A research team led by Yue Gao at Fudan University’s Department of Macromolecular Science has now pursued a radically different route to this problem. Rather than trying to make batteries smaller and denser, the researchers asked a deceptively simple question: could a robot harvest energy directly from the surface it walks on? The world is full of active materials such as aluminum, zinc, silicon, tin, and lead, and these metals and semiconductors are ubiquitous in pipes, buildings, data centers, and industrial equipment. If a robot’s foot could trigger a chemical reaction on contact with such a surface, the robot’s runtime would no longer be capped by the amount of energy it can carry. The environment itself would become the fuel tank, and every step across a suitable substrate would become a step across a power source.

The team’s answer is an open electrochemical power system built as a crosslinked potassium polyacrylate membrane, attached directly to the microrobot’s foot like a layer of engineered skin. This membrane converts chemical energy from the substrate, together with atmospheric moisture and oxygen, into electricity. The design is deliberately open rather than sealed, which is what allows it to draw reactants continuously from the air and the ground instead of relying on a finite internal supply. The work, published in National Science Review, demonstrates a system that can power more than 10,000 walking steps and remain stable after one million steps, a durability figure that addresses one of the most common failure modes of electrochemical interfaces.

Manufacturing the skin is strikingly straightforward. The membrane is made in a single step by polymerizing acrylic acid monomer, crosslinker, initiator, and potassium hydroxide directly on the robot’s foot. A flexible platinum/carbon film serves as the reaction site where oxygen and water participate in the electrochemical process. The resulting skin can be as thin as 135 micrometers and as small as one square millimeter, dimensions compatible with the smallest class of crawling microrobots. On zinc, the membrane delivers a power density of 133 milliwatts per square centimeter, and on aluminum it reaches 103 milliwatts per square centimeter. Those values are roughly an order of magnitude higher than those of typical microbatteries, and the system retains its current capability even when scaled down to 0.0004 cubic centimeters, precisely the regime where conventional microbatteries collapse.

What makes the achievement technically demanding is that the membrane must satisfy several conflicting requirements simultaneously. It has to hold water in dry conditions, remain flexible under repeated bending, stick firmly to surfaces during locomotion, release cleanly when the foot lifts, and sense the properties of the ground it touches. Water retention is handled at the molecular level: the membrane’s carboxylate groups, potassium ions, and hydroxide ions interact strongly with water molecules, anchoring them within the polymer network. Even at 20 percent relative humidity, conditions comparable to the Sahara Desert, the membrane retains most of its water and continues to discharge after 48 hours. This resilience against desiccation is essential for a device whose entire energy conversion scheme depends on the presence of water at the reaction interface.

The membrane is equally robust against temperature extremes. At minus 20 degrees Celsius, potassium ions disrupt the ordered hydrogen-bond network of water within the polymer, preventing the kind of ice-like structuring that would normally shut down ion transport. The result is that the membrane remains ionically conductive at deep subzero temperatures, with its voltage dropping by only about 0.2 volts compared with room temperature performance. The crosslinked structure also tolerates heat, allowing operation at 80 degrees Celsius. Perhaps most practically, the system is recoverable: after water evaporates, simply adding water restores performance. This combination of cold tolerance, heat tolerance, and reversibility suggests a power skin that could operate across the wide environmental range real deployments would demand, from refrigerated facilities to sun-exposed metal infrastructure.

The electricity generation itself follows an elegant contact-driven mechanism. The membrane produces current when it touches an active substrate and stops the moment the foot lifts. During contact, the substrate loses electrons, while on the platinum/carbon side oxygen and water accept those electrons to produce hydroxide ions. The reaction begins in about 0.1 milliseconds, fast enough to keep pace with a walking gait, and terminates as soon as contact ends. Each walking step therefore refreshes the reaction interface, presenting a clean patch of substrate to the membrane. Crucially, the discharge products remain on the substrate rather than accumulating on the membrane itself. This self-cleaning behavior avoids the performance decay that plagues static batteries, whose electrodes gradually accumulate reaction byproducts over their lifetime, and it explains how the system can sustain more than 10,000 powered steps and survive one million steps overall.

