Improving water electrolysis assisted by anodic biochar oxidation for clean hydrogen production

Biochar-assisted water electrolysis (BAWE) for hydrogen production is an effective way to integrate renewable electricity and biomass utilization. But it is limited by slow biochar oxidation reaction (BOR). Here we adopted the biochar derived from pyrolysis (PB) and hydrothermal carbonization (HB) of rice husk. Replacement of oxygen evolution reaction with BOR leaves a significantly reduced onset potential (E-onset) and an increased current density. Strongly related to carbonization temperature, the physicochemical properties of biochar markedly affected BOR. The abundant -OH groups in HB contributed to a low E-onset, while the well-developed pore structure and high specific surface area of PB enhanced its reactivity at higher potential. Exposure of functional groups on PB surface after pickling made an increase in current density, but the simultaneous elimination of easily oxidized solutes in HB dominated and caused current density decline. H2SO4 electrolyte of 1 mol/L was most appropriate for the uniform dispersion of biochar particles. The oxidation of PB derived at 800 degrees C with a slurry concentration of 10 g/L showed the lowest charge-transfer resistance and a favorable kinetics. Continuous BAWE indicated that PB was more superior than HB in increasing current density and H-2 production. This work provides favorable strategies for improving BAWE. (C) 2021 Elsevier Ltd. All rights reserved.