Defect Engineering on Amorphous NiFeB Alloys for the Selective Conversion of KA Oil Into Adipic Acid

Developing high-performance electrocatalysts for the efficient conversion of KA oil (a mixture of cyclohexanol and cyclohexanone) to adipic acid holds great significance. Herein, a series of Ni-based catalysts, including NiM (M = Fe, Cr, and Mn) layered double hydroxides (LDHs), NiMB LDHs and amorphous NiMB alloys, were synthesized for KA oil conversion. Among the samples, Ni₄Fe₁B alloy exhibited the highest ECSA-normalized current density of 581.5 mA cm^-2 and adipic acid selectivity of 52.7% at 1.6 V. Such superior catalytic performance is attributed to the abundant defects induced by boron incorporation, leading to modified electronic structures of nickel sites and optimized adsorption toward KA oil and intermediates. Operando electrochemical x-ray absorption fine structure analyses, combined with operando Raman spectra, suggested that the oxidation of KA oil by Ni₄Fe₁B alloy involved the transformation of Ni²⁺ into higher valence states, indicative of a possible indirect oxidation pathway. In contrast, the valence state of Ni²⁺ in the Ni₄Fe₁B and Ni₄Fe₁ LDHs remained unchanged, suggesting a possible direct oxidation mechanism. Theoretical calculations revealed that the Ni₄Fe₁B alloy exhibited strong adsorption toward cyclohexanol and cyclohexanone molecules and a low energy barrier (0.76 eV) for the rate-determining step, consistent with the experimental results.