Evaluating Properties of Carbon-Free Nano-NiCoFe-LDHs with Molybdate as Oxygen Evolution Catalysts and Their Applications in Rechargeable Air Electrodes

The issues of carbon corrosion, oxidation, and catalytic stability for most electrocatalysts of oxygen evolution reaction (OER) remain great challenges under high oxidizing environments. Herein, we report carbon-free nano-NiCoFe layered double hydroxides (LDHs) with MoO42- anions to alleviate these issues. An excellently active catalyst of nanocarbon-free NiCo1.5Fe0.5-LDH with 14.9 at. % MoO42- was synthesized by a chemical coprecipitation method that shows superior OER performance having an overpotential of 239 mV@10 mA cm(Geo)(-2), a Tafel slope of 43 mV dec(-1), and excellent long-term stability (200 h no degradation) at 100 mA cm(Geo)(-2). The outstanding performance is ascribed to the excellent stability of carbon-free powder catalysts with no carbon corrosion under high oxidizing environments, while the high catalytic activity is attributed to the enhanced synergistic effects between multiple metals of Ni-III, Co-III, and Fe-III, the size reduction and formation of high specific surface areas, and poor crystallinity after molybdate introduction. In this work, a durably rechargeable air electrode for metal-air batteries was fabricated using the electrocatalyst, which exhibits low charging voltage (1.882 V@20 mA cm(-2) vs Zn), excellent cycling stability, and a low voltage gap (0.67 V) at 20 mA cm(-2) in the atmosphere environment (air as the reactive gas). The paper discussed two strategies to promote OER activities and presents a feasible approach to tackle the tricky issues of carbon corrosion and oxidation for rechargeable air electrodes in alkaline medium under high oxidizing environments.