Cost and durability of proton-exchange-membrane water electrolyzer (PEMWE) components are the two main drawbacks with existing PEMWE technology. A major driver of cost in PEMWE systems is the iridium catalyst, which is expensive and limited in supply. For example, with an iridium loading of about 2 mg Ir/cm2, an annual increase of PEMWE capacity of 10 GW would exceed current worldwide Ir production. Therefore, iridium use must be drastically reduced or eliminated to meet worldwide electrolyzer production goals.The primary objective of the Revolutionizing Green Hydrogen Production with Next Generation PEM Water Electrolyzer Electrodes (HOPE) project is to reduce the anode loading of Ir catalyst in PEMWE below 50 mg Ir/kW. To achieve this goal, we pursue two approaches: optimization of the interface between the catalyst layer (CL) and the porous transport layer (PTL), and development of ruthenium pyrochlore catalysts to replace iridium as the OER catalyst.Optimizing the interface of the catalyst layer (CL) and the porous transport layer (PTL) on the anode side is critical for reducing catalyst loading. The structure of this interface influences the catalyst utilization as well as the transport of mass, heat, and charge, which all affect cell efficiency. Current PEMWE installations use PTLs made of sintered titanium, which were originally intended for other applications like filtration and have not been optimized for PEMWE applications. In this project, we have begun to develop various methods, such as tape casting of Ti particle slurries, for fabrication of MPLs for PEMWE anodes.Another strategy to reduce iridium loading is to replace the iridium catalyst with another catalyst material. Some pyrochlore oxide materials using ruthenium have shown high activity for the oxygen evolution reaction and sufficient stability for PEMWE systems, but their low electrical conductivity prevents use in traditional PEMWE systems. With good control of the MPL structure, however, the density of contact points between the catalyst layer and PTL can be increased, and the catalyst conductivity should have less of an impact on performance. In this project, we are developing synthesis methods for ruthenium pyrochlore catalyst materials of varying composition to understand how compositional changes influence catalytic activity and conductivity.These two approaches for reduction of iridium loading will be supplemented with electrochemical characterization, as well as computational modelling, of an electrolyzer cell using the developed components. To understand the impacts of CL/PTL interface structure and catalyst choice on electrolyzer performance, we have begun to develop an open-source model of a PEMWE cell. This model will be used to guide MPL development and optimization work.This work has been performed within the HOPE (Revolutionizing Green Hydrogen Production with Next Generation PEM Water Electrolyser Electrodes) project financially supported by the Research Council of Norway under project number 325873.
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Jul 10, 2024
Cheng Shen + 5
Open Access