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

TLDR: In this paper, 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.

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.