# Multiway Analysis of the Electrochemical Oxidation Pathway of a Lignin Using Chemometrics

## TL;DR

This study explores how lignin breaks down during electrochemical oxidation, finding that both electrocatalysts and hydroxyl radicals contribute to the process.

## Contribution

The study identifies the dual role of electrocatalysts and hydroxyl radicals in lignin depolymerization.

## Key findings

- Electrochemical depolymerization of lignin produces phenolic compounds, phthalate esters, furan derivatives, and carboxylic acid esters.
- Both the Ni-Co electrocatalyst and hydroxyl radicals contribute to lignin depolymerization.
- Radical-mediated depolymerization results in a broader range of products.

## Abstract

The electrochemical oxidation mechanism of biopolymer lignin is challenging to characterize due to its complex structure. Controlling the oxidation process is crucial for ensuring the economic feasibility of electrochemical depolymerization of lignin, as it often generates numerous undesirable compounds. Regulating the depolymerization process can lead to the production of high-yield aromatic compounds, such as phenols and carboxylic acids. In addition to the depolymerization of lignin by the electrocatalyst, hydroxyl radicals (•OH) during the electrochemical oxidation could also depolymerize lignin. Previous studies have reported that •OH forms during electrochemical oxidation; however, it is still uncertain whether these radicals or electrocatalysts are responsible for depolymerizing lignin. This study investigates the pivotal issue of whether the depolymerization process is driven by •OH or by a direct electrochemical route. In this study, lignin compounds were electrochemically oxidized using a nickel-cobalt (Ni-Co) electrocatalyst at several electrode potentials, and the oxidized products were analyzed using headspace solid-phase micro-extraction gas chromatography–mass spectrometry (SPME-GC-MS) and factor analysis (FA). Electrochemical depolymerization of lignin yielded mainly phenolic compounds (e.g., tert-butyl phenols), phthalate esters (e.g., dibutyl phthalate, bis(2-methylpropyl) phthalate), furan derivatives (e.g., 2-butyltetrahydrofuran), and short-chain carboxylic acid esters. This work has successfully predicted that both electrocatalyst and •OH radicals contribute to the electrochemical depolymerization of lignin. Radical-mediated depolymerization yielded a broader range of products.