nitrilotriacetic acid moieties that subsequently captured polyhistidine-tagged heat shock protein 10 via nickel(II) coordination—entirely avoiding the activating agents required by traditional APTMS and APTES chemistry. In a separate application, BTS-based adlayers were imposed onto aluminum nitride thin films, an alternative piezoelectric substrate being considered for future acoustic wave biosensors, and validated with thiolated biotin as a proof of concept.

Perhaps the most consequential advance highlighted in the review involves ethylene glycol (EG) as an organic backbone. EG moieties are well documented for their ability to reduce adsorption of proteins and cells from biological fluids, a property that directly addresses non-specific adsorption—the fouling problem that undermines biosensor selectivity and sensitivity in real-world samples. The Toronto group’s MEG-OH spacer molecule, containing a single EG unit and terminating in a hydroxyl head function, was synthesized via a trifluoroacetyl ester precursor (MEG-TFA) that is deprotected after assembly. When incorporated into acoustic wave biosensor experiments on AT-cut quartz, this single EG moiety produced a dramatic reduction in fouling from undiluted serum. Molecular dynamics calculations and neutron reflectometry experiments suggest the EG backbone facilitates formation of a distinct interfacial water barrier that imposes an energetic cost to perturbation and suppresses the protein dehydration process during adsorption.

Counterintuitively, more EG is not always better. The team synthesized trifluoroacetyl ester-bearing trichlorosilanes with seven, ten, and thirteen EG units, deprotected them to expose hydroxyl head functions, and tested the resulting adlayers against undiluted goat serum. The shortest chain, 7-OEG, exhibited substantially lower fouling than its longer counterparts, despite containing fewer EG groups. The authors attribute this to packing density: shorter molecules leave gaps that allow water to penetrate and form the protective interstitial zone, while longer, more densely packed chains obstruct this hydration layer. It is a striking example of how molecular-scale geometry, not simply chemical composition, governs macroscopic biosensor performance.

The review also showcases MEG-Cl, a sister molecule to MEG-OH that functions simultaneously as a probe-attachment linker and an antifouling spacer. MEG-Cl chemistry has been used to attach nickel-NTA groups for recombinant protein capture and to reduce fouling from serum and milk samples. Most strikingly, it has been deployed in an aptamer-based acoustic wave sensor for Escherichia coli, where the aptamer is covalently tethered to the quartz surface through the antifouling linker. That sensor achieved detection limits of 35 and 8 colony-forming units per milliliter in phosphate-buffered saline and cow’s milk, respectively—well below safety thresholds for commercial dairy products.

Looking forward, Chan and Thompson identify several unresolved challenges that will shape the next generation of silane chemistry. Transducer materials must present sufficient surface hydroxyl groups for condensation chemistry to proceed, which is straightforward for metals but difficult for polymers, where oxygen plasma treatment may be required. Achieving ideal lateral spacing of probes—dense enough for sensitivity, yet spaced enough to avoid steric interference between neighboring recognition sites—remains a delicate balancing act. And the question of probe orientation, rarely addressed in the field, looms large: attachment chemistry can inadvertently block the very recognition site a sensor depends on. Their proposed solution is a new class of head groups designed to target biologically meaningful motifs, such as polyhistidine tags terminally generated during protein expression, offering a route to immobilize virtually any protein of interest with controlled orientation. If successful, this could close the loop on decades of silane chemistry, transforming a workhorse technique into a precision tool for the biosensors of tomorrow.

Subject of Research: Organosilane surface chemistry for probe attachment to biosensor substrates

Article Title: Appraisal of organosilane surface modification for probe attachment to biosensor substrates

Article References: Chan, E., & Thompson, M. (2026). Appraisal of organosilane surface modification for probe attachment to biosensor substrates. Frontiers in Sensors, 7, Article 1774304. https://doi.org/10.3389/fsens.2026.1774304

Image Credits: AI Generated

DOI: 10.3389/fsens.2026.1774304

Keywords: biosensors, organosilane, surface chemistry, antifouling, probe immobilization, acoustic wave sensors, ethylene glycol, non-specific adsorption, Appraisal, surface, modification, probe

The research team, led by Qiaona Wang and Yuan Yu, set out to address a stubborn engineering problem. Conventional oils and greases evaporate, decompose, or oxidize under high-temperature or vacuum conditions, leading to unstable viscosity, carbonaceous deposits, and catastrophic film failure. They also conduct heat and electricity poorly, which is a serious handicap in bearings that must simultaneously manage thermal loads and survive intense irradiation in confined spaces. Traditional liquid metals such as lead and mercury offer superb thermal and electrical conductivity, but their toxicity severely limits their use. Gallium-based alloys, particularly the ternary mixture of gallium, indium, and tin known as Galinstan or GIS, sidestep these objections with a low melting point near room temperature, negligible vapor pressure, and comparatively low toxicity.

