Investigation of Perovskite Structures as Oxygen-Exchange Redox Materials for Hydrogen Production from Thermochemical Two-Step Water-Splitting Cycles

Abstract

This study addresses the synthesis, characterization, and thermochemical redox performance evaluation of perovskites and parent structures (Ruddlesden–Popper phases) as a class of oxygen-exchange materials for hydrogen generation via solar two-step water splitting. The investigated materials are La x Sr1–x MO3 (M = Mn, Co, Fe), Ba x Sr1–x (Co,Fe)O3, LaSrCoO4, and LaSrFeO4, also used as mixed ionic-electronic conductors in fuel cells. Temperature-programmed reduction, powder X-ray diffraction, and thermogravimetric analysis were used to obtain a preliminary assessment of these materials performances. Most of the perovskites studied here stand out by larger thermal reduction capabilities and oxygen vacancies formation at modest temperatures in the range 1000–1400 °C when compared with reference nonstoichiometric compounds such as spinel ferrites or fluorite-structured ceria-based materials. In addition, these materials offer noticeable access to metallic valence transitions during reoxidation in steam atmosphere that are not available in stoichiometric oxides. The promising behaviors characterized here are discussed in regard to the crystal chemistry of the perovskite and parent phases.

Phase transformations during HLnTiO4 (Ln=La, Nd) thermolysis and photocatalytic activity of obtained compounds

“…Until present time perovskite-like compounds are actively studied as materials with wide range of important physical and chemical properties, such as super-conductivity [1], colossal magnetoresistance [2], ferroelectricity [3,4], catalytic and photocatalytic activity [5][6][7], thermochemical properties [8] and electrochemical properties [9]. In recent years, there has been a constant interest in using the soft chemistry methods for development of new layered perovskitelike compounds with specified physicochemical properties, as well as design of these materials based on perovskite structure [10][11][12][13][14].…”

Redox chemistry of CaMnO3 and Ca0.8Sr0.2MnO3 oxygen storage perovskites

“…17 This is a fundamental limitation of the crystal motifs of these materials, and thus perovskite oxides, regardless of composition, will likely have a lower entropy of vacancy formation than ceria. This has important implications for designing materials for thermochemical fuel production cycles, where perovskites 28,29 have been suggested as a lower temperature alternative to the ceria cycle. 30 In this particular application, the oxide must have a large enough enthalpy of reduction Dh to reduce steam or carbon dioxide (>300 kJ mol À1 ).…”

Solar thermochemical splitting of water to generate hydrogen

“…7B) tering (38, 42, 45). Few other transition metal-(Fe, Co, and Cr) based perovskites also show good fuel production activity (46,47).Changing the Rare Earth in the A-Site. Properties of rare earth manganites depend strongly on the rare earth ion in the A site (48,49).…”