The Nonlinear Frequency Response Method for the Diagnosis of the PEM Water Electrolyzer Performance

A better grasp of the underlying phenomena occurring in electrochemical technologies is crucial for their further development and, consequently, a much-needed step forward to a greener economy. Diagnostic methods that can reliably determine the state of health and causes of the performance shortcomings are indispensable. The ease of obtaining electrochemical data makes the analysis of current and voltage responses the preferred diagnostic approach. Traditional techniques, like steady-state polarization and electrochemical impedance spectroscopy are limited by their inability to distinguish between different processes due to the constraints of steady-state and linearity of system response, respectively. The nonlinear frequency response (NFR) method is an advanced diagnostic method that has the potential to overcome these issues. In this work, the NFR method was applied both experimentally and theoretically to study polymer electrolyte membrane water electrolysis (PEMWE). The model-based analysis provides insights into the losses in the PEMWE at different current densities. It shows that the contributions of the cathode to the overpotential losses at high current densities cannot be neglected. This has been much discussed in the literature and was often attributed only to mass transport losses. The contribution of mass transport has also been identified at higher current densities but is less pronounced than the kinetic contributions. Furthermore, we show that including the nonlinear dynamics in the analysis was crucial for identifying the appropriate parameter set. Overall, this work showed a considerable potential of the NFR method for the diagnosis of PEMWE due to its prospects of identifying different processes occurring within.

深入理解电化学技术中发生的内在现象，对其进一步发展至关重要，亦是推动绿色经济发展的必要一环。能够可靠判定设备健康状态与性能缺陷成因的诊断方法，是电化学技术发展不可或缺的核心支撑。由于电化学数据易于获取，电流与电压响应分析成为了主流的诊断手段。传统诊断技术例如稳态极化法与电化学阻抗谱（Electrochemical Impedance Spectroscopy），分别因稳态条件限制与系统响应线性性约束，无法区分不同的反应过程，因此存在固有局限。非线性频率响应（Nonlinear Frequency Response，NFR）方法是一种先进的诊断手段，有望解决上述局限。本研究通过实验与理论结合的方式，将非线性频率响应方法应用于质子交换膜水电解槽（Polymer Electrolyte Membrane Water Electrolysis，PEMWE）的研究。基于模型的分析揭示了不同电流密度下质子交换膜水电解槽的损耗机制。研究表明，高电流密度下阴极对过电位损耗的贡献不容忽视。该结论在已有文献中已有广泛讨论，过往研究通常仅将其归因于传质损耗。在更高电流密度下，传质损耗的贡献也被观测到，但相较于动力学损耗，其影响相对较弱。此外，本研究证实，在分析中纳入非线性动力学特征，是确定合理参数集的关键所在。综上，本研究证实非线性频率响应方法在质子交换膜水电解槽诊断中具有可观的应用潜力，因其能够有效识别装置内部发生的各类反应过程。