Influence of NiCoOx Synthesized Under Air Versus Argon on Its Phase Composition and Oxygen Evolution Reaction Activity

ABSTRACT

Developing oxygen evolution reaction (OER) electrocatalysts with high activity and durable stability can accelerate the advancement of hydrogen production through water splitting. In this work, we synthesized two different structures of NiCoOx by high‐temperature annealing in air (NCO‐O) and in high‐purity argon (NCO‐N), respectively. The unique NaCl‐type structure of NCO‐N results in a smaller Tafel slope (103.71 mV dec ⁻¹ ) than that of NCO‐O (112.55 mV dec ⁻¹ ) and lower OER overpotentials of Ni _0.67 Co _1.33 O ₂ are 330 mV and 390 mV at j = 10 and 50 mA cm ⁻² , respectively than those of NCO‐O (380 and 440 mV, respectively). Moreover, the NCO‐N exhibits a faster charge transfer rate and superior intrinsic OER catalytic activity compared to NCO‐O. However, during the 25 h OER durability test, the gradual formation of metal hydroxide/oxyhydroxide species on the surface of NCO‐N hinders the exposure of its genuinely active sites for OER, leading to its OER activity with a ∆ E = 46 mV decay significantly and irreversibly before and after the durability test. Therefore, suppressing the excessive formation of metal hydroxide/oxyhydroxide on the Ni/Co active sites of NCO‐N is crucial for achieving both high efficiency and long‐term stability.