The case for moving away from alkaline electrolytes is rooted in the peculiar chemistry of the zinc anode. In concentrated alkaline solutions, zinc metal is thermodynamically restless. It corrodes, converting itself into soluble zincate ions and releasing hydrogen gas as a byproduct. That hydrogen evolution dries out cells, builds pressure, and wastes capacity. At the same time, uneven dissolution and redeposition of zinc during repeated charge and discharge cycles encourages the growth of dendrites, needle-like metallic structures that can pierce separators and short-circuit the cell. These parasitic processes, well documented across the zinc-battery literature, are the principal reason alkaline zinc-air prototypes often fade after relatively few cycles. Neutral electrolytes, operating near pH 7, dramatically slow all three failure modes: corrosion, hydrogen evolution, and dendrite propagation. The catch is that neutral electrolytes are less conductive and less kinetically forgiving, so the rest of the cell, especially the air cathode, has to work harder to compensate.

The Sichuan group attacked both halves of the problem simultaneously. On the electrolyte side, they formulated a hydrogel built from gelatin, the same protein-derived polymer that gives dessert jelly its bounce. Gelatin carries abundant functional groups along its polypeptide chains, including carboxyl and amine groups, which can bind water and interact with dissolved ions, helping the gel retain electrolyte and conduct charge. Because the hydrogel is a soft, conformable solid rather than a free-flowing liquid, it eliminates the leakage and infiltration problems that plague liquid-electrolyte flexible cells, and it maintains intimate contact with both electrodes even when the battery is folded around a wrist or a fingertip. The researchers prepared this gelatin hydrogel under neutral conditions, creating a mechanically resilient ion-conducting bridge between the zinc anode and the air-breathing cathode.

The cathode, however, is where the study makes its most distinctive contribution. Air cathodes are the workhorses of zinc-air chemistry: during discharge they must catalyze the oxygen reduction reaction, in which oxygen molecules from the air accept electrons to form hydroxide or related species, and during recharge they must run the reverse oxygen evolution reaction. Both reactions are notoriously sluggish, and the catalysts that drive them well, typically platinum-group metals or complex transition-metal oxides, are expensive or difficult to synthesize. Titanium dioxide, an abundant, cheap, and chemically robust semiconductor, has attracted attention as an oxygen reduction catalyst when its surfaces are properly engineered, but its poor electrical conductivity has always limited its usefulness in a battery electrode where electrons must arrive at every catalytic site.

The researchers’ solution was to decorate titanium dioxide particles with a small, controlled loading of silver nanoparticles, prepared by chemical reduction. Silver is one of the best electrical conductors known, and even a modest fraction of it, dispersed as nanoscale islands across the oxide surface, creates conductive pathways that let electrons flow efficiently through the composite cathode material. The team designated their best formulation TA-0.05, indicating the optimized silver loading level. Beyond simply wiring the oxide particles together, the silver-titania interface can also influence the catalytic chemistry itself, since metal-semiconductor junctions alter how charge is distributed at active sites. The result is a cathode that conducts better, catalyzes oxygen reduction more effectively, and holds up under the repeated potential swings of cycling, all while using only a low loading of a relatively affordable noble metal rather than a heavy dose of platinum.

When the TA-0.05 cathode was coupled with the gelatin hydrogel electrolyte and a zinc anode to form a complete flexible cell, the performance figures were striking for a neutral-electrolyte device. The battery sustained stable charge-discharge cycling for more than fifty hours at a current density of one milliampere per square centimeter, a benchmark that matters because flexible wearables typically draw currents in precisely this low-to-moderate range. Fifty hours of continuous cycling implies that the cell resisted the corrosion, gas evolution, and dendrite problems that would have degraded an alkaline equivalent, while the conductive cathode kept the voltage gaps between charge and discharge acceptably narrow, preserving round-trip energy efficiency. In the world of neutral zinc-air batteries, where sluggish kinetics often inflate those voltage gaps and erode efficiency, this combination of stability and efficiency is a meaningful advance.

The demonstration that will likely capture the public imagination, though, is the simplest one. The researchers connected two of their flexible batteries in series and used the pair to light a light-emitting diode, not on a laboratory bench but while the assembly was being bent. The LED stayed illuminated under deformation, showing that the gelatin hydrogel maintained ionic contact and the cathode retained its structural integrity through mechanical stress. For a wearable device, that is the test that counts: a battery that only works when it is flat is not a wearable battery at all. The image of a soft, protein-based power cell glowing steadily while flexed is exactly the kind of proof-of-concept that moves a technology from an electrochemistry paper toward a product roadmap.

