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Journal ArticleDOI

The impact of semiconductors on the concepts of electrochemistry

01 Nov 1990-Electrochimica Acta (Pergamon)-Vol. 35, pp 1677-1699
TL;DR: In this article, it was realized that semiconductor electrodes behave differently in many respects and offer new insights into the role played by the electronic properties of a solid in its electrochemical reactivity.
About: This article is published in Electrochimica Acta.The article was published on 1990-11-01. It has received 410 citations till now.
Citations
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Journal ArticleDOI
24 Oct 1991-Nature
TL;DR: In this article, the authors describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency.
Abstract: THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.

26,457 citations

Journal ArticleDOI
TL;DR: In this article, the authors reviewed the use of sunlight to produce the OH radicals by TiO2 photocatalysis and photo-Fenton process and summarized most of the research carried out related to solar photocatalytic degradation of water contaminants and how it could significantly contribute to the treatment of persistent toxic compounds.

2,541 citations

Journal ArticleDOI
TL;DR: The current state of research on nanoscale-enhanced photoelectrodes and photocatalysts for the water splitting reaction with special emphasis of Fe(2)O(3) with an outlook on the challenges in solar fuel generation with nanoscales inorganic materials is reviewed.
Abstract: The increasing human need for clean and renewable energy has stimulated research in artificial photosynthesis, and in particular water photoelectrolysis as a pathway to hydrogen fuel. Nanostructured devices are widely regarded as an opportunity to improve efficiency and lower costs, but as a detailed analysis shows, they also have considerably disadvantages. This article reviews the current state of research on nanoscale-enhanced photoelectrodes and photocatalysts for the water splitting reaction. The focus is on transition metal oxides with special emphasis of Fe2O3, but nitrides and chalcogenides, and main group element compounds, including carbon nitride and silicon, are also covered. The effects of nanostructuring on carrier generation and collection, multiple exciton generation, and quantum confinement are also discussed, as well as implications of particle size on surface recombination, on the size of space charge layers and on the possibility of controlling nanostructure energetics via potential determining ions. After a summary of electrocatalytic and plasmonic nanostructures, the review concludes with an outlook on the challenges in solar fuel generation with nanoscale inorganic materials.

1,779 citations

References
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Journal ArticleDOI
07 Jul 1972-Nature
TL;DR: Water photolysis is investigated by exploiting the fact that water is transparent to visible light and cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm.
Abstract: ALTHOUGH the possibility of water photolysis has been investigated by many workers, a useful method has only now been developed. Because water is transparent to visible light it cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm (ref. 1).

27,819 citations

Journal ArticleDOI
TL;DR: In this paper, a mechanism for electron transfer reactions is described, in which there is very little spatial overlap of the electronic orbitals of the two reacting molecules in the activated complex, and a quantitative theory of the rates of oxidation reduction reactions involving electron transfer in solution is presented.
Abstract: A mechanism for electron transfer reactions is described, in which there is very little spatial overlap of the electronic orbitals of the two reacting molecules in the activated complex. Assuming such a mechanism, a quantitative theory of the rates of oxidation‐reduction reactions involving electron transfer in solution is presented. The assumption of "slight‐overlap" is shown to lead to a reaction path which involves an intermediate state X* in which the electrical polarization of the solvent does not have the usual value appropriate for the given ionic charges (i.e., it does not have an equilibrium value). Using an equation developed elsewhere for the electrostatic free energy of nonequilibrium states, the free energy of all possible intermediate states is calculated. The characteristics of the most probable state are then determined with the aid of the calculus of variations by minimizing its free energy subject to certain restraints. A simple expression for the electrostatic contribution to the free energy of formation of the intermediate state from the reactants, ΔF*, is thereby obtained in terms of known quantities, such as ionic radii, charges, and the standard free energy of reaction. This intermediate state X* can either disappear to reform the reactants, or by an electronic jump mechanism to form a state X in which the ions are characteristic of the products. When the latter process is more probable than the former, the over‐all reaction rate is shown to be simply the rate of formation of the intermediate state, namely the collision number in solution multiplied by exp(—ΔF*/kT). Evidence in favor of this is cited. In a detailed quantitative comparison, given elsewhere, with the kinetic data, no arbitrary parameters are needed to obtain reasonable agreement of calculated and experimental results.

5,265 citations

Journal ArticleDOI
TL;DR: In this article, the behavior of semiconducting electrodes for photoelectrolysis of water is examined in terms of the physical properties of the semiconductor and the photocurrent is described using a simple Schottky barrier.
Abstract: The behavior of semiconducting electrodes for photoelectrolysis of water is examined in terms of the physical properties of the semiconductor. The semiconductor‐electrolyte junction is treated as a simple Schottky barrier, and the photocurrent is described using this model. The approach is appropriate since large‐band‐gap semiconductors have an intrinsic oxygen overpotential which removes the electrode reaction kinetics as the rate‐limiting step. The model is successful in describing the wavelength and potential dependence of the photocurrent in WO3 and allows a determination of the band gap, optical absorption depth, minority‐carrier diffusion length, flat‐band potential, and the nature of the fundamental optical transition (direct or indirect). It is shown for WO3 that minority‐carrier diffusion plays a limited role in determining the photoresponse of the semiconductor‐electrolyte junction. There are indications that the diffusion length in this low carrier mobility material is determined by diffusion‐controlled bulk recombination processes rather than the more common trap‐limited recombination. It is also shown that the fundamental optical transition is indirect and that the band‐gap energy depends relatively strongly on applied potential and electrolyte. This effect seems to be the result of field‐induced crystallographic distortions in antiferroelectric WO3.