Adhesion posed its own engineering puzzle, and the membrane resolves it with a directional asymmetry that mirrors how a foot should behave. Carboxylate groups create electrostatic adhesion to metal substrates, and in the walking direction this adhesion is strong enough to prevent slipping, providing the shear grip a crawling robot needs to propel itself. In the vertical direction, however, the detachment resistance is low, so the robot can lift its foot efficiently without expending excessive energy or damaging the interface. This combination of strong shear adhesion and easy normal detachment is what allows the microrobot to crawl on inclined aluminum surfaces, a capability that would be impossible with a uniformly sticky or uniformly slippery interface. The material effectively behaves like a well-designed shoe sole, gripping where it should and releasing where it must.

Beyond powering locomotion, the membrane doubles as a sensory organ, reading the ground through ions. Different substrate materials drive different electrochemical reaction rates and different levels of hydroxide consumption, which in turn cause directed migration of potassium ions and produce a characteristic potential signal for each material. Surface roughness adds a second channel of information: rough surfaces deform the membrane and alter the ion distribution, generating a distinct signal of their own. The two signal types are naturally decoupled, with material changes producing stable square-wave signals and roughness changes producing millivolt-level spikes, so the robot can distinguish what it is standing on from how textured that surface is. Equipped with an X-Y electrode array, the membrane can even locate where contact occurs on its surface.

This sensing capability transforms the power skin from a passive generator into the foundation of an active energy-seeking strategy. Because the robot can recognize substrate material and roughness in real time, it can identify energy-rich paths and navigate toward them, pursuing the surfaces that yield the most power rather than wandering blindly. In effect, the robot forages for energy the way an animal forages for food, using its skin both to harvest and to map its environment. For a field long constrained by the tyranny of small batteries, the implications are considerable: microrobots that walk across the metal infrastructure of the modern world, drawing power from pipes, panels, and equipment with every step, carrying no fuel at all and stopping only when the ground beneath them runs out of chemistry.

Subject of Research: A crosslinked potassium polyacrylate membrane that harvests electrochemical energy from metal and silicon substrates to power battery-free microrobots

Article Title: No battery needed: Robot skin harvests power as it walks

Article References: No battery needed: Robot skin harvests power as it walks. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: microrobots, energy harvesting, potassium polyacrylate, polymer membrane, electrochemistry, power density, zinc, aluminum, atmospheric moisture, oxygen reduction, substrate sensing, National Science Review

What makes carbon nitride so attractive begins with its chemistry. Graphitic carbon nitride is a metal-free polymer built from carbon and nitrogen atoms arranged in heptazine or triazine units, stacked into layers that resemble the architecture of graphite. This arrangement gives the material a set of properties that catalyst designers prize: it is chemically stable in acids, bases and organic solvents, it tolerates high temperatures, and it possesses a band gap of roughly 2.7 electronvolts, wide enough to drive photochemical reactions yet narrow enough to absorb a meaningful slice of visible sunlight. Because it contains only abundant elements, it is inexpensive and scalable in ways that many metal-based catalysts are not. Its surface is also rich in nitrogen-containing sites, including pyridinic and amino functionalities, which can anchor metal atoms, activate small molecules and participate directly in bond-forming chemistry.

The volume devotes substantial attention to how synthesis choices ripple through to catalytic performance. Carbon nitride can be prepared by thermal condensation of inexpensive precursors such as melamine, urea, thiourea or dicyandiamide, and the choice of precursor, the heating profile and the atmosphere all leave fingerprints on the final material. Thermal polycondensation at moderate temperatures tends to yield highly polymerized, well-ordered frameworks, while routes from urea can produce defect-rich structures with enhanced surface area. Post-synthetic treatments, including exfoliation into two-dimensional nanosheets, protonation, and the introduction of vacancies or heteroatom dopants, further tune the electronic structure. Each of these levers changes how the material absorbs light, how charge carriers migrate through its framework and how substrates adsorb to its surface, which in turn governs activity and selectivity in the reactions it catalyzes.

