Assessing the potential of thermo-chemical water splitting cycles: A bridge towards clean and sustainable hydrogen generation

Abstract

Thermochemical water separation methods are one of the clean and green hydrogen production methods. Thermochemical cycles are divided into two groups; hybrid thermochemical cycles which are using electrical energy and thermal energy, and pure thermochemical cycles which are using only thermal energy. In this study, the most studied S-I, HyS, Fe-Cl, Cu-Cl and Mg-Cl pure/hybrid thermochemical cycles available in the open literature are examined in terms of efficiency and cost comparatively. Besides, its advantages, disadvantages and challenges are also summarized. Thermochemical cycles have promising values both in terms of cost and environmental impact. Cu-Cl thermochemical cycle offers 0.0023 ADP (kg Sb eq), 0.0026 AP (kg SO2 eq), 0.3370 GWP (kg CO2 eq), 2.27 × 10–08 ODP (kg CFC-11 eq) and 2.4235 HTP (kg 1, 4-DB eq). These values can be said to be more environmentally friendly than other hydrogen production methods. The Cu-Cl hybrid cycle is promising in terms of multigenerational integration. Apart from these cycles, thermochemical cycles that are new in the literature are examined and explained in detail. Among them, the NaOH, Cu-Cl and Boron thermochemical cycles appear to be promising in terms of efficiency, cost and productivity. In these cycles, the NaOH cycle is promising as it operates at 500 °C. It also has the highest energy efficiency with 82% among new cycles. More importantly, such thermeochemical/hybrid cycles are suitable to use the renewable heat and electricity.