Supercapacitor-isolated water electrolysis for renewable energy storage

Abstract

This study addresses a significant technological challenge in hydrogen production through electrolysis: the issue of gas crossover across the diaphragm between the cathode and anode, particularly under variable power conditions associated with renewable energy sources. We introduce a novel supercapacitor-isolated alkaline water electrolysis system utilizing a carbon-based supercapacitor sheet approximately 1 mm thick as an alternative to traditional diaphragms, effectively reducing gas crossover. At 25 °C and in 2.0 M KOH, our electrolysis system achieved a high current density of 0.736 A cm−2 for hydrogen evolution at 2.0 V, which was maintained at 0.023 A cm−2 even when the voltage was reduced to 0.9 V. Notably, the concentration of hydrogen to oxygen (HTO) remained low at 0.42 vol% with a current density of 0.01 A cm−2, surpassing the 28.5 vol% observed with a traditional diaphragm under similar conditions. At 70 °C, the electrolysis system exhibited an average hydrogen evolution rate of 0.952 A cm−2, with a specific energy consumption of 4.786 kWh Nm−3 (H₂) and a Faradaic efficiency of 99.5 %. Following a 55-day test under near-industrial conditions, the capacitive electrode demonstrated exceptional durability. These results represent a significant advancement in decoupled water electrolysis, indicating that the direct utilization of renewable energy for hydrogen production is feasible.