# To Carbon or Not to Carbon: Rethinking Electrode Design in Unitized Reversible Fuel Cells

## TL;DR

This paper explores how carbon-based materials improve the performance of unitized reversible fuel cells for energy storage and CO2 capture.

## Contribution

The study introduces a novel electrode design with carbon-based microporous layers for chlor-alkali-based reversible fuel cells.

## Key findings

- Electrodes with 2 mgC/cm2 in the microporous layer showed optimal performance with reduced resistance and enhanced hydrophobicity.
- Hydrogen production efficiency reached 15 mgH2/Wh at 60 °C, surpassing industrial benchmarks.
- The system achieved high Faradaic efficiency (>98%) and enabled CO2 capture via cathodic alkaline absorption.

## Abstract

The development of efficient and scalable energy storage
systems
remains a major challenge in the transition to renewable energy. Unitized
reversible fuel cells (URFCs), capable of operating in both electrolysis
and fuel cell modes, offer a promising solution. In this context,
integrating the chlor-alkali process into URFCs enables not only cost-effective
energy storage but also environmental benefits such as CO2 capture via alkaline absorption. While chlor-alkali electrolysis
is well established, the reversible operation is not well known. This
study addresses a key design question: the role of carbon-based materials
in electrode architecture, specifically in the use of a carbon-based
microporous layer. Titanium felt electrodes were modified with microporous
layers (MPLs) containing 1, 2, and 3 mgC/cm2 and coated
with a RuO2–Pt catalyst using a Pechini-type polymeric
precursor method. The results showed that increasing the carbon content,
the electrode resistance was reduced and surface hydrophobicity was
enhanced, achieving the best results with 2 mgC/cm2 in
the MPL. Moreover, in electrolysis mode, the hydrogen production efficiency
improved with temperature, reaching 15 mgH2/Wh at 60 °C
(surpassing industrial benchmarks). The system also achieved high
Faradaic efficiency for hydrogen production (>98%) and enabled
simultaneous
CO2 capture via cathodic alkaline absorption. In fuel cell
mode, the optimized electrode reached a peak power density of ∼30
mW/cm2 at 60 °C, an order of magnitude higher than
previously reported in the literature for similar systems. The results
are very promising and position chlor-alkali-based reversible electrochemical
cells as a promising platform for efficient, scalable, and multifunctional
energy storage and conversion technologies.