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

The electrochemical CO 2 reduction reaction (CO 2 RR) 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-Cu 2 O/graphene (Cu/G) composites with tunable Cu + /Cu 0 ratios via electrolyte-mediated electrochemical synthesis. By varying tetraalkylammonium/phosphonium electrolytes (TBABF 4 , TBAPF 6 , TBACF 3 SO 3 , TBPBF 4 ), 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-TBABF 4 ) favor the production of formate via O-bound intermediates, while Cu 0 -dominated interfaces (Cu/G-TBAPF 6 ) promote the formation of CO through C-bound pathways. Mixed Cu + /Cu 0 systems (Cu/G-TBACF 3 SO 3 , Cu/G-TBPBF 4 ) enable C C coupling, with ethylene (FE = 28 %) and ethanol (FE = 30.2 %) selectivity governed by the Cu + /Cu 0 balance. Ultraviolet photoelectron spectroscopy (UPS) results reveal that lower work functions enhance *CO coverage and stabilize C 2+ intermediates, elucidating the electronic structure-activity relationship. This work demonstrates electrolyte-mediated oxidation state engineering as a versatile strategy to steer CO 2 RR pathways, offering a generalizable approach for designing multi-valent electrocatalysts with tailored selectivity.