Structure Design for Ultrahigh Power Density Proton Exchange Membrane Fuel Cell.

Next-generation ultrahigh power density proton exchange membrane fuel cells rely not only on high-performance membrane electrode assembly (MEA) but also on an optimal cell structure. To this end, this work comprehensively investigates the cell performance under various structures, and it is revealed that there is unexploited performance improvement in structure design because its positive effect enhancing gas supply is often inhibited by worse proton/electron conduction. Utilizing fine channel/rib or the porous flow field is feasible to eliminate the gas diffusion layer (GDL) and hence increase the power density significantly due to the decrease of cell thickness and gas/electron transfer resistances. The cell structure combining fine channel/rib, GDL elimination and double-cell structure is believed to increase the power density from 4.4 to 6.52 kW L-1 with the existing MEA, showing nearly equal importance with the new MEA development in achieving the target of 9.0 kW L-1 .

High-consistency proton exchange membrane fuel cells enabled by oxygen-electron mixed-pathway electrodes via digitalization design.

Proton exchange membrane (PEM) fuel cell has been regarded as a promising approach to the decarbonization and diversification of energy sources. In recent years, durability and cost issues of PEM fuel cells are increasingly significant with the rapid increase of power density. However, the failure to maintain the cell consistency, as one major cause of the above issue, has attracted little attention. Therefore, this study intends to figure out the underlying cause of cell inconsistency and provide solutions to it from the perspective of multi-physics transport coupled with electrochemical reactions. The PEM fuel cells with electrodes under two compression modes are firstly discussed to fully explain the relationship of cell performance and consistency to electrode structure and multi-physics transport. The result indicates that one main cause of cell inconsistency is the intrinsic conflict between the separated transport and cooperated consumption of oxygen and electron throughout the active area. Then, a mixed-pathway electrode design is proposed to reduce the cell inconsistency by enhancing the mixed transport of oxygen and electron in the electrode. It is found that the mixing of pathways in electrodes at under-rib region is more effective than that at the under-channel region, and can achieve an up to 40% reduction of the cell inconsistency with little (3.3%) sacrificed performance. In addition, all the investigations are implemented based on a self-developed digitalization platform that reconstructs the complex physical-chemical system of PEM fuel cells. The fully observable physical information of the digitalized cells provides strong support to the related analysis.

Porous Flow Field for Next-Generation Proton Exchange Membrane Fuel Cells: Materials, Characterization, Design, and Challenges.

Porous flow fields distribute fuel and oxygen for the electrochemical reactions of proton exchange membrane (PEM) fuel cells through their pore network instead of conventional flow channels. This type of flow fields has showed great promises in enhancing reactant supply, heat removal, and electrical conduction, reducing the concentration performance loss and improving operational stability for fuel cells. This review presents the research and development progress of porous flow fields with insights for next-generation PEM fuel cells of high power density (e.g., ∼9.0 kW L-1). Materials, fabrication methods, fundamentals, and fuel cell performance associated with porous flow fields are discussed in depth. Major challenges are described and explained, along with several future directions, including separated gas/liquid flow configurations, integrated porous structure, full morphology modeling, data-driven methods, and artificial intelligence-assisted design/optimization.

Alternating Flow Field Design Improves the Performance of Proton Exchange Membrane Fuel Cells.

The flow field structure of a proton exchange membrane fuel cell (PEMFC) is a determining factor for improving the cell power density. In this study, a universal alternating flow field design for the first time is proposed, which arranges structural units with different flow resistances in an alternating way to significantly improve the gas transfer rate into the electrode, with the advantages of easy machining and low pumping loss. Based on the design, it is proposed and tested large-scale fuel cells with three novel flow fields by combining a parallel channel, baffled channel, serpentine channel, and narrowed channel. The results show that the design can significantly enhance the gas supply efficiency and that the novel baffled flow field improves the PEMFC performance by 23% with low pumping loss. The design employed in the study offers additional options for flow field optimization and contributes to the early achievement of next-generation ultrahigh power density fuel cells.

De Novo Design of Covalent Organic Framework Membranes toward Ultrafast Anion Transport.

The emergence of all-organic frameworks is of fundamental significance, and designing such structures for anion conduction holds great promise in energy conversion and storage applications. Herein, inspired by the efficient anion transport within organisms, a de novo design of covalent organic frameworks (COFs) toward ultrafast anion transport is demonstrated. A phase-transfer polymerization process is developed to acquire dense and ordered alignment of quaternary ammonium-functionalized side chains along the channels within the frameworks. The resultant self-standing COFs membranes exhibit one of the highest hydroxide conductivities (212 mS cm-1 at 80 °C) among the reported anion exchange membranes. Meanwhile, it is found that shorter, more hydrophilic side chains are favorable for anion conduction. The present work highlights the prospects of all-organic framework materials as the platform building blocks in designing ion exchange membranes and ion sieving membranes.

Multi-functional anodes boost the transient power and durability of proton exchange membrane fuel cells.

Proton exchange membrane fuel cells have been regarded as the most promising candidate for fuel cell vehicles and tools. Their broader adaption, however, has been impeded by cost and lifetime. By integrating a thin layer of tungsten oxide within the anode, which serves as a rapid-response hydrogen reservoir, oxygen scavenger, sensor for power demand, and regulator for hydrogen-disassociation reaction, we herein report proton exchange membrane fuel cells with significantly enhanced power performance for transient operation and low humidified conditions, as well as improved durability against adverse operating conditions. Meanwhile, the enhanced power performance minimizes the use of auxiliary energy-storage systems and reduces costs. Scale fabrication of such devices can be readily achieved based on the current fabrication techniques with negligible extra expense. This work provides proton exchange membrane fuel cells with enhanced power performance, improved durability, prolonged lifetime, and reduced cost for automotive and other applications.

Mechanism of Water Content on the Electrochemical Surface Area of the Catalyst Layer in the Proton Exchange Membrane Fuel Cell.

Combined molecular dynamics (MD) simulation and experiment are adopted to gain the mechanism of water content on the electrochemical surface area (ECSA) of the catalyst layer in a proton exchange membrane fuel cell. The morphology of water domains in the catalyst layer has a strong impact on the ECSA via MD simulation. The morphology of the water domains is isolated water clusters at low water content, resulting in the poor ECSA due to the lack of proton transport paths. The transport paths of protons tend to be quickly established with increasing water content during the transition process of the morphology of water domains from isolated water clusters to the water channel network, thereby leading to the rapid increase of the ECSA. However, the slight increase of the ECSA at high water content mainly results from the improved contact area between water domains and Pt particle instead of the formation of new transport paths. In addition, the stronger binding of water molecules and the Pt particle at low temperature results in a higher ECSA.