Controlled self-template synthesis of CoNiFe-PBA hollow structure with enhanced electrocatalytic oxygen evolution reaction activity

The microstructure and composition of electrocatalysts play a crucial role in determining their oxygen evolution reaction (OER) performance. Herein, we report a controlled self-template synthesis of hollow CoNiFe Prussian blue analogues (PBAs) and their phosphide derivatives with enhanced OER activity. Cobalt-nickel basic acetates with tunable metal ratios were first synthesized via a solvothermal method, followed by anion exchange with potassium hexacyanoferrate to form CoNiFe-PBAs, and subsequent phosphorization to obtain hollow CoNiFe phosphides (CoNiFe-PBA-Ps). Among these, the Co₃Ni₁Fe composition exhibits an optimal combination of reduced particle size and hollow architecture, resulting in more exposed active sites and increased electrolyte accessibility. The final Co₃Ni₁Fe-PBA-P displays a low overpotential of 273 mV at 10 mA cm⁻² and a Tafel slope of 59 mV dec⁻¹, outperforming other Co_xNi_yFe-PBA-Ps and many reported Co, Ni, Fe-based electrocatalysts. DFT calculations confirm that the improved activity stems from the lower energy barriers of the key OER intermediates. This work provides a versatile strategy to design multi-metallic hollow nanostructures with small particle size, offering new insights into the development of high-performance electrocatalysts.