(519a) U.S. Doe Reversible Fuel Cell R&D to Support Grid-Scale Energy Storage (invited)

The increasing penetration of renewable energy sources like solar and wind on the grid gives rise to a need for energy storage technologies, as intermittency creates a temporal mismatch between energy supply and demand. Reversible fuel cells (RFCs or unitized RFCs, URFCs) are capable of operating in both power production (fuel cell) and energy storage (electrolysis) modes when there is an energy demand and oversupply, respectively. RFCs are a promising way to store large amounts of electrical energy at low cost as hydrogen to enable better utilization of renewables and existing baseload resources. Furthermore, RFCs can address the dearth of long-duration energy storage technologies for storage needs ranging from eight or more hours up to a season. The U.S. Department of Energy (DOE) funds research and development (R&D) of materials and components for RFCs for their potential to increase the flexibility, resiliency, and reliability of the electric grid and to contribute to the DOE’s H2@Scale vision of widely available low-cost hydrogen.

In order for RFCs to compete with other storage technologies, significant improvements are needed to their performance, durability, and cost. The performance and durability of RFC stacks significantly lag that of discrete fuel cell and electrolyzer stacks. Efficiently performing both fuel cell and electrolyzer functions in a single device poses significant materials and design R&D challenges, including water management (particularly in low-temperature RFCs), membrane stability, and the performance of bifunctional catalysts, particularly for oxygen reduction/evolution. All components must also have very high durability when cycling between the two operating modes, which necessitates stability over a larger voltage window than encountered in discrete systems.

To meet these challenges, several possible technologies are of interest. Existing efforts in the DOE R&D portfolio include reversible polymer electrolyte membrane, alkaline exchange membrane, solid oxide, and proton-conducting ceramic fuel cells. The near-term performance metric is based on the roundtrip efficiency, the ratio of the voltages for fuel cell operation divided by electrolyzer operation at a given current density. For low-temperature applications, a ≥ 50% roundtrip efficiency at 1 A/cm² in both operating modes with reasonable PGM loadings (< 2 mg_PGM/cm²), and high-temperature applications should exceed 50% roundtrip efficiency at 1 A/cm² in both operating modes. This presentation will summarize the technical requirements of RFCs and recent innovations to improve the competitiveness of RFCs with incumbent technologies.