Photoelectrochemical Cells PECs

A typical construction of a photoelectrochemical cell (PEC) using P(Ac) as one of the electrodes is shown in Fig. 23-15. Photogenerated electron-hole pairs generated in the p-type P(Ac) become separated at the CP/electrolyte interface, and electrons are injected into the electrolyte, resulting in a current. The net reactions are shown in the figure. A Vqc of ca. 0.3 V is observed under AMI (one midday sun) illumination, but with low current densities, ca. 4 pA/cm [977-979]. Fig. 23-16 shows I-V curves for a Pt/P(3-Me-T)/(LiC104/acetonitrile) PEC [31]. Table 23-3 lists photocurrent densities as a function of CP and dopant for several poly(thiophenes). 

Fig 23-15 Photoelectrochemical photovoltaic cell using poly(acetylene) as an 

In PEC cells employing CPs, it was at one point felt that the high sur ce area of CP electrodes due to the unique morphology of CPs (said to be up to 40 mVg for P(Ac)) would lead to greater electrode/electrolyte contact and thus higher efficiencies, but results did not bear this out. 

Yohannes et al. [992, 993] demonstrated a PEC based on neutral poly(3-Me-thiophene) on ITO/glass as the photoactive electrode, a nearly transparent Pt film on ITO/glass as the counter electrode, and a solid electrolyte based on Ij-PEO. The short circuit current and open circuit potential obtained under while light illumination of 100 mW/cm were 0.35 pAlcta and +0.14 V respectively. Quantum efficiencies between 0.3% and 0.6% were observed. Fig. 23-17 shows typical characterization (I-V) data for this PEC. 

23-17 Current-voltage curves (a) in the dark and (b) under white light 

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Of the photocatalytic systems and structures composed of a single active material, eventually coupled with redox catalysts and/or metals, only a wide band gap oxide semiconductor, like Pt/Ti02, requiring UV irradiation, showed some photoactivity for water photosplitting. Water splitting with visible light requires the irradiation of multiple band gap photoelectrochemical cells (PEC) or Z-scheme systems (like the photosynthesis system of plants etc.). 

Fig. 4.1 Skeleton structure of a photoelectrochemical cell (PEC) comprised of a photoanode and cathode. Potentials of both are measured with reference to a third electrode, the standard calomel electrode.

The overall reaction of the photoelectrochemical cell (PEC), H2O + hv H2 -I- I/2O2, takes place when the energy of the photon absorbed by the photoanode is equal to or larger than the threshold energy of 1.23 eV. At standard conditions water can be reversibly electrolyzed at a potential of 1.23 V, but sustained electrolysis generally requires -1.5 V to overcome the impedance of the PEC. Ideally, a photoelectrochemical cell should operate with no external bias so as to maximize efficiency and ease of construction. When an n-type photoanode is placed in the electrolyte charge distribution occurs, in both the semiconductor and at the semiconductor-... 

Hodes G, Cahen D, Mannasen J. (1976) Xungsten trioxide as a photoanode for photoelectrochemical cell (PEC). Nature 260 312-313... 

One of the attractive features of CD is its simplicity (in terms of carrying out the deposition, that is, not always in understanding the deposition itselO. The same property of simplicity is often ascribed to photoelectrochemical cells (PECs). Therefore it is not surprising that CD has often been used to fabricate the semiconductor electrodes for PECs. 

It is known that the photoelectrochemical cell (PEC), which is composed of a photoelectrode, a redox electrolyte, and a counter electrode, shows a solar light-to-current conversion efficiency of more than 10%. However, photoelectrodes such as n- and p-Si, n-and p-GaAs, n- and p-InP, and n-CdS frequently cause photocorrosion in the electrolyte solution under irradiation. This results in a poor cell stability therefore, many efforts have been made worldwide to develop a more stable PEC. 

Most detailed studies of water photodissociation on SrTi03 and Ti02 have concentrated on photoelectrochemical cells (PEC cells) operating under conditions of optimum efficiency, that is with an external potential applied between the photoanode and counterelectrode. We have become interested in understanding and improving reaction kinetics under conditions of zero applied potential. Operation at zero applied potential permits simpler electrode configurations (11) and is essential to the development of photochemistry at the gas-semiconductor interface. Reactions at the gas-sold, rather than liquid-solid, interface might permit the use of materials which photocorrode in aqueous electrolyte. 

Cd-chalcogenides (CdS, CdSe, CdTe) are among the most studied materials as photoelectrodes in a photoelectrochemical cell (PEC) (1,2 /3,4). Interest in such PEC s stems from the fact that, in aqueous polysulfide or polyselenide solutions, a drastic decrease in photocorrosion is observed, as compared to other aqueous solutions, while reasonable conversion efficiencies can be attained. 

Using n-Ti02 electrodes, either naked or platinized, we have studied reaction [2] in a photoelectrochemical cell (PEC) under conditions of controlled electrolyte pH, illumination intensity and external applied bias (Tafalla and Salvador, 1987). These results can be extrapolated to the case of Ti02 suspensions help to go further into the mechanisms of 02 photo-uptake. ... 

ANON, 10 % Efficient Photoelectrochemical Cell (PEC), World Wide Web, http //www.nrel.gov/basic sciences/chemsci.html. National Renewable Energy Laboratory, Golden (1998), and KHASELEV, O., TURNER, J.A., A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production via Water Splitting, Science 280 (1998) 425-427. 

Conversion of solar light into chemical fuels translates into the ultimate design of an artificial leaf device. This can be accomplished by a tailored assembly of suitable chemical modules and their organization within a photoelectrochemical cell (PEC). The simplest set up foresees the... 

One of other conventional processes for H2O decomposition is photoelectrochemical. In this method, H2O is broken down into H2 and O2 by electrolysis, but the electrical energy is obtained by a photoelectrochemical cell (PEC) process. A photoelectrochemical H2O decomposition process is a zero emission process and uses free solar energy or ultraviolet (UV) light (Alenzi et al., 2010 Currao, 2007 Nowotny, Bak, Nowotny, Sheppard, 2007). Many studies have been presented for finding the best material candidate for the photoelectrochemical process discovered by Fujishima and Honda (1972) as a first approach. The main criteria for these materials are low cost. 

Fujishima and Honda have carried out significant research in the field of water splitting. Most of their work is conducted using a photoelectrochemical cell consisting of titania as the photoanode and platinum as the cathode under UV radiation. In other words, generation of solar hydrogen is carried out in the photoelectrochemical cell (PEC) which consists of a photoanode made up of semiconductor material and a cathode of metal immersed in an electrolyte [3]. 

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