Thermochemical hydrogen production from water using reducible oxide materials: a critical review

Abstract

This review mainly focuses on summarizing the different metal oxide systems utilized for water-splitting reaction using concentrated solar energy. Only two or three cyclic redox processes are considered. Particle size effect on redox reactions and economic aspect of hydrogen production via concentrated solar energy are also briefly discussed. Among various metal oxides system CeO 2 system is emerging as a promising candidate and researchers have demonstrated workability of this system in the solar cavity-receiver reactor for over 500 cycles. The highest solar thermal process efficiency obtained so far is about 0.4 %, which needs to be increased for real commercial applications. Among traditionally studied oxides, thin-film ferrites looks more promising and could meet US Department of energy target of $2.42/kg H 2 by 2025. The cost is mainly driven by high heliostat cost which needs to reduced significantly for economic feasibility. Overall, more work needs to be done in terms of redox material engineering, reactor technology, heliostat cost reduction and gas separation technologies before commercialization of this technology.

High performance cork-templated ceria for solar thermochemical hydrogen production via two-step water-splitting cycles

“…Currently, hydrogen is mostly generated from fossil fuels.1 Besides reforming, hydrogen can be produced from solid bioresources2 and from water.3 Electrolysis of water is promising as electricity supplied from solar energy can be stored as hydrogen (power to gas).4 Another compelling approach is the conversion of solar energy into H 2 via two-step thermochemical cycles driven by concentrated solar thermal heat, using reducible metal oxides. 5,6,7,8 A comprehensive review of the applications and limitations of two step metal oxide thermochemical redox cycles highlighted the benefits of using such cycles to split H 2 O and CO 2 , offering a high-potential route to renewable fuel production.9 By using a redox pair such as SnO 2 /SnO, ZnO/Zn, Fe 3 O 4 /FeO, or CeO 2 /Ce 2 O 3 , as well as non-stoichiometric materials, such as ceria (CeO 2− ) 10 and perovskite oxides (ABO 3− ), 11 the water splitting reaction can be performed in two steps: an endothermic step at high temperature (∼1200−2000 °C), in which the oxide is reduced in inert atmosphere, and a subsequent exothermic step at lower temperature, in which water oxidises the metal oxide producing H 2 (at ∼400−1200 °C). The working temperature of each step, O 2 and H 2 yields, and the fuel production rate depend strongly on the type and form of metal oxide involved.…”

Alloy 800H under supercritical water conditions: a flow reactor study of corrosion and hydrogen evolution

“…Several research papers have been published on the corrosion behavior of various materials including stainless steel and Nibased alloys, under SCW conditions [10][11][12][13][14][15][16][17][18][19][20][21][22]. At high temperatures, these materials can release significant amounts of hydrogen gas during the formation of a corrosion layer via the oxidation of the surface, and this has an effect on the corrosion rate of the material [23][24][25][26][27][28][29][30]. Hence it is important to estimate the steady state hydrogen evolution from the oxidized metal surface to develop chemistry control strategies to minimize material degradation and the transport of corrosion products.…”

Green Synthetic Fuels: Renewable Routes for the Conversion of Non-Fossil Feedstocks into Gaseous Fuels and Their End Uses

“…2M + 2H 2 O → 2MOH + H 2 (8) Many thermochemical cycles with metal oxide redox couple have been proposed [82], including Fe 3 O 4 /FeO [83][84][85][86], TiO 2 /TiO x [87], Mn 3 O 4 /MnO [88], Co 3 O 4 /CoO [89,90], ZnO/Zn [86,91,92], SnO 2 /SnO [93][94][95], CeO 2 /Ce 2 O 3 [96,97], CdO/Cd [98,99] and W/WO 3 [100]. The most investigated materials are zinc, iron and ceria metal oxides.…”