ABSTRACT While Kirkendall oxidation (KO) facilely fabricates transition metal oxides for oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWEs), it concomitantly triggers detrimental lattice expansion. For Co 3 O 4 , an appealing IrO 2 ‐alternative catalyst, KO generates a free lattice expansion above 2.4%, resulting in suboptimal activity and stability. Here, we design a confined KO approach and coat the precursor Co nanoparticles with atomic carbon layers, enabling controllable lattice expansion of Co 3 O 4 between 0.2% and 1.8%. For the first time, a strain‐dependent OER activity of Co 3 O 4 is established in acidic media, with an expansion strain of 1.4% exhibiting the lowest overpotential of 377 mV at 10 mA cm −2 . Synchrotron X‐ray absorption spectroscopies and theoretical calculations unravel the adjustable lattice strain regulates the d‐band center of Co sites and further modifies the oxygenate adsorptions. When integrated into a PEMWE, the 1.4%‐strained Co 3 O 4 catalyst sustainably operates at 250 mA cm −2 over 100 h. The reported confined KO provides a new means for strain engineering of transition metal oxides for energy electrocatalysis.
Tang et al. (Mon,) studied this question.