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 CuOx nanowire forest on 3D porous Cu foam (CuOx-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 CuOx 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 (FEC2H5OH) and a total Faradaic efficiency of 69.4% for all carbonaceous compounds (FEC-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 FEC-total than that of Cu nanowire forest supported on 3D porous Cu foam (Cu-NWF@Cu-F) obtained by in-situ reduction of the CuOx-NWF@Cu-F via annealing at H2 atmosphere, and thereby effectively suppressed the hydrogen evolution side-reaction.