Electrocatalytic Oxidation of 1,2-Cyclohexanediol to Adipic Acid with high Faradaic Efficiency under High Current Density Over a CoFe₂O₄@CuO/CF Catalyst

Abstract

Adipic acid (AA) is an important chemical raw material used to prepare polymers (nylon-66). The traditional preparation method relies on a strong oxidation to produce AA. However, these methods are limited by environmental pollution, fossil fuel dependence, and low conversion efficiency and selectivity. Here, we report an electrocatalytic strategy for the oxidation of biomass-derived 1,2-Cyclohexanediol (CHD) to AA and the production of H2 on CoFe₂O₄@CuO/CF hierarchical heterostructure nanoarray catalyst. CuO nanowire array grown on copper foam (CF) surface, CoFe₂O₄ nanosheets further modified on CuO nanowires. Remarkably, CoFe₂O₄@CuO/CF exhibited top-level activity for the electrooxidation of CHD to AA (10 mA cm-2 at 1.20 V vs RHE), with 93.8% CHD conversion rate, 84.8% AA selectivity, outstanding Faraday efficiency (FE) of 88.9%, and long-term stability (120 h). The improved electrocatalytic performance has been studied by various characterization techniques, including in-situ Raman spectroscopy, Open-circuit potential (OCP), apparent activation energy (Eapp) tests, and the operando EIS measurements. And the intermediates of the electrocatalytic CHD were investigated using in-situ ATR-FTIR spectroscopy. The test results indicate that the synergistic effect of CuO and CoFe₂O₄ is the key to improving the performance of the catalyst. CuO has a better ability to adsorb and activate CHD, and the adsorbed CHD can be quickly oxidized by high valence active CoIII/CoIV species generated in-situ by electrochemical processes, promoting the cleavage of C-C bonds to obtain AA. Furthermore, a coupled electrolytic cell that simultaneously generates AA and H2 is constructed by CoFe₂O₄@CuO/CF anode and Pt sheet cathode. The coupled electrolytic cell requires an ultra-low potential of 1.12 V to drive hydrogen evolution at current density of 10 mA cm-2. Significantly, at an industrial current density of 300 mA cm-2, the coupled system exhibits a record-breaking CHD FE up to 82.3% and a productivity of 1715 μ mol cm-2 h-1 for the production of AA, while achieving stability for over 50 h. This greatly solves the limitations of its industrial feasibility, namely the limitations of low current density (but high FE) and high current density (with low FE, competitive oxygen evolution reaction). This work demonstrates an efficient catalyst for the electro synthesis of AA, which has high production efficiency and demonstrates industrial potential.