In recent years water electrolysis technologies have grown in demand with hydrogen as promising storage solution in mega-watt scale applications or as precursor for chemical industry. Mature technologies in the field include the classical alkaline water electrolyzer (AWE) and proton exchange membrane water electrolyzer (PEMWE) for operations in the temperature ranges of 50-100 °C. High material cost, inefficient current density operations and material stability are some of the challenges that have supported the development of zero-gap water electrolyzers with anion exchange polymer electrolytes (AEMWE) and combined AEM and PEM systems in bipolar membrane water electrolyzers (PBMWE).
Alkaline water electrolysis
Alkaline systems are more attractive, as use of non-noble based catalysts offer stability, high activity at lower cost. Although classic AWE is well established commercially, the caustic electrolyte and high ohmic losses due to the large gap between electrodes restrict application to moderately sufficient large scale operations. Within the team different materials, components and assembly designs are investigated for mitigating the high cross-over occurrence suffered by use of diaphragms, while lowering cell voltages for current density operation ranges > 500 mA/cm².
State-of-the-art PEMWE systems are generally operated at lower temperatures to maintain acceptable overpotentials and ensure longer operation life times, although limits performance to a certain extent. For this purpose building of water electrolysis stations with the capacity for higher temperature (>120 °C) and pressure operations have been undertaken in the team to evaluate the possible advances attainable. Parameters such as temperature, pressure and feed are of interest to ensure optimal operations of both commercial and novel materials. Electrochemical performance tests are to be coupled with cross-over studies and include long term stability tests in further stages.
Advances in anion exchange polymer materials over recent years has opened the possibility for implementation of zero-gap membrane electrode assemblies (MEAs) in alkaline environments. Our activities include optimizing electrode fabrication techniques by use of various non-PGM support structures and catalyst materials. The challenge remains to ensure high performing MEAs with optimized interfacial properties that prove stable over time. Performance evaluation includes the recording of polarization curves with accompanying electrochemical impedance spectroscopy and long term measurements.
Bipolar membrane electrode assemblies in deionized water
Could the advantages of an acidic and alkaline WE system be combined within a bipolar membrane electrode assembly for optimum performance at neutral pH? We build on past knowledge of manufacturing high performing PEMWE electrodes and investigate how the nature and position of the bipolar interface effects the electrochemical reactions at respective electrodes and ultimately cell performance.