In-situ grown CuO x nanowire forest on copper foam: A 3D hierarchical and freestanding electrocatalyst with enhanced carbonaceous product selectivity in CO 2 reduction

Electrocatalytic carbon dioxide (CO₂) reduction is considered as an economical and environmentally friendly approach to neutralizing and recycling greenhouse gas CO₂. However, the design of preeminent and robust electrocatalysts for CO₂ electroreduction is still challenging. Herein, we report the in-situ growth of dense CuO_x nanowire forest on 3D porous Cu foam (CuO_x-NWF@Cu-F), which can be directly applied as a freestanding and binder-free working electrode for highly effective electrocatalytic CO₂ reduction. By adjusting the surface morphology and chemical composition of CuO_x nanowires via surface reconstruction, large electrochemically active surface area and abundant Cu(+1) sites were generated, leading to remarkable activity for CO₂ electroreduction. The as-prepared hierarchical conductive electrode exhibited an enhanced Faradaic efficiency of 15.0% for ethanol formation (FE_C2H5OH) and a total Faradaic efficiency of 69.4% for all carbonaceous compounds (FE_C-total) at a mild applied potential of –0.45 V vs. RHE in 0.1 M KHCO₃ electrolyte. It achieved a 4-fold increase in FE_C-total than that of Cu nanowire forest supported on 3D porous Cu foam (Cu-NWF@Cu-F) obtained by in-situ reduction of the CuO_x-NWF@Cu-F via annealing at H₂ atmosphere, and thereby effectively suppressed the hydrogen evolution side-reaction.