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Regulating oxidation state of Cu-based chalcogenides catalysts during electrolysis is of great significance for efficient CO 2 electrochemical reduction reaction (CO 2 RR) to methanol, which still remains a dramatic challenge. Herein, we construct a heterogeneous Cu 3 VS 4 /CuS electrocatalyst (denoted as CuV x S), in which the in-situ growing Cu-S-V bonds avoid the accumulated electrons on oxidized Cu sites and inhibit the deep reduction of CuS to metallic Cu during electrolysis, maintaining stable and abundant reactive Cu+/Cu2+ species to promote CO 2 RR performance to methanol. By this design, the CuV 0.1 S catalyst achieves an ultrahigh methanol selectivity of 79.8 %. In-situ FTIR measurement reveals that the synergistic effect of Cu+/Cu2+ species and Cu-S-V bonding facilitates the *CO adsorption and the subsequent *CO hydrogenation process, which improve the generation of *CHO and *OCH 3 intermediates for enhanced methanol selectivity. This work provides a new insight into stabilizing high oxidation state of Cu-based electrocatalyst to maintain sufficient active sites for CO 2 RR. [Display omitted] • A strategy to stabilize active Cu+/Cu2+ species in copper chalcogenides during CO 2 RR was proposed. • A heterogeneous CuS/Cu 3 VS 4 composite catalyst with robust Cu-S-V bonds was successfully synthesized. • The in-situ growing Cu-S-V bonds continuously protected active Cu+/Cu2+ species through electron distribution to V sites. • An ultrahigh methanol FE of 79.8 % for CO 2 RR in aqueous electrolyte was achieved. [ABSTRACT FROM AUTHOR]

Achieving precise selectivity control towards the sustainable production of biofuels and chemicals in biomass resources valorization via selective C-O bond activation is an important but challenging target. Herein, a selective conversion strategy of lignocellulosic-derived γ-valerolactone (GVL) using MFI-type HZSM-5 zeolite-mediated Co-based synergetic catalysts is reported. The as-synthesized Co@HZSM-5 catalyst with highly dispersed and stable Co nanoparticles inside microcrystal enables exceedingly high selectivity for the valeric biofuel production from GVL, whereas the zeolite-supported Co/HZSM-5 catalyst exhibits a selectivity switching towards pentane biofuel under otherwise identical conditions. This selectivity difference stems from the diverse synergetic catalysis between metallic Co and acidic HZSM-5 support of Co@HZSM-5 versus Co/HZSM-5 in GVL upgrading. Theoretical calculations further demonstrate the distinct ring C-O bond strength of GVL under these two Co chemical microenvironments, which is crucial to tune the C-O bond activation modes in GVL ring-opening, affording a flexible selectivity switching toward valeric- or pentane-oriented reaction channels. [Display omitted] • Highly dispersed and stable Co nanoparticles was finely encapsulated in HZSM-5. • Selectivity switching of valeric/pentane biofuels from GVL upgrading was achieved. • Diverse Co-acid synergetic effects under two Co chemical environments were found. • Well-controlled ring C-O bond activation mode in GVL ring-opening was achieved. [ABSTRACT FROM AUTHOR]