Stabilization of Unconventional Body‐Centered Tetragonal Phase in Copper Nanowires for Efficient Carbon Dioxide Electroreduction to Multi‐Carbon Products

ABSTRACT Copper nanomaterials with the common face‐centered cubic (fcc) phase have been widely used in the electrocatalytic carbon dioxide (CO 2 ) reduction reaction (CO 2 RR). However, copper with an unconventional phase is rarely reported as it is thermodynamically unfavorable. Here, through analyzing the strain within copper nanowires, we reveal the phase transition of copper from fcc to body‐centered tetragonal (bct)/fcc heterophase. By systematically investigating copper nanowires with different diameters and copper nanocubes in CO 2 RR, we explain the relationship between their crystal phase and catalytic performance. Compared with the standard fcc lattice, copper nanowires’ surfaces have different electron states due to a phase transition. Copper nanowires with a diameter of about 30 nm exhibit the optimum catalytic performance, and their Faradaic efficiency of multi‐carbon products is much higher than that of fcc copper nanocubes. Theoretical calculations have demonstrated that the presence of the strained bct phase induces significant upshifts of the d ‐band center, which not only improves the overall electroactivity but also optimize the C‐C couplings, leading to improved Faradaic efficiency of multi‐carbon products during CO 2 RR.