Nanopore Confinement of Electrocatalysts Optimizing Triple Transport for an Ultrahigh-Power-Density Zinc-Air Fuel Cell with Robust Stability.

Metal-air fuel cells with high energy density, eco-friendliness, and low cost bring significantly high security to future power systems. However, the impending challenges of low power density and high-current-density stability limit their widespread applications. In this study, an ultrahigh-power-density Zn-air fuel cell with robust stability is highlighted. Benefiting from the water-resistance effect of the confined nanopores, the highly active cobalt cluster electrocatalysts reside in specific nanopores and possess stable triple-phase reaction areas, leading to the synergistic optimization of electron conduction, oxygen gas diffusion, and ion transport for electrocatalysis. As a result, the as-established Zn-air fuel cell shows the best stability under high-current-density discharging (>90 h at 100 mA cm-2 ) and superior power density (peak power density: >300 mW cm-2 , specific power: 500 Wgcat -1 ) compared to most reported non-noble-metal electrocatalysts. The findings will provide new insights in the rational design of electrocatalysts for advanced metal-air fuel cell systems.

Ultrathin Cobalt Oxide Layers as Electrocatalysts for High-Performance Flexible Zn-Air Batteries.

Synergistic improvements in the electrical conductivity and catalytic activity for the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) are of paramount importance for rechargeable metal-air batteries. In this study, one-nanometer-scale ultrathin cobalt oxide (CoOx ) layers are fabricated on a conducting substrate (i.e., a metallic Co/N-doped graphene substrate) to achieve superior bifunctional activity in both the ORR and OER and ultrahigh output power for flexible Zn-air batteries. Specifically, at the atomic scale, the ultrathin CoOx layers effectively accelerate electron conduction and provide abundant active sites. X-ray absorption spectroscopy reveals that the metallic Co/N-doped graphene substrate contributes to electron transfer toward the ultrathin CoOx layer, which is beneficial for the electrocatalytic process. The as-obtained electrocatalyst exhibits ultrahigh electrochemical activity with a positive half-wave potential of 0.896 V for ORR and a low overpotential of 370 mV at 10 mA cm-2 for OER. The flexible Zn-air battery built with this catalyst exhibits an ultrahigh specific power of 300 W gcat -1 , which is essential for portable devices. This work provides a new design pathway for electrocatalysts for high-performance rechargeable metal-air battery systems.

3D Nitrogen-Anion-Decorated Nickel Sulfides for Highly Efficient Overall Water Splitting.

Developing non-noble-metal electrocatalysts with high activity and low cost for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of paramount importance for improving the generation of H2 fuel by electrocatalytic water-splitting. This study puts forward a new N-anion-decorated Ni3 S2 material synthesized by a simple one-step calcination route, acting as a superior bifunctional electrocatalyst for the OER/HER for the first time. The introduction of N anions significantly modifies the morphology and electronic structure of Ni3 S2 , bringing high surface active sites exposure, enhanced electrical conductivity, optimal HER Gibbs free-energy (ΔGH* ), and water adsorption energy change (ΔGH2O* ). Remarkably, the obtained N-Ni3 S2 /NF 3D electrode exhibits extremely low overpotentials of 330 and 110 mV to reach a current density of 100 and 10 mA cm-2 for the OER and HER in 1.0 m KOH, respectively. Moreover, an overall water-splitting device comprising this electrode delivers a current density of 10 mA cm-2 at a very low cell voltage of 1.48 V. Our finding introduces a new way to design advanced bifunctional catalysts for water splitting.