New Insight into the Electronic Effect for Cu Porphyrin Catalysts in Electrocatalytic of CO<sub>2</sub> into CH<sub>4</sub>
Hao Jiang, Peng Zhao, Haidong Shen, Shaowei Yang, Runze Gao, Ying Guo, Yueling Cao, Qiuyu Zhang, Hepeng Zhang
Abstract
Abstract Perturbation of the copper (Cu) active site by electron manipulation is a crucial factor in determining the activity and selectivity of electrochemical carbon dioxide (CO 2 ) reduction reaction (e‐CO 2 RR) in Cu‐based molecular catalysts. However, much ambiguity is present concerning their electronic structure–function relationships. Here, three molecular Cu‐based porphyrin catalysts with different electron densities at the Cu active site, Cu tetrakis(4‐methoxyphenyl)porphyrin (Cu─T(OMe)PP), Cu tetraphenylporphyrin (Cu─THPP), and Cu tetrakis(4‐bromophenyl)porphyrin (Cu─TBrPP), are prepared. Although all three catalysts exhibit e‐CO 2 RR activity and the same reaction pathway, their performance is significantly affected by the electronic structure of the Cu site. Theoretical and experimental investigations verify that the conjugated effect of ─OCH 3 and ─Br groups lowers the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbitals (LUMO) gap of Cu─T(OMe)PP and Cu─TBrPP, promoting faster electron transfer between Cu and CO 2 , thereby improving their e‐CO 2 RR activity. Moreover, the high inductive effect of ─Br group reduces the electron density of Cu active site of Cu─TBrPP, facilitating the hydrolysis of the bound H 2 O and thus creating a preferable local microenvironment, further enhancing the catalytic performance. This work provides new insights into the relationships between the substituent group characteristics with e‐CO 2 RR performance and is highly instructive for the design of efficient Cu‐based e‐CO 2 RR electrocatalysts.