Engineering the electronic structure of Ni–Co bimetallic sites toward efficient electrochemical biomass upgrading and CO2 reduction

Abstract

Electrochemical coupling of the 5-hydroxymethylfurfural oxidation reaction (HMFOR) and CO₂ reduction reaction (CO₂RR) offers a promising route to produce high-value chemicals while lowering the energy input. A critical bottleneck in the CO₂-HMF coupled system is the poor ability of the anode catalyst to adsorb and desorb HMF and OH⁻, resulting in prohibitively high energy consumption. We construct an anode catalyst NiCo₂O₄ by regulating the tetrahedral site to increase the ratio of Co³⁺/Co²⁺, which achieves a faradaic efficiency (FE) for 2,5-furandicarboxylic acid (FDCA) of 99.1% at 1.5 V vs. RHE. The CO₂-HMF coupled system with NiCo₂O₄ as an anode and Au as a cathode at a low cell voltage of 1.7 V affords a total energy conversion efficiency of 43.3%; the FE_FDCA of the anode is 91.9%, and the FE of the cathode is 94.7% (66.1% for CO and 28.6% for H₂). In-situ surface-enhanced Raman spectroscopy further elucidates the dynamic evolution of the surface state and intermediates of the integrated system: the NiCo₂O₄ anode promotes HMF-to-FDCA conversion via potential-dependent formation of Ni³⁺ and Co³⁺ intermediates for OH⁻ capture. Meanwhile, the key intermediate *CO for CO₂-to-CO conversion is detected at the cathode, and the simultaneous progress of the anodic and cathodic reactions significantly reduces the energy consumption of the coupled system. This work provides important theoretical support and a technical approach for the design and amplification of CO₂-HMF coupled systems.