关键词: 电解, 制氢, 气体交叉, 氧中氢, 旁路电流, 实验验证, 负载操作下限

Abstract:

Alkaline water electrolysis is considered a key technology for sustainable hydrogen production. However, gas crossover at low current densities limits the load range of electrolyzers, introducing challenges in coupling them to renewable power sources. Current research primarily focuses on analyzing the mass transfer mechanism of impurity gases within the electrolysis cell, but it insufficiently considers the impact of shunt current in large-scale electrolyzers. Also, the dominant crossover mechanism is still under debate. This study investigated the relative contributions of different gas crossover mechanisms, including diffusive and convective transport mechanisms to gas crossover in electrolysis cells, circulated electrolyte mixing and shunt current electrolysis. A mathematical model for HTO (hydrogen-to-oxygen) calculation was established. To validate the HTO model, experiments were carried out in a fully automated industrial-scale alkaline water electrolysis system with a hydrogen production capacity of 1000 m³/h. The electrolyzer is equipped with the polyphenylene sulfide (PPS) diaphragm, and uses approximately 30%(mass) KOH. The results revealed that the HTO model's prediction aligns closely with experiment data, exhibiting a relative error of 4.1%. The model suggests that the overall crossover is primarily influenced by mixing the electrolyte cycles, which makes up a share of 64.42% at 500 A/m² and 17.4 bar (1 bar=10⁵ Pa), followed by hydrogen concentration gradient diffusion across the membrane, which accounts for 28.77%. Shunt current electrolysis and differential pressure convective crossover have relatively minor impacts on HTO, however, the presence of shunt current reduces oxygen production, which is an important indirect factor contributing to the rapid increase of HTO during low load conditions. Orthogonal experiments suggest that the separation pressure, flow rate, and electrolyte concentration have more significant impacts on HTO levels, while the electrolyte temperature exerts a relatively minor influence. Measures such as optimizing the operating parameters of the hydrogen production device and increasing the oxygen flow rate at low load can be taken to control hydrogen in oxygen. The research findings can provide a reference for the design and operation of large-scale renewable energy-coupled alkaline water electrolysis hydrogen production systems.

Key words: electrolysis, hydrogen production, gas crossover, hydrogen-to-oxygen, shunt current, experimental validation, minimum operation load