Valorizing Lignocellulosic Waste through Mediated Electrochemical Oxidation for Efficient, Low-voltage Hydrogen Production

Biomass-assisted electrolysis (BAE) is a promising alternative to conventional water electrolysis for hydrogen production, significantly reducing operating voltage and energy consumption by replacing the anodic oxygen evolution reaction with biomass oxidation. In this work, the phosphomolybdic acid (PMA)-mediated electrochemical process was investigated for the valorization of lignocellulosic biomass coupled with low-voltage hydrogen generation. Two lignocellulosic substrates, steam-exploded lignin and paper mill sludge, were subjected to oxidative pretreatment in aqueous solution using PMA at 100 °C. During this step, biomass components were partially oxidized while PMA was reduced. The reduced mediator was then electrochemically regenerated in an H-type cell, simultaneously enabling hydrogen evolution at the cathode. The process operated at a cell potential of 0.7 V vs SHE at 25 °C, corresponding to an energy consumption of 67 MJ/kg H2, substantially lower than conventional water electrolysis (~190 MJ/kg H2). GC-MS, HPLC, voltammetric analyses, chronoamperometry, and elemental analysis confirmed significant substrate degradation and enabled evaluation of oxidation efficiencies. The results highlight PMA-mediated BAE as an effective strategy for sustainable hydrogen production from renewable lignocellulosic feedstocks.