Solar-Assisted PEM Water Electrolysis with Symmetric IrO2 Electrodes for Hydrogen-Rich Water Production

Hydrogen-rich water (HRW) has attracted significant attention for its physiological and therapeutic potential, driving efforts to develop a green and direct production approach. In particular, if solar energy could be utilized to power the process and the power-generation and water-production modules could be integrated into a single device, it would greatly enhance portability and user convenience, making it an ideal solution for personalized healthcare and outdoor applications. We demonstrate solar-assisted proton exchange membrane (PEM) electrolysis using symmetric IrO2 electrodes at both cathode and anode to directly generate HRW. The symmetric design simplifies manufacturing, mitigates lifetime mismatch and metal-ion cross-contamination. IrO2 films were electrodeposited on stainless steel substrates and annealed at 400–700 °C. When coupled with a 100 cm2 Si solar cell, the electrode annealed at 550 °C—featuring ~6 nm IrO2 nanocrystals embedded in an amorphous matrix—exhibited the highest hydrogen production rate. At an applied voltage of 4 V, this 550 °C-annealed IrO2 electrode produced approximately 1800 μmol h−1 of H2, corresponding to about 44 mL h−1 of H2 at 25 °C and 1 atm. Corrosion tests show the HRW is less aggressive to iron than DI, RO, and tap water, suggesting better compatibility with metallic components. During water splitting, the oxidation–reduction potential (ORP) rapidly decreases to <−300 mV within 0–10 min and then stabilizes, with the 550 °C–annealed electrode exhibiting the lowest ORP. Upon air exposure, the ORP increases by ~200 mV over 45–70 min yet remains reductive for >120 min, indicating persistent dissolved H2 and sustained performance. Overall, the symmetric IrO2 architecture provides a green, stable, and direct route to HRW production.