Emerging and persistent challenges of transitioning to solid-state electrolytes for hydrogen production from water splitting

Abstract

One of the biggest challenges we are faced with in the 21st century is closing the anthropogenic carbon cycle and shifting away from a fossil-fuel dependent society. One of the alternative fuels is hydrogen which is seeing unprecedented investment and deployment. However, obtaining cost competitive green hydrogen at scale remains a difficult challenge. Water electrolysis is, in this context, an increasingly important process. Currently, a major portion of electrolytic green hydrogen is generated by aqueous alkaline electrolytes, but their limitation to relatively low current densities, low operating pressures and the corrosion of metallic components including electrodes over prolonged use and other fluctuating parameters raise the price of hydrogen to an uncompetitive level. Water electrolysers using solid-state electrolytes (SSEs) such as proton exchange membranes (PEMs), anion exchange membranes (AEMs) and solid oxides (SO) have been gaining more interest in recent years in an attempt to accelerate cost competitive electrolytic green hydrogen production at scale. Despite many advantages, SSE based electrolysers are still facing limitations such as sub-optimal ionic conductivity, inefficient electrode/electrolyte interface and short operating lifetimes. In this review, we aim to offer an overview of both the current state-of-the-art SSE technologies, such as PEM, AEM and SO electrolytes, as well as the most recent material designs aiming to overcome these limitations. We outline advancements made in the field of electrolysis technologies which we believe could serve as inspiration for the further improvement of SSEs in water electrolysis. Lastly, we summarize the remaining open questions and emerging trends, hoping that further research will use the improvements made in various fields to improve the efficiency of SSEs in water electrolysis.