Abstract
Electrocatalysis plays a prominent role in the development of carbon dioxide utilisation technologies. Many new and improved CO2 conversion catalysts have been developed in recent years, progressively achieving better performance. However, within this flourishing field, a disconnect in catalyst performance evaluation has emerged as the Achilles heel of CO2 electrolysis. Too often, catalysts are assessed in electrochemical settings that are far removed from industrially relevant operational conditions, where CO2 mass transport limitations should be minimised. To overcome this issue, gas diffusion electrodes and gas-fed electrolysers need to be developed and applied, presenting new challenges and opportunities to the CO2 electrolysis community. In this review, we introduce the reader to the fundamentals of gas diffusion electrodes and gas-fed electrolysers, highlighting their advantages and disadvantages. We discuss in detail the design of gas diffusion electrodes and their operation within gas-fed electrolysers in both flow-through and flow-by configurations. Then, we correlate the structure and composition of gas diffusion electrodes to the operational performance of electrolysers, indicating options and prospects for improvement. Overall, this study will equip the reader with the fundamental understanding required to enhance and optimise CO2 catalysis beyond the laboratory scale.
Highlights
There are strong evidence and consensus on the leading role of anthropogenic greenhouse gas emissions in global warming and climate change [1]
The value of ∆P controls the position of the plane of penetration of the electrolyte into the gas diffusion electrodesCatalysts (GDEs), swinging the operation between two mutually excluding situations: one where the plane does not penetrate the GDE resulting in a dry electrode, and the other with the plane entirely pushed through the electrode in the gas compartment, resulting in a flooded electrode
Electrolyser and electrode design have a great influence on CO2 reduction (CO2 R) since productivity, selectivity, energy efficiency, and stability are dependent on the electrocatalyst
Summary
There are strong evidence and consensus on the leading role of anthropogenic greenhouse gas emissions in global warming and climate change [1]. GDEs are Among already used in these limitations, low CO2 solubility and diffusivity in aqueous electrolytes hinder high conversion electrochemical energy-conversion devices such as fuel cells, delivering excellent performance [15,16,17]. Due to high CO2 mass transport and reduced diffusion lengths within the catalyst layer, GDEs can applications, long-term stability, of up to 30,000 h, and selectivity with current densities higher than achieve current densities higher than those of traditional electrodes [14]. Most of the gas-fed electrolysers suffer from limited (non-gas-fed) electrochemical cells and equip the reader with the fundamental knowledge and durability, leading to a detrimental decay of performance after several, yet insufficient, operational understanding to further investigate and implement two technologies crucial to overcome the key hours [18].
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