Developing efficient and durable oxygen evolution reaction (OER) electrocatalysts for acidic media is vital for advancing proton exchange membrane water electrolyzers (PEMWEs) but remains highly challenging. In this work, a lattice-engineered Cr-doped Co 3 O 4 (Cr 0.3 -Co 2.7 O 4 ) electrocatalyst is constructed and achieves high activity and robustness for acidic OER. Spectroscopic and theoretical analyses reveal that Cr preferentially substitutes Co 3+ octahedral sites to form “CrO 6 ” units and transfers charge from Cr to the coordinated O atoms, activating them as intrinsic proton receptors. This unique functionality enables the formation of a bridged *O-O-H-O* intermediate, which circumvents the scaling relationship in the adsorbate evolution mechanism and accelerates OER kinetics. Meanwhile, Cr incorporation strengthens neighboring Co-O bonds, preserving structural integrity under acidic conditions. As a result, the Cr 0.3 -Co 2.7 O 4 electrocatalyst delivers an overpotential of 404 mV at 50 mA cm -2 , outperforming commercial IrO 2 (417 mV). In a PEMWE, it delivers 200 mA cm -2 at 1.71 V with 500 h continuous operation and only 18 μV h -1 degradation. This work establishes lattice engineering of intrinsic proton-accepting motifs as a viable strategy for designing efficient, durable and noble-metal-free electrocatalysts for acidic OER. The Cr-doped Co 3 O 4 (Cr 0.3 -Co 2.7 O 4 ) electrocatalyst is designed through the lattice-engineered strategy featuring precise control over the Cr substituting Co 3+ octahedral site to form “CrO 6 ” unit. Cr-to-O charge transfer enables the O atom to act as a proton acceptor that couples with *O-O-H to form a bridged *O-O-H-O* intermediate, promoting an effective oxygen evolution reaction via H-receptor-mediated adsorbate evolution mechanism. • Cr-doped Co 3 O 4 (Cr 0.3 -Co 2.7 O 4 ) catalyst is constructed by a lattice-engineered strategy. • Cr substituting Co 3+ octahedral site forms “CrO 6 ” unit with Cr-to-O charge transfer. • atoms function as proton acceptors to form a *O-O-H-O* intermediate that breaks the OER scaling relationship. • Efficient and robust proton-exchange-membrane water electrolyzer is realized with the Cr 0.3 -Co 2.7 O 4 catalyst.
Liu et al. (Sun,) studied this question.