Reducible Co3+–O Sites of Co–Ni–P–Ox on CeO2 Nanorods Boost Acidic Water Oxidation via Interfacial Charge Transfer-Promoted Surface Reconstruction

Developing efficient and durable earth-abundant electrocatalysts for the acidic oxygen evolution reaction (OER) is the bottleneck for water splitting using proton-exchange membrane electrolyzers. Herein, a heterostructured CeO2 nanorod-supported Co–Ni–P oxide (CeO2/Co-Ni–P–Ox) catalyst is prepared for acidic OER electrocatalysis and the valence states of Co is precisely tuned from 2 to 2.51 by introducing heterojunction interfaces and trace P atoms. The increased Co states favor the in situ transformation of surface Co2+–O sites into highly active reducible Co3+–O sites, which promotes the deprotonation of water molecules and accelerates the OER kinetics. Therefore, this catalyst exhibits extraordinarily low OER overpotentials of 166 and 262 mV at 5 and 10 mA cm–2, respectively, in 0.5 M H2SO4, which are among the best reported for precious-metal-free electrocatalysts so far. The stability of the catalyst is also greatly improved due to the increased vacancy formation energy of the Co site that restricts its dissolution in an acid.