Tailoring the product selectivity of electrochemical CO₂ reduction at copper-tin composite oxide nanofibers

Electrochemical reduction of carbon dioxide (CO₂RR) has been receiving attention as an attractive technique to convert CO₂ into various useful resources. Because CO₂RR generally produces diverse products and competes with hydrogen reduction reaction (HER), the development of efficient electrocatalysts exhibiting high product selectivity is required. This paper demonstrates a simple approach to synthesize Cu-Sn bimetallic oxide nanofibers with various Cu/Sn composition ratios using electrospinning and post-calcination. The prepared nanofibers (denoted as Cu₁Sn_xO_y, x = 0.5, 1, 2) showed excellent electrocatalytic activity and product selectivity for CO₂RR, which were drastically improved from those of single metal oxides (i.e, CuO and SnO₂). Of great importance, the product selectivity could be finely controlled by changing the Cu/Sn content ratio in Cu₁Sn_xO_y nanofibers. In fact, Cu-enriched Cu₁Sn_0.5O_y showed nearly exclusive faradaic efficiency (FE) for carbon monoxide (CO) at −0.8 V_RHE (∼95 %); and Sn-enriched Cu₁Sn₂O_y exhibited high FE for formic acid at −0.9 V_RHE (∼91 %), supporting the exceptionally high selectivity to CO and formic acid, respectively. In addition, both Cu₁Sn_0.5O_y and Cu₁Sn₂O_y nanofibers barely generated hydrogen during CO₂RR, suppressing HER successfully.