Continuous electro-oxidation of lignin to vanillic and syringic acid at near 100 mA·cm-2

The use of lignin as a renewable feedstock for valuable chemicals has gained significant momentum due to the ongoing depletion of fossil fuel reserves and the environmental harm caused by their overuse. However, extracting useful products from this recalcitrant biopolymer requires a highly selective fragmentation process. This article demonstrates that such a process can be effectively achieved through an electrochemical approach. While Ni- and Co-based catalysts have been previously employed for lignin electrooxidation, the optimal composition of mixed metal oxyhydroxides—crucial for achieving higher yields and faradaic efficiencies—has not been thoroughly investigated until now. This optimization was made possible by a comprehensive study beginning with lignin model compounds, which elucidated the reaction mechanism and facilitated the subsequent scaling of the reaction using organosolv pine lignin. Remarkably, this approach yielded up to 6.0 wt% vanillic acid. These unprecedented results were achieved through the meticulous design of an electrochemical flow cell, ensuring that the electrochemical production of lignin monomers is not only cost-effective and selective but also easily scalable.