With the rapid growth and development of proton exchange membrane fuel cell (PEMFC) technology there has been an increasing demand for clean and sustainable global energy applications.While there are many device-level and infrastructure challenges still to be overcome before wide commercialization can be realized, increasing the PEMFC power density is a critical technical challenge, with ambitious goals proposed globally. For example, the short-term and long-term goals of the Japan New Energy and Industrial Technology Development Organization (NEDO) are 6 kW L -1 by 2030 and 9 kW L -1 by 2040, respectively. To this end, we propose technical development directions required for next-generation high power density PEMFCs. This perspective comprehensively embraces the latest advanced ideas for improvements in the membrane electrode assembly (MEA) and its components, bipolar plate (BP), integrated BP-MEA design, with regard to water and thermal management, and materials. The realization of these ideas is expected to be encompassed in next-generation PEMFCs with the aim of achieving a high power density.
Proton exchange membranes with short-pathway through-plane orientated proton conductivity are highly desirable for use in proton exchange membrane fuel cells. Magnetic field is utilized to create oriented structure in proton exchange membranes. Previously, this has only been carried out by proton nonconductive metal oxide-based fillers. Here, under a strong magnetic field, a proton-conducting paramagnetic complex based on ferrocyanide-coordinated polymer and phosphotungstic acid is used to prepare composite membranes with highly conductive through-plane-aligned proton channels. Gratifyingly, this strategy simultaneously overcomes the high water-solubility of phosphotungstic acid in composite membranes, thereby preventing its leaching and the subsequent loss of membrane conductivity. The ferrocyanide groups in the coordinated polymer, via redox cycle, can continuously consume free radicals, thus helping to improve the long-term in situ membrane durability. The composite membranes exhibit outstanding proton conductivity, fuel cell performance and durability, compared with other types of hydrocarbon membranes and industry standard Nafion® 212.
Summary The cross flow in the under‐land gas diffusion layer (GDL) between 2 adjacent channels plays an important role on water transport in proton exchange membrane fuel cell. A 3‐dimensional (3D) two‐phase model that is based on volume of fluid is developed to study the liquid water‐air cross flow within the GDL between 2 adjacent channels. By considering the detailed GDL microstructures, various types of air‐water cross flows are investigated by 3D numerical simulation. Liquid water at 4 locations is studied, including droplets at the GDL surface and liquid at the GDL‐catalyst layer interface. It is found that the water droplet at the higher‐pressure channel corner is easier to be removed by cross flow compared with droplets at other locations. Large pressure difference Δp facilitates the faster water removal from the higher‐pressure channel. The contact angle of the GDL fiber is the key parameter that determines the cross flow of the droplet in the higher‐pressure channel. It is observed that the droplet in the higher‐pressure channel is difficult to flow through the hydrophobic GDL. Numerical simulations are also performed to investigate the water emerging process from different pores of the GDL bottom. It is found that the amount of liquid water removed by cross flow mainly depends on the pore's location, and the water under the land is removed entirely into the lower‐pressure channel by cross flow.
A comprehensive proton exchange membrane fuel cell (PEMFC) system model is developed, including a pseudo two-dimensional transient multiphase stack model, a one-dimensional transient multiphase membrane humidifier model, a one-dimensional electrochemical hydrogen pump model, an air compressor model with proportion-integral-derivative control and a ribbon-tubular fin radiator model. All sub-models have been rigorously validated against experimental data to guarantee the system model accuracy. The effects of stack operating temperature, gas flow pattern and humidifier structural design are investigated to cast insights into the interaction among stack and auxiliary subsystems. The results indicate that the stack is successfully maintained at required operating temperatures (60 ℃, 70 ℃, 80 ℃) with help of the radiator when the whole system starts from ambient temperature (25 ℃).However, the stack is likely to suffer from membrane dehydration when operated at 70 ℃, and the problem becomes more severe at 80 ℃, causing significant performance deterioration. The water and temperature distribution inside the system are further demonstrated. The co-current flow pattern contributes to better water utilization of the whole system which may lead to higher output performances. But the counter-current flow pattern has positive effects on parameter distribution uniformity inside fuel cell, which is beneficial for the stack durability. As regards the membrane dehydration, it is found that optimizing membrane humidifier area does not fundamentally solve the problem. Increasing humidifier area contributes to higher water vapor transfer rate, however, it results in much slower humidification responses. *Revised Manuscript with Changes Marked Click here to download Revised Manuscript with Changes Marked: Manuscript_revise_2019.9.12(marked).docx
Aligned nano-sponges accommodate only non-freezable water and facilitate efficient water retention in the membrane, even under low relative humidity conditions.
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