Adsorption of energy in photocatalytic reactors

Conference · Mon Jul 01 00:00:00 EDT 1985

OSTI ID:5334206

Somorjai, G A

The dissociation of water to hydrogen and oxygen requires energy ..delta..G/sub 298/ = 228 kJ/mole. By irradiating a semiconductor with light of energy greater than this amount, one may produce electrons in the excited state and electron vacancies at the surface that can perform the photochemical reduction (2H/sup +/ + 2e/sup -/ ..-->.. 2H ..-->.. H/sub 2/) and oxidation (20H/sup -/ + 2/sup +/ ..-->.. H/sub 2/O/sub 2/ ..-->.. H/sub 2/O + (1/2)O/sub 2/). There are several semiconductors, SrTiO/sub 3/, TiO/sub 2/, CdS, and Fe/sub 2/O/sub 3/ among them, that can photodissociate water. Some possess sites for both reduction and oxidation, while others carry out the two processes at different surfaces. A reversible solid state reaction that involves changes in the transition metal and ion oxidation state must accompany the splitting of water. Platinum, rhodium, and ruthenium oxide, when deposited on the semiconductor, serve as catalysts that accelerate the water photodissociation. These additives accelerate the recombination of hydrogen and oxygen atoms, shift the semiconductor Fermi level to a more favorable position that improves the thermodynamic feasibility for the process, accelerate electron transport, and inhibit side reactions like the photoreduction of oxygen. Many of the elementary reaction steps leading to photoproduction of hydrogen and oxygen over SrTiO/sub 3/ and Fe/sub 2/O/sub 3/ have been identified and will be discussed.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5334206
• Report Number(s): LBL-17824; CONF-840571-1; ON: DE85017639; TRN: 85-022257
• Resource Relation: Conference: Fundamentals and developments of photocatalytic and photoelectrochemical processes course, Erice, Italy, 20 May 1984; Other Information: Portions of this document are illegible in microfiche products
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
14 SOLAR ENERGY
08 HYDROGEN
CADMIUM SULFIDES
CATALYTIC EFFECTS
HYDROGEN PRODUCTION
PHOTOLYSIS
IRON OXIDES
STRONTIUM OXIDES
TITANIUM OXIDES
EXPERIMENTAL DATA
FERMI LEVEL
PHOTOELECTRIC EFFECT
WATER
ALKALINE EARTH METAL COMPOUNDS
CADMIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
DATA
DECOMPOSITION
ENERGY LEVELS
HYDROGEN COMPOUNDS
INFORMATION
INORGANIC PHOSPHORS
IRON COMPOUNDS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PHOSPHORS
PHOTOCHEMICAL REACTIONS
PHOTOELECTROMAGNETIC EFFECTS
STRONTIUM COMPOUNDS
SULFIDES
SULFUR COMPOUNDS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
400500* - Photochemistry
140505 - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)
080106 - Hydrogen- Production- Biosynthesis & Photochemical Processes