On the Limits of Photocatalytic Water Splitting

2019-01-01
The major drawbacks on the limited H2 and O2 evolution activities of one-step photocatalytic water splitting systems are given here with the emphasis on charge recombination, back-oxidation reactions, and mass transfer limitations. Suppression of these unwanted phenomena is shown to be possible with the usage of small crystal-sized photocatalysts with low defect concentrations, presence of phase junctions, selection of co-catalyst that would be active for H2 evolution but inactive for O2 reduction, coating of the co-catalyst or the whole photocatalyst with selectively permeable nanolayers, and usage of photocatalytic systems with high solid–liquid and liquid–gas surface areas. The mass transfer limitations are shown to be important especially in the liquid–gas interfaces for agitated and suspended systems with estimated H2 transfer rates in the range of ∼200–8000 μmol/h.

Suggestions

On the Electrochemical Reduction Mechanism of CaWO4 to W Powder
Erdogan, Metehan; Karakaya, İshak (2012-08-01)
The reduction mechanism of CaWO4 to W in molten eutectic CaCl2-NaCl electrolyte has been studied. Cyclic voltammetry and constant potential electrolysis tests were performed to determine the reversible cell potential. Analyses of the experimental results revealed that at least 2.2 V was required to compensate the potentials for the accompanying cell reaction and the electrode polarizations. A cell reaction was proposed by associating the experimental results and the Gibbs energy changes of the possible reac...
On the theory of internal photoemission in heterojunctions
Aslan, B; Turan, Raşit (Elsevier BV, 2005-08-01)
The theory of internal photoemission in semiconductor heterojunctions has been reviewed and the existing model has been extended by incorporating the effects of the difference in the effective masses in the active region and the substrate, non spherical-nonparabolic bands, and the energy loss per collisions. This complete model has been applied to describe the experimental results obtained from Si1-xGex/Si heterojunction infrared photodetectors. The barrier heights (correspondingly the cut-off wavelengths) ...
A Combinatorial study on hydrogen separation membranes
Pişkin, Fatih; Öztürk, Tayfur; Department of Metallurgical and Materials Engineering (2018)
Metallic membranes among the hydrogen separation membranes are quite attractive due to their very high hydrogen selectivity and hydrogen permeability. The efforts in metallic membranes generally concentrate on to identify membrane compositions which have a high hydrogen permeability with a reduced cost. Among the metallic membranes, Pd and Pd alloys, i.e. f.c.c. membranes are quite common as separation membranes. However, the high cost of Pd limits its widespread use in industrial applications. The efforts ...
On the mechanism of photocatalytic CO2 reduction with water in the gas phase
Üner, Deniz (2012-02-12)
The mechanism of photocatalytic reduction of CO2 with H2O over Pt-TiO2 films produced by the sol-gel deposition over glass beads was investigated. The accumulation of significant amount of carbonaceous intermediate on the surface followed by deactivation indicated the rate limiting reaction is the water splitting reaction, similar to the natural photosynthetic systems. When gas phase hydrogen was allowed in the system, the carbonaceous intermediates were converted to methane at rates higher than the artific...
ON THE THERMODYNAMICS OF MICROBIAL-GROWTH PROCESSES
SANDLER, SI; ORBEY, H (Wiley, 1991-10-05)
In this article, we provide a rigorous thermodynamic analysis of microbial growth processes, clarify the role of the generalized degree of reduction concept as it is used in both stoichiometric equations and as a characterizing factor for thermophysical properties, and introduce a classification method to account for errors when using the generalized degree of reduction to estimate the energy and free energy contents of molecules. We maintain the advantages of using the generalized degree of reduction whil...
Citation Formats
B. İpek Torun and D. Üner, On the Limits of Photocatalytic Water Splitting. 2019, p. 1.