Analysing the Degradation Phenomena of a Commercial Proton Exchange Membrane Water Electrolyzers

Abstract

Decarbonization of our energy system has become a priority to mitigate climate change. Therefore, the use of renewable energies is mandatory which also requires a long-term storage possibility. Proton exchange membrane water electrolyzers (PEMWE) are ideal for producing green hydrogen for transport, industry and heat. Important advantages are their compactness and high flexibility to operate under dynamical conditions. To be competitive it is necessary on the one hand to reduce the investment costs and on the other hand to ensure a long life of electrolyzers to limit operational expenses. Industry often faces the problem that the operating histories of their stacks are unknown when they are operated by customers. Nevertheless, understanding of the degradation mechanisms is of great importance to develop new components with reduced cost and enhanced durability. Here we analyse the cell components of a commercial PEMWE stack, which has been operated by a customer for long periods of time under unknown conditions, with the help of electrochemical and physical methods. Samples of the operated components were cut at specific locations and characterized in a 4 cm2 single cells. The aged components were successively replaced by new ones or regenerated to isolate and quantify the contribution of individual components on performance losses. This way, we have identified the catalyst coated membrane (CCM) as the component strongest affected by degradation. By using X-ray photoelectron spectroscopy (XPS) we identified different types of contamination like Pb and Fe. Remarkably, they were found on aged and unused components which is an indication for impurities due to the production process. In addition, energy dispersive X-ray spectroscopy (EDS) analysis showed Ca traces which is characteristic of CCM contamination when insufficiently deionized water is used for cleaning cell components, in particular the Ti porous transport layers (PTL). The CCM notably degrades by defects of the catalytic layer, due to contaminations and ionomer rearrangement. Signs of erosion were observed on the cathodic side of the Bipolar Plate (BBP) by means of SEM and atomic force microscopy (AFM), while the electronic conductivity remained unchanged. In contrast a pronounced oxidation concurrent with reduced conductivity is measured for the BPP on the anode side. The combination of electrochemical characterization with stepwise regeneration processes and physical ex situ analysis allows to draw conclusions about the impact of different components on degradation and to analyse the underlying aging mechanism occurring in each component.