Thermodynamic phase control of Cu-Sn alloy electrocatalysts for selective CO 2 reduction.

In the electrochemical CO 2 reduction reaction (CO 2 RR), Cu alloy electrocatalysts can control the CO 2 RR selectivity by modulating the intermediate binding energy. Here, we report the thermodynamic-based Cu-Sn bimetallic phase control in heterogeneous catalysts for selective CO 2 conversion. Starting from the thermodynamic understanding about Cu-Sn bimetallic compounds, we established the specific processing window for Cu-Sn bimetallic phase control. To modulate the Cu-Sn bimetallic phases, we controlled the oxygen partial pressure (pO 2 ) during the calcination of electrospun Cu and Sn ions-incorporated nanofibers (NFs). This resulted in the formation of CuO-SnO 2 NFs (full oxidation), Cu-SnO 2 NFs (selective reduction), Cu 3 Sn/CNFs, Cu 41 Sn 11 /CNFs, and Cu 6 Sn 5 /CNFs (full reduction). In the CO 2 RR, CuO-SnO 2 NFs exhibited formate (HCOO - ) production and Cu-SnO 2 NFs showed carbon monoxide (CO) production with the faradaic efficiency (FE) of 65.3% at -0.99 V ( vs. RHE) and 59.1% at -0.89 V ( vs. RHE) respectively. Cu-rich Cu 41 Sn 11 /CNFs and Cu 3 Sn/CNFs enhanced the methane (CH 4 ) production with the FE of 39.1% at -1.36 V ( vs. RHE) and 34.7% at -1.50 V ( vs. RHE). However, Sn-rich Cu 6 Sn 5 /CNFs produced HCOO - with the FE of 58.6% at -2.31 V ( vs. RHE). This study suggests the methodology for bimetallic catalyst design and steering the CO 2 RR pathway by controlling the active sites of Cu-Sn alloys.