The broader significance of the work lies in its systems-level design philosophy. Rather than optimizing a single component in isolation, the team matched the electrolyte and the cathode to each other’s constraints. The neutral hydrogel tames the zinc anode’s destructive side reactions, but it demands a cathode with excellent conductivity and catalytic activity to overcome the kinetic penalties of near-neutral operation. The low-loading silver-titania composite answers that demand with inexpensive, scalable materials: titanium dioxide is a commodity chemical, silver is far cheaper than platinum, and gelatin is a biopolymer produced industrially on enormous scales. None of the ingredients is exotic, which matters enormously for any technology hoping to be manufactured by the kilometer for consumer wearables. The chemical reduction synthesis used to deposit the silver nanoparticles is likewise a routine, low-temperature procedure compatible with large-area flexible substrates.

Challenges remain before such cells can power a smartwatch on a store shelf. Neutral zinc-air batteries generally deliver lower power densities than their alkaline cousins, and the reported cycling was conducted at a modest current density, so performance under the heavier loads of, say, a wireless radio burst remains to be demonstrated. Long-term questions about hydrogel dehydration, gelatin biostability over months of use, and the durability of the silver-titania interface across thousands of cycles will need answers from extended testing. The authors themselves frame the work as a promising strategy for next-generation wearable electronics rather than a finished product. Still, by showing that a food-safe polymer gel and a sprinkle of silver on cheap titanium dioxide can keep a flexible battery glowing through fifty hours of cycling and through repeated bending, the Sichuan team has sketched a credible, low-cost path to power sources that flex as naturally as the skin they sit on.

Subject of Research: Development of a silver nanoparticle-decorated TiO2 air cathode with a gelatin hydrogel electrolyte for flexible neutral zinc-air batteries

Article Title: Low-loading Ag nanoparticle-decorated TiO2 air cathode coupled with a gelatin hydrogel electrolyte for flexible neutral zinc–air batteries

Article References: Kong, X., Qin, Q., Wang, Z., Li, J., & Zeng, M. (2026). Low-loading Ag nanoparticle-decorated TiO2 air cathode coupled with a gelatin hydrogel electrolyte for flexible neutral zinc–air batteries. Ionics. https://doi.org/10.1007/s11581-026-07495-y

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07495-y

Keywords: zinc-air battery, flexible battery, gelatin hydrogel, titanium dioxide, silver nanoparticles, air cathode, oxygen reduction reaction, neutral electrolyte, wearable electronics, electrocatalysis, energy storage, nanomaterials

The core of the problem is chloride. Seawater carries a high concentration of chloride ions, and at the cathode of a seawater air battery these ions behave as aggressive interlopers. They adsorb onto the very metal centers that are supposed to bind oxygen intermediates, blocking active sites, degrading catalytic performance and accelerating the corrosion of the catalyst layer itself. Iron-based single-atom catalysts, prized for their high intrinsic oxygen reduction activity in alkaline conditions, are particularly vulnerable. The result is a painful trade-off: catalysts that are highly active on the bench tend to lose their edge quickly in real seawater, while corrosion-resistant materials are often too sluggish to deliver competitive power.

The Hainan University group, led by corresponding author Peng Rao, approached this dilemma with a concept they describe as p-d orbital hybridization. Instead of leaving iron atoms to fend for themselves on a carbon support, the researchers paired each iron active site with an adjacent tin atom, creating what is known as a dual single-atom catalyst. Tin, a p-block element with its own distinct orbital character, does not simply sit nearby as a passive neighbor. Through overlap between its p orbitals and the d orbitals of iron, it reshapes the local electronic structure of the iron center, tuning how strongly the site binds oxygen-containing intermediates and how hospitably it treats chloride ions in the surrounding electrolyte.

This electronic engineering addresses a well-known limitation of conventional iron sites. In many iron-nitrogen-carbon catalysts, the binding of oxygen reduction intermediates is too strong, meaning that reaction intermediates such as hydroperoxyl species linger on the surface longer than they should and slow the overall turnover of the catalyst. The Fe-Sn interaction weakens this overly strong adsorption into a more favorable intermediate regime, while simultaneously creating a locally negatively charged interface around the iron site. Because chloride ions are negatively charged, that charged microenvironment electrostatically discourages them from approaching and poisoning the active center. In effect, the catalyst builds a nanoscale fence around its most valuable atom.

