Increasing the capacity of pseudocapacitive WO3 auxiliary electrode for enhanced two-step decoupled acid water electrolysis

Decoupled water electrolysis has all the necessary properties to become an effective hydrogen production tool. Hydrogen evolution is decoupled from oxygen evolution using red-ox mediator electrodes in decoupled electrolysis. Therefore, oxygen and hydrogen are not produced simultaneously or in the same space. This simplifies the design of electrolysers and opens up the possibility of not using membranes and diaphragms for gas separation as conventional electrolysers do. Also, membrane-free technology improves the durability and efficiency of electrolysers. The reduction and oxidation of the red-ox mediator electrode must be reversible. Also, the electrode material should have a high charge capacity and be durable. In this work, we demonstrate WO3 as a red-ox mediator electrode in decoupled water electrolysis with acid electrolyte and investigate the effect of lyophilisation and annealing conditions on WO3 capacity. Indeed, the WO3 electrode can successfully act as a red-ox mediator through intercalation and deintercalation of H+ ions. Lyophilisation increases capacity more than two times than the air-dried sample, 495.55 and 201.41 F/g, respectively. Such high capacities as 837.43 F/g were reached when an inert annealing atmosphere was used. The electrolysis faradaic efficiency of 98–99 % was achieved in all prepared samples, with an energetical efficiency of 34–58 %.