What makes the new work distinctive is the choice of rubbing materials. Previous liquid-metal lubrication studies mostly examined copper, aluminum, and steel combinations, but precision bearings in radiation equipment are typically built from molybdenum and its alloys, which combine high melting points, high hardness, excellent high-temperature strength, and low thermal expansion. The researchers therefore tested a self-mated molybdenum pair — a pin rotating against a disk of the same metal — lubricated with GIS from room temperature up to 300 degrees Celsius, in both air and argon. Under dry sliding in air, the bare molybdenum surfaces performed poorly, with friction coefficients hovering between 0.51 and 0.65 and severe adhesive wear, plowing, and spalling visible across the worn tracks.

Introducing the liquid metal in air transformed the picture. The average friction coefficient dropped to 0.31 at room temperature and 0.32 at 100 degrees, remaining below the dry-sliding values across the entire range. More striking still was the wear suppression: the wear rate of the molybdenum disk plummeted from 135.2 to just 0.8 thousandths of a cubic millimeter per newton-meter at room temperature, and stayed between 0.8 and 2.7 in those units all the way to 300 degrees — a reduction of 90.9 to 99.4 percent. Electron microscopy of the worn surfaces confirmed the visual difference: instead of deep tearing and spalling pits, the lubricated surfaces appeared shallow and smooth, with only fine abrasive traces.

The surprise came when the same tests were repeated in argon, an inert atmosphere where oxidation is suppressed. At room temperature, the liquid metal actually performed slightly better in argon than in air, achieving a friction coefficient of 0.27. But as the temperature climbed, the inert-atmosphere results deteriorated dramatically. Friction rose to 0.54 at 100 degrees, 0.64 at 200 degrees, and 0.70 at 300 degrees — approaching or exceeding the dry-sliding values — while the wear rate at 300 degrees reached 15.6, roughly nine times higher than in air. A lubricant that thrives in a vacuum-like environment is normally the goal of space tribology; here, the absence of oxygen turned a winning lubricant into a failing one.

The explanation lies in the delicate chemistry of the interface. Using X-ray photoelectron spectroscopy, the team detected both metallic gallium and oxidized gallium on the worn surfaces, with the oxidized Ga3+ component dominating in air. As temperature increased, the proportion of gallium oxides grew, and the XPS Ga3+/Ga0 ratio was 3.30 in air compared with only 2.86 in argon, confirming that the inert atmosphere partially throttled gallium oxidation. Notably, the Mo 3d spectra showed only metallic molybdenum, with no evidence of gallium-molybdenide compounds forming up to 300 degrees — the protective film is not a reaction product of the two metals but a Ga-O-rich layer built on the liquid metal itself.

Cross-sectional analysis of the samples tested in argon revealed why the failure was so severe. Energy-dispersive mapping showed gallium concentrated near the worn surface and, more troublingly, extending into the mechanically damaged subsurface region of the molybdenum. Nanoindentation measurements in these gallium-affected zones recorded lower hardness and reduced resistance to plastic deformation compared with the pristine substrate. In other words, when oxygen is unavailable to lock the gallium into a stable oxide film, the liquid metal seeps into surface defects and softens the near-surface material, promoting cracking, layered delamination, and shear instability under the repeated stresses of sliding.

Temperature also produced a curious non-monotonic pattern in air, with the wear rate under liquid-metal lubrication rising from room temperature to a peak at 200 degrees before falling again at 300 degrees. The researchers attribute this to an intermediate state: at 200 degrees, gallium oxidation is still insufficiently extensive, so the Ga-O-rich tribofilm remains patchy and delamination features appear on the worn surface. By 300 degrees, more thorough oxidation produces a continuous, protective film that separates the surfaces effectively. The team proposes an overall mechanism in which the liquid metal first spreads into surface asperities and reduces direct metal-to-metal contact, then the oxygen-driven oxide film forms and reforms under frictional shear, repeatedly rupturing and replenishing while shielding the molybdenum from direct exposure to the softening gallium.

Load-dependence tests at 7 and 13 newtons confirmed that the 10-newton condition used in the main experiments delivered the lowest friction and wear among the tested loads, and the wear measurements were repeated at least three times for statistical reliability. The authors are candid about the study’s limits: the tests used fixed operating conditions, so stability under broader loads, speeds, and long-duration service remains unverified, and the absence of pristine-liquid-metal XPS controls and nanoscale transmission electron microscopy means the relative contributions of native, thermal, and friction-assisted oxidation cannot yet be fully separated.

Even so, the study delivers a genuinely counterintuitive design principle with wide implications. For molybdenum bearings destined for X-ray sources, nuclear installations, and medical equipment, the trick is not to exclude oxygen but to embrace a moderate, regulated amount of it, allowing engineers to co-design the lubricant and the atmosphere as a single system. Gallium-based liquid metals, with their metallic conductivity and vapor-free fluidity, could anchor a new generation of functional lubricants in which the environment itself becomes part of the machinery — provided the oxygen supply is tuned just right.

