A switchable pH-differential unitized regenerative fuel cell with high performance

• A pH-differential technique breaking the thermodynamic limitation from window of water.
• High output power density and round-trip efficiency recorded.
• Electrode potentials moved closer to equilibrium status and hence reduce loss.
• Heat generation and interfacial neutralization well controlled.
• Feasible cyclic operation in the novel microfluidic reactor.

Regenerative fuel cells are a potential candidate for future energy storage, but their applications are limited by the high cost and poor round-trip efficiency. Here we present a switchable pH-differential unitized regenerative fuel cell capable of addressing both the obstacles. Relying on a membraneless laminar flow-based design, pH environments in the cell are optimized independently for different electrode reactions and are switchable together with the cell process to ensure always favorable thermodynamics for each electrode reaction. Benefiting from the thermodynamic advantages of the switchable pH-differential arrangement, the cell allows water electrolysis at a voltage of 0.57 V, and a fuel cell open circuit voltage of 1.89 V, rendering round-trip efficiencies up to 74%. Under room conditions, operating the cell in fuel cell mode yields a power density of 1.3 W cm−2, which is the highest performance to date for laminar flow-based cells and is comparable to state-of-the-art polymer electrolyte membrane fuel cells.