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 −1.50 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.