Subject of Research: Atmosphere-regulated lubrication of molybdenum friction pairs by gallium-based liquid metal across a wide temperature range

Article Title: Oxidation-regulated wide-temperature tribological behavior and mechanism of a Mo/Mo tribopair lubricated by Ga-based liquid metal

Article References: Wang, Q., Liu, H., Zhang, G., Li, T., Cui, H., Feng, X., Yu, Y., Ma, Z., Wang, X., Qiao, Z., & Tang, H. (2026). Oxidation-regulated wide-temperature tribological behavior and mechanism of a Mo/Mo tribopair lubricated by Ga-based liquid metal. iScience, 29(11), Article 117805. https://doi.org/10.1016/j.isci.2026.117805

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117805

Keywords: gallium-based liquid metal, tribology, molybdenum, lubrication, Ga-O tribofilm, high-temperature friction, oxidation, wear reduction, Galinstan, precision bearings, XPS, surface chemistry

The appeal of model catalysts lies in their simplicity. Industrial ethylene epoxidation catalysts consist of silver particles dispersed on porous alumina, often promoted with chlorine, cesium, and other additives. That complexity is a nightmare for mechanistic studies: signals from the support, the promoters, and the metal all overlap in spectroscopic measurements, and the roughness of the porous support frustrates high-resolution imaging. A model catalyst replaces this tangled system with a flat, chemically well-defined substrate carrying metal particles whose size, shape, and density are controlled by the experimenter. HOPG, with its atomically flat and chemically inert basal planes, has long been a favorite support for such studies. The catch is that silver does not wet graphite well, so depositing enough metal to cover a useful fraction of the surface without producing a continuous film is a genuine materials challenge.

The Novosibirsk group, led by Anna Nartova together with coauthors including Alexandra Ananina, Aleksey Dmitrachkov, Ren Kvon, Maxim Panafidin, Boris Andryushechkin, and Valerii Bukhtiyarov, set out to prepare samples with large silver particles and high surface coverage, precisely the combination needed for X-ray photoelectron spectroscopy, or XPS, studies of the epoxidation reaction. XPS is exquisitely sensitive to the chemical state of surface atoms, but it needs a substantial amount of the element of interest to produce strong, interpretable signals. If silver particles are too small or too sparse, the spectrum is dominated by the graphite support and the oxygen-bearing species on the silver cannot be tracked reliably. Large particles, in contrast, generate robust Ag 3d and O 1s signals, but growing them uniformly across a flat support is easier said than done.

The researchers compared several preparation routes, and the results reveal how sensitively the final catalyst morphology depends on the details of the deposition process. One approach involved damaging the graphite basal plane by etching with argon ions before depositing silver. The logic is straightforward: defects on the otherwise inert graphite surface act as nucleation sites where silver atoms can anchor, potentially increasing the density of particles and the coverage they achieve. In practice, however, the strategy produced two unwelcome side effects. First, the dense population of closely spaced particles merged as they grew, forming a film-like silver coating rather than the discrete, well-separated particles that mechanistic studies require. Second, and perhaps more insidiously, the damaged graphite promoted encapsulation of silver particles by carbon layers, a phenomenon known as Ag-C encapsulation, in which the metal becomes partially buried beneath graphitic material.

Both effects are fatal for the intended purpose. A film-like coating no longer models the dispersed particles of a real catalyst, so any particle-size or geometry effects on reactivity are lost. Encapsulation is worse still, because it changes which silver atoms are actually exposed to the reactant gases and can create misleading spectroscopic signatures. A sample whose active surface is partially hidden under carbon cannot serve as a trustworthy platform for studying how oxygen species on silver convert ethylene to ethylene oxide. The authors conclude that argon-ion etching of the graphite basal plane, whatever its benefits for nucleation density, makes such samples unsuitable for reaction mechanistic studies, a cautionary finding for anyone tempted to use defect engineering to boost metal loading on graphitic supports.

The winning strategy was far less invasive: thermal vacuum deposition of silver using an electron-beam evaporator onto freshly peeled HOPG. By cleaving the graphite immediately before deposition, the researchers ensured an atomically clean basal plane free of adsorbed contamination, and the gentle thermal evaporation allowed silver to aggregate into discrete particles on the pristine surface. The resulting samples featured uniformly distributed, relatively flat silver particles with mean sizes that could be controlled across a range of roughly 30 to 100 nanometers. Crucially, the silver coverage reached up to 0.59 of the support surface area, meaning that nearly sixty percent of the graphite was decorated with silver particles, a loading high enough to yield strong XPS signals while still preserving the discrete-particle morphology that mechanistic work demands.

Quantifying these morphologies required more than eyeballing micrographs. The team combined scanning electron microscopy, scanning tunneling microscopy, and XPS with deep-learning image analysis, using tools developed by the group to extract particle-size distributions, the number of silver particles per unit area, and the fraction of the support covered by metal. This is a notable methodological point in its own right: manual counting of thousands of nanoparticles across multiple imaging modalities is slow and prone to operator bias, whereas convolutional neural networks can process microscopy images consistently and at scale. The deep-learning approach, which the authors have previously applied to scanning transmission electron microscopy data and to automated analysis of X-ray photoelectron spectra, allowed rigorous comparison between preparation methods on objective, quantitative footing.

