Methods of Studying Electrocatalysts in Polymer Electrolyte Membrane Cells

The demand for flexible energy storage solutions increases as we gradually shift towards the utilization of renewable energy sources. Polymer electrolyte membrane (PEM) cell technologies provide easily scalable devices that can store energy through water splitting as hydrogen and, if necessary, restore the energy with high efficiency. The PEM technologies have not yet generalized due to the high cost and partially non-durable cell components. Thus, fundamental material research is needed for the development of these technologies. The development of electrocatalysts is particularly urgent, as none other than critical raw material categorized platinum group metals have been extensively used in PEM cells. This thesis focuses on the two currently most commercially viable PEM cell types: PEM water electrolyser and PEM fuel cell. Novel electrocatalyst material solutions are presented with the aim of reducing the amount of required critical raw materials and to increase the durability of these devices. The experimental material research of electrocatalysts takes place in two types of systems: half-cell and full-cell systems. Half-cell experiments are useful for catalyst material screening, but for commercialization, extensive full-cell tests are required. Since the protocols of full-cell experiments have high variation and since their theoretical background is not always fully understood, this thesis reviews the different experimental full-cell methods used for electrocatalysts. Emphasis is applied to durability experiments and the analysis of electrochemical impedance spectroscopy to understand loss mechanisms in these cells. In full-cell experiments, both the anode and cathode influence the performance of the full cell. In order to separate their impact, a reference electrode is required. In this thesis, a novel reference electrode design is presented for PEM water electrolyser and it is used to study the degradation of the state-of-the-art anode and cathode in a long-term experiment. A rapid platinum nanoparticle growth and corrosion of the carbon support were detected in the cathode catalyst. A novel catalyst utilizing carbon nanotubes as the support material is proposed and verified to have a significantly lower rate for these degradation mechanisms. In the PEM fuel cell, a novel mesoporous film catalyst is proposed to solve the fast growth of nanoparticles on the cathode. The novel catalyst indeed has a low degradation rate in comparison to the state-of-the-art catalyst. The mass activity of mesoporous platinum can be increased further by alloying with cobalt. The understanding of what catalyst experiences during full-cell operation is essential for catalyst development. Using the methods provided in this thesis, it is possible to enhance that understanding to improve the existing catalysts and help to design the next generations.