Toward highly efficient bifunctional electrocatalysts for zinc-air batteries: from theoretical prediction to a ternary FeCoNi design.

3d Transition-metal nitrogen-carbon nanocomposites (T-N-C, T = Fe, Co, Ni, etc.) with highly active M-Nx sites have received much attention in the field of rechargeable zinc-air battery research. However, how to rationally dope metallic elements to decorate T-N-C catalysts and enhance their electrocatalytic performances remains unclear. Herein, we demonstrated that cobalt-doped Fe-rich catalysts are effective in improving ORR performances by density functional theory (DFT) calculations. On this basis, we reported a kind of novel bifunctional electrocatalyst of hollow nitrogen-doped carbon tubes with coexisting M-N-C single atoms and alloy nanoparticles (denoted FexCoyNiz@hNCTs). Benefiting from the synergistic effect between different components, the as-prepared Fe4Co1Ni2@hNCT catalyst exhibited a small overpotential difference of 0.75 V between an OER potential at 10 mA cm-2 and an ORR half-wave potential, as well as an excellent zinc-air battery performance, when serving as the air cathode. This work provided a scalable design concept for multi-metal doping toward high-performance T-N-C electrocatalysts.

Defect-Engineered Co3 O4 @Nitrogen-Deficient Graphitic Carbon Nitride as an Efficient Bifunctional Electrocatalyst for High-Performance Metal-Air Batteries.

The ability to craft high-efficiency and non-precious bifunctional oxygen catalysts opens an enticing avenue for the real-world implementation of metal-air batteries (MABs). Herein, Co3 O4 encapsulated within nitrogen defect-rich g-C3 N4 (denoted Co3 O4 @ND-CN) as a bifunctional oxygen catalyst for MABs is prepared by graphitizing the zeolitic imidazolate framework (ZIF)-67@ND-CN. Co3 O4 @ND-CN possesses superb bifunctional catalytic performance, which facilitates the construction of high-performance MABs. Concretely, the rechargeable zinc-air battery based on Co3 O4 @ND-CN shows a superior round-trip efficiency of ≈60% with long-term durability (over 340 cycles), exceeding the battery with the state-of-the-art noble metals. The corresponding lithium-oxygen battery using Co3 O4 @ND-CN exhibits an excellent maximum discharge/charge capacity (9838.8/9657.6 mAh g-1 ), an impressive discharge/charge overpotential (1.14 V/0.18 V), and outstanding cycling stability. Such compelling electrocatalytic processes and device performances of Co3 O4 @ND-CN originate from concurrent compositional (i.e., defect-engineering) and structural (i.e., wrinkled morphology with abundant porosity) elaboration as well as the well-defined synergy between Co3 O4 and ND-CN, which produce an advantageous surface electronic environment corroborated by theoretical modeling. By extension, a rich diversity of other metal oxides@ND-CN with adjustable defects, architecture, and enhanced activities may be rationally designed and crafted for both scientific research on catalytic properties and technological development in renewable energy conversion and storage systems.