The study also probed how the prepared samples behave under thermal treatment, a question of direct relevance to reaction conditions. When a sample containing 100-nanometer silver particles was annealed in vacuum at 500 degrees Celsius, the particles underwent Ostwald ripening, the classic coarsening process in which small particles shrink and disappear as their atoms migrate to feed larger neighbors. Ripening reduces the number of particles and shifts the size distribution upward, which means that any catalytic measurement performed after high-temperature treatment reflects a different surface than the one initially prepared. Documenting this behavior on the model system provides a benchmark for how much thermal history a given sample has experienced and helps researchers design experiments in which the particle population is stable, or at least well characterized, throughout the measurement.

The final validation came from the oxygen signal. Analysis of the O 1s XPS line confirmed that the prepared low-oxygen Ag/HOPG systems are suitable model catalysts for instrumental studies of ethylene epoxidation. In other words, the surfaces carry silver in a state where adsorbed and reactive oxygen species can be detected and distinguished from background oxygen on the support, opening the door to in situ experiments that track the chemical identity of the oxygen species responsible for selective epoxidation. That question, whether electrophilic oxygen species, nucleophilic oxygen, or some combination drives the selective pathway, has animated the epoxidation literature for years, and clean model systems are the key to answering it with spectroscopic rather than circumstantial evidence.

The broader significance of the work extends beyond one reaction. Ethylene epoxidation is a touchstone of heterogeneous catalysis, the rare example of a direct, selective oxidation of a hydrocarbon by molecular oxygen, and silver remains the only metal that performs it industrially. Recent studies continue to probe particle-size effects, the role of chlorine promoters, and the structure of active oxygen species on silver, and some groups are even exploring whether additives such as nickel can extend selective epoxidation beyond silver itself. All of these efforts depend on well-characterized surfaces, and the Novosibirsk study delivers a practical recipe: avoid damaging the graphite, deposit silver gently on freshly cleaved HOPG, control the mean particle size through deposition conditions, and verify the morphology with machine-learning-assisted microscopy. The result is a family of model catalysts with large, flat, uniformly distributed silver particles and coverage approaching sixty percent of the support, ready for the in situ XPS and scanning tunneling microscopy experiments that may finally pin down how silver turns ethylene into one of the chemical industry’s most valuable building blocks. The work was supported by the Russian Science Foundation under grant 24-63-00037.

Subject of Research: Preparation of silver-on-graphite model catalysts for ethylene epoxidation studies

Article Title: Model Ag/HOPG Catalysis for Ethylene Epoxidation: Comparison of Methods for the Preparation of Large Ag Particles with High Surface Coverage

Article References: Nartova, A. V., Ananina, А. A., Dmitrachkov, A. M., Kvon, R. I., Panafidin, M. A., Andryushechkin, B. V., & Bukhtiyarov, V. I. (2026). Model Ag/HOPG Catalysis for Ethylene Epoxidation: Comparison of Methods for the Preparation of Large Ag Particles with High Surface Coverage. Catalysis Letters, 156(11), Article 295. https://doi.org/10.1007/s10562-026-05538-7

Image Credits: AI Generated

DOI: 10.1007/s10562-026-05538-7

Keywords: silver catalysts, HOPG, ethylene epoxidation, XPS, scanning tunneling microscopy, scanning electron microscopy, nanoparticles, Ostwald ripening, deep learning image analysis, surface chemistry, heterogeneous catalysis, model catalysts

Biochar-derived activated carbon, abbreviated BAC in the literature, begins its life as ordinary biomass. Feedstocks are converted to biochar through pyrolysis—heating in the absence of oxygen—or through hydrothermal carbonization, a wet process that uses pressurized water at moderate temperatures. Each route leaves a distinct fingerprint on the resulting material. Pyrolysis tends to produce more aromatic, carbon-rich structures, while hydrothermal carbonization yields hydrochars with abundant oxygen-containing functional groups and is particularly well suited to wet feedstocks such as food-industry sludge and sewage. The review emphasizes that the choice of feedstock matters enormously: lignin-rich woods behave differently from cellulose-rich agricultural residues, and the mineral content of the original biomass—its inherent potassium, calcium, or silica—can itself influence pore development during subsequent processing.

The real magic happens during activation, the step that converts a relatively inert char into a highly porous adsorbent. Physical activation uses steam or carbon dioxide at high temperatures, gently gasifying the carbon skeleton and carving out an intricate network of pores. Chemical activation, by contrast, impregnates the char with agents such as potassium hydroxide, phosphoric acid, or zinc chloride before heating, dramatically accelerating pore formation and often producing far higher surface areas. The review notes that chemical activation with KOH remains the workhorse of the field, generating microporous materials with exceptional adsorption capacities, but it comes at an environmental cost: corrosive chemicals, substantial water consumption for washing, and energy-intensive heating. Physical activation with CO2, while yielding lower surface areas, is considerably greener—and, intriguingly, studies cited in the review show that CO2-activated carbons can outperform KOH-activated counterparts in certain electrochemical applications, suggesting that greener is not always worse.

