Studies of the ECL of rubrene in thin layer cells containing two gold electrodes separated by 20-500 #m and viewed parallel to the electrode surface are reported. The agreement between calculated and experimental currents and intensities was good and operating lifetimes of 30 min to 4 hr were observed. Flow cells in which solution is recirculated through two mesh electrodes into a mixing chamber where electron transfer and emission occurs are also described. Higher light intensities were obtainable with the flow cells, which appear to be a more favorable configuration for application to ECL devices. ** Eleetrochemmal Society Active Member. J Oo~ J J J J 1'o Ins 2~o ECL INTENSITY (Photon/sec) x 1011 ABSTRACTThe Warburg impedance of a rotating disk electrode is analyzed by means of an inverse Laplace transformation of the governing differential equation. This new formulation reduces the problem to a partial differential equation for which approximate solutions are known. The results obtained agree with exact numerical values for a wide range of low and high frequencies.

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During a photoelectrochemical reaction only a portion of the light energy absorbed by the semiconductor (CdS or TiO2 single crystal) is utilized in the electrode reaction. The unused portion of energy is expended through various mechanisms as heat. Therefore by monitoring temperature changes within the photoanode as a function of electrode potential and light intensity, information concerning the efficiency of the process can be obtained. Experimental results are presented and interpreted using a model for the energy balance within the system. This permits the determination of the quantum and energy efficiencies simultaneously without the need to calibrate the light source.A number of photoelectrochemical cells based on semiconductor electrodes for photoelectrosynthesis (e.g,, the photodecomposition of water) and the conversion of solar energy to electricity have ,been reported (!-15). The major factors determining the efficacy of these semiconductor electrode ceils are the quantum efficiency for electron flow (i.e., number of electrons flowing/number of photons absorbed), and the power conversion efficiency (i.e., chemical or electrical power output/input radiant power). It is not uncommon to find near unity quantum yields for electron flow at a sufficiently high bias (positive for the case of n-type semiconductors) during irradiation with greater than bandgap energy light for many semiconductors. However, even when high quantum efficiencies have been obtained, the power efficiencies were much lower (10-15). For example, for photooxidation at a CdS single crystal anode, Wrighton et al. (15) reported that with an Se 2-solution the maximum monochromatic power efficiency obtained was 3.4% with a maximum quantum efficiency of 49%. Such findings demonstrate that the major part of the light energy absorbed by the semiconductor is not used for the photo-assisted oxidation but rather is converted to heat energy probably via radiationless transitions within the conduction band of the semiconductor (i.e., when the photon energy is in excess of the bandgap energy) or electron-hole recombination processes. Consequently, thermal measurements of the semiconductor electrode during etectroIysis can aid in the determination of the efficiencies and perhaps in the elucidation of the mechanism of the cell processes.We recently described a new spectroscopic method called Photothermal Spectroscopy (PTS) (16). This technique involves placing a thermistor on or in close proximity to a sample and measuring temperature changes (i.e., thermistor resistance changes) during sample irradiation with monochromatic light. This technique can be easily adapted to cases when the sample is a semiconductor electrode (17). Cahen (18) has also shown that similar measurements with photoacoustic spectroscopy can be used to determine the efficiency of solid-state photovoltaic devices. We report in this paper measurements of the conversion of light energy to chemical and/or electrical energy at * Electrochemical Society Active Member. ~ Electrochemical So...