Enhanced Cuprophilic Interactions in Crystalline Catalysts Facilitate the Highly Selective Electroreduction of CO2 to CH4

Abstract

Cu(I)-based catalysts have proven to play an important role in the formation of specific hydrocarbon products from electrochemical carbon dioxide reduction reaction (CO₂RR). However, it is difficult to understand the effect of intrinsic cuprophilic interactions inside the Cu(I) catalysts on the electrocatalytic mechanism and performance. Herein, two stable copper(I)-based coordination polymer (NNU-32 and NNU-33(S)) catalysts are synthesized and integrated into a CO₂ flow cell electrolyzer, which exhibited very high selectivity for electrocatalytic CO₂-to-CH₄ conversion due to clearly inherent intramolecular cuprophilic interactions. Substitution of hydroxyl radicals for sulfate radicals during the electrocatalytic process results in an in situ dynamic crystal structure transition from NNU-33(S) to NNU-33(H), which further strengthens the cuprophilic interactions inside the catalyst structure. Consequently, NNU-33(H) with enhanced cuprophilic interactions shows an outstanding product (CH₄) selectivity of 82% at -0.9 V (vs reversible hydrogen electrode, j = 391 mA cm^-2), which represents the best crystalline catalyst for electrocatalytic CO₂-to-CH₄ conversion to date. Moreover, the detailed DFT calculations also prove that the cuprophilic interactions can effectively facilitate the electroreduction of CO₂ to CH₄ by decreasing the Gibbs free energy change of potential determining step (*H₂COOH → *OCH₂). Significantly, this work first explored the effect of intrinsic cuprophilic interactions of Cu(I)-based catalysts on the electrocatalytic performance of CO₂RR and provides an important case study for designing more stable and efficient crystalline catalysts to reduce CO₂ to high-value carbon products.