Comparison of Anode-Catalyst-Layer Coating Methods for Low-Temperature Electrolysis

Abstract

Iridium oxide (IrO2) anode catalyst layers are prepared by liquid film coating a dispersion of the IrO2 catalyst and ionomer onto a substrate. In many research studies these catalyst layers are prepared by ultrasonic spray coating or hand-painting. However, for gigawatt-scale deployment of electrolyzers which is required to enable a hydrogen economy, the catalyst layers will likely need to be produced using higher-throughput continuous roll-to-roll (R2R) coating methods that are capable of coating speeds of square meters per minute (if not per second). Many of the cost estimates for electrolyzer production at scale assume the use of R2R coating methods,1 however it is yet to be proven that these methodologies are capable of producing low-loading catalyst layers with similar performance and durability to those produced with lab-scale coating methods. In this study we have compared various lab-scale and R2R-coating methods to determine their impact on catalyst layer morphology and performance. Ultrasonic spray coating is used as the baseline coating method. Mayer rod and blade coating, which represent scalable coating methods with ink formulations and coating and drying physics similar to R2R coating, are used to prepare small-scale coatings. In addition, direct gravure coating is used as another R2R coating method. Device testing of membrane electrode assemblies (MEAs) fabricated using catalyst layers prepared from the different coating methodologies show that using blade coating and R2R-gravure coating produce catalyst layers with the same performance as ultrasonic spray coating while increasing production rate by orders of magnitude. Interestingly, the catalyst layers produced using scalable coating methods show better kinetic performance than spray coated layers. These results show that R2R-coating methods are likely viable for large-scale manufacturing of electrolyzers.This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Hydrogen and Fuel Cell Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.References(1) Mayyas, A. T.; Ruth, M. F.; Pivovar, B. S.; Bender, G.; Wipke, K. B. Manufacturing Cost Analysis for Proton Exchange Membrane Water Electrolyzers; NREL/TP-6A20-72740; National Renewable Energy Lab. (NREL), Golden, CO (United States), 2019. https://doi.org/10.2172/1557965. Figure 1