Development of Novel Thin Membrane Electrode Assemblies (MEAs) for High-Efficiency Energy Storage

Hydrogen is a ‘zero-emission’ energy carrier, which could be an important part of environment-friendly solutions to the global energy crisis via energy storage without producing greenhouse gases. The proton exchange membrane electrolyzer cell (PEMEC) is one of the most practical and energy efficient methods for producing high purity hydrogen from renewable sources, such as wind, hydro and solar energy. Since the wide commercialization of PEMECs is still hindered by their performance, cost and durability, superior performance PEMECs with low-cost and high-efficiency are strongly desired. The membrane electrode assembly (MEA), which consists of liquid/gas diffusion layers (LGDLs), catalyst layers (CLs) and membrane, is the core component of the PEMECs. LGDLs play an important role in enhancing the performance of PEMECs. They are expected to transport electrons, heat, and reactants/products simultaneously with minimum electrical, thermal, interfacial, and fluidic losses. CLs are mainly formed by noble metals or their oxides, which has great impact on PEMEC performance, durability and cost. The objective of this research is to develop novel MEAs coupled with the titanium-based thin/tunable LGDLs (TT-LGDLs) that has the well-controlled pore morphologies. The main achievements of this research include: (a) The TT-LGDLs can achieve superior performance due to the remarkably reduced ohmic and activation losses, and the effects of pore morphologies have been identified. (b) The gold electroplating is a promising method for the PEMEC performance enhancement by surface modifications. (c) The microporous layers (MPLs) offer some improved PEMEC performance under specific conditions, but may not be required for optimum TT-LGDLs. (d) The novel GDEs with ultra-low Pt catalyst loadings have been developed, which has obtained an acceptable performance with a significantly improved catalyst mass activity. (e) The theoretical analysis is adopted to study the true electrochemical reaction mechanism in PEMECs, and a model is developed, which is used to simulate the PEMEC performance and optimize the parameters of the electrodes. The novel thin MEAs developed in this research point out a promising direction for future MEA development, and can be a guide for the high-efficiency and large scale energy storage

Mass transport in PEM water electrolysers: A review

While hydrogen generation by alkaline water electrolysis is a well-established, mature technology and currently the lowest capital cost electrolyser option; polymer electrolyte membrane water electrolysers (PEMWEs) have made major advances in terms of cost, efficiency, and durability, and the installed capacity is growing rapidly. This makes the technology a promising candidate for large-scale hydrogen production, and especially for energy storage in conjunction with renewable energy sources – an application for which PEMWEs offer inherent advantages over alkaline electrolysis. Improvements in PEMWE technology have led to increasingly high operational current densities, which requires adequate mass transport strategies to ensure sufficient supply of reactant and removal of products. This review discusses the current knowledge related to mass transport and its characterisation/diagnosis for PEMWEs, considering the flow channels, liquid-gas diffusion layer, and polymer electrolyte membrane in particular

Towards Improved Understanding of Mass Transport in Polymer Electrolyte Membrane Water Electrolysers

The advent of a global societal and governmental movement to curb climate change has put low-carbon technologies at the centre stage of public interest and scientific efforts. In the wake of rising concerns around the carbon footprint of personal mobility and the energy sector, the concept of a ‘Hydrogen Economy’ has experienced yet another rapid spur of popularity. Polymer electrolyte membrane water electrolysers (PEMWEs) are a promising candidate for large-scale hydrogen production, and improvements in the technology have led to increasingly high operational current densities exceeding 2 A cm-2, which requires adequate mass transport strategies to ensure sufficient supply of reactant and removal of products. Optimization and diagnosis of mass transport processes in PEMWEs has long been neglected despite its significance, but the amount of scientific literature has recently increased sharply. This thesis uses existing diagnostic tools to gather new insights into the processes within PEMWE flow channels and liquid-gas diffusion layers, aims at providing new low-cost diagnostic tools to accelerate the investigation of mass transport processes, and consequently deduces novel approaches to the design of PEMWEs components, cells, and stacks. Neutron and X-ray imaging are used to demonstrate the effect of liquid-gas diffusion layer microstructure on the water-gas distribution in a PEMWE, revealing significant inhomogeneity across the active area. Due to cost and accessibility issues around radiation imaging, acoustic methods are explored as alternative diagnostic tools. Acoustic emission is successfully demonstrated as an operando technique to monitor two-phase flow in the flow channels, detecting the transition from bubbly to slug flow. Bubbly flow is observed at the onset of electrochemical activity and low current densities, with a high number of small bubbles, while at higher current densities these small bubbles coalesce and form larger slug bubbles. Lastly, acoustic time-of-flight imaging is used to monitor the water-gas distribution in the liquid-gas diffusion layer and the flow channels, with results being consistent with expectations and previous results obtained via neutron imaging