Binary CoNi and Ternary FeCoNi Alloy Thin Films as High-Performance and Stable Electrocatalysts for Oxygen Evolution Reaction

To improve the efficiency of electrochemical water splitting and oxygen evolution reactions (OER), it is essential to develop thin film electrocatalysts that are highly active, extremely stable, and based on non-noble metals. Most of the existing electrocatalysts are nano powders or costly electrode materials that require complex synthesis methods, which limit their practical application in water splitting. In this study, we show that a simple AACVD process can produce high-performance OER catalysts from binary CoNi and ternary FeCoNi alloy thin films on nickel foam substrates. The ternary FeCoNi thin films obtained after 2 h deposition have a three-dimensional flower-like morphology, which enhances the contact with the electrolyte and exposes more active sites for the OER. As a result, the OER activity in alkaline medium is improved, achieving a lower potential of 1.49 V vs RHE (260 mV overpotential at 10 mA cm^-2) and a higher current density of 1.8 A cm^-2 at a lower voltage of 1.69 V vs RHE. A small Tafel slope value of 41 mV dec^-1 and excellent long-term stability, with no significant decay in current density for 96 h of chronoamperometric testing, demonstrate the superior performance of the FeCoNi-2h catalyst, compared to state-of-the-art RuO₂ and various FeCoNi-based transition metal catalysts. This work provides a promising strategy for developing thin film electrocatalysts based on low-cost and transition metals that can greatly enhance oxygen evolution performance.