China's Breakthrough: Stable 200-Hour Zinc-Air Batteries for Seawater

Researchers in China have taken a new approach using catalysts to enhance oxygen reduction in alkaline seawater zinc‑air batteries. As maritime electrification and blue-energy harvesting accelerate, conventional Pt/C cathodes collapse in natural seawater because chloride ions poison active sites and shift the oxygen-reduction pathway from the desired route. Researchers from Central South University and Xi’an Jiaotong-Liverpool University have unveiled a universal oxidative-polymerization route that axially clamps Fe–N₄ single-atom sites with heteroatoms (Cl or S) to create square-pyramidal “Cl–Fe–N4” catalysts that repel Cl⁻ while doubling reaction kinetics. Seawater-based zinc-air battery offers stable cycling performance The seawater-based zinc-air battery fabricated with Cl–Fe–N4 demonstrates a power density of 187.7 mW cm−2 at 245.1 mA cm−2 and maintains stable cycling performance for 200 h. Published in Nano-Micro Letters, the work reveals that the Cl–Fe–N4 catalyst achieves a limiting current density of 5.8 mA cm−2 and a half-wave potential of 0.931 V vs. RHE in alkaline synthetic seawater, outperforming commercial Pt/C (40 wt%). Universal synthetic strategy Researchers also noted that seawater zinc-air batteries are promising energy storage devices due to their high energy density and use of seawater electrolytes. However, their efficiency is hindered by sluggish oxygen reduction reaction (ORR) kinetics and chloride-induced degradation in conventional catalysts. In this study, researchers proposed a universal synthetic strategy to construct heteroatom-axially coordinated Fe–N4 single-atom seawater catalysts (Cl–Fe–N4 and S–Fe–N4). X-ray absorption spectroscopy confirmed their five-coordinated square pyramidal structure. The study reveals that Cl–Fe–N4 exhibits stronger Cl–poisoning resistance in seawater environments. Chronoamperometry tests and zinc-air battery cycling performance evaluations confirmed its enhanced stability. Density functional theory calculations revealed that the introduction of heteroatoms in the axial direction shifts the electron center of the Fe single atom, leading to more active reaction intermediates and increased electron density at Fe single sites, thereby enhancing the reduction of adsorbed intermediates and, consequently, the overall ORR catalytic activity. This comprehensive study provides a materials-by-design playbook for turning the most abundant anion in the ocean—chloride—from a poison into a performance descriptor, paving the way for truly seawater-robust energy storage and conversion devices, according to a press release. Coupled with printable Zn anodes, the catalyst enables pouch cells that operate directly in ocean water, promising buoy-based sensors and unmanned underwater vehicles. It also offers off-grid desalination, as high current density at low overpotential allows SZAB-driven membrane pumps that consume 30 % less energy than conventional reverse-osmosis systems. The precursor ink is water/ethanol-based, and the maximum processing temperature is <1000 °C, making roll-to-roll production compatible with existing carbon-fiber lines, according to researchers. In this study, researchers proposed a universal synthesis strategy for obtaining five-coordinated square pyramidal configurations via oxidative polymerization. Introducing strong electronegative heteroatoms (S and Cl) through axial coordination can significantly alter the symmetry and modulate the electronic structure of the conventional Fe–N4 configuration. Unlike conventional batteries, SZABs use seawater as the electrolyte due to its high ionic conductivity, thereby avoiding the need for freshwater resources and enabling cost-effective, scalable applications in marine environments, according to the study.