Promotion of PEM water electrolyzers for power to gas technology which will contribute to the realization of a hydrogen economy
TOKYO, October 06, 2022–(BUSINESS WIRE)–Toshiba Corporation (TOKYO: 6502) has developed a large-scale production technology for electrodes that achieves a high level of efficiency in Power to Gas (P2G) technology, essential knowledge in advancing towards a carbon neutral society, while reducing the use of iridium, one of the rarest precious metals in the world, to 1/10*1.
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Figure 1: MEA Structure (Graphic: Business Wire)
P2G uses the electrolysis of water to convert renewable energy into hydrogen, for storage and transport to where it is needed. Polymer Electrolyte Membrane Electrolysis (PEM) is considered a very promising conversion method as it reacts quickly to power fluctuations and is very durable. However, PEM uses iridium, one of the rarest traded precious metals, as a catalyst in its electrodes. The practical application requires the reduction of the iridium used, a real challenge.
Toshiba developed a catalyst laminated with iridium oxide nanosheets that reduced the iridium requirement to 1/10 in 2017. Now, the company has developed a large-scale production technology that deposits the catalyst in a maximum area of 5 mtwo in one go. This breakthrough is expected to drive early commercialization of P2G for large-scale power conversion and contribute to achieving carbon neutrality. Toshiba targets commercialization in fiscal year 2023 or later.
More than 120 countries and regions have set a goal of carbon neutrality by 2050, and decarbonisation measures are being considered at national, regional and corporate levels. Renewables are essential to achieve the goal and reduce CO2 emissions, but their production fluctuates greatly with climate and weather conditions, and installations can only be located in suitable regions. To maximize its potential and ensure a stable and affordable energy supply, a method of storing and transporting electricity from renewable energies is required.
P2G is seen as an essential solution to achieving carbon neutrality by 2050. It uses electrolysis to convert electricity from renewables into hydrogen, ready for storage and transportation. The key technology in the process is water electrolysers that convert energy into hydrogen without emitting COtwo. PEM water electrolysis, which offers excellent adaptability to power fluctuations and high durability, and Europe and the US have led the development of the current process.
PEM uses a membrane electrode assembly (MEA) that integrates the membrane electrolyte and the electrode (Fig. 1). Large-scale conversion of electricity with hydrogen requires a large number of MEAs, and forecasts anticipate a market scale of approximately $580 million by 2028*two.
However, the MEA electrode relies on a large amount of iridium to ensure sufficient electrolytic efficiency. Iridium is one of the rarest precious metals. Annual world production is in the region of 7 to 10 tons, much less than the 200 tons of platinum, and costs four to five times as much.*3. Electrode formation requires a uniform layer of fine iridium oxide particles, but reduction of iridium oxide results in uneven application and non-uniform reactions that degrade water electrolysis performance.
Toshiba’s multilayer catalyst uses a new sputtering technology (Fig. 2) to deposit alternating layers of iridium oxide nanosheet films and void layers (Fig. 3). In sputtering, ions, such as argon, bombard a deposition material, the target, in a vacuum and deposit the ejected particles onto a substrate (Fig. 2). In Toshiba’s process, iridium is the target and a thin film of iridium oxide is formed by injecting oxygen as the target is deposited on the substrate. Thickness control is carried out at the nanometric level, performing the deposition of uniform layers of iridium oxide with a smaller amount of iridium.
The use of Toshiba’s laminated nanosheet structure in the catalyst layer successfully reduces the required iridium to 1/10, while maintaining the yield of water electrolysis (Fig. 4). It also significantly expands the deposition surface area. Since sputtering is carried out in a vacuum, deposition over a large area is difficult. However, by modifying the deposition distribution ratio for multiple metal targets, including iridium, and the level of oxygen input, Toshiba has successfully developed a large-scale production technology that performs catalyst deposition in one area. up to 5mtwo at once (Fig. 5).
In collaboration with Toshiba Energy Systems & Solutions Corporation, Toshiba has built MEA prototypes with electrodes based on the developed technology and has started evaluation tests with a manufacturer of water electrolyzers. Going forward, the company will improve performance and quality towards mass production of MEA, with the goal of commercializing in fiscal year 2023 or later.
*1: https://www.global.toshiba/content/dam/toshiba/migration/corp/techReviewAssets/tech/review/2018/03/73_03pdf/a03.pdf
https://www.global.toshiba/content/dam/toshiba/jp/technology/corporate/review/2022/04/a04.pdf
*2: Toshiba estimate
*3: https://matthey.com/pgm-market-report-2022
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