One of the most important conceptual contributions of the review is its insistence that the widely reported BET surface area—a standard measure of internal surface derived from nitrogen gas adsorption—is an incomplete predictor of adsorption performance. Two carbons with identical surface areas can behave very differently in real water treatment. What matters is pore accessibility: whether contaminant molecules can actually reach the adsorption sites. Micropores, those smaller than two nanometers, are ideal traps for small molecules and hydrated metal ions, but they can exclude or slow the diffusion of larger contaminants. Mesopores, between two and fifty nanometers, act as transport highways that speed larger molecules such as dyes and pharmaceuticals toward the interior. The most effective adsorbents are often hierarchically porous, combining both regimes in a single particle. Crystallinity and the degree of structural disorder also play a role, as does the transport behavior of water within the pore network.

Surface chemistry is the second pillar of the framework. Oxygen-containing groups such as carboxyl, hydroxyl, and carbonyl functionalities can dramatically enhance the uptake of polar contaminants and heavy metals through electrostatic attraction, hydrogen bonding, and complexation. Nitrogen doping introduces basic sites that bind acidic pollutants, while sulfur and phosphorus functionalities offer additional binding chemistries. The review stresses that these groups are not merely decorative; they determine the point of zero charge of the material, its wettability, and its affinity for specific classes of pollutants. For heavy metals such as lead, manganese, iron, and zinc, surface complexation with oxygen groups often dominates. For organic dyes such as methylene blue and Rhodamine B, a combination of pi-pi stacking interactions with the aromatic carbon skeleton and electrostatic interactions with charged surface groups governs uptake.

Perhaps the most timely section of the review concerns per- and polyfluoroalkyl substances, the notorious PFAS family of ‘forever chemicals’ that includes PFOA and PFOS. These compounds, used for decades in non-stick coatings, firefighting foams, and water-repellent fabrics, are extraordinarily resistant to degradation and have contaminated water supplies worldwide. Adsorption is currently one of the most practical remediation strategies, and the review highlights that PFAS capture is strongly influenced by hydrophobic and fluorophilic interactions rather than simple pore filling. The fluorinated tails of PFAS molecules seek out hydrophobic carbon domains, while the charged head groups interact with surface functionalities. Recent studies cited in the review demonstrate that biochar-derived carbons—including those made from invasive water hyacinth and from microalgae residues left over after lipid extraction—can achieve meaningful PFOS removal under neutral pH conditions, particularly when activated by microwave-assisted methods that rapidly develop the right pore architecture.

The breadth of contaminants addressed by BAC is remarkable. The reviewed literature documents successful removal of pharmaceuticals such as amoxicillin, ibuprofen, acetaminophen, tetracycline, and fluoroquinolone antibiotics; industrial dyes; the herbicide glyphosate; the endocrine disruptor bisphenol A; arsenic from contaminated drinking water in Pakistan; and phosphate recovered from wastewater for reuse as fertilizer. In many cases, adsorbents made from humble feedstocks—mango seeds, olive stones, tea stalks, date palm waste, ginkgo leaves, potato peel—achieve removal efficiencies approaching those of commercial activated carbon, at a fraction of the cost and with the added benefit of valorizing waste streams. Kinetic and thermodynamic analyses across these studies consistently show that adsorption is fast in the initial stages, slows as sites fill, and follows pseudo-second-order kinetics in many systems, indicating chemisorption contributions alongside physical adsorption.

Yet the review is refreshingly honest about the sustainability challenges that stand between laboratory success and real-world deployment. Chemical activation consumes large quantities of corrosive reagents and generates acidic or alkaline wastewater that must itself be treated. Pyrolysis and activation furnaces are energy-hungry, and if that energy comes from fossil fuels, the net environmental benefit shrinks. Regeneration of spent adsorbent—essential for economic viability—often requires thermal treatment that can degrade surface functionality and collapse pore structure. Scale-up remains the elephant in the room: a synthesis that works beautifully with grams of feedstock in a muffle furnace may fail economically at the ton scale. The authors argue that rigorous life cycle assessment and techno-economic analysis must become standard companions to adsorption studies, rather than afterthoughts.

To overcome these hurdles, the review proposes three forward-looking strategies. Hybrid activation, which combines mild chemical pre-treatment with physical activation, can reduce chemical consumption while preserving high porosity. Low-chemical processing routes, including mechanochemical activation—where ball milling induces porosity without liquid reagents—and microwave-assisted heating, which delivers energy directly to the carbon and slashes processing times, offer greener alternatives. Most intriguingly, the authors highlight artificial intelligence as an emerging tool: machine learning models trained on published datasets can predict how feedstock composition and process parameters will shape pore structure and adsorption capacity, allowing researchers to navigate the vast design space of biomass, activation agent, temperature, and residence time far more efficiently than trial and error. Evolutionary algorithms have already been used to optimize co-pyrosis of biomass with plastic wastes, and similar approaches are being applied to porous carbon design for energy storage, a field whose insights transfer readily to adsorption.

