Unitized Regenerative Fuel Cell Technologies

Unitized regenerative fuel cells (URFCs) are electrochemical devices that combine water electrolysis and fuel cell functions within a single assembly. In charging mode they split water into hydrogen and oxygen, storing energy in chemical form, and in discharging mode they recombine these gases to generate electricity with water as the only by-product. By sharing key components such as the membrane electrode assembly, bipolar plates and flow fields, URFCs promise lower system cost, reduced footprint and simplified balance-of-plant compared with separate electrolyser–fuel cell chains. Typical architectures employ proton-exchange membranes, bifunctional catalysts and optimised water and thermal management to accommodate rapid mode switching. Current challenges centre on improving roundtrip efficiency, minimising performance hysteresis during transitions, extending catalyst durability under alternating oxidising and reducing conditions, and reducing reliance on scarce noble metals. Advances in materials science, reactor design and system integration are converging to make URFCs a compelling option for grid balancing, renewable energy storage, off-grid power and mobile applications.

Research from Nature Portfolio

Recent studies have demonstrated that discrete regenerative configurations can alleviate mode-switching hysteresis and stabilise water cycling in proton-exchange-membrane URFCs. By operating the fuel cell mode with pure oxygen generated in situ rather than ambient air, the device achieves more uniform electrochemical kinetics and avoids mass-transport limitations associated with nitrogen dilution. Scale-up experiments show that stacking multiple unit cells with serpentine flow fields preserves the low-hysteresis behaviour across larger active areas. These findings underscore the importance of synchronising gas generation and consumption pathways to sustain reversible operation with minimal performance loss.

Unitized Regenerative Fuel Cell Technologies publication trend

The graph below shows the total number of articles in unitized regenerative fuel cell technologies across all publications each year (not limited to Nature Index journals).

Technical terms

Unitized regenerative fuel cell (URFC): A single device capable of alternating between water electrolysis and fuel cell operation to store and generate energy.

Proton-exchange membrane (PEM): A polymer electrolyte that conducts protons between electrodes while electrically insulating them.

Oxygen reduction reaction (ORR): The electrochemical process by which oxygen molecules are reduced to water in fuel cell mode.

Oxygen evolution reaction (OER): The electrochemical process of generating oxygen from water during electrolysis mode.

Roundtrip efficiency: The ratio of energy output in fuel cell mode to energy input in electrolysis mode for a reversible system.

References

1. Unitized regenerative fuel cells: Fundamental challenges and advancements. Renewable and Sustainable Energy Reviews (2025).
2. Numerical Study of the Dynamic Response of Heat and Mass Transfer to Operation Mode Switching of a Unitized Regenerative Fuel Cell. Energies (2016).
3. Carbonized Polydopamine-Based Nanocomposites: The Effect of Transition Metals on the Oxygen Electrocatalytic Activity. Nanomaterials (2023).
4. Advances and prospects to achieve high-performing and durable proton-exchange-membrane unitized regenerative fuel cells. Current Opinion in Electrochemistry (2023).
5. Performance and Durability of Proton Exchange Membrane Vapor-Fed Unitized Regenerative Fuel Cells. Journal of The Electrochemical Society (2022).
6. Discrete regenerative fuel cell reduces hysteresis for sustainable cycling of water. Scientific Reports (2014).