Development of Noble-Metal Free Bifunctional Catalysts for Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) for the Application in an Electrical Rechargeable Galvanic Hydrogen Storage System
Authors: Rittel Merel Viola , Hauke Philipp , Rosenfeld Oren , Hahn Robert , Strasser Peter 
Published: December 2024

With the growing shift towards renewable energy sources, it has become significantly more urgent to explore and develop new energy storage solutions with high capacity, abundant materials and low cost. Conventional electrochemical storage systems (batteries) have been developed rapidly, but only pose as a partial solution due to their still low storage density and high cost.[1] Hydrogen occupies a key position within the energy transition attributable to its high storage density (33.33 kWh/kg) and its wide use as energy storage and as an essential raw material in industry.[2] However, two of the main problems are high investment costs and high cost of stored electricity due to the low efficiency of the conversion chain.[3]
Both of these problems could be significantly improved by a new approach as described by Hahn et al. combining the functionalities of a battery and an electrolyzer. In this concept (see Fig. 1), water is oxidized to oxygen at the gas electrode during charging and zinc oxide is reduced to metallic zinc at the counter electrode. When the storage cell is being discharged as required, zinc is converted back to zinc oxide and water is reduced at the gas evolution electrode to produce hydrogen with an efficiency near 80%.[4][5] Due to the very low material costs of the galvanic Zn cell as well as the high energy density of the deposited zinc of 820Ah/kg and thus low overall dimensions, the capital costs can be reduced significantly.[6]
At the core of this concept, we are working on the development of a noble-metal free bifunctional catalyst for the gas evolution electrode, realizing both hydrogen generation and oxygen generation over thousands of cycles. For this we applied multiple synthesis methods (microwave-assisted solvothermal synthesis, spray-coating technique, electrodeposition) to achieve various steel substrate-based catalysts doped with different metals (Ni, Co, Mo). The best results in terms of activity, overpotential and stability have been achieved using the microwave-assisted solvothermal synthesis. Apart from electrochemical activity and stability tests, simulating hundreds of charge and discharge cycles, we used microscopic and spectroscopic characterization methods such as SEM-EDX, thin-film XRD and ICP-OES.
[1] ENERGY STORAGE ASSOCIATION. Hydrogen Energy Storage - Energy Storage Association. 4/8/2021. Available also from http://energystorageassociationarchive.org/why-energy-storage/technologies/hydrogen-energy-storage/
[2] LUDWIG-BÖLKOW-SYSTEMTECHNIK GMBH. H2data.de - Hydrogen fact sheet. 2/12/2021. Available also from: http://www.h2data.de/.
[3] BREEZE, P. Chapter 8 - Hydrogen Energy Storage. In: BREEZE, P. (ed.). Power system energy storage technologies. London: Elsevier, AP, Academic Press, 2018, pp. 69–77. The power generation series. ISBN 978-0-12-812902-9. Available from doi: 10.1016/B978-0-12-812902-9.00008-0.
[4] Robert Hahn, Andreas Gabler, Axel Thoma, Fabian Glaw, K.-D. Lang, Small fuel cell system with cartridges for controlled hydrogen generation. Int. Journal of Hydrogen Energy 40 (2015) pp. 5340-5345
[5] Robert Hahn, Oren Rosenfeld, Chaim Markheim, Andreas Schamel, The Zn-H2 storage system, Fuel Cells, Electrolysers & H2 Processing, EFCF 2023, 4-7 July 2023 Lucerne, to be published in Fuel Cells 2024

[6] RUAN, P. et al. Design Strategies for High-Energy-Density Aqueous Zinc Batteries. Angewandte Chemie International Edition. 2022, vol. 61, no. 17, e202200598. issn 1521-3773. Available from doi: 10.1002/ anie.202200598.

Figure 1