Enzymatic depolymerization of lignin and electrocatalytic hydrodeoxygenation for the production of reduced aromatic compounds: A review and perspective

The depletion of fossil resources and growing environmental concerns have intensified the search for sustainable alternatives for fuel and chemical production. Lignin, an abundant yet underutilized component of lignocellulosic biomass, presents significant potential as a renewable source of aromatic compounds. In this review and perspective, we highlight recent advancement in lignin valorization through enzymatic depolymerization using bacterial and fungal lignin degrading enzymes, and electrocatalytic hydrodeoxygenation (ECHDO). The review delves into the structure and inherent recalcitrance of lignin, alongside the mechanisms and efficiencies of various lignin-degrading enzymes, such as peroxidases and laccases, as reported in recent studies. It also provides a critical evaluation of the principles, benefits, and progress in ECHDO for upgrading lignin-derived compounds, with a focus on reactor design, catalyst systems, and energy efficiency. Key challenges and opportunities for advancing both processes are explored, along with future directions for their integration and optimization. While these technologies are currently being investigated separately, we provide a perspective for their potential integration by highlighting key challenges and opportunities for the development of an integrated bioelectrochemical platform for sustainable lignin valorization. By synthesizing current knowledge, this comprehensive review offers valuable insights for researchers and industry professionals striving to advance the sustainable utilization of lignin within biorefineries, contributing to the advancement of the circular bioeconomy.