Nitrogen-Doped Carbon Polyhedrons Confined Fe–P Nanocrystals as High-Efficiency Bifunctional Catalysts for Aqueous Zn−CO₂ Batteries

Emerging Fe bonded with heteroatom P in carbon matrix (Fe-P-C) holds great promise for electrochemical catalysis, but the design of highly active and cost-efficient Fe-P-C structure for the electrocatalytic CO₂ reduction reaction (CO₂RR) and aqueous Zn-CO₂ batteries (ZCBs) is still challenging. Herein, polyhedron-shaped bifunctional electrocatalysts, Fe-P nanocrystals anchored in N-doped carbon polyhedrons (Fe-P@NCPs), toward a reversible aqueous Zn-CO₂ battery, are reported. The Fe-P@NCPs are synthesized through a facile strategy by using self-templated zeolitic imidazolate frameworks (ZIFs), followed by an in situ high-temperature calcination. The resultant catalysts exhibit aqueous CO₂RR activity with a CO Faradaic efficiency up to 95% at −0.55 V versus reversible hydrogen electrode (RHE), comparable to the previously best-reported values of Fe-N-C structure. The as-constructed ZCBs with designed Fe-P@NCPs cathode, show the peak power density of 0.85 mW cm⁻² and energy density of 231.8 Wh kg⁻¹ with a cycling durability over 500 cycles, and outstanding stability in terms of discharge voltage for 7 days. The high selectivity and efficiency of the battery are attributed to the presence of highly catalytic Fe-P nanocrystals in N-doped carbon matrix, which can effectively increase the number of catalytically active sites and interfacial charge–transfer conductivity, thereby improving the CO₂RR activity.