Microenvironment Matters: Destabilization of Iridium Anode Catalyst by CO Reduction Products

TL;DR

This study shows that CO2 and CO electrolysis byproducts like ethanol and acetaldehyde can damage iridium anode catalysts, causing instability and faster dissolution.

Contribution

The study reveals that CO electrolysis products, not just pH, destabilize iridium anode catalysts through competitive oxidation reactions.

Findings

Ethanol and acetaldehyde reduce iridium anode stability by competing with the oxygen evolution reaction.

Oxidation of ethanol/acetaldehyde prevents formation of a protective oxide layer on iridium.

Iridium dissolution increases under these conditions, observed via ICP-MS techniques.

Abstract

Iridium is one of the most frequently employed anode
electrocatalysts
in CO2 and CO electrolysis, thanks to its reasonable overpotential
for the oxygen evolution reaction (OER) and high stability under operating
conditions. The latter has been challenged recently by a handful of
studies where destabilization of iridium was observed, which was explained
solely by thermodynamics (iridium is unstable at strong alkaline pH
and OER potentials). In this study, we demonstrate that liquid CO
and CO2 electrolysis products (such as ethanol and acetate)
crossing over to the anode side under long-term operation have a severe
effect on the stability of iridium. Its dissolution was studied by
both ex-situ inductively coupled plasma mass spectrometry (ICP-MS)
and in situ (online ICP-MS) techniques. Based on our electrolysis
experiments carried out in a broad pH range (pH = 4–14), ethanol,
and its partially oxidized counterpart, acetaldehyde, decreases the
stability of the anode catalyst. Ethanol/acetaldehyde oxidation competes
with the OER and starts in conjunction with the surface oxidation
of the Ir catalyst particles. The oxygenated species are consumed
by the alcohol/aldehyde oxidation process, preventing the formation
of a passivating surface oxide layer, resulting in an increased iridium
dissolution rate.

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