# Influence of Impurities on the Electrochemical Upcycling of Biomass

## TL;DR

Tiny impurities in biomass compounds like HMF and furfural, undetectable by standard methods, hinder their electrochemical conversion to useful products, but distillation and recrystallization can fix this issue.

## Contribution

The study reveals that trace impurities in HMF and furfural, below detection limits, impair electrochemical oxidation and identifies effective purification methods.

## Key findings

- Impurities in HMF and furfural, undetectable by NMR and HPLC, slow down electrochemical oxidation.
- Distillation of furfural and recrystallization of HMF improve electrochemical conversion kinetics.
- Purification methods are practical and can be adopted for scalable biomass refinery processes.

## Abstract

The electrochemical oxidation of sugar‐derived compounds such as furfural and 5‐hydroxymethyl furfural (HMF) to the corresponding carboxylic acids is a crucial step in unlocking biomass as a renewable carbon feedstock. For instance, 2,5‐furandicarboxylic acid, the oxidation product of HMF, can replace crude‐oil derived terephthalic acid in the ubiquitous polymer polyethylene terephthalate. Hence, establishing an electrochemical process for the refinery of biomass requires oxidation of furfural and HMF with high current densities. It is therefore noteworthy that we show in this work that trace impurities undetectable by NMR spectroscopy and HPLC analysis impair the kinetics of electrochemical HMF and furfural oxidation. We therefore evaluate different methods for the removal of impurities from HMF and furfural that form during synthesis and storage of both chemicals. We find that purification by distillation of furfural and by recrystallization of HMF improves the kinetics of their electrochemical conversion best. Since both procedures can be adopted readily by other labs, the present work provides practical guidelines for the pretreatment of chemicals, which may also prove relevant for the development of processes at scale.

5‐hydroxymethyl furfural (HMF) and furfural contain impurity levels that lie below the detection limit of common analysis techniques. Yet, these impurity levels have an adverse effect on the electrochemical conversion of these compounds. In this study, we show that distillation of furfural and recrystallization of HMF facilitates their electrochemical oxidation best.© 2026 WILEY‐VCH GmbH