The development of a hydrogen economy has become a strategic priority for South Africa. In March 2022, the country announced a national plan to integrate hydrogen-related technologies into various sectors of the South African economy, for the purpose of transitioning into a carbon neutral society by 2050 [1]. The establishment of the Hydrogen Valley in partnership with the private sector [2] and implementation of the hydrogen society roadmap especially for the decarbonization of heavy-duty transport and energy intensive industries is expected to significantly stimulate economic recovery. Proton exchange membrane water electrolysis (PEMWE) is considered the key technology for the creation of an export market for South African green hydrogen.

HySA Catalysis is a Centre of Competence established in South Africa to focus on mineral beneficiation with a mandate to commercialize catalysts and membrane electrode assemblies (MEAs) for proton exchange membrane fuel cells (PEMFCs) and more recently PEMWEs. The Centre is actively engaged with the Government and private stakeholder partners for research and technology development while focusing on human capital development for future employment in the hydrogen sector.

Iridium or iridium oxide based catalysts are currently the only commercially available state-of-the-art catalysts utilized in PEMWE anodes that meet the performance and durability requirements. However, iridium is one of the scarcest metals on earth with an abundance of 0.821 atoms/10⁶ Si atoms compared to 1.625 atoms/10⁶ Si atoms for platinum [3]. South Africa holds 63000 metric tons of platinum group metal (PGM) reserves, which is 90% of total world reserves [4]. The chromite and sulphide ores are the main sources of PGM metals in the Bushveld complex [3]. While platinum and palladium are present in concentrations of 40–55% and 20–40% respectively, iridium concentration is an order of magnitude lower and varies between 0.9–3.9% depending on the mining location [5]. As PEMWE industrialization is gearing up, iridium availability, production and supply to support the technology deployment and integration are becoming increasingly important discussion topics.

Recent work by Minke et al. critically discussed the iridium demand as a potential bottleneck in the context of PEMWE commercialization for next fifty years [6]. A dramatic reduction of the iridium loadings has been suggested (to 0.05 gkW^-1 by 2035) along with establishing the infrastructure and methods for iridium catalyst recycling. While focusing on energy transition in Germany, Kiemel et al. also discussed critical materials for water electrolysis and associated risks from the perspective of capacity scale-up [7]. It has been recognized that the development of innovative approaches to reduce the material inputs per kW in PEMWE is necessary.

In this paper we provide an overview of our research activities and achievements towards reducing the amount of Ir in PEMWE via development of highly active and durable supported catalysts and optimizing the Ir utilization in catalyst coated membranes (CCMs). Along with electrochemical characterization methods, scanning electron microscopy (SEM), scanning transmission electron microscopy coupled energy dispersive X-ray analysis (STEM-EDX) and X-ray photoelectron spectroscopy (XPS) are used to understand the nature of synthesized catalysts, elucidate the effect of the substrate, and explore the CCM catalyst layer microstructure. This knowledge will inspire future technology development strategies targeting the reduction of Ir loadings and support forthcoming deployment of PEMWEs.

References

1. Department of Science and Innovation, Republic of South Africa, Hydrogen Society Roadmap for South Africa, 2021, Available online: https://www.dst.gov.za/images/South_African_Hydrogen_Society_RoadmapV1.pdf
2. Department of Science and Innovation, Republic of South Africa, South Africa Hydrogen Valley Final Report October 2021, Available online: https://www.dst.gov.za/images/2021/Hydrogen_Valley_Feasibility_Study_Report_Final_Version.pdf
3. Anthony E. Hughes, Nawshad Haque, Stephen A. Northey and Sarbjit Giddey, Platinum Group Metals: A Review of Resources, Production and Usage with a Focus on Catalysts, Resources, 10(9) 93 (2021) pp. 1-40, https://doi.org/10.3390/resources10090093
4. S. Geological Survey, Mineral Commodity Summaries, U.S. Geological Survey (2022) pp. 127, https://doi.org/10.3133/mcs2022
5. Implats – Mineral Resource and Mineral Reserve Statement as at 30 June 2021, Available online: https://www.implats.co.za/pdf/reports/2021/mrr-2021.pdf
6. Christine Minke, Michel Suermann, Boris Bensmann and Richard Hanke-Rauschenbach, Is Iridium Demand a Potential Bottleneck in the Realization of Large-Scale PEM Water Electrolysis?, Int. J Hydrogen Energy, 46 (2021) pp. 23581-23590, https://doi.org/10.1016/j.ijhydene.2021.04.174
7. Steffen Kiemel, Tom Smolinka, Franz Lehner, Johannes Full, Alexander Sauer and Robert Miehe, Critical Materials for Water Electrolysers at the Example of the Energy Transition in Germany, Int J Energy Res. 45 (2021) pp. 9914-9935, https://doi.org/10.1002/er.6487