In conventional water electrolysis systems, hydrogen and oxygen are produced simultaneously and must be separated by a membrane to prevent the formation of an explosive gas mixture. Membranes impose major limitations that significantly increase costs and hinder the widespread adoption of hydrogen production. Recently, the decoupled water electrolysis (DWE) concept has been introduced. In DWE, water is split into two steps to separate OER and HER, eliminating the need for membranes. The OER and HER in DWE are performed independently in both space and time. Membrane-free water splitting has been achieved using a solid (pseudo)capacitive electrode as a redox mediator. While alkaline DWE does not require expensive catalysts for gas evaluation, the hydroxide-based redox mediators exhibit some stability issues. For this reason, acid decoupled water electrolysis using WO3 redox mediators has been reported as a more stable approach [1].
Here, we will discuss how photoanodes can be directly exploited in acidic DWE cells to enhance performance. Previously, photoanodes have been used to power DWE devices. However, DWE devices, with the photoanode directly integrated into the DWE cell, have not been demonstrated. In our DWE system, we combine WO3-based redox mediators with WO3 photoanodes and a Pt working electrode. Light irradiation is provided in the OER cycle, during which H+ is intercalated into the WO3 redox mediator, forming tungsten bronze [2]. In the HER cycle, the photoanode is disconnected, and the Pt electrode is used. In this step, tungsten bronze is transformed back to WO3. The exploitation of the photoanode reduced the potential for H+ intercalation, thereby enhancing the energetic efficiency from 65% to 82%.
References
[1] M. Iesalnieks, M. Vanags, L.L. Alsiņa, R. Eglītis, L. Grīnberga, P.C. Sherrell, A. Šutka, Adv. Sci., 11, 2024, 2401261.
[2] Vanags, M.; Iesalnieks, M.; Jēkabsons, L.; Zukuls, A.; Šutka, A. Two-Step Decoupled Electrolysis Approach Based on Pseudocapacitive WO3 Auxiliary Electrode. Int. J. Hydrog. Energy 2023, 48 (54), 20551–20561.
Acknowledements
The LACISE project is supported by the Swiss contribution to reducing economic and social disparities in the EU. It is carried out within the Swiss-Latvian Cooperation Programme ‘Partnership in Applied Research,’ under Grant Agreement No LZP/LV-CH-RESEARCH/PC2, implemented by the Ministry of Education and Science and the Latvian Council of Science.