Catalyst-Free Lignosulfonate Electro-Oxidation for Oxygen Management via Paired Electrolysis

This study explores paired electrolysis, leveraging the oxygen reduction reaction (ORR) and industry-relevant lignosulfonate oxidation to enhance sustainable electrochemical processes. The anode reaction is driven by the direct oxidation of lignosulfonate, an abundant biopolymer derived from sulfite pulping, on bare graphite electrodes, eliminating the need for costly catalysts. This process occurs in a membrane electrolyzer, where the cathode catalyst dictates ORR selectivity: a carbon paper cathode modified by the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) favors hydrogen peroxide formation via a 2-electron pathway, while a platinum-modified carbon paper cathode facilitates full oxygen reduction to water via a 4-electron pathway. When applying a cell voltage of 0.7 V (a geometrical current density of 0.04 mA cm–2), the air-saturated catholyte had an 8-fold decrease in dissolved oxygen, which corresponded to 68% faradaic efficiency and an electrical energy consumption of 0.0233 W hour l–1. Removing the low molecular weight lignosulfonate (<3.5 kDa) via dialysis minimizes membrane crossover but also reduces oxygen consumption rates. The oxidation process preserves the lignosulfonate backbone while enriching its quinone content, offering a novel, energy-efficient approach to biomass valorization. By integrating lignosulfonate oxidation with ORR, this work presents a cost-effective and sustainable alternative to conventional anodic processes, with potential applications in green hydrogen peroxide production and biobased electrochemical systems.