Mechanism analyses and optimization strategies for performance improvement in low-temperature water electrolysis systems via the perspective of mass transfer: A review

The development of hydrogen energy is an important part of putting carbon neutralization into action, and hydrogen production via water electrolysis is a potential approach for the sustainable development of energy. Mass transfer limitation is a challenge for the commercialization of low-temperature water electrolysis systems with high current densities in the future. To explore possible paths for improving the cell performance and efficiency, the electrolytic process in a low-temperature electrolytic cell and the mechanism and optimization strategy for performance improvement via mass transfer are comprehensively analyzed in this review. The effects and optimization strategies for a porous electrode and the main structure of the proton exchange membrane and alkaline electrolysis system are summarized. The bubble effect of the electrolytic process and advanced methods for the removal of bubbles are discussed. Porous electrode modification and flow field optimization are presumably effective approaches for reducing polarization loss and enhancing mass transfer. The optimal flow field design is a trade-off between uniform temperature and current density distributions and pressure drops. Developing a novel advanced porous separator as a substitute for a traditional diaphragm is beneficial for alleviating gas crossover. In addition, the bubble size upon separation from the electrode should be as small as possible to inhibit cell overpotential and superimpose the external field during the process of water electrolysis to effectively strengthen gas release, thereby simultaneously enhancing the efficiency of hydrogen production. This work lays the foundation for further improving mass transfer during electrolysis and designing a high-performance electrolytic cell. Further, it improves the hydrogen production efficiency by identifying associated global energy challenges and provides practical strategies.