Hydrogen and oxygen evolution reactions for high-performance electrocatalytic water splitting by tuning cobalt content in cobalt ferrite

• Bifunctional catalysis enhanced by stoichiometric control of Co x Fe 3−x O 4 nanoparticles. • Cobalt enrichment drives better performance by maximizing active sites and charge density. • Optimal Co 1.5 Fe 1.5 O 4 achieves low overpotentials for OER (341 mV) and HER (331 mV). • Optimized Co/Fe ratios double the turnover frequency (TOF) for the oxygen evolution reaction. • Excellent stability of Co 1.5 Fe 1.5 O 4 catalyst retaining over 97% of its activity. This study investigates the use of Co x Fe 3-x O 4 with different cobalt ratios (x = 1, 1.2, and 1.5) for the electrocatalytic water splitting process. Experimental measurements showed that the electrocatalytic performance of cobalt ferrite toward both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) was systematically enhanced by cobalt enrichment. In particular, the Co 1.5 Fe 1.5 O 4 catalyst showed a lower OER overpotential compared to the CoFe 2 O 4 composition (341 mV vs. RHE at 10 mA/cm 2 compared to 467 mV), while the HER overpotential decreased from 370 to 331 mV at −10 mA/cm 2 . These enhancements are attributed to an increase in the electrochemically active surface area (ECSA) from 11.72 to 20.03 cm 2 and an improvement in the OER turnover frequency (TOF) from 1.9 to 2.8 s −1 . Additionally, Co 1.5 Fe 1.5 O 4 showed excellent stability, maintaining over 96% of its activity during 48 h of continuous operation. The HER and OER processes appear to be favored by the presence of cationic metal sites and oxygen vacancies, which are particularly promoted by the oxidation of Co 2+ to Co 3+ . This study reports a strong correlation between the Co/Fe ratio and electrocatalytic efficiency of water splitting, thus providing valuable insights for the design of robust and cost-effective catalysts for sustainable hydrogen and oxygen production.