Solar Hydrogen Productivity of Ceria–Scandia Solid Solution Using Two-Step Water-Splitting Cycle

Abstract

The reactivity of CeO2–Sc2O3 solid solution for solar hydrogen production via two-step water-splitting reaction has been studied in this work. The CeO2–Sc2O3 solid solution was synthesized by polymerized complex method (PCM) with various Sc content between 0 and 20 mol. %. Analysis results from online direct gas mass spectrometry (DGMS) suggest that Ce3 + formed by CeO2–Sc2O3 solid solution in the O2-releasing step could be completely oxidized by H2O to generate hydrogen and return to Ce4 + in the H2-generation step. A Ce0.97Sc0.03O1.985 generates the largest amount of O2 and H2 among present samples, and the reduction and oxidation ratios are about 9.9% (Ce) and 10% (Ce), respectively. An estimated H2-generation reaction rate is about 4 ml g−1min−1 for Ce0.97Sc0.03O1.985. This value is about seven times greater than that of Ce0.89Zr0.11O2. The high reaction rate of Ce0.97Sc0.03O1.985 makes all formed Ce3 + completely oxidized by H2O in 5 min in the H2-generation step. The reasons for high performance are discussed from the views of lattice distortion and the amount of oxygen vacancies formed in the lattice.

Reactivity of Doped Ceria-Based Mixed Oxides for Solar Thermochemical Hydrogen Generation via Two-Step Water-Splitting Cycles

“…Ceria (CeO 2 ) and metal doped-ceria have recently gained tremendous amount of interest as potential candidate materials for the thermochemical production of renewable solar fuels via H 2 O-and CO 2 -splitting cycles [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] . These materials are capable of splitting water (and/or carbon dioxide) using solar energy according to a generic two-step redox cycle (Fig.…”

A review on solar thermal syngas production via redox pair-based water/carbon dioxide splitting thermochemical cycles

“…A plethora of dopants, basically lanthanides and alkaline earths, has been tested to improve the redox/thermal stability characteristics [38,125,[133][134][135][136]. A consensus on the beneficial effect ofanyway well-known from automotive emission control catalysts [137,138] -blending of CeO 2 with ZrO 2 with additions of La 2 O 3 to induce thermal stability seems to having been established [38,128,139].…”

Metal Oxides Applied to Thermochemical Water-Splitting for Hydrogen Production Using Concentrated Solar Energy

“…While the oxygen exchange capability of ceria is lower compared to iron oxide-based cycles, sintering is less problematic because the melting point is considerably higher. Different research works have evidenced the high promise of ceria for application to solar fuel production according to the redox cycle represented in Figure 13, using various ceria microstructures and morphologies including dispersed powders [140][141][142][143][144][145][146][147][148][149], three-dimensionally ordered macroporous (3DOM) powders featuring templated macro-scale porosity [154,155], porous structured monoliths [137][138][139], porous felts or fibers [156,157], or reticulated porous foams [158][159][160]. The morphologies enabling both enhanced available geometric surface area and bulk interconnected pore system that facilitate the mass transport of reacting species to and from the oxidation sites, are the most suitable for rapid fuel production.…”

“…However, the material shaping process represents an additional step required for the preparation of tailored materials and for their incorporation in suitable solar reactors, which could have an impact on the process economics. The thermodynamic and kinetic properties of ceria can be altered by doping its fluorite structure with transition metals and rare earth metal oxides [135][136][137][138][139][140][141][142][143][144][145][146][147][148][149][150][151][152][153][154]. Indeed, ceria is an active compound used in many catalytic systems, and it is attractive due to its thermal stability (good resistance to sintering) and ability to exchange oxygen via storing and releasing oxygen reversibly.…”