High Formate Selectivity and Deactivation Mechanism of CuS Nanoparticles in CO₂ Electrocatalytic Reduction Reaction

CO₂ electroreduction into liquid fuels is of broad interest and benefits reducing the energy crisis and environment burdens. CuS has been reported to be a desirable candidate for CO₂ electroreduction into formate; however, its formate selectivity and stability are still far from the demands of practical application. Herein, we report CuS nanoparticles exhibiting good Faradaic efficiency of formate (about 98 %) in CO₂ electroreduction and its deactivation mechanism during the reaction. The deactivation of CuS was found to be associated with the reconstruction and S loss of CuS, which deteriorates the Faradaic efficiency of formate. Combined with ionic and gas analyses, the S atom in CuS was lost in the form of H₂S, SO₂, and SO₄²⁻, followed by the reconstruction of CuS into copper oxides. Such a catalyst reconstruction facilitates electroreductions of CO₂ and H₂O, respectively, into CO and H₂, etc., resulting in the degradation of catalytical performance of CO₂ electroreduction into formate. This work reveals the important role of S loss and reconstruction of metal sulfide catalysts during the electroreduction reaction, which may benefit the further development of CuS-based electro-catalyst for CO₂ electroreduction.