Effects of pretreatment on biochar oxidation reaction and hydrogen production in lignocellulosic biochar-assisted water electrolysis

Substituting the oxygen evolution reaction in water electrolysis with the thermodynamically more favorable biochar oxidation reaction (BOR) constitutes biochar-assisted water electrolysis (BAWE), presenting a promising strategy for energy-efficient hydrogen production and high-value utilization biochar. Nevertheless, the BOR suffers from the sluggish kinetics and ambiguous selectivity with respect to ungraded biochar. Herein, we demonstrate the effects of elution treatment on pyrolytic lignocellulosic biochar concerning BOR kinetics and hydrogen production, as well as the efficiency of electrooxidized biochar in Cr(VI) removal. The original lignocellulosic biochar washed by alkali, acid, and water exhibited an improved BOR kinetics. Notably, the moderate water washing favored the removal of ash and soluble substances, thereby exposing more easily oxidizable functional groups such as C–OH and COOH, which substantially enhanced BOR kinetics. The water-washed biochar-assisted water electrolysis achieved a Faradaic efficiency of 99.5% for hydrogen production at 50 mA cm −2 , necessitating lower cell voltages compared to unwashed biochar. Water elution pretreatment also promoted the sufficient oxidation of biochar during electrolysis, with enriched oxygen-containing functional groups like C–O contributing to an increase in Cr(Ⅵ) removal rate from 20.81% to 65.10%. This work offers strategies for achieving efficient biochar upgrading and hydrogen production in the BAWE process.