Sustainable hydrogen production via a promising electrocatalyst prepared from Ni-Fe Prussian blue analog

Development of a highly active electrocatalyst is essential for dropping the overall activation energy of water splitting, thereby enhancing H₂ and O₂ production. Among the various catalysts, Prussian blue analogs (PBAs) that are cyanide-based coordination polymers exhibit excellent water-splitting performance due to their tunable metal active sites, large specific surface areas, open-framework architectures, and uniform catalytic centers in electrolysis. In this study, a green synthesis method was developed to obtain Ni₂Fe₈CN, a PBA-based bifunctional catalyst for efficient electrolysis. Ni₂Fe₈CN deposited on NF displays an overpotential of 142 mV (95 mV dec^-1) vs RHE for hydrogen evolution reaction (HER) and 280 mV (105 mV dec^-1) vs RHE for oxygen evolution reaction (OER) at 10 mA cm^-2 in 1.0 M KOH. The Ni₂Fe₈CN demonstrates significant stability, maintaining activity up to 150 h with negligible current density losses of 4.8 % under OER and 3.9 % under HER conditions. The higher catalytic presentation and durability of Ni₂Fe₈CN are attributed to the interaction between Ni, Fe, and CN during electrolysis, which enhances the catalytic sites and charge transfer kinetics. Notably, in a bifunctional two-electrode configuration (Ni₂Fe₈CN/NF//Ni₂Fe₈CN/NF), effective electrolysis is achieved, delivering a stable current density of 10 mA cm^-2 at a bias of 1.54 V vs RHE with exceptional stability over 180 h with a minor current loss of 5.1 %.