Amorphous NiFe oxide derived from an air-pyrolyzed Prussian blue analogue with rapid complete reconstruction for enhanced oxygen evolution reaction

Abstract

Developing efficient and stable non-precious metal electrocatalysts for the oxygen evolution reaction (OER) is crucial for sustainable hydrogen production via electrochemical water splitting. In this work, a facile air-pyrolysis strategy converts a NiFe-Prussian blue analogue (PBA) into an amorphous NiFe oxide catalyst (NiFe-250) with outstanding OER performance. The optimized catalyst exhibits an ultralow overpotential of 255 mV at 10 mA cm⁻², a Tafel slope of 39.4 mV dec⁻¹, and excellent long-term stability, significantly outperforming both cyanide vacancy-containing catalysts and crystalline oxide catalysts derived from the same precursor. We demonstrate that the amorphous structure undergoes rapid and complete reconstruction into active NiFeOOH under OER conditions. Furthermore, the direct growth of the catalyst on nickel foam (NiFe-250@NF) results in a further reduced overpotential of 220 mV at 10 mA cm⁻² and stable operation for over 100 hours, highlighting its practical applicability. This study elucidates the structural evolution of the PBA during air pyrolysis and the OER performance of the resulting catalysts. By unraveling the reconstruction behavior and electrochemical characteristics of the amorphous structure, we reveal the origin of the superior performance, offering a universal strategy for designing high-performance OER electrocatalysts.