Hybrid Water-Splitting Technology as a Novel Approach to Efficiently Produce Green Hydrogen

As a non-toxic, renewable, transportable, and emission-free energy carrier, hydrogen is becoming a popular alternative fuel in the energy sector. We have recently developed a hybrid water-splitting technology based on the chemical looping principle by combining "hydrothermal" and "electrochemical" processes capable of delivering green hydrogen at high efficiency. At the heart of the patented process, a hydrothermal reactor, functioning as the oxidation unit, operates side-by-side with a modified alkaline electrolyser as the reduction unit to deploy a complete red-ox loop for water splitting. The hydrothermal reactor facilitates the reaction between water and an active metallic reagent in an alkali solution at 150 – 400 °C to directly produce hydrogen (1 – 200 bar). The thermodynamically favoured reaction between water and the active metal generates excess heat, which can be recovered as superheated steam and potentially converted to electricity to balance the renewable input. The modified-alkaline electrolyser operating at 15 – 85 °C reactivates the spent metal oxide composite (reduction step) and simultaneously produces hydrogen at the cathode surface. Such a dual hydrogen harvesting approach, plus the heat recovery system, leads to a much higher energy efficiency (~90%, measured with Surrey's prototype lab-scale system) compared to the state-of-the-art water electrolysis technologies like PEM and alkaline electrolysers (~60 - 70%). The process can be deployed as a containerised modular unit integrated with various forms of renewable (solar, wind, hydroelectric, etc.) for large-scale onshore, offshore, or remote applications.