# Activated Nickel Foam Anodes for Sustainable Biomass Valorization: Competitive Oxidation of Organic Molecules vs the Oxygen Evolution

## TL;DR

This paper studies how activated nickel foam anodes can efficiently convert biomass molecules into useful products instead of producing oxygen.

## Contribution

The study reveals competitive oxidation of biomass substrates over oxygen evolution using activated nickel foam anodes.

## Key findings

- Glucose and xylose oxidation fully suppresses oxygen evolution at 30 mM concentration.
- HMF oxidation requires higher concentrations to suppress oxygen evolution.
- Formate is a main byproduct of glucose electrolysis.

## Abstract

A systematic study on the competitive oxidation of glucose
(Glc),
xylose (Xyl), and 5-hydroxy­methyl­fur­fural (HMF)
vs the oxygen evolution reaction (OER) was performed by coupling H-cell
electrochemical experiments with in situ O2 monitoring in the anodic chamber using an activated Ni foam as the
anode. At a substrate concentration of 10 mM, multipotential steps
showed similar OER onset potential values for Glc and Xyl (1.49 VRHE), while the value for HMF was slightly lower (1.47 VRHE). Chronoamperometry tests at 1.6 VRHE (30 min)
with varying concentrations showed that both Glc and Xyl oxidation
reactions fully suppressed the OER at 30 mM, while 100 mM was required
for HMF. A Langmuir–Hinshelwood analysis of the current–substrate
concentration dependence revealed the slower kinetics and inhibitory
effects impacting HMF oxidation, which account for the significant
difference in performance with respect to both aldoses. Given its
relevance as both a model and a promising substrate for membraneless
electrolysis operation, Glc was further investigated in a long-term
chronoamperometry experiment with in situ O2 monitoring (15 h at 1.6 VRHE, 30 mM Glc). The results
suggested the feasibility of sustaining OER-free operational conditions
for approximately 4 h from an initial Glc concentration of 100 mM.
HPLC analysis indicated the presence of formate as the main coproduct
of hydrogen via glucose electrolysis.