The role of proton battery technologies in future global energy storage.

The very large global demand for energy storage as inherently-variable renewable-energy sources meet an increasing proportion of total electricity demand will be difficult to meet solely with existing technologies. Hence additional storage technologies that are safe and based on abundant primary resources are likely to come into play to facilitate the transition to zero net emissions at the global level. One such promising technology is the 'proton battery', which in its most general form is a rechargeable battery based on proton transfer and reversible electrochemical hydrogen storage. In the present review, a general definition of a proton battery is first proposed, since the term has been used broadly and somewhat inconsistently to date. The literature over the past thirty years on this technology is then critically reviewed, covering both proton batteries that meet the definition proposed in this paper as well as those that are merely self-identified. To the extent possible through published information, the performances of this range of cells are compared in terms of key parameters such as electrical energy stored per unit mass, cyclability, self-discharge and scale reached. The proton battery design developed by our group at RMIT is described in more detail, both theoretically and in terms of experimentally-measured performance, as an exemplar of a system that has already demonstrated a competitive storage capacity at a significant scale. In conclusion, potential future applications for proton batteries, and some directions for the research and development necessary to enable this potential to be realised, are proposed. [ABSTRACT FROM AUTHOR]