Lignin Electrolysis at Room Temperature on Nickel Foam for Hydrogen Generation: Performance Evaluation and Effect of Flow Rate

Abstract

Water electrolysis is a thermodynamically energy-intensive process. One approach employed to make water electrolysis kinetically favorable is replacing the oxygen evolution reaction (OER) at the anode by facile electrooxidation of biomass-feedstocks such as ethanol, methanol, glycerol, and lignin due to the presence of readily oxidizable functional groups. In this work, we report a simplistic approach for hydrogen generation by lignin electrolysis, utilizing a low-cost nickel foam as both anode and cathode sandwiched with hydroxide ion (OH-) exchange membrane in a 3D printed reactor. The performance of the lignin electrolysis was analyzed under various flow rates of anolyte (lignin)/catholyte (KOH) in the anode and cathode chambers. The lignin electrolysis outcompetes traditional water electrolysis by achieving higher current density in the applied voltage range from 0 to 2.5 V at room temperature. The charge transfer resistance for the lignin electrolysis is lower than that of the water electrolysis characterized by impedance spectroscopy. The enhanced current density from the lignin electrolysis at low overvoltage has been presumed from the oxidation of reactive functional groups present in the lignin, facilitating faster electron transfer. Moreover, the hydrogen production rate calculated from the chronoamperometry test of the lignin electrolysis is 2.7 times higher than that of water electrolysis. Thus, the electrochemical oxidation of lignin can potentially lower the capital cost of renewable hydrogen production.