Research Requirements to Move the Bar forward Using Aqueous Formate Salts as H2 Carriers for Energy Storage Applications

In this perspective on hydrogen carriers, we focus on the needs for the development of robust active catalysts for the release of H<sub>2</sub> from aqueous formate solutions, which are non-flammable, non-toxic, thermally stable, and readily available at large scales at reasonable cost. Formate salts can be stockpiled in the solid state or dissolved in water for long term storage and transport using existing infrastructure. Furthermore, formate salts are readily regenerated at moderate pressures using the same catalyst as for the H<sub>2</sub> release. There have been several studies focused on increasing the activity of catalysts to release H<sub>2</sub> at moderate temperatures, i.e., < 80 °C, below the operating temperature of a proton exchange membrane (PEM) fuel cell. One significant challenge to enable the use of aqueous formate salts as hydrogen carriers is the deactivation of the catalyst under operating conditions. In this work we provide a review of the most efficient heterogeneous catalysts that have been described in the literature, their proposed modes of deactivation, and the strategies reported to reactivate them. We discuss potential pathways that may lead to deactivation and strategies to mitigate it in a variety of H<sub>2</sub> carrier applications. We also provide an example of a potential use case employing formate salts solutions using a fixed bed reactor for seasonal storage of energy for a microgrid application.