Electrolyte-mediated Cu+/Cu0 ratio control in Cu/graphene catalysts for divergent CO2 electroreduction pathways.

The electrochemical CO2 reduction reaction (CO2RR) to multi‑carbon products offers a promising route for sustainable fuel production, yet achieving high selectivity remains challenging due to the complex interplay between catalyst structure and reaction pathways. Here, we report a rational design of Cu-Cu2O/graphene (Cu/G) composites with tunable Cu+/Cu0 ratios via electrolyte-mediated electrochemical synthesis. By varying tetraalkylammonium/phosphonium electrolytes (TBABF4, TBAPF6, TBACF3SO3, TBPBF4), we precisely control Cu oxidation states, as validated by the results of X-ray absorption fine structure (XAFS), X-ray diffraction (XRD), and high-resolution transmission electron microscope (HRTEM). In-situ Fourier transform infrared (In-situ FTIR) spectra and in-situ Raman spectra indicate Cu+-rich surfaces (Cu/G-TBABF4) favor the production of formate via O-bound intermediates, while Cu0-dominated interfaces (Cu/G-TBAPF6) promote the formation of CO through C-bound pathways. Mixed Cu+/Cu0 systems (Cu/G-TBACF3SO3, Cu/G-TBPBF4) enable CC coupling, with ethylene (FE = 28 %) and ethanol (FE = 30.2 %) selectivity governed by the Cu+/Cu0 balance. Ultraviolet photoelectron spectroscopy (UPS) results reveal that lower work functions enhance *CO coverage and stabilize C2+ intermediates, elucidating the electronic structure-activity relationship. This work demonstrates electrolyte-mediated oxidation state engineering as a versatile strategy to steer CO2RR pathways, offering a generalizable approach for designing multi-valent electrocatalysts with tailored selectivity.