In organic synthesis, carbon nitride-based catalysts have proven capable of mediating reactions that traditionally demand stoichiometric reagents or precious-metal complexes. The book surveys their roles in carbon–carbon and carbon–heteroatom bond formation, the two workhorse transformations of synthetic chemistry, as well as in oxidation reactions and the construction of heterocyclic scaffolds that underpin much of pharmaceutical and agrochemical chemistry. Because the catalyst is heterogeneous, it can be recovered by filtration and reused, addressing one of the persistent criticisms of homogeneous catalysis. The nitrogen-rich surface can act as a Lewis base, a hydrogen-bonding platform or an electron-transfer mediator, and when combined with light absorption it enables photocatalytic variants of classical reactions that proceed under mild conditions, often at ambient temperature and pressure with molecular oxygen or water as the terminal oxidant.

Photocatalysis is arguably where carbon nitride first made its name, and the volume gives this field careful treatment. When g-C₃N₄ absorbs a photon, an electron is promoted from the valence band to the conduction band, leaving behind a hole. These charge carriers can reduce or oxidize species adsorbed on the catalyst surface before they recombine, and the art of photocatalyst design lies largely in preventing that recombination. Strategies covered in the book include coupling carbon nitride with other semiconductors to form heterojunctions that separate charges across an interface, decorating the surface with co-catalysts such as metals that act as electron sinks, and doping the framework to shift band edges. Applications range from the degradation of organic pollutants in water to the photosynthesis of value-added organic compounds, and the editors emphasize that rational functionalization, rather than trial and error, is increasingly the route to high activity and selectivity.

Water splitting, the light-driven decomposition of water into hydrogen and oxygen, receives particular scrutiny as a flagship application for sustainable energy conversion. Carbon nitride’s conduction band sits at a potential sufficiently negative to reduce protons to hydrogen, making it a candidate photocatalyst for solar fuel production. The material’s limitations, including modest visible-light absorption beyond a certain wavelength and rapid charge recombination, are precisely the problems that doping, defect engineering and composite formation are designed to solve. Alongside water splitting, the book examines oxygen reduction, the cathodic half-reaction central to fuel cells and metal–air batteries, where carbon nitride-based materials can serve as metal-free electrocatalysts or as supports that stabilize single metal atoms in highly active configurations.

Electrocatalysis and electrochemical sensing form a second major pillar of the volume. The same conductive and adsorptive properties that make carbon nitride useful for driving reactions make it valuable for detecting them. The book highlights electrochemical sensors built on carbon nitride platforms for monitoring environmental pollutants, exploiting the material’s ability to accumulate analytes at nitrogen-rich sites and transduce their presence into measurable electrical signals. Such sensors target contaminants in water and air, offering routes to monitoring tools that are inexpensive, robust and potentially deployable outside specialized laboratories. The editors frame this sensing capability as a natural companion to the materials’ environmental remediation roles: the same chemistry that destroys pollutants can be harnessed to detect them.

Threaded through all of these applications is a unifying theme that the editors return to repeatedly: the relationship between catalyst design and catalytic outcome. Activity and selectivity in carbon nitride catalysis are not fixed properties of a formula but consequences of structure at multiple scales, from the polymerization degree of the framework to the density of surface defects to the geometry of metal sites deposited upon it. A metal-decorated derivative may behave entirely differently from its pristine parent, and a composite with a second semiconductor can open reaction pathways unavailable to either component alone. The volume’s chapters collectively argue that understanding these structure–performance relationships is the key to moving carbon nitride catalysts from laboratory demonstrations to technologies that compete with, and in some cases outperform, conventional metal-based systems.

