Shielding effect in the synthesis of Gd-doped copper oxide catalysts with enhanced CO2 electroreduction to ethylene†

The electrocatalytic carbon dioxide reduction reaction (CO₂RR) to ethylene can achieve efficient conversion and utilization of CO₂, which also provides a new and sustainable way to mitigate climate change. Copper based catalysts exhibit specific activity for the CO₂RR to obtain C₂H₄ but are limited by their low selectivity and high overpotential. Controlled doping of rare-earth metal ions into the copper catalyst is supposed to modulate the electron density of Cu active sites and thus promote the C–C coupling reaction and enhance the selectivity of C₂H₄. Herein, we report a Gd-doped copper oxide catalyst (Gd-CuO) synthesized by a typical solvothermal method, in which the content of Gd doping and chemical state of Cu can be regulated precisely through the shielding effect of solvents used. The shielding effect contributes to the modification of cation–anion and cation–solvent interactions, which affects the crystallization of CuO and incorporation of Gd in the solvothermal process. Under optimal conditions, the Faraday efficiency of the ethylene product can reach up to 58.6% at −1.2 V vs. RHE in an H-cell. When applied in a flow cell, the Faraday efficiency of ethylene can reach 52.4% with a current density of 397.8 mA cm⁻² at the same applied voltage. In situ FTIR and DFT calculations demonstrate that the controlled doping of Gd by means of the shielding effect in synthesis facilitates the improvement of the electron density of Cu active sites and promotes the C–C coupling and adsorption of *COCOH intermediates, thus enhancing the selectivity of ethylene. This work provides insights for the design and development of rare earth doped Cu-based catalysts in the future.