Electrocatalytic hydrogenation and depolymerization pathways for lignin valorization: Toward mild synthesis of renewable chemicals and fuels from biomass
Lignin is a prospective resource for renewable commodity organic chemicals and fuels. In the scheme of a sustainable biorefinery, lignin valorization is essential for enhancing the economic feasibility of the overall biomass transformation processes. Electrocatalysis and electrochemical processes are expected to play a major role in biomass valorization due to the possibility of using renewable electricity sources for in situ production of ‘green’ H2 and other reagents that are necessary for biomass conversion. Recent advances in the electrocatalytic hydrogenation and hydrogenolysis of lignin derivatives, including oxygenated aromatic compounds, suggest promising pathways for the synthesis of industrially relevant chemicals such as ketone-alcohol (KA) oil, the mixture of cyclohexanone and cyclohexanol for Nylon polymers. This review presents a comprehensive comparative analysis of various electrocatalyst configurations indicating that high current density electrolysis could be performed without the expense of detrimental decrease in Faradaic efficiency. Diverse electrolyte choices in catholyte-anolyte combinations could facilitate the electrocatalytic reduction and oxidation processes for lignin valorization using different metal electrocatalysts. Finally, challenges and opportunities for future development of the electrocatalytic pathways for lignin valorization are discussed.