In-situ measurement of current density distribution in polymer electrolyte membrane water electrolysis cells

Kurzfassung

The integration of renewable energy sources in the electricity grid raises new challenges regarding intermediate storage of energy to cover the energy demand at any time and to overcome the gap between temporal availability of renewable energy and the actual needs. Hydrogen represents one of the most promising options for solving this issue. It can be electrochemically generated by water electrolysis using surplus energy produced by wind, solar, or hydro power plants. In general, there are three available low temperature electrolysis technologies: alkaline water electrolysis (AWE), proton exchange membrane water electrolysis (PEMWE), and anion exchange membrane water electrolysis (AEMWE). Due to its high efficiency, compactness, wide operation range and high dynamic behavior, PEMWE can be beneficially used to convert the intermittent surplus energy from renewable energy sources into hydrogen. Nevertheless, technological challenges have to be overcome for a wide spread commercialization of this technology, including stack costs, stack lifetime and suitable operation strategies. The joint R&D project INSIDE - In-situ Diagnostics in Water Electrolysers develops in-situ diagnostics tools for monitoring of the locally resolved current densities in different water electrolysis technologies. The project is funded by the EU Fuel Cell and Hydrogen Joint Undertaking (FCH-JU) and the involved partners are listed in Table 1. The investigated tools are based on the segmented printed circuit board (PCB) technology patented by DLR and widely used already in the fuel cell community. For the adaption to the new application of PEMWE, new requirements regarding the layout and the used materials had to be taken into account. Thereby, the major layout requirement is that the electrochemical and thermal conditions in the electrolysis cell as well as in the electrolysis stack are as close to the real operating conditions as possible. The PCB materials have to be compatible with the chemical and electrochemical conditions in this application, namely low pH, high electrochemical, high pressure and temperature, and a wide range of current densities. The first PCB prototype for PEMWE is based on the design of a DLR-internal single cell in the lab scale of 25 cm². Based on the first results of this prototype, the presented work demonstrates that the developed PCB is a powerful tool for further developments in the field of PEMWE. It allows the optimization of cell components, such as the current collectors and the flow field design, and can be an indicator for the clamping force distribution within the cell. Based on these investigations, operating conditions and cell components can be attained with highly homogeneous conditions in the entire cell, thereby avoiding local degradation effects. Such local degradation effects would otherwise strongly affect the lifetime of a PEMWE. Additionally, faulty conditions, such as water starvation, can be monitored using the PCB tool and influenced areas in the cell can be detected. Ongoing work will integrate the established PCB technology in commercial PEMWE stacks. The objective of this work is to monitor performance and local anomalies during real operation, and to correlate these with the operation parameters in a system. Degradation can be identified and mitigated by adjusting operation modes. Additionally, the correlation to ex-situ characterisation will be used to identify local deficiencies and ageing mechanisms. The implementation of the newly developed on-line diagnostic tool in PEMWE allows targeting a systematic optimisation of the operation strategies for high performance and extended life-time and of the stack design. This undertaking receives funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 621237 (INSIDE).