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

In the electrochemical CO reduction reaction (CORR), Cu alloy electrocatalysts can control the CORR selectivity by modulating the intermediate binding energy. Here, we report the thermodynamic-based Cu-Sn bimetallic phase control in heterogeneous catalysts for selective CO 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) during the calcination of electrospun Cu and Sn ions-incorporated nanofibers (NFs). This resulted in the formation of CuO-SnO NFs (full oxidation), Cu-SnO NFs (selective reduction), CuSn/CNFs, CuSn/CNFs, and CuSn/CNFs (full reduction). In the CORR, CuO-SnO NFs exhibited formate (HCOO) production and Cu-SnO NFs showed carbon monoxide (CO) production with the faradaic efficiency (FE) of 65.3% at -0.99 V ( RHE) and 59.1% at -0.89 V ( RHE) respectively. Cu-rich CuSn/CNFs and CuSn/CNFs enhanced the methane (CH) production with the FE of 39.1% at -1.36 V ( RHE) and 34.7% at -1.50 V ( RHE). However, Sn-rich CuSn/CNFs produced HCOO with the FE of 58.6% at -2.31 V ( RHE). This study suggests the methodology for bimetallic catalyst design and steering the CORR pathway by controlling the active sites of Cu-Sn alloys.