The sustainability case for these materials is central to the book’s argument. Catalysis underpins the majority of industrial chemical production, and the environmental costs of precious-metal catalysts, stoichiometric oxidants and energy-intensive processes have pushed chemists toward alternatives grounded in earth-abundant elements and renewable energy inputs. Carbon nitride fits that brief unusually well: it is synthesized from cheap organic precursors, contains no metals, can harvest sunlight directly, and can drive oxidations with air or water. The editors position the material as relevant to sustainable chemistry, energy conversion and environmental monitoring simultaneously, a rare breadth that reflects the tunability of the underlying platform. For industries seeking greener routes to fine chemicals, fuels and clean water, the message is that a single material family may serve multiple points in the same sustainability pipeline.

By gathering contributions that span organic chemistry, materials science, photocatalysis and electrochemistry, the volume offers an interdisciplinary map of a field that has often advanced in disconnected pockets. The editors, Vijai Kumar Rai, Manorama Singh and Ankita Rai, have assembled a reference aimed at researchers and advanced readers in organic chemistry, materials science, catalysis, nanotechnology and chemical engineering, and its scope suggests that carbon nitride-based nanomaterials have moved decisively beyond a single-application curiosity. Whether the next breakthrough comes from a more selective organic transformation, a more efficient water-splitting device or a more sensitive pollutant sensor, the common denominator will be the same: a metal-free, nitrogen-rich framework whose properties chemists can now design with increasing precision. For a field racing toward efficient and environmentally responsible catalytic technologies, graphitic carbon nitride has earned its place at the center of the conversation.

Subject of Research: Catalytic applications of graphitic carbon nitride-based nanomaterials

Article Title: Catalytic applications of carbon nitride-based nanomaterials

Article References: Catalytic applications of carbon nitride-based nanomaterials. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: carbon nitride, g-C3N4, catalysis, photocatalysis, electrocatalysis, water splitting, organic synthesis, nanomaterials, sustainable chemistry, environmental sensing, oxygen reduction, heterogeneous catalysis

The starting materials belong to a family of cyanometallate coordination polymers with the general framework T[Fe(CN)₅NO], where T is a transition-metal ion. In the study, T was cobalt, nickel, or copper. Pyridine molecules bind to the outer metal centers and change the architecture from a three-dimensional bulk structure into layered two-dimensional sheets. This transformation is important because the parent nitroprussides have limited surface area and disperse poorly, whereas thin layers can be distributed across a conductive carbon support. Pyridine is therefore not introduced primarily as an oxygen-evolution promoter. Its principal role is structural: by selectively replacing axial metal–cyanide connections, it enables the layered morphology and helps stabilize neighboring sheets through pi–pi and dipole–dipole interactions. The resulting materials were combined with reduced graphene oxide in a one-to-one weight ratio. The graphene network provides pathways for electron transport and helps expose the coordination-polymer domains to the alkaline electrolyte.

Several complementary measurements confirmed that the metal identity altered both the structure and the electronic environment of the composites. X-ray diffraction showed layered materials with characteristic basal-plane reflections for the cobalt and nickel systems, while the copper composite displayed different stacking behavior. Electron microscopy revealed average particle sizes of approximately 133 nanometers for the cobalt material, 47 nanometers for the nickel material, and 214 nanometers for the copper material. Infrared and Raman spectroscopy detected the cyanide, nitrosyl, pyridine, and graphene-related signatures expected from the composite design. The cyanide stretching frequency shifted systematically as the metal changed from cobalt to copper, reflecting differences in the cations’ polarizing power. Raman measurements also indicated a defect-rich reduced graphene oxide support. The disorder can be useful in electrocatalysis because defects may create additional sites for oxygen-related reactions, although the measured surface area alone did not determine which composite performed best.

