Controlling electrochemical lignin depolymerization via halide chemistry at boron-doped diamond electrodes

Area of Science:

• Green Chemistry
• Electrochemistry
• Biopolymer Valorization

Background:

• Lignin is an abundant biopolymer with untapped potential for producing aromatic chemicals.
• Current lignin valorization methods often require harsh conditions or sacrificial oxidants.
• Developing sustainable and efficient lignin conversion pathways is crucial.

Purpose of the Study:

• To explore a sustainable electrochemical approach for lignin valorization.
• To investigate the influence of halide redox chemistry on lignin oxidation.
• To optimize electrochemical conditions for high yields of aromatic products.

Main Methods:

• Utilized boron-doped diamond electrodes for electrochemical lignin oxidation.
• Investigated the effects of different halides (Cl-, Br-, I-) and membrane configurations.
• Employed cyclic voltammetry and extended electrolysis for reactivity and stability studies.
• Analyzed depolymerization products using chromatography and spectroscopy.

Main Results:

• Iodide enabled efficient solution-phase oxidation via electrogenerated iodine, minimizing electrode fouling.
• Chloride and bromide mediated direct oxidation but led to surface passivation.
• β-O-4 cleavage was the primary depolymerization pathway, yielding vanillin as the main product.
• A cation-exchange membrane significantly enhanced product yields and promoted deeper oxidation.

Conclusions:

• Electrochemical lignin valorization is tunable via halide choice and electrode material.
• Iodide-mediated electrochemistry offers a promising route for sustainable aromatic chemical production from lignin.
• This method avoids sacrificial oxidants and minimizes electrode passivation, paving the way for industrial applications.