Hydrogen Production by Solar Thermochemical Water-Splitting/Methane-Reforming Process

Abstract

Two different routes of solar thermochemical hydrogen production are reviewed. One is two-step water splitting cycle by using a metal-oxide redox pair. The first step is based on the thermal reduction of metal oxide, which is a highly endothermic process driven by concentrated solar thermal energy. The second step involves water decomposition with the thermally-reduced metal oxide. The first thermal reduction process requires very-high temperatures, which may be realized in sun-belt regions. Another hydrogen production route is solar reforming of natural gas (methane), which can convert methane to hydrogen via calorie-upgrading by using concentrated solar thermal energy. Solar reforming is currently the most advanced solar thermochemical process in sun belt. There is also possibility for the solar reforming to be applied for worldwide solar concentrating facilities where direct insolation is weaker than that in sun belt. Our experimental studies to improve the relevant catalytic technologies are shown and discussed.

A review of solar methane reforming systems

“…Since the Ru with Alumina support had the most stable activity, it also had the highest chemical efficiency of approximately 50% and the highest methane conversion of 73% [49]. Figure 10 shows that the metal absorber achieves better conversion than the ceramic absorber under the same conditions [48,49,50]. The higher conductivity of the metallic absorber improves the temperature uniformity and hence the chemical efficiency; however, other factors could effect the latter including catalyst dispersion and radiative heat transfer so it is unclear which factors lead to better performance.…”

“…Moving on to systems that utilize a catalyst, a lab-scale study of dry reforming was done using a porous absorber reformer with different absorbers and catalysts integrated with a solar-simulated Xe-arc lamp light [48,49,50].…”

Materials-Related Aspects of Thermochemical Water and Carbon Dioxide Splitting: A Review

“…The coated ZrO 2 particles were tested and the cyclic reaction could be repeated at temperatures of 1673 K for thermal reduction and 1273 K for water splitting. ZrO 2 alleviated the sintering of the solid reactant ferrite, and the phase transformation between Fe 3 O 4 and FeO occurred on the crystals of ZrO 2 [61]. Pure Fe 3 O 4 as well as different ferrites of the form M x Fe 3− x O 4 were coated on ZrO 2 particles (particle size of about 1 µm) and tested, (M = Mn, Co, Mg Ni) [49,62,63].…”

Thermochemical two-step water-splitting reactor with internally circulating fluidized bed for thermal reduction of ferrite particles

“…This is due to melting and sintering of iron oxide particles at high temperature. The present authors first demonstrated repeatable two-step water-splitting in 2003, using highly active ''ZrO 2 -supported'' ferrite particles [11][12][13]. The supporting ZrO 2 alleviated agglomeration or sintering of the solid ferrite reactant, and as a result the cyclic reaction could be repeated with relatively good activity in the temperature range of 1000-1400 1C.…”