• Energy Research

Aligned nano-sponges accommodate only non-freezable water and facilitate efficient water retention in the membrane, even under low relative humidity conditions.

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.apenergy.2018.08.125 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/

Abstract Water dynamics in the flow channel of a proton exchange membrane fuel cell is significantly important to water management and removal. In this study, volume-of-fluid method is used to investigate numerically the three-dimensional water dynamics in a flow channel with a hydrophilic needle. It is found that water transport and dynamics in this novel flow channel are quite different from the conventional channel. Liquid water droplet, introduced on the electrode surface, is removed through capillary effect once touching the hydrophilic needle. This is desirable since the electrode surface becomes free of liquid water, avoiding the flooding and blockage of reactant gas transport into the electrode. Increasing the contact area between the water droplet and needle, through an increase in the diameter or length of the needle, can facilitate water removal from the electrode surface because of greater capillary effect, but it also increases the pressure drop in the channel due to greater blockage by the needle. Overall, the pressure drop in the modified channel is still small compared to the pressure drop in a serpentine flow channel, making the present approach viable for use in the conventional parallel flow channels for proton exchange membrane fuel cells.

With performance improvement of low-temperature fuel cell (FC), high reactant supply and water generation rates may induce air-water turbulence in the FC flow channel. In this research, an air-water turbulent direct numerical simulation (DNS) model is developed to simulate different droplet sizes, locations and interactions in the air-water transport processes comprehensively. It is found that a larger droplet breaks up more easily in turbulence, and a smaller droplet tends to keep lumped. The droplet at corner does not break up because it is away from channel center. The droplet interaction simulations show that the small droplets merge to form slugs, but still keep lumped in turbulence. It is suggested that two conditions need to be satisfied for droplet break up in FC flow channel, one is turbulent flow, and another is that the droplet needs to be large enough and occupy the center region of flow channel to suffer sufficient turbulence fluctuations. The DNS results illustrate some unique phenomena in turbulent flow, and show that the turbulence has significant effect on the air-water flow behavior in FC flow channel.

Abstract In this study, a whole-cell 3D multiphase non-isothermal model is developed for hydrogen alkaline anion exchange membrane (AAEM) fuel cell, and the interfacial effect on the two-phase transport in porous electrode is also considered in the model. The results show that the insertion of anode MPL, slight anode pressurization and reduction of membrane thickness generally improve the cell performance because the water transport from anode to cathode is enhanced, which favors both the mass transport and membrane hydration. The effect of cathode MPL is generally insignificant because liquid water rarely presents in cathode. It is demonstrated that slight pressurization of anode, which might not lead to apparent damage to the membrane, can effectively solve the anode flooding and cathode dryout issues.

Abstract Proton exchange membrane fuel cell is a promising clean energy conversion device. Proton exchange membrane fuel cell power system has great potential in the automotive applications. A fuel cell stack and an air compressor are two important components in a fuel cell power system and it is meaningful to study their properties for better system performance. The aim of this study is to enhance the performance of a 20 kW vehicular proton exchange membrane fuel cell power system incorporating a fuel cell stack and an air compressor, through the cathode operating pressure optimization. The fuel cell stack is investigated numerically and the air compressor characteristics are obtained experimentally. The fuel cell stack and the air compressor are matched properly, and then the operating pressure optimization for the power system is carried out. The results of this study show that the fuel cell stack power generation is increased with the system operating pressure. The compressor power consumption is also increased with the system operating pressure, but it can be reduced by using a two-speed compressor operation mode. The optimum system operating pressure is found to be 1.2 atm. The optimum system operating pressure is influenced by the compressor efficiency and is increased with the compressor efficiency.

With the rapid growth and development of proton-exchange membrane fuel cell (PEMFC) technology, there has been increasing demand for clean and sustainable global energy applications. Of the many device-level and infrastructure challenges that need to be overcome before wide commercialization can be realized, one of the most critical ones is increasing the PEMFC power density, and ambitious goals have been proposed globally. For example, the short- and long-term power density goals of Japan's New Energy and Industrial Technology Development Organization are 6 kilowatts per litre by 2030 and 9 kilowatts per litre by 2040, respectively. To this end, here we propose technical development directions for next-generation high-power-density PEMFCs. We present the latest ideas for improvements in the membrane electrode assembly and its components with regard to water and thermal management and materials. These concepts are expected to be implemented in next-generation PEMFCs to achieve high power density.