Unraveling the Role of MoO _x Clusters in Ternary Mo/Co ₃ NiO _x for Boosting Acidic Oxygen‐Evolution Performance

Abstract Developing efficient transition metal electrocatalysts with low cost for the acidic oxygen evolution reaction (OER) confronts an enormous challenge. This work reveals the promising potential of ternary Mo/Co ₃ NiO _x OER electrocatalysts, exhibiting good overpotentials of 249 mV@10 mA cm ⁻² and 429 mV@50 mA cm ⁻² and a small Tafel slope of 219 mV dec ⁻¹ in OER tests (in a 0.5 m H ₂ SO ₄ electrolyte), much better than those for the corresponding com‐RuO ₂ (330 mV@10 mA cm ⁻² and 445 mV dec ⁻¹ ). Furthermore, it exhibits good durability, lasting for ≈200 hours at a current density of 10 mA cm ⁻² , which can be attributed to the synergistic effect of the ternary heterostructure. The deactivation of Mo/Co ₃ NiO _x catalyst is attributed to the loss of Ni species, which then leads to the structural destruction, corroborated by methods of in situ inductively coupled Plasma‐optical emission spectroscopy and X‐ray photoelectron spectroscopy. Finally, in situ attenuated total reflection‐surface enhanced infrared absorption spectroscopy (ATR‐SEIRAS) combined with DFT results show that the pristine Co ₃ NiO _x prefers the adsorbate evolution mechanism (AEM), and proceeds via a synergistic interplay between AEM and lattice oxygen oxidation mechanism (LOM).