In-Plane Channel-Structured Catalyst Layer for Polymer Electrolyte Membrane Fuel Cells

Overcoming the Limitation of Ionomers on Mass Transport and Pt Activity to Achieve High-Performing Membrane Electrode Assembly

The membrane electrode assembly (MEA) is one of the critical components in proton exchange membrane fuel cells (PEMFCs). However, the conventional MEA cathode with a covered-type catalyst/ionomer interfacial structure severely limits oxygen transport efficiency and Pt activity, hardly achieving the theoretical performance upper bound of PEMFCs. Here, we design a noncovered catalyst/ionomer interfacial structure with low proton transport resistance and high oxygen transport efficiency in the cathode catalyst layer (CL). This noncovered interfacial structure employs the ionomer cross-linked carbon particles as long-range and fast proton transport channels and prevents the ionomer from directly covering the Pt/C catalyst surface in the CL, freeing the oxygen diffusion process from passing through the dense ionomer covering layer to the Pt surface. Moreover, the structure improves oxygen transport within the pores of the CL and achieves more than 20% lower pressure-independent oxygen transport resistance compared to the covered-type structure. Fuel-cell diagnostics demonstrate that the noncovered catalyst/ionomer interfacial structure provides exceptional fuel-cell performance across the kinetic and mass transport-limited regions, with 77% and 67% higher peak power density than the covered-type interfacial structure under 0 kPagauge of oxygen and air conditions, respectively. This alternative interfacial structure provides a new direction for optimizing the electrode structure and improving mass-transport paths of MEA.

Hierarchical Wrinkle-Structured Catalyst Layer/Membrane Interface for Ultralow Pt-Loading Polymer Electrolyte Membrane Fuel Cells (PEMFCs)

The optimal architecture of three-dimensional (3D) interface between a polymer electrolyte membrane (PEM) and catalyst layer (CL) is one of the most important issues to improve PEM fuel cells' (PEMFCs) performance. Here, we report the fabrication of hierarchical wrinkled PEM/CL interface over a large area. We fabricated the hierarchical wrinkles on a multiscale from nanometers to micrometers by bottom-up-based facile, scalable, and simple method. Notably, it allows one to go beyond the limit of the catalyst utilization by extremely enlarged interfacial area. The resulting hierarchical wrinkled PEM/CL displays a dramatically increased electrochemically active surface area (ECSA) and power performance by the enhancement factors of 89% and 67% compared with those of flat interface, which is one of the best enhancements compared to previous PEMFCs. We believe the scalability of hierarchical wrinkled interface can be exploited to design advanced 3D interfaces for high-performance PEMFCs even with ultralow Pt-loading.

Multifunctional Nafion/CeO2 Dendritic Structures for Enhanced Durability and Performance of Polymer Electrolyte Membrane Fuel Cells

The development of a novel approach to achieve high-performance and durable fuel cells is imperative for the further commercialization of proton-exchange (or polymer electrolyte) membrane fuel cells (PEMFCs). In this work, multifunctional dendritic Nafion/CeO₂ structures were introduced onto the cathode side of the interface between a membrane and a catalyst layer through electrospray deposition. The dendritic structures enlarged the interfacial contact area between the membrane and the catalyst layer and formed microscale voids between the catalyst layer and gas diffusion medium. This improved the PEMFC performance through the effective utilization of the catalyst and enhanced mass transport of the reactant. Especially, under low-humidity conditions, the hygroscopic effect of CeO₂ nanoparticles also boosted the power density of PEMFCs. In addition to the beneficial effects on the efficiency of the PEMFC, the incorporation of CeO₂, widely known as a radical scavenger, effectively mitigated the free-radical attack on the outer surface of the membrane, where chemical degradation is initiated by radicals formed during PEMFC operation. These multifunctional effects of the dendritic Nafion/CeO₂ structures on PEMFC performance and durability were investigated using various in situ and ex situ measurement techniques.

Electrochemical Compression Technologies for High-Pressure Hydrogen: Current Status, Challenges and Perspective

Abstract

Hydrogen is an ideal energy carrier in future applications due to clean byproducts and high efficiency. However, many challenges remain in the application of hydrogen, including hydrogen production, delivery, storage and conversion. In terms of hydrogen storage, two compression modes (mechanical and non-mechanical compressors) are generally used to increase volume density in which mechanical compressors with several classifications including reciprocating piston compressors, hydrogen diaphragm compressors and ionic liquid compressors produce significant noise and vibration and are expensive and inefficient. Alternatively, non-mechanical compressors are faced with issues involving large-volume requirements, slow reaction kinetics and the need for special thermal control systems, all of which limit large-scale development. As a result, modular, safe, inexpensive and efficient methods for hydrogen storage are urgently needed. And because electrochemical hydrogen compressors (EHCs) are modular, highly efficient and possess hydrogen purification functions with no moving parts, they are becoming increasingly prominent. Based on all of this and for the first time, this review will provide an overview of various hydrogen compression technologies and discuss corresponding structures, principles, advantages and limitations. This review will also comprehensively present the recent progress and existing issues of EHCs and future hydrogen compression techniques as well as corresponding containment membranes, catalysts, gas diffusion layers and flow fields. Furthermore, engineering perspectives are discussed to further enhance the performance of EHCs in terms of the thermal management, water management and the testing protocol of EHC stacks. Overall, the deeper understanding of potential relationships between performance and component design in EHCs as presented in this review can guide the future development of anticipated EHCs.

Graphic Abstract