Highly Tensile\nStrained Cu(100) Surfaces by Epitaxial\nGrown Hexagonal Boron Nitride for CO<sub>2</sub> Electroreduction\nto C<sub>2+</sub> Products

Copper (Cu) has been considered as the most promising\ncatalyst\nfor the electrochemical conversion of CO<sub>2</sub> to multicarbon\n(C<sub>2+</sub>) products. However, insufficient coverage of the *CO\nintermediate on the C<sub>2+</sub> formation Cu(100) facet largely\nhinders the C–C coupling process and thus the C<sub>2+</sub> conversion efficiency. Herein, we developed an epitaxial growth\nstrategy to generate highly tensile-strained Cu(100) facets via the\nepitaxial growth of hexagonal boron nitride (hBN) on Cu(100) facets\nto promote *CO coverage for efficient CO<sub>2</sub> to C<sub>2+</sub> conversion. The highest ∼6% tensile strain on the Cu(100)\nfacets was obtained by lattice mismatch between the Cu(100) and hBN(002)\nfacets. Theory calculations indicated that tensile-strained Cu(100)\nfacets deliver a notable <i>d</i>-band center upshift to\nenhance *CO adsorption. As a result, the obtained highly tensile-strained\nCu(100) facets enabled an 8-fold improvement of *CO coverage and thus\na 83.4% C<sub>2+</sub> Faradaic efficiency at 1.2 A cm<sup>–2</sup> in strongly acidic electrolyte (pH = 1).