The vision that emerges from this review is one of circular economy chemistry at its most elegant: agricultural waste becomes a purification material, contaminated water becomes clean, and the carbon locked in biomass is kept out of the atmosphere in the process. Biochar itself is increasingly recognized as a carbon sequestration tool, and diverting a portion of biochar production into high-value adsorbents could improve the economics of carbon removal schemes. For the billions of people who lack access to safely managed drinking water, and for the ecosystems degraded by industrial effluents, the prospect of cheap, locally produced adsorbents made from regional waste streams is genuinely transformative. The Indonesian-led team, supported by the country’s Ministry of Higher Education, Science and Technology, has provided the field with a coherent roadmap—one that links the molecular details of activation chemistry to the global challenge of clean water, and that makes clear the path forward runs through smarter processing, honest sustainability accounting, and a willingness to let machines help us design the materials of a cleaner future.

Subject of Research: Biochar-derived activated carbon for sustainable water purification and contaminant adsorption

Article Title: Green activated carbon from biochar waste: linking activation pathways, surface chemistry, and adsorption performance for water purification

Article References: Zharvan, V., Ihsan, N., Subaer, S., Samnur, S., Sutikno, S., Diantoro, M., Suryana, R., & Sujiono, E. H. (2026). Green activated carbon from biochar waste: linking activation pathways, surface chemistry, and adsorption performance for water purification. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38281-y

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38281-y

Keywords: activated carbon, biochar, water purification, adsorption, PFAS, pyrolysis, hydrothermal carbonization, surface chemistry, porous materials, circular economy, wastewater treatment, sustainability

The paradox centers on two classic tools of the synthetic chemist: Lewis acids and Lewis bases. A Lewis base is a molecule that donates an electron pair, and it naturally seeks out positively charged, or cationic, defects on the perovskite surface. A Lewis acid, which accepts an electron pair, does the complementary job on negatively charged, or anionic, defects. In principle, adding both to a solar cell should heal both classes of defect at once. In practice, the strategy has repeatedly failed for the most fundamental of reasons: acids and bases react with each other. When mixed, they form stable adducts, quenching one another’s reactivity before either molecule ever reaches the defect it was designed to neutralize. The result is a passivation cocktail that neutralizes itself.

The new study, published in Nature Chemistry on 23 September 2026 and led by Donghoon Shin and Shuta Kitade under the supervision of Bin Chen and Edward H. Sargent, with Chad A. Mirkin and Mercouri G. Kanatzidis among the senior co-authors, sidesteps this self-defeating chemistry by making the two passivators chemically orthogonal. Orthogonality here means that each molecule reacts with its intended target on the perovskite surface but essentially ignores its partner in the solution. The key insight is geometric rather than electronic: the researchers exploited steric hindrance, the physical bulk of molecular groups, to keep the acid and base from getting close enough to share electrons.

The molecular design hinges on a family of bulky sp3-phosphine Lewis bases. Phosphines, compounds built around a trivalent phosphorus atom, are workhorse Lewis bases in coordination chemistry. By decorating the phosphorus center with bulky substituents arranged in tetrahedral, sp3-hybridized geometry, the team created bases whose lone electron pair is shielded by a thicket of atoms. When paired with fluorinated aromatic Lewis acids, these sterically congested phosphines simply cannot achieve the orbital overlap needed to form a conventional acid-base adduct. The fluorinated aromatic acids, for their part, are relatively weak and geometrically restrained acceptors, so the mutual attraction that normally dooms mixed acid-base formulations is suppressed at its source.

Crucially, the strategy works because of an asymmetry in accessibility. The defect sites on the perovskite surface, such as undercoordinated lead ions and halide vacancies, protrude from the crystal lattice and are more sterically exposed than the crowded acid-base pair is to itself. In other words, each passivator can still reach its target defect even though the two passivators cannot reach each other. The researchers describe this as a sterically gated arrangement, in which molecular bulk acts as a selective filter: small, exposed defect sites pass through the gate, while the bulky acid-base encounter does not. Spectroscopic measurements, including nuclear magnetic resonance and infrared techniques, along with defect-profiling methods such as drive-level capacitance profiling, support the picture that the two additives suppress trap states additively rather than destructively.

The photophysical consequences are exactly what defect passivation should deliver. Photoluminescence quantum yield measurements, which track how many absorbed photons are re-emitted rather than lost as heat, improve markedly when the orthogonal pair is applied, indicating that fewer photoexcited carriers are falling into trap states. Time-resolved photoluminescence shows longer carrier lifetimes, and transient absorption spectroscopy corroborates the reduction in non-radiative recombination pathways. Density functional theory calculations, performed with the VASP and ORCA packages, provide a molecular-level account of the binding energies involved, showing that each passivator binds effectively to its intended ionic defect while the acid-base interaction between the two molecules remains weak.

