Charge-mediated cyclohexanone enrichment and intermediate stabilization at MoNi4/MoO2 heterostructures enable paired cyclohexanone electrooxidation-hydrogen production at ampere-level current

doi:10.1016/S1872-2067(25)64858-3

Abstract

Abstract:

Electrocatalytic oxidation of cyclohexanone (KOR) to adipic acid provides a sustainable and value-added pathway for coupled hydrogen evolution (HER). However, the weak adsorption of the reactants and intermediates leads to poor reaction kinetics and product yield. Herein, we synthesized MoNi₄/MoO₂ heterostructures via phase conversion to engineer a large work function difference that optimizes the Ni electronic structure. This design enhances cyclohexanone adsorption and regulates intermediates, achieving 85% Faradaic efficiency for production of adipic acid and a 2 mmol h^-1 cm^-2 production rate, along with an ampere-level current. In a membrane electrode assembly electrolyzer for KOR-assisted HER, this catalyst displays 1 A current with 12.1 mol adipic acid production and 3.34 L H₂ generation over 8 h, maintaining stability for 56 h at 3 A. Optimized Ni electronic structure achieved through heterojunction-induced charge redistribution strengthens cyclohexanone adsorption and lowers the energy barriers for key intermediates (C₆H₁₀O₂^* and C₆H₁₀O₃^*), boosting oxidation activity. This study presents a novel heterojunction engineering strategy that synergistically enhances reactant adsorption and optimizes intermediate reaction kinetics, offering a tailored approach for efficient catalytic systems.

Key words: MoNi₄/MoO₂ heterostructures, Cyclohexanone electrooxidation, Charge redistribution, Strengthen adsorption, Intermediate stabilization

Rui Yang, Zimin Han, Yin Gao, Guoqing Feng, Huaizhi Liu, Yiyin Huang, Zhongkai Wang, Yaobing Wang. Charge-mediated cyclohexanone enrichment and intermediate stabilization at MoNi₄/MoO₂ heterostructures enable paired cyclohexanone electrooxidation-hydrogen production at ampere-level current[J]. Chinese Journal of Catalysis, 2026, 81: 344-354.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(25)64858-3

https://www.cjcatal.com/EN/Y2026/V81/I2/344

Figures/Tables 6

Fig. 1. Structural and morphological characterization. (a) Schematic of the process for the preparation of MoNi4/MoO2/NF. SEM image (inset: size distribution) (b), HRTEM image (c), XRD pattern (d), and corresponding elemental mapping images (e−h) of MoNi4/MoO2 electrocatalysts.

Fig. 2. Atomic and electronic structure characterizations. (a) Ni K-edge XANES spectra. Wavelet transforms (WT) of MoNi4/MoO2 (b) and MoNi4 samples (c). (d) Fourier transform curves. (e) k3×(k) oscillation curves. (f) XPS spectra of MoNi4 and MoNi4/MoO2 samples.

Fig. 3. Cyclohexanone electrooxidation over MoNi4/MoO2, MoNi4 and MoO2 catalysts. (a) LSV curves in 1 mol L−1 KOH with cyclohexanone. (b) Potential of KOR and OER with MoNi4/MoO2 catalyst at different current densities. (c) Tafel slopes for MoNi4/MoO2, MoNi4 and MoO2 catalysts in 1 mol L−1 KOH with cyclohexanone. Faradaic efficiency of adipic acid production over MoNi4/MoO2, MoNi4 and MoO2 catalysts at various potentials (d) and corresponding adipic acid productivity (e). Relative concentration of cyclohexanone and oxidation products during long-term electrocatalysis (f) and corresponding time-dependent HPLC spectra (g). (h) Corresponding Faradaic efficiency and adipic acid productivity for cyclohexanone electrooxidation on MoNi4/MoO2 as a function of number of electrolysis cycles. (i) Comparison with recently reported studies.

Fig. 4. (a) OCP of the MoNi4/MoO2, MoNi4, and MoO2 samples in 1 mol L−1 KOH solution before and after cyclohexanone was injected. In-situ Raman spectra of MoNi4/MoO2 in KOH without (b) and with (c) cyclohexanone. (d) Periodic sampling experiments on MoNi4/MoO2 (at 1.45 V vs. RHE, open-circuit state, and 0.95 V vs. RHE, respectively). In-situ Bode phase plots of MoNi4/MoO2 in KOH without (e) and with (f) cyclohexanone.

Fig. 5. (a) Charge density difference distribution of MoNi4/MoO2. Purple: Mo atoms. Red: O atoms. Gray: Ni atoms. (b) UPS spectra of MoNi4 and MoO2. Φ = hv − |Ecutoff − EF|, where hv, Ecutoff, and EF are the energy of the excitation light (21.22 eV), secondary electron cutoff energy, and Fermi energy, respectively. (c) Calculated Gibbs free energy. Blue: Mo atoms. Red: O atoms. Purple: Ni atoms. Gray: C atoms. White: H atoms.

Fig. 6. MEA electrochemical reactor. Schematic (a) and photographs (b) of MEA. (c) LSV curves. (d) Productivity of adipic acid at a current of 1 A (inset: photograph of purified adipic acid). (e) Stability at 3 A after seven cycles, each lasting 8 h.

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Charge-mediated cyclohexanone enrichment and intermediate stabilization at MoNi₄/MoO₂ heterostructures enable paired cyclohexanone electrooxidation-hydrogen production at ampere-level current

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