Unraveling the Role of MoO_x Clusters in Ternary Mo/Co₃NiO_x for Boosting Acidic Oxygen-Evolution Performance

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/Co₃NiO_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 H₂SO₄ electrolyte), much better than those for the corresponding com-RuO₂ (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/Co₃NiO_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 Co₃NiO_x prefers the adsorbate evolution mechanism (AEM), and proceeds via a synergistic interplay between AEM and lattice oxygen oxidation mechanism (LOM).