Electrochemical testing revealed a clear division of labor among the three materials. For OER in alkaline solution, the nickel composite showed the lowest onset potential and the strongest current response, reaching 10 milliamperes per square centimeter at an overpotential of about 398 millivolts. The cobalt and copper versions required approximately 437 and 518 millivolts, respectively, under the same benchmark. Nickel also exhibited the lowest charge-transfer resistance across the tested potential range. Cobalt, however, produced the lowest fitted OER Tafel slope, 61 millivolts per decade, compared with 74 for nickel and 156 for copper. The researchers caution that a lower Tafel slope by itself does not establish the fastest overall reaction; onset potential, overpotential, resistance, and operating conditions must be considered together. For ORR, the pattern reversed. The copper composite delivered the lowest onset potential and the highest limiting current, indicating the most favorable oxygen-reduction behavior among the tested materials.

Rotating-disk experiments provided further information about the oxygen-reduction pathway. Koutecky–Levich analysis indicated that all three composites predominantly followed a four-electron route, which is desirable in zinc-air batteries because it converts oxygen more directly and limits peroxide formation. The estimated electron-transfer numbers were approximately 3.95 for cobalt, 3.63 for nickel, and 3.97 for copper. The nickel value suggests that a mixture of four-electron and two-electron pathways may occur, potentially producing some hydrogen peroxide. The authors note that rotating-ring-disk measurements would be needed to investigate that possibility directly. Together, the half-cell results show why optimizing a rechargeable zinc-air battery is difficult: nickel favors the charging reaction, copper favors the discharging reaction, and neither is automatically the best complete-device material. The measurements instead point toward a compromise in which both reactions remain sufficiently active.

That compromise emerged when the composites were assembled into working zinc-air batteries. The cobalt-based cathode produced the highest peak power density, 54 milliwatts per square centimeter, narrowly exceeding the nickel system at 53 and clearly surpassing the copper system at 39. It also maintained higher discharge-voltage plateaus, particularly as the current density increased. During galvanostatic cycling at 10 milliamperes per square centimeter, the cobalt battery began with a voltage gap of 0.99 volts between charge and discharge and reached 1.18 volts after 24 hours. The corresponding gaps for copper were 1.05 and 1.29 volts, while nickel showed 1.43 and 1.36 volts. Initial round-trip energy efficiencies were 52 percent for cobalt, 50 percent for copper, and 34 percent for nickel. After the cycling period, they were 46, 42, and 33 percent, respectively. The cobalt device also retained a relatively stable impedance and delivered an average energy above 8.5 watt-hours per square meter per cycle.

The study’s central chemical finding is that the synthesized nitroprussides do not remain unchanged during battery operation. Post-cycling analysis of the best-performing cobalt electrode showed that the characteristic cyanide signal disappeared, while hydroxyl and metal–oxygen signatures emerged. X-ray diffraction and Raman spectroscopy likewise indicated conversion into a cobalt hydroxide or oxyhydroxide phase. The original material is therefore a precursor rather than the final catalyst. Importantly, X-ray photoelectron spectroscopy detected a pyridinic nitrogen signal after cycling, suggesting that the pyridine ligand remained associated with the reconstructed active phase instead of being completely lost. The researchers propose that the retained molecules act as structural pillars and electronic modifiers, helping prevent the newly formed oxyhydroxide sheets from agglomerating. The same alkaline environment that drives the battery reactions promotes this reconstruction. Similar hydroxide or oxyhydroxide phases are considered likely for the nickel and copper composites, although direct post-cycling structural confirmation was performed most extensively for cobalt.