Translated into devices, the dual-passivation strategy produced impressive numbers. Solar cells fabricated with the sterically gated acid-base pair achieved power conversion efficiencies up to 27.4 percent, with an independently certified steady-state efficiency of 25.8 percent, placing the devices among the leading perovskite cells reported to date. Beyond raw efficiency, the team reported gains in operational stability, an equally important metric for a technology hoping to displace silicon in commercial panels. Because the passivation suppresses the charged surface defects that also serve as nucleation points for ion migration and chemical degradation, the molecular repair kit addresses both efficiency loss and instability with a single intervention.

The work also showcases an unusually broad collaboration across chemistry subdisciplines. Mirkin’s group contributed high-throughput spray-based screening methods for rapidly evaluating candidate passivators, developed with Jaewon Lee, while Kanatzidis brought deep expertise in halide perovskite materials chemistry. The team’s computational and spectroscopic characterization spanned X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and microscopy performed at Northwestern’s shared facilities. The underlying datasets have been deposited openly on Zenodo, and the authors have filed an invention disclosure with Northwestern University covering the molecular mutual passivation strategy, signaling interest in translating the chemistry toward commercial fabrication.

For the perovskite field, the significance of the result may lie less in the headline efficiency number than in the design principle behind it. Researchers have long known that single-function passivators leave half the defect population untouched, and that simply mixing acids and bases fails. The demonstration that steric gating can decouple two mutually reactive passivators gives the community a generalizable rule for building multi-component surface treatments: choose partners whose mutual reaction geometry is blocked but whose targets remain accessible. As perovskite technology pushes toward the detailed-balance efficiency limit set by Shockley and Queisser in 1961, every remaining percentage point must be wrested from non-radiative losses at surfaces and grain boundaries. Orthogonal, sterically engineered passivation offers a rational route to squeeze out those losses, and it suggests that the next generation of record-breaking cells may be designed as much by molecular architects thinking about shape and crowding as by device engineers optimizing layer thicknesses.

Subject of Research: Orthogonal Lewis acid-base defect passivation in perovskite solar cells

Article Title: Sterically gated Lewis acid and base pairs enable orthogonal defect passivation in perovskite solar cells

Article References: Shin, D., Kitade, S., Duan, L., Liu, C., Li, C., Huang, C., Kazianga, U. H., López-Arteaga, R., Reitz, S. A., Choi, D., Yang, Y., Kim, H. J., Lee, J., Beights, J., Kwon, H. W., Song, J.-Y., Liu, Y., Choi, J., Mirkin, C. A., … Sargent, E. H. (2026). Sterically gated Lewis acid and base pairs enable orthogonal defect passivation in perovskite solar cells. Nature Chemistry. https://doi.org/10.1038/s41557-026-02261-z

Image Credits: AI Generated

DOI: 10.1038/s41557-026-02261-z

Keywords: perovskite solar cells, Lewis acids, Lewis bases, defect passivation, steric hindrance, phosphines, power conversion efficiency, non-radiative recombination, surface chemistry, Nature Chemistry, photovoltaics, trap states

The research team set out to answer a deceptively simple question: when hydrogen gas bubbles off a nickel electrode in an alkaline solution, which of the surface species that form on nickel is actually doing the catalytic work? Nickel electrodes in alkaline media are never chemically naked. Depending on the applied potential and local conditions, their surfaces can host nickel oxide, nickel hydroxide, and nickel hydride phases, each with distinct electronic structures and bonding geometries. For decades, researchers have debated whether these species are innocent bystanders, harmful blockers, or hidden active sites. Because real electrodes present a patchwork of all three, isolating their individual contributions has been extraordinarily difficult.

The breakthrough of the new work lies in its systematic approach to well-defined nickel surfaces. Rather than studying polycrystalline foams or nanoparticles, where grain boundaries and defects confound interpretation, the researchers prepared carefully controlled nickel surfaces and deliberately generated each candidate species under known conditions. By systematically varying the presence and coverage of nickel oxide, nickel hydride, and nickel hydroxide, and then measuring the hydrogen evolution activity of each configuration, they could assign catalytic roles with a clarity that previous ensemble measurements could not achieve. The strategy echoes a classic theme in surface electrochemistry: only when a surface is well defined can the link between structure and function be drawn unambiguously.

What emerged is a picture in which no single species can claim sole credit. Nickel oxide species, the team found, contribute to the reaction in ways that depend sensitively on their exact chemical state and distribution on the metallic surface. Nickel hydroxide, which forms readily in alkaline environments and has often been invoked as the key promoter of alkaline hydrogen evolution, plays a role that must be carefully separated from the contributions of the oxide and hydride phases. Meanwhile, nickel hydride, the species formed when adsorbed hydrogen penetrates the metal lattice or binds in hydride-like configurations, emerges as a central participant in the hydrogen formation chemistry itself. The study’s central achievement is showing how these three species interact and divide the labor of the reaction rather than acting in isolation.

