Study of the factors affecting the photoelectrode characteristics of a perylene/phthalocyanine bilayer working in the water phase

Abstract

Some types of phthalocyanines (MPc (M = