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

摘要：

针对大型碱性水电解制氢系统的气体交叉问题，分析了氧气中杂质氢气的引入机制，建立了氧中氢（HTO）计算模型，采用千标方级制氢装置验证了模型的准确性，通过模型量化了各引入机制对HTO的贡献比例，研究了操作参数对HTO的影响规律，提出了氧中氢控制措施。结果表明：模型对HTO的预测精度较高，可有效反映低负载工况下系统氧中氢特性；碱液循环混合、氢气跨膜浓差扩散是形成HTO的主要机制，旁路电流电解、压差对流对HTO影响较小，但旁路电流对系统低负载时的产氧量影响较大，间接导致了HTO升高；可采取优化制氢装置操作参数、提高低负载时氧气流量等措施对氧中氢进行控制。研究结果能够为大型可再生能源耦合碱水制氢系统的设计和项目运行提供参考。

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