Solar Thermal and Efficient Solar Thermal/Electrochemical Photo Hydrogen Generation

Abstract

Actualization of a hydrogen, rather than fossil fuel, economy requires H 2 storage, utilization and generation processes; the latter is the least developed of these technologies. Solar-energy driven water splitting combines several attractive features for energy utilization. The energy source (sun) and reactive media (water) for solar water splitting are readily available and are renewable, and the resultant fuel (generated H 2 ) and its discharge product (water) are each environmentally benign. This chapter presents an efficient renewable energy approach to produce H 2 fuel, the hybrid thermochemical solar generation of hydrogen. This energy source is capable of sustaining the highest solar-energy conversion efficiencies and fits well into a clean hydrogen energy cycle.To better understand the significance of an efficient solar hybrid hydrogen-formation process, it is useful to introduce it in the context of other solar hydrogen processes. Solar water splitting can provide clean, renewable sources of hydrogen fuel without greenhouse-gas evolution. A variety of approaches have been studied to achieve this important goal, for example, photosynthetic, direct or indirect photothermochemical, and photovoltaic or photoelectrochemical water splitting. As summarized in Table 21.1, each of these processes has exhibited a limited conversion of solar energy to hydrogen; photosynthetic, biological and photochemical solar water splitting [1][2][3][4][5] have exhibited solar energy to hydrogen conversion efficiencies, Z solar , on the order of only 1%; single [6-9] or multistep [10-14] photothermal

Porous Cobalt Titanate Nanorod: A New Candidate for Visible Light‐Driven Photocatalytic Water Oxidation

“…Solar energy is considered as a major renewable energy source that can be scaled sufficiently to replace fossil fuels, thus meeting the rising global energy demand in the future 1. To use such a perfect resource, solar energy is converted into different forms of energies such as electric energy,2 thermal energy,3 and chemical energy 4. Of the various processes used, photocatalytic water splitting with inorganic semiconductors is of significant interest and regarded as a promising route for the large‐scale production of hydrogen and oxygen 5.…”

STEP (Solar Thermal Electrochemical Production) of Energetic Molecules: A synergy of photovoltaics and solar thermal to form a new, higher efficiency solar energy process

“…The STEP theory arose from studies to use sunlight to split water to hydrogen more efficiently by applying heat to tune the energetics of this process (tuning the electrochemical potential, rather than the semiconductor bandgap), and the use of electrochemical redox processes to store solar energy (9)(10)(11)(12). A synergy of solar photovoltaics and solar thermal capture forms a higher efficiency solar energy process.…”

“…The new STEP approach for solar energy conversion (1) was based on our theory and experimental observation, that even a semiconductor with bandgap smaller than the water splitting potential (E(H 2 O)=1.23V at 25°C) can split water at elevated temperature. Hence, silicon (band-gap 1.1 eV) was used to directly form hydrogen fuel from water splitting at elevated temperature in a novel molten alkali hydroxide electrolyzer (9)(10)(11)(12). STEP broadens this process, from solar hydrogen production, to the general production of all useful, energetic molecules formed by endothermic electrolyses (2).…”

STEP (Solar Thermal Electrochemical Photo) Generation of Energetic Molecules: A Synergy of Solar Photovoltaics and Solar Thermal to Form a New, Higher Efficiency Solar Energy Process

“…The new STEP approach for solar energy conversion [1] is based on our theory and experimental observation, that even a semiconductor with bandgap smaller than the water splitting potential (E(H 2 O)=1.23V at 25°C) can split water at elevated temperature. Hence, silicon (band-gap 1.1 eV) was used to directly form hydrogen fuel from water at elevated temperature in a novel molten alkali hydroxide electrolyzer [2][3][4]. STEP generalizes this solar hydrogen process to the endothermic formation of all useful, energetic molecules [1].…”