Effect of polytetrafluoroethylene distribution in the gas diffusion layer on water flooding in proton exchange membrane fuel cells

An Overview and Future Perspectives of Rechargeable Flexible Zn-Air Batteries

Environmental friendliness and low-cost zinc-air batteries for flexible rechargeable applications have great potential in the field of flexible electronics and smart wearables owing to high energy density and long service life. However, the current technology of flexible rechargeable zinc-air batteries to meet the commercialization needs still facing enormous challenges due to the poor adaptability of each flexible component of the zinc-air batteries. This review focused on the latest progress over the past 5 years in designing and fabricating flexible self-standing air electrodes, flexible electrolytes and zinc electrodes of flexible Zn-air batteries, meanwhile the basic working principle of each component of flexible rechargeable zinc-air batteries and battery structures optimization are also described. Finally, challenges and prospects for the future development of flexible rechargeable zinc-air batteries are discussed. This work is intended to provide insights and general guidance for future exploration of the design and fabrication on high-performance flexible rechargeable zinc-air batteries.

Similarities and Differences between Gas Diffusion Layers Used in Proton Exchange Membrane Fuel Cell and Water Electrolysis for Material and Mass Transport

Proton-exchange membrane fuel cells (PEMFCs) and water electrolysis (PEMWE) are rapidly developing hydrogen energy conversion devices. Catalyst layers and membranes have been studied extensively and reviewed. However, few studies have compared gas diffusion layers (GDLs) in PEMWE and PEMFC. This review compares the differences and similarities between the GDLs of PEMWE and PEMFC in terms of their material and mass transport characteristics. First, the GDL materials are selected based on their working conditions. Carbon materials are prone to rapid corrosion because of the high anode potential of PEMWEs. Consequently, metal materials have emerged as the primary choice for GDLs. Second, the mutual counter-reactions of the two devices result in differences in mass transport limitations. In particular, water flooding and the effects of bubbles are major drawbacks of PEMFCs and PEMWE, respectively; well-designed structures can solve these problems. Imaging techniques and simulations can provide a better understanding of the effects of materials and structures on mass transfer. Finally, it is anticipated that this review will assist research on GDLs of PEMWE and PEMFC.

Mechanism and Model for Optimizing Polytetrafluoroethylene Distribution to Improve the Electrical and Thermal Conductivity of Treated Carbon Fiber Paper in Fuel Cells

Employing polytetrafluoroethylene (PTFE)-treated carbon fiber paper (CFP) as the substrate of the gas diffusion layer (GDL) is a common practice to improve water management in proton exchange membrane fuel cells (PEMFCs), but the resulting increase in electrical and thermal resistance is a critical problem that restricts the performance output of PEMFCs. Hence, studying the mechanism and prediction model for both the electrical and thermal conductivity in CFP is essential. This work established a mathematical graph theory model for CFP electrical and thermal conductivity prediction based on the observation and abstraction of the CFP characteristic structures. For the PTFE-treated CFP, the electrical and thermal conductivity of CFP can be effectively increased by optimizing the PTFE distribution in CFP. A "filter net effect" mechanism was proposed to reasonably explain PTFE distribution's influence on the CFP performance. Finally, the equivalent effect of multiple factors on conductivity was revealed using contour maps, which provides inspiration for further reducing the electrical and thermal resistance in CFP.

Coating Distribution Analysis on Gas Diffusion Layers for Polymer Electrolyte Fuel Cells by Neutron and X-ray High-Resolution Tomography

Coating load and distribution in gas diffusion layers (GDLs) for polymer electrolyte fuel cells (PEFCs) have a major influence on mass transport losses. To be able to optimize the coating distribution and get more accurate data about the influence of the coating on the PEFC performance, better characterization techniques are necessary. Common analysis techniques are limited to selected sections of the material, or they are not sensitive to small amounts of coating. We propose a new methodology to get a complete description of the coating distribution and the GDL structure by combining high-resolution X-ray tomography with high-resolution neutron tomography. Using an isotopic gadolinium staining method to enhance the neutron and X-ray absorption contrast, lower quantities of coating can be detected. The combination of both imaging techniques allows for a more detailed analysis of the coating distribution.