The distinction matters enormously for the alkaline hydrogen evolution reaction because its mechanism differs fundamentally from the one that operates in acid. In acidic media, the reaction proceeds through adsorbed hydrogen atoms that form directly on the metal surface and combine into hydrogen molecules. In alkaline electrolytes, however, water itself is the proton source, so every hydrogen molecule produced requires a water molecule to dissociate on the surface, cleaving an O-H bond and liberating a hydroxide ion. This initial water dissociation step is widely regarded as the kinetic bottleneck on pure metals, and it is precisely where adjacent oxide or hydroxide species have been proposed to help, by offering oxygen-affine sites that cleave water while neighboring metallic sites assemble the hydrogen. The new results put this bifunctional picture on a much firmer experimental footing for nickel.

For the electrolyser industry, the implications are immediate. Alkaline water electrolysis is the most mature and lowest-cost electrolysis technology on the market, but its cathodes and anodes still trail the performance achievable with platinum-group catalysts. Nickel is already the workhorse electrode material in commercial alkaline electrolysers, prized for its corrosion resistance in concentrated potassium hydroxide and its reasonable activity. If engineers can now identify which surface species to stabilize—and in what proportion—they can rationally tune electrode preparation protocols, whether through surface oxidation treatments, controlled potential cycling, or the deliberate engineering of oxide-hydride interfaces, instead of relying on empirical trial and error. The study effectively converts a long-standing controversy into an engineering design principle.

The findings also carry weight for the broader search for precious-metal-free catalysts. Earth-abundant transition metals such as nickel, cobalt, iron, and molybdenum have all been explored as hydrogen evolution catalysts, and many of the most successful candidates are not pure metals at all but composites in which metallic domains coexist with oxide or hydroxide phases. The nickel study provides a conceptual template for deconvoluting such systems: prepare well-defined versions of each phase, measure their individual kinetics, and then interrogate their combinations. Applied across the periodic table, this methodology could accelerate the discovery of catalysts that match platinum’s performance at a fraction of the cost, a goal that would ripple through green hydrogen production, fuel cells, and carbon-neutral synthesis of fuels and chemicals.

There are also cautionary lessons in the results. Because nickel hydride participates directly in the reaction, the subsurface and bulk hydride chemistry of nickel electrodes deserves renewed attention, particularly under the strongly reducing potentials of cathodic operation where hydride formation is thermodynamically favored. Hydride formation can induce lattice strain, alter electronic properties, and even degrade electrode morphology over time, so understanding its catalytic role may simultaneously illuminate pathways to more durable electrodes. Similarly, the finding that oxide and hydroxide species make separable, state-dependent contributions suggests that the dynamic potential-dependent evolution of surface chemistry during electrolyser start-up, shutdown, and fluctuating renewable power input could shift which species dominates, with consequences for both efficiency and lifetime.

The study arrives at a moment when green hydrogen is scaling from demonstration projects to gigawatt deployments, and every millivolt saved at the cathode translates into real energy and cost savings at industrial scale. By systematically dissecting the individual roles of nickel oxide, nickel hydride, and nickel hydroxide on well-defined nickel surfaces, the researchers have replaced a murky, contested narrative with a mechanistically grounded one. The work does not end the search for better alkaline hydrogen evolution catalysts, but it decisively sharpens it: the target is no longer simply nickel, or nickel oxide, or nickel hydroxide, but the precisely engineered coexistence of all three. For a field racing to strip precious metals out of the hydrogen economy, that clarity may prove as valuable as any single catalyst.

Subject of Research: The individual roles of nickel oxide, nickel hydride, and nickel hydroxide surface species in the alkaline hydrogen evolution reaction on nickel electrodes.

Article Title: The role of individual nickel surface species in the hydrogen evolution reaction on nickel in alkaline electrolytes

Article References: Kozlica, D. K., Finšgar, M., Farinazzo Bergamo Dias Martins, P., Huš, M., Genorio, B., Connell, J. G., Martins, M., Hývl, M., Žibert, T., Andrina Varda, K., Osmić, A., Bele, M., Likozar, B., Tomc, B., Gaberšček, M., & Strmčnik, D. (2026). The role of individual nickel surface species in the hydrogen evolution reaction on nickel in alkaline electrolytes. Nature Catalysis. https://doi.org/10.1038/s41929-026-01605-9

Image Credits: AI Generated

DOI: 10.1038/s41929-026-01605-9

Keywords: hydrogen evolution reaction, nickel, alkaline electrolytes, water electrolysis, nickel oxide, nickel hydride, nickel hydroxide, electrocatalysis, green hydrogen, surface chemistry, precious-metal-free catalysts, Nature Catalysis