Tuning molecular electrophilicity on Cu catalysts to steer CO2 electroreduction selectivity

Cu is the only transition metal that can achieve electrochemical CO2 reduction (CRR) with the generation of hydrocarbons and oxygenates. However, it is still challenging to regulate CRR selectivity in a broad product distribution on Cu. Here, we selected a series of molecules with varying electrophilicity to modify Cu catalysts that achieve a high CRR selectivity towards either CH4 or C2H4. Theoretical analysis shows that molecular electrophilicity determines catalyst's proton availability, which promotes or inhibits the critical proton-coupled electron transfer (PCET) process in CRR. Consequently, the molecule with low electrophilicity (e.g., 1,2-bis(4-pyridyl)ethane) can facilitate proton transfer to hydro-genate *CO intermediates to generate CH4 with a Faradaic efficiency (FE) of 58.2%, while the molecule with high electrophilicity (e.g., trans-1,2-bis(4-pyridyl)ethylene) can build stronger hydrogen bonds to stabilize *CO for further dimerization, realizing an FE of 65.9% for C2H4. The combination of theoretical computation and in situ spectroscopic characterizations reveal that using molecular electrophilicity can tune catalyst's proton availability, thereby altering its CRR pathway of either *CO hydrogenation or *CO-*CO dimerization. This work provides new understanding of CRR selectivity by tuning the PCET process instead of materials engineering.