Unravelling the chemistry of catalyst surfaces and solvents towards C–C bond formation through activation and electrochemical conversion of CO2 into hydrocarbons over micro-structured dendritic copper

Herein, we report the results from our study towards understanding the role of electrocatalyst surfaces and solvents (aqueous versus wet organic media) in C–C bond formation on microstructured spheres, polygons, aggregates and dendrites of copper, which is a crucial aspect for the selective and sustainable conversion of CO2 into high energy density hydrocarbons like ethylene. Our results establish that apart from morphology, the crystal orientations and characteristic electrode/electrolyte interfacial physico-chemical aspects significantly affect the electrochemical carbon dioxide reduction (ECR) reaction activity and selectivity of copper electrocatalysts. Moreover, we report that an appropriate combination of catalyst properties and solvent/electrode interface ensures selective electroreduction of CO2 into C1 and C2 hydrocarbons, especially ethylene, over dendritic copper electrocatalysts. We demonstrate that for a given solvent system, the morphology of the electrocatalyst is the sole determinant of its catalytic activity, with elaborate dendritic shape enhancing the ECR reaction irrespective of the solvent used. A detailed account of the electrocatalytic performance, product selectivity, and faradaic efficiency of Cu-electrodeposits for ECR in aqueous medium and wet-organic (DMSO) electrolyte is presented. In aqueous 0.2 M KHCO3 solution, the catalyst exhibits a faradaic efficiency of 43% for ethylene production at −1.0 V vs. RHE and a selectivity of 74% among all the hydrocarbon products. Importantly, the Cu-based electrocatalysts fabricated for the present study inhibit the parasitic hydrogen evolution reaction and production of parallel products, viz. CO, CH4, and C2H6, during the ECR. Our results further establish that C–C coupling for the formation of ethylene is affected by the nano-morphology of the electrocatalyst and the composition of the electrolyte system employed for the electroreduction.