Selective upgrading coal-based humic acid to fulvic acid through electrochemical oxidation coupled with hydrogen production

This study presents an efficient approach to selectively upgrade coal-based humic acid (CBHA) from depolymerized lignite to fulvic acid (FA) while co-producing H₂ via electro-catalytic oxidation using NiCoOOH supported on nickel foam (NF) as the anode. In comparison, the prepared NiCoOOH/NF demonstrated a superior electro-catalytic oxidation performance than NiCuOOH/NF, NF, and Pt. The results showed that a 50.30 % conversion of CBHA with FA selectivity exceeding 85 % was achieved by conducting electrolysis in 1 mol/L KOH at 1.42 V (vs. RHE) for 2 h, meanwhile H₂ was produced with a Faradaic efficiency (FE) of 98 % at the cathode. Following this, a series of analytical techniques including SEM, XRD, CV, and LSV were utilized to characterize the structure and electrochemical performances of NiCoOOH/NF. Based on the results from ESI FT-ICR/MS, MALDI TOF/MS, and ¹³C NMR, the degradation of CBHA involves oxidative ring-opening of aromatic nuclei, which leads to the formation of polycarboxylic acids, including aromatic and aliphatic carboxylic acids. Overall, this study introduces a highly efficient and selective electro-oxidation upgrading strategy, presenting a promising method for the low-carbon and high-value utilization of lignite and its CBHA.