Magnetic measurements offered an unusual window into the reconstructed electrodes, indicating that the active hydroxides are locally disordered rather than simple, perfectly ordered crystals. Measurements of magnetic susceptibility showed metal-dependent interactions, including antiferromagnetic correlations, weak ferromagnetic-like behavior, metamagnetic transitions, and magnetic relaxation. The cobalt and nickel hydroxide phases displayed low-temperature features associated with competing or complex interactions, while the copper material showed behavior consistent with antiferromagnetic correlations and a distorted local environment. These observations matter because local disorder can change the electronic states available for binding oxygen intermediates. Valence-band X-ray photoelectron spectra placed the approximate d-band centers in the order nickel below cobalt below copper. Within the commonly used d-band framework, a higher d-band center can strengthen adsorption of oxygen intermediates, helping ORR but potentially making OER less favorable. The results fit that qualitative picture: copper was strongest for ORR, nickel for OER, and cobalt, with an intermediate electronic position, offered the best balance. The authors emphasize that the d-band values are approximate descriptors, not proof of a single causal mechanism.

The work presents coordination polymers as tunable molecular precursors for practical oxygen electrocatalysis, while also highlighting the limits of laboratory battery demonstrations. The cobalt composite approached a zinc-specific capacity of 809.2 milliampere-hours per gram at 5 milliamperes per square centimeter, close to the theoretical value of 820, but the researchers caution that this result reflects a relatively low current density, a high-purity zinc anode, and a particular concentrated alkaline electrolyte. Further studies will be needed to assess operation at higher rates, longer lifetimes, different electrolyte compositions, and larger electrode areas. In situ spectroscopy and density-functional calculations could also test how the retained pyridine, disordered hydroxide structure, and d-band position cooperate during cycling. Even with those questions unresolved, the comparison demonstrates a useful design principle: the best bifunctional catalyst is not necessarily the material that wins either half-reaction independently. In this series, deliberately balancing electronic structure, conductive architecture, and electrochemical reconstruction allowed the cobalt-based pre-electrocatalyst to deliver the most practical zinc-air battery performance.

The precursor strategy also addresses a practical materials challenge beyond catalytic activity. Conventional oxygen electrocatalysts often rely on platinum for reduction or iridium- and ruthenium-based oxides for evolution, but the scarcity and cost of these elements complicate deployment at scale. Nitroprusside coordination polymers offer a different platform because their metal sites, cyanometallate framework, and organic coordination environment can be varied systematically. The cobalt, nickel, and copper comparison therefore functions as a controlled probe of how first-row transition-metal chemistry affects a common molecular architecture, rather than as a simple search for a single universally optimal composition.

That architecture may be especially valuable for studying catalyst reconstruction under realistic operation. Because the electrochemically generated hydroxide is the working phase, evaluating only the pristine powder could obscure the properties that govern a battery’s behavior. The reported combination of spectroscopy, diffraction, microscopy, and magnetic susceptibility illustrates why identifying active materials requires measurements before and after polarization. It also suggests a broader design opportunity: coordination ligands can serve as temporary structure-directing components while influencing the local environment retained after conversion. Determining how much pyridine survives, where it is located, and whether its effect persists over extended cycling will be important for distinguishing a genuine electronic contribution from a short-lived synthesis advantage. Such questions are relevant to translating these composites from proof-of-concept electrodes into durable, scalable air-cathode materials.

Subject of Research: Transition-metal nitroprusside and reduced graphene oxide pre-electrocatalysts for rechargeable zinc-air batteries

Article Title: Pyridine-based nitroprussides coupled to reduced graphene oxide as bifunctional pre-electrocatalysts for zinc-air batteries

Article References: Quintanilla-Serrano, E. A., Acevedo-Peña, P., Ávila, Y., González, M., & Reguera, E. (2026). Pyridine-based nitroprussides coupled to reduced graphene oxide as bifunctional pre-electrocatalysts for zinc-air batteries. Discover Electrochemistry, 3(1), Article 77. https://doi.org/10.1007/s44373-026-00164-9

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00164-9

Keywords: zinc-air batteries, electrocatalysis, reduced graphene oxide, nitroprussides, oxygen reduction, oxygen evolution, cobalt hydroxide, d-band center, Pyridine-based, coupled, reduced, graphene