1,758 citations

Journal ArticleDOI
TL;DR: In this article, it is shown that in principle three reference levels can be chosen to measure an absolute value of the electrode potential, and a thermodynamic analysis of the components of the emf of an elec- trochemical cell is shown.
Abstract: The document begins with the illustration of the most widespread misunderstandings in the literature about the physical meaning of absolute electrode potential. The correct expression for this quantity is then de— rived by a thermodynamic analysis of the components of the emf of an elec— trochemical cell. It is shown that in principle three reference levels can be chosen to measure an absolute value of the electrode potential. Only one of these possesses all the requisites for a meaningful comparison on a con— mon energy scale between electrochemical and physical parameters. Such a comparison is the main problem for which the adoption of a correct scale for absolute electrode potentials is a prerequisites. The document ends with the recommendation of a critically evaluated value for the absolute potential of the standard hydrogen electrode in water and in a few other protic solvents. The \"electrode potential\" is often misinterpreted as the electric potential difference between a point in the bulk of the solid conductor and a point in the bulk of the electrolyte solution (L4) (Note a). In reality, the transfer of charged particles across the electrode/electrolyte solution interface is controlled by the difference in the energy levels of the species in the two phases (at constant T and p), which includes not only electrical (electric potential difference) but also chemical (Gibbs energy difference) contributions since the two phases are compositionally dissimilar (refs. 1,2). The value of the tjq of a \"single\" electrode, e.g. one consisting of an electronic conductor in contact with an ionic conductor, is not amenable of direct experimental determination. This is because the two metallic probes from the measuring instruments, both made of the same material, e.g. a metal M1, have to be put in contact with the bulk of these two phases to pick up the signal there. This creates two additional interfaces: a M1/solution interface, and a M1/electrode metal interface. The experimental set-up can be sketched as follows: M1 SIMIMI (1) where M is the metal of the electrode under measure, S is the electrolyte solution, M1 is the metal of the \"connections\" to the measuring instrument and the prime on M indicates that this terminal differs from the other one (M1) by the electrical state only. It is expedient to replace the M1/S interface with a more specific, reproducible and stable system known as the reference electrode. It ensues that an electrode potential can only be measured against a reference system. The measured quantity is thus a relative electrode potential. For the specific example of cell (1), the measured quantity E, the electrode potential of M relative to M1 (Note b), is conventionally split into two contributions, each pertaining to one of the electrodes: EEM_EM1 (2) EM and EM1 can be expressed in their own on a potential scale referred to another reference electrode. In this respect, the hydrogen electrode is conventionally taken as the universal Note a: This quantity, known as the Galvani potential difference between M and 5, has been defined in ref. 3. Note b: In accord with the IUPAC convention on the sign of electrode potentials, all electrode potentials in this document are to be intended as \"reduction potentials\", i.e. the electrode reaction is written in the direction of the reduction (refs. 3,4). 956 Absolute electrode potential (Recommendations 1986) 957 (for solutions in protic solvents) reference electrode for which, under standard conditions, E°(H/H2) = 0 at every temperature (Note c). Since EM as measured is a relative value, it appeals to many to know what the absolute value may be: viz. , the value of EM measured with respect to a universal reference system not including any additional metal/solution interface. Actually, for the vast majority of practical electrochenilcal problems, there is no need to bring in absolute potentials . The one outstanding example where this concept is useful is the matching of semiconductor energy levels and solution energy levels . However, from a fundamental point of view, this problem comes necessarily about in every case one wants to connect the \"relative\" electrode potential to the \"absolute\" physical quantities of the given system. On a customary basis, since the electrode potential is envisaged as the electric potential drop between M and S, the cell potential difference for system (1) is usually written as the electric potential difference between the two metallic terminals: EMi M1 (3) Since three interfaces are involved in cell (1), eqn.(3) can be rewritten as: E (M{ M) + (M S) + (S Mi) (4) Comparison of eqn. (4) with eqn. (2) shows that the identification of the absolute electrode potential with (M S) is not to be reconmended because it is conceptually misleading. Since M' and M are in electronic equilibrium, then (ref. 3): (4M ) = ('/F pr/F) (5) where the right hand side of eqn. (5) expresses the difference in chemical potential of electrons in the two electrode metals. Substitution of eqn.(5) into eqn.(4) gives: E = (p ii'/F) (E'q p'/F) (6) The two exoressions in brackets do not contain quantities pertaining to the other interfaces. They can thus be defined as single electrode potentials (Note d). Since eqn. (6) has been obtained with the two electrodes assembled into a cell, it is possible that terms common to both electrodes do not appear explicitly in eqn. (6) because they cancel out ultimately. The relationship between the truly absolute electrode potential and the single electrode potential in eqn.(6) can thus be written in the form (Note e) (ref. 5): EM(abs) = EM(r) + K (7) where K is a constant depending on the \"absolute\" reference system, and

1,205 citations

Journal ArticleDOI
David E. Aspnes1
TL;DR: The theoretical basis and experimental procedures for third-derivative modulation spectroscopy, which is the same as low-field electroreflectance, are reviewed in this article, in terms of the effect of a uniform electric field on the translational symmetry of the unperturbed crystal.

1,056 citations

Trending Questions (1)
How to use Gamry for electrochemistry study of semiconductors?

The paper does not provide information on how to use Gamry for the electrochemistry study of semiconductors. The paper discusses the impact of semiconductors on the concepts of electrochemistry and their role in improving the understanding of interfacial reactions.