Green hydrogen is expected to become a major pillar for the decarbonization of the energy and industrial landscapes. Most initiatives worldwide in this direction, from purely scientific projects to small size industrial pilot plants, aim to combine renewable energy with water electrolysis, are yielding thousands of results with promising results and open questions. Arguably, the major challenge remains to improve the efficiency of the processes while limiting costs and avoiding the use of critical raw materials. In addition, two divergent approaches are competing: centralized and decentralized. On the former, solar power would be transformed into electricity (by photovoltaic or wind farms) and then grid distributed for the production of (green) hydrogen from water electrolysis at industrial hubs.[1,2] On the later, the integration of solar energy capture and water splitting in a single device may offer significant advantages, although through higher complexity. In all cases, catalysis is crucial to speed-up the chemical reactions to proceed at industrially relevant conditions, while minimizing energy loses.[3,4]

In this talk, we will discuss some of the most representative achievements in water electrolysis for (green) hydrogen production, highlighting their advantages, and addressing their current limitations, if any. Many successful catalysts are based on noble metals or critical raw materials, far away from practical applications. When discussing green hydrogen as a plausible contribution to decarbonization, energy security and environmental mitigation plans, sustainability and scaling are additional constrains that must be taken into account. There are many hurdles between a promising lab-scale discovery and a technology, many of them involving economic and societal considerations.

We will address the different challenges in the development of cost and energy efficient processes, starting from the design of the electrocatalysts, and their validation in industrially-ready electrolyzer architectures. We will describe the major problems looking at the activity/stability paradigms, along the successful (or not) strategies that we are exploring to further improve their electrochemical performance: nanostructuration, doping effects, external magnetic fields, coordination frameworks, etc.

[1] Xia, R.; Overa, S.; Jiao, F. Emergung electrochemical processes to decarbonize the chemical industry. JACS Au 2022, 2, 1054–1070.

[2] Xu, Q.; Zhang, L.; Zhang, J.; Wang, J.; Hu, Y.; Jiang, H.; Li, C. Anion exchange membrane water electrolyzer: Electrode design, Lab-scale testing system and performance evaluation. EnergyChem 2022, 4, 100087.

[2] Romano, V.; D'Angelo, G.; Perathoner, S.; Centi, G. Current density in solar fuel technologies. Energy Environ. Sci. 2021, 14, 5760–5787.

[3] H. Nishiyama, H.; Yamada, T.; Nakabayashi, M.; Maehara, Y.; Yamaguchi, M.; Kuromiya, Y.; Nagatsuma, Y.; Tokudome, H.; Akiyama, S.; Watanabe, T.; Narushima, R.; Okunaka, S.; Shibata, N.; Takata, T.; Hisatomi, T.; Domen, K. Photocatalytic solar hydrogen production from water on a 100 m² scale. Nature 2021, 598, 7880.