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. © Science China Press 2023