Pyridine-based nitroprussides coupled to reduced graphene oxide as bifunctional pre-electrocatalysts for zinc-air batteries

Abstract

This work evaluated pyridine-based transition-metal nitroprussides (TPyNP, where T = Co, Ni, or Cu) coupled with reduced graphene oxide (rGO) as tunable pre-electrocatalysts for zinc-air batteries (ZABs). Comprehensive characterization confirmed that the transition-metal identity influences the structural and electronic properties, with spectroscopic techniques revealing metal-dependent shifts that correlate with the metal cation’s polarizing power. Electrochemical evaluation demonstrated distinct bifunctional activity governed by the d-band center position: CuPyNP: rGO exhibited superior oxygen reduction reaction performance, while NiPyNP: rGO showed enhanced oxygen evolution reaction activity. However, the CoPyNP: rGO composite, with an intermediate d-band center, delivered the most balanced performance in assembled ZABs, achieving a high peak power density of 54 mW·cm− 2 and a low voltage gap of 1.18 V. Post-mortem analysis confirmed the in-situ transformation into active hydroxides, with the pyridine ligand remaining as a structural pillar and modulator of the electronic structure of the hydroxide. AC magnetic susceptibility measurements on the cycled electrodes further revealed structural disorder and complex magnetic interactions in the active hydroxide phases, underscoring the nontrivial local structure of these phases. This work demonstrates that balancing the dual role of the d-band center is key to designing high-performance electrocatalysts, establishing coordination polymers as viable candidates for next-generation energy storage devices. Graphical abstract