A Goldilocks Approach to Water Management: Hydrochannel Porous Transport Layers for Unitized Reversible Fuel Cells

Abstract

sources, such as wind and solar, are intermittent in nature, and must be combined with large-scale energy storage to provide stable and reliable power. Hydrogen-based reversible fuel cells (RFCs), which combine the functionality of a polymer electrolyte membrane (PEM), fuel cell (FC), and water electrolyzer (WE), could play a crucial role in providing this energy storage. During periods of excess renewable power generation, RFCs can electrolyze water to generate hydrogen. During periods of excess demand and insufficient renewable power generation, the stored hydrogen can be utilized in FC mode to generate power. Combination of FC and WE functionality into a single electrochemical device, that is, a unitized reversible fuel cell (URFC), could provide smaller, simpler, and less expensive systems. [1] However, the conflicting needs of FC and WE operation, particularly with regard to water management, have constrained progress on development of robust URFC technology. Herein, we report a new approach to URFC design based on hydrochannel porous transport layers (PTLs), which enables effective water management in both URFC operation modes. This hydrochannel PTL enables substantial improvements in performance and round-trip efficiency (RTE).A schematic representation of the URFC operation and the membrane electrode assembly (MEA) configuration is shown in Figure 1. In WE mode, water is supplied to the oxygen electrode (anode), where the water is split into oxygen and protons (H + ) through use of an oxygen evolution reaction (OER) catalyst. The resulting H + are transported through the PEM to the hydrogen electrode (cathode), which utilizes a hydrogen evolution reaction (HER) catalyst to combine H + with electrons to generate hydrogen. In FC operation mode, the hydrogen is supplied to the hydrogen electrode (anode) for the hydrogen oxidation reaction (HOR), and oxygen (air) is supplied to the oxygen electrode (cathode) for the oxygen reduction reaction (ORR). In the present work, the URFC is operated in the constant gas electrode mode, where OER and ORR (or HOR and HER) occur on the same electrode to avoid fuel and oxidant mixing. [2] For constant gas electrode mode operation, as shown in Figure 1, the hydrogen electrode catalyst consists of a supported platinum catalyst, which serves as both HOR and HER catalyst. The oxygen electrode catalyst consists of a combination This work presents a novel porous transport layer (PTL), the hydrochannel PTL, that enables improved water management and record high round trip efficiency in unitized reversible fuel cells (URFCs). URFCs require rapid transport of O 2 and H 2 O to provide high performance in both fuel cell and water electrolyzer operation, but cell design is complicated by conflicting water management requirements: electrolyzers perform best with high liquid water saturation, whereas fuel cells perform best when liquid water saturation is as low as possible while still maintaining effective ionomer hydration. The hydrochannel PTL circumvents this obstacle by providing ...

A Viewpoint on X-ray Tomography Imaging in Electrocatalysis

“…Neutron imaging is a valuable complement to X-ray imaging, since neutrons can penetrate common metals while attenuating hydrogen, lithium, and water. This feature makes neutron imaging an attractive technique for characterizing various electrochemical systems, including fuel cells, water electrolyzers, unitized reversible fuel cells, and CO 2 electrolyzers . Moreover, neutron imaging is particularly well-suited for imaging fuel cells and electrolyzers since neutrons can penetrate conventional hardware without requiring special equipment or design modifications.…”

“…This method involves imaging with hardware rotation, similar to X-ray CT, and has already been reported in several studies. − Neutron imaging is widely used to characterize water in various components of fuel cells and electrolyzers, where effective water management is crucial for optimal performance and durability. Specifically, it has been utilized to study water distribution across membrane electrode assemblies, water or oxygen saturation in porous transport layer and gas diffusion layer, as well as the impact of operating conditions . Neutron tomography offers an added advantage by allowing for precise imaging of water distribution in electrochemical systems, thereby providing a better understanding of the heterogeneity present within these systems.…”

4D Neutron Imaging of Solute Transport and Fluid Flow in Sandstone Before and After Mineral Precipitation

“…Several recent studies have demonstrated the capabilities of time‐resolved neutron imaging to study fluid flow in rocks, for example, to reveal the relationship between wormhole advancement and permeability variation in dissolving rocks (Cooper et al., 2023), or to investigate the interactions between imbibition and pressure‐driven flow in microporous deformed limestone (Lewis et al., 2023). Neutron imaging has also been used to study transport properties in other porous media, such as the migration of condensed water vapor through cracked concrete (Gupta et al., 2022), hydro‐channel porous transport layer designed for unitized reversible fuel cells (Komini Babu et al., 2023), as well as salt precipitation and water transport in CO 2 electrolysis (Disch et al., 2022). These studies demonstrate the versatility of the neutron imaging technique and its ability to provide a deeper understanding of fluid transport in various porous media.…”