Thermodynamic Phase Control of Cu-Sn Alloy Electrocatalysts for Selective CO2 Reduction

In the electrochemical CO₂ reduction reaction (CO₂RR), Cu alloy electrocatalysts can control the CO₂RR selectivity by modulating the intermediate binding energy. Here, we report the thermodynamic-based Cu-Sn bimetallic phase control in heterogeneous catalysts for selective CO₂ 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 (pO₂) during the calcination of electrospun Cu and Sn ions-incorporated nanofibers (NFs). This resulted in the formation of CuO-SnO₂ NFs (full oxidation), Cu-SnO₂ NFs (selective reduction), Cu₃Sn/CNFs, Cu₄₁Sn₁₁/CNFs, and Cu₆Sn₅/CNFs (full reduction). In the CO₂RR, CuO-SnO₂ NFs exhibited formate (HCOO^-) production and Cu-SnO₂ 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 Cu₄₁Sn₁₁/CNFs and Cu₃Sn/CNFs enhanced the methane (CH₄) production with the FE of 39.1% at -1.36 V (vs RHE) and 34.7% at -1.5 V (vs RHE). However, Sn-rich Cu₆Sn₅/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 CO₂RR pathway by controlling the active sites of Cu-Sn alloys.