Solar Cell with Photocatalyst Layers on Both the Anode and Cathode Providing an Electromotive Force of Two Volts per Cell

Abstract

Solar cells and fuel cells are essential devices that convert sustainable energy into electricity. However, the electromotive forces they provide are in principle limited to less than 1 V, and consequently, they need to be connected in series for practical use. In this study, photocatalyst layers with thicknesses of 0.8–2.1 μm were applied to both electrodes. The primary particle size of TiO2 was optimized (15–21 nm), and its performance was further improved by doping with organic dyes, e.g., anthocyanins. The electron conductivity of TiO2 was found to be a primary factor in the performance of the cells, but the film flatness also reduced resistance and improved cell performance. Interestingly, the efficiency of TiO2 could be evaluated based on the exchangeable surface O atoms via its 18O2 exchange tests to suppress the reverse reaction step in water photo-oxidation, which occurs on the anode. UV and visible light were absorbed by TiO2 and the organic dyes, respectively, creating an electron flow path from the valence band to the conduction band of TiO2, then, the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) of the organic dyes, then the anode, and finally the cathode via the external circuit. The flow of electrons and holes (separated from electrons in BiOCl on the cathode by UV–visible light) enabled a V OC value of 2.11 V and maximum power of 73.1 μW cm–2.

Polarizability and Catalytic Activity Determine Good Titanium Oxide Crystals but Not Homogeneity in Solar Cells Using Photocatalysts on Both Electrodes

“…The P25-Slide film was the best for the SC performance on the photoanode (Table 2a′, Figure S2a,c). The V OC of 1.96 V was based on the energylevel difference between the CB minimum (CBM) of TiO 2 and the valence band maximum (VBM) of BiOCl, 12 which exceeded the electromotive force reported for similar SCs: TiO 2 and polyterthiophene (0.90 V), 13,24 and W-doped BiVO 4 /Bi 4 V 2 O 11 and undoped BiVO 4 /Bi 4 V 2 O 11 (1.54 V). 25 Furthermore, the effects of the electrolyte pH on the SC performance were assessed using the optimized combination of photocatalysts: P25-Slide and BiOCl-Cast (Table 2a′).…”

“…An iron nail (front curvature radius 0.5 mm) was perpendicularly in contact with the TiO 2 /BiOCl film surface utilizing a micrometer, and the ITO/Pyrex plate was electrically in contact via a Au/Ni-coated stainless steel clip (Toyo Corporation, Japan). 12 The applied alternating voltage was 500 mV, and the frequency was scanned between 10 2 and 10 6 Hz. Another series of impedance measurements were performed by applying both an alternating voltage of 500 mV and a direct voltage of 2 V.…”

“…Clearly, the exchange reaction in 18 O 2 was faster with TiO 2 crystals having a uniform size and shape than with conventional P25-TiO 2 and JRC6-TiO 2 . 12 If we assume complete Cubic-TiO 2 (anatase phase), 67% of {1 0 0} and 33% of (0 0 1) faces were exposed. 22 For Rhomb-TiO 2 (anatase phase), ∼two-thirds of thermodynamically unstable {1 0 1} facets and ∼one-third of stable (0 1 0) facets were exposed.…”

“…Conversely, JRC6-TiO 2 is only one pure rutilephase sample in this study and the 18 O 16 O formation rate was the lowest: 6.4 μmol h −1 g cat −1 . A different type of rutile TiO 2 with a surface O population of 8.7 nm −2 and a specific SA of 8.0 m 2 g −1 was tested in another study, 12 and the 18 O 16 O formation rate was also sufficiently slow (34 μmol h −1 g cat −1…”

“…A SC utilizing photocatalysts on both electrodes achieved an electromotive force of 0.90−2.11 V using TiO 2 and polyterthiophene, 13,24 W-doped BiVO 4 /Bi 4 V 2 O 11 and undoped BiVO 4 /Bi 4 V 2 O 11 , 25 and TiO 2 /anthocyanidin and BiOCl. 12 Dual photoelectrodes were also simultaneously utilized to remove waste materials. 14,15,26,27 In this study, the key parameters to improve the SC performance were investigated by scanning electron microscopy (SEM), fluorescence spectroscopy, film impedance measurements, exchange reactions in 18 O 2 gas, and Bi L 3 -edge extended X-ray absorption fine structure (EXAFS).…”