Interface Engineering a High Content of Co 3+ Sites on Co 3 O 4 Nanoparticles to Boost Acidic Oxygen Evolution.

Non-noble metal oxides have emerged as potential candidate electrocatalysts for acidic oxygen evolution reactions (OERs) due to their earth abundance; however, improving their catalytic activity and stability simultaneously in strong acidic electrolytes is still a major challenge. In this work, we report Co 3 O 4 @carbon core-shell nanoparticles on 2D graphite sheets (Co 3 O 4 @C-GS) as mixed-dimensional hybrid electrocatalysts for acidic OER. The obtained Co 3 O 4 @C-GS catalyst exhibits a low overpotential of 350 mV and maintains stability for 20 h at a current density of 10 mA cm -2 in H 2 SO 4 (pH = 1) electrolyte. X-ray photoelectron and X-ray absorption spectroscopies illustrate that the higher content of Co 3+ sites boosts acidic OER. Operando Raman spectroscopy reveals that the catalytic stability of Co 3 O 4 @C nanoparticles during the acidic OER is enhanced by the introduction of graphite sheets. This interface engineering of non-noble metal sites with high valence states provides an efficient approach to boost the catalytic activity and enhance the stability of noble-metal-free electrocatalysts for acidic OER.