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Electrocatalytic hydrogenation (ECH) of guaiacol for production of chemical and fuel in a divided cell using earth abundant metal electrodes. Specific energies shown below the organics are their higher heating values (HHV).

Lignin valorization is essential for biorefineries to produce fuels and chemicals for a sustainable future. Today's biorefineries pursue profitable value propositions for cellulose and hemicellulose; however, lignin is typically used mainly for its thermal energy value. To enhance the profit potential for biorefineries, lignin valorization would be a necessary practice. Lignin valorization is greatly advantaged when biomass carbon is retained in the fuel and chemical products and when energy quality is enhanced by electrochemical upgrading. Though lignin upgrading and valorization are very desirable in principle, many barriers involved in lignin pretreatment, extraction, and depolymerization must be overcome to unlock its full potential. This Review addresses the electrochemical transformation of various lignins with the aim of gaining a better understanding of many of the barriers that currently exist in such technologies. These studies give insight into electrochemical lignin depolymerization and upgrading to value‐added commodities with the end goal of achieving a global low‐carbon circular economy.

Lignin valorization is increasingly important as biomass fractionation approaches achieve higher technology readiness levels. One approach to upgrade lignin first involves its deconstruction by fast pyrolysis to create a lignin-derived bio-oil. The phenolics-rich liquid product is a promising feedstock for electrocatalytic hydrogenation, as aromatics can be deoxygenated and saturated by hydrogen chemisorbed on catalytic cathodes, mitigating the product’s corrosivity and raising its energy content. By integrating biomass fractionation with pyrolytic deconstruction and electrocatalytic upgrading, lignin can be valorized to fuels and chemicals that significantly enhance the profitability of biorefineries. In this study, model compounds representing lignin bio-oil components were subjected to electrocatalytic hydrogenation (ECH) at mild temperatures using ruthenium on activated carbon cloth. Phenol, guaiacol, syringol, and several related alkyl phenols and aryl methyl ethers were studied. In addition to hydrogenation, C–O and C–C hydrogenolysis were observed. Conversion of the alkyl phenols decreased with increasing alkyl chain length. Similarly, for alkyl-substituted guaiacols, conversion decreased as alkyl chain length increased, and selectivity shifted away from demethoxylation, favoring alkyl-substituted 2-methoxycyclohexanol. Increasing substrate concentration improved the Faradaic efficiency up to a plateau at higher concentrations. By mapping out electrocatalytic conditions and reactivities of lignin-relevant substrates, this work further opens the door to the promise of biomass upgrading to fuels and chemicals via the pyrolysis–electrocatalysis pathway.

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