The design did not emerge by guesswork. The team first carried out density functional theory calculations, comparing several candidate pairings of iron with different p-block metals in dual-site configurations. Among the candidates, the iron-tin combination stood out with the best balance between oxygen reduction activity and chloride resistance, providing the theoretical justification for an ambitious synthesis. The researchers then produced the material using what they call a movable-type printing strategy, a modular approach that positions the two metal precursors with atomic precision on a nitrogen-doped carbon support before activation locks them into place.

Advanced characterization confirmed that the synthesis had achieved its goal. Microscopy and X-ray spectroscopy showed that both iron and tin were atomically dispersed across the carbon framework, stabilized as adjacent dual single-atom sites rather than clustering into nanoparticles. That atomic dispersion matters enormously. It maximizes the density of accessible active sites, ensures that every iron atom benefits from a tin neighbor, and prevents the formation of larger metal particles that could serve as initiation points for corrosion in the harsh chloride-rich environment.

Electrochemical testing in alkaline seawater electrolyte delivered striking results. The FeSn dual single-atom catalyst achieved a half-wave potential of 0.900 volts versus the reversible hydrogen electrode, outperforming both single-metal iron and tin catalysts prepared in the same way and beating commercial platinum-on-carbon, the traditional benchmark for oxygen reduction. The catalyst followed a near four-electron oxygen reduction pathway, the most efficient route that converts oxygen directly to hydroxide and delivers the maximum possible cell voltage. Equally important for real deployment, the material showed negligible activity decay after 30,000 accelerated durability test cycles, a punishing stress test that simulates years of charge-discharge operation.

Perhaps the most convincing evidence came from post-mortem analysis. After extended testing in the chloride-laden electrolyte, X-ray photoelectron spectroscopy revealed no observable iron-chloride signal on the catalyst surface, indicating that chloride adsorption on the iron active sites had been effectively suppressed throughout the testing period. This directly validates the design hypothesis: the negatively charged microenvironment generated by the Fe-Sn electronic interaction had done its job, keeping the poison away from the active center even as the catalyst worked hard for tens of thousands of cycles.

“For seawater batteries, activity alone is not enough,” said Peng Rao, the corresponding author of the study. “The catalyst also needs to drive oxygen conversion efficiently while resisting chloride-induced poisoning. The Fe-Sn dual-site structure gives us a way to combine these two functions at the atomic level.” The quote captures the central lesson of the work: in marine electrochemistry, selectivity against chloride is not an optional extra but a design requirement on par with activity itself.

The practical payoff was demonstrated when the catalyst was assembled into flow-type seawater air batteries. Devices built with the FeSn dual single-atom catalyst reached a peak power density of 255.6 milliwatts per square centimeter, higher than comparable cells based on platinum-on-carbon or the iron-only single-atom catalyst, and operated stably for more than 500 hours under the reported testing conditions. That combination of high power and long endurance in a realistic seawater-fed architecture suggests the material is ready to be taken seriously for marine energy systems rather than remaining a laboratory curiosity.

Beyond the immediate application, the study positions p-d orbital engineering as a general strategy for designing electrocatalysts that must simultaneously deliver high activity and resist chloride attack. Many reactions of interest in seawater electrochemistry, from oxygen evolution to chlorine-tolerant hydrogen production, face the same fundamental challenge of selective chemistry in an ionically aggressive medium. If pairing active transition-metal sites with judiciously chosen p-block partners proves general, the design principle demonstrated here could extend well beyond iron and tin, and well beyond oxygen reduction.

The research, published in Science Bulletin, arrives at a moment of growing investment in ocean-based energy infrastructure. Offshore wind farms, autonomous underwater systems and remote marine sensors all need durable storage, and seawater batteries are among the few options whose electrolyte comes free with the deployment site. By showing that a simple atomic partnership, one iron atom and one tin atom held in place on a carbon support, can defuse the corrosive chemistry of the ocean while accelerating the very reaction the battery depends on, the Hainan University team has moved the field a meaningful step closer to seawater batteries that survive, and thrive, in the environment they are built to harness.

Subject of Research: Development of an iron-tin dual single-atom catalyst using p-d orbital hybridization to improve oxygen reduction activity and chloride resistance in seawater batteries

Article Title: How can seawater batteries survive chloride corrosion?

Article References: How can seawater batteries survive chloride corrosion?. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: seawater batteries, oxygen reduction reaction, dual single-atom catalyst, chloride corrosion, p-d orbital hybridization, iron-tin catalyst, electrocatalysis, alkaline electrolyte, marine energy storage, density functional theory, nitrogen-doped carbon, air cathode