Defect-Engineered Multimetal-Electrocatalysts for Sustainable Furfural Electrodimerization toward Hydrofuroin

The electrodimerization of furfural to hydrofuroin provides a promising route for producing high-energy-density aviation-fuel precursors, yet achieving high selectivity, productivity, and long-term stability remains difficult due to marginal control over the intrinsic physicochemical properties of electrocatalysts that govern reaction pathways and intermediate stabilization. Here, a series of electrocatalysts with tunable oxyhydroxide composition, lattice oxygen, and oxygen-vacancy density was synthesized via controlled electrodeposition to achieve uniform active-site distribution on nickel foam. Although all oxygen-vacancy-rich catalysts were active toward furfural electrodimerization, Co/NF, featuring high-valence Ni–Co centers and 80.7% of its O 1s envelope attributed to hydroxylated and defect-associated oxygen species, outperformed FeCo/NF and FeCoCu/NF (74% and 77.5%, respectively). Further operando DRT analysis confirms a robust structure-relaxation-activity relationship: Co/NF exhibits a short interfacial charge-transfer relaxation time (3.2 μs) and the highest turnover frequency (4.76 × 109 s–1). The results revealed that Co/NF balanced defect distribution (oxygen vacancies 46.77%, lattice oxygen 19.52%, surface hydroxyls 33.71%) enhances conductivity without overstabilizing intermediates. In contrast, FeCoCu/NF, despite its faster electron-transfer channel (τp1 = 2.65 μs), shows the lowest relative TOF (2.04 × 109 s–1) due to excessive oxygen vacancy density (49.17%) that shifts rate-determining steps toward C–C coupling, surface restructuring, and desorption. Therefore, Co/NF achieves 2.4 g. h–1 hydrofuroin production and a productivity of 14.82 gHydrofuroin gcat–1 h–1 at η = 118 mV, sustaining 0.660 Acm–2 and a 2.29 V cell voltage for 5 h, demonstrating its promise for scalable jet-fuel precursor synthesis.