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

Abstract

Electrochemical coupling of the oxidation of 5-hydroxymethylfurfural (HMFOR) and CO2 reduction (CO2RR) offers a promising route to produce high-value chemicals while lower 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 Co 3+ /Co 2+ , which achieves a Faradaic efficiency (FE) for 2,5-furandicarboxylic acid (FDCA) of 99.0% at 1.5 V vs. RHE. The CO2-HMF coupled system with NiCo2O4 as anode and Au as cathode at low cell voltage of 1.7 V affords the total energy conversion efficiency is 43.3 %, the FEFDCA 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 Ni 3+ and Co 3+ intermediates for OH -capture. Meanwhile, the key intermediates *CO for CO2-to-CO are detected at the cathode, the simultaneous progression of the anodic and cathodic reactions significantly reduces the energy consumption of coupled system. This work provides an important theoretical support and technical approach for the design and amplification of CO2-HMF coupled system.