Copper oxide derived nanostructured self-supporting Cu electrodes for electrochemical reduction of carbon dioxide

Abstract

Due to their unique activity towards formation of alcohols and hydrocarbons, copper (Cu) based catalysts have been widely used in the electrochemical reduction of carbon dioxide (ERCD). Cu foam naturally possesses three-dimensional (3D) porous structure and catalytically active Cu elements, exhibiting very good catalytic ability for ERCD. Herein, nanostructured self-supporting Cu electrodes with Cu foam as the substrate, with progressive morphologies of nanowires (CuNW), nanosheets (CuNS) and nanoflowers (CuNF), are in-situ prepared by simply adjusting the reaction time in a strongly alkaline oxidizing solution. It is found that the performance and products distribution of ERCD are affected by both the morphology of the as prepared nanostructured self-supporting Cu electrodes and the electrolyte species. As electrode micromorphology evolves from nanowire to nanoflower, the initial electrode potential required for C2 products generation shifts to more positive values. The CuNS electrode shows the highest Faradaic efficiency (FE) of 86.9% at −0.4 V (vs. RHE) and superior performance, owing to its nanosheet morphology that can better stabilize the intermediate state products. Moreover, both total FE and products distribution are affected by the electrolyte anion species. The highest total FE in the investigated electrolyte on CuNS electrode obeys the following order: KHCO3 (86.9%, −0.4 V (vs. RHE)) > KCl (54.7%, −0.5 V (vs. RHE)) > KH2PO4 (1.0%, −0.9 V (vs. RHE)). In 1.0 mol L−1 KHCO3, the CuNS electrode shows a very complex products distribution; in 1.0 mol L−1 KCl, the products distribution can be feasibly controlled by the applied potential; while in 1.0 mol−1 L KH2PO4, ERCD is almost totally suppressed by hydrogen evolution reaction (HER). It is the first time that the CuNS electrodes are applied for ERCD with low cost, simple synthesis, easy scale-up and high activity. Combined with the flexible control ability in FE and products distribution, CuNS electrode possesses great potential for the industrial application of ERCD. © 2019 Elsevier Ltd