Engineering Twins within Lattice-Matched Co/CoO Heterostructure Enables Efficient Hydrogen Evolution Reactions

Twinning, as an effective strain engineering strategy, has demonstrated significant potential in modifying cost-effective transition metal electrocatalysts. However, controllable construction and structure-activity relationships of twinning in electrocatalysts remain formidable challenges. Here, we engineered a lattice-matched Co/CoO heterostructure with enriched twin boundaries through flash Joule heating, where the twins form via lattice matching within homogeneous space groups. XAFS analysis reveals significantly reduced Co coordination numbers in the heterostructure, indicating substantial atomic displacement from the equilibrium positions. The coherent twinning interfaces induce trapped strain, downshifting the d-band center by 0.4 eV and flattening bands near the Fermi level, optimizing the electronic structure for the hydrogen evolution reaction. Consequently, the engineered heterostructure exhibits exceptional performance with an ultralow overpotential of 49 mV at 10 mA cm^-2 in alkaline media and remarkable stability over 500 h. Notably, the water splitting can be driven with an ultralow cell voltage of 2.05 V at 1 A cm^-2.