Synthesis and characterization of perovskites for hydrogen production: study and modelling of a two-step thermochemical green water splitting cycle

Human activity and energy demand are responsible for the majority of atmospheric emissions, so research into innovative technologies for their reduction will be of paramount interest in the coming decades. Concentrating solar plants (CSP) can convert heat from concentrated solar power into chemical energy which can then be used for several applications, such as thermal green hydrogen production. In this regard, two-step thermochemical water-splitting cycles (TWSC) using perovskite powders are pioneering technologies for contributing to decarbonise the energy sector, as these processes can reduce operating temperatures, facilitating a more efficient coupling with CSP. The present work is concerned with the evaluation of the redox capabilities of three different perovskites, selected after a screening of the powders already considered in the literature. The selected perovskites are: and , which are known from the literature, and , which is a new material not investigated yet. To understand the best way to produce the powders, taking into account scalability and safety criteria, several synthesis methods were tested. Considering a maximum thermal limit at 1000°C, which allows an efficient use of heat from currently available CPSs, the thermodynamics of the redox reactions were analysed to find a couple of temperatures, one for reduction and one for oxidation; in these conditions, the standard Gibbs free energy of the oxidation reaction with steam is equal or lower than zero, making hydrogen formation favourable. In addition, to fully characterise the redox reactions, a kinetic study was also carried out implementing with Matlab a shrinking core model. To estimate the hydrogen yield, a laboratory-scale system was designed, representative of both the cycles reactions. All these evaluations were supported by an exhaustive experimental campaign, including X-ray diffraction (XRD), to check the purity of the synthetized powders, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to calculate conversion rates along with specific and reaction heats, and scanning electron microscopy (SEM) to estimate the average particles size.