Operando X-ray studies of gas evolving and consuming catalysts

Abstract

The inherent intermittency of renewable energy production is one of the major challenges facing a future powered by renewable sources. Electrolysers are a potential solution to buffer this intermittency through production of green hydrogen. The electrochemical conversion of carbon dioxide (CO2) to useful chemicals and fuels is another a promising route toward the achievement of carbon neutral and carbon negative energy technologies. Fully understanding the catalytic and degradation mechanisms at current densities relevant for industrial application of these processes is therefore paramount for further catalyst improvement.

In this work a novel in situ specto-electrochemical X-ray absorption cell is presented as a new setup for collecting XAS data of gas evolving and consuming electrocatalysts at high overpotentials. Utilising a thin, porous PTFE membrane coated in gold to act as a current collector, coupled with efficient gas and electrolyte circulation loops, interference from bubble formation is minimised. The ability of the cell in characterising gas evolution / consumption reactions is demonstrated in the study of three reactions, the oxygen reduction reaction, oxygen evolution reaction and carbon dioxide reduction reaction.

A detailed XAS investigation of highly dispersed platinum during the oxygen reduction reaction is presented, along with comparative data in nitrogen. These measurements show the preservation of oxygen on the surface of the platinum nanoparticles below the platinum oxide reduction peak (0.48 VRHE). A range of highly active iridium oxides were investigated for the oxygen evolution reaction. Hydrated and rutile type iridium oxide XAS spectra were measured potentiodynamically, and it is found that a plateau region occurs in the oxidation states of hydrated iridium oxide at characteristic potentials for each material. This plateau region is attributed to the formation of a low conductivity Ir3+ species, the formation of which is also found in iridium oxides prepared by Adams Fusion method and demonstrates the structural variations in the materials that lead to their high activity. Finally, oxide derived copper is investigated for the CO2 reduction reaction during reduction / re-oxidation cycles and various oxides of copper are formed which are reduced immediately upon CO2 reduction.

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Identifiers

ORCID for Connor Matthew Sherwin: orcid.org/0000-0002-2710-5991

ORCID for Andrea Russell: orcid.org/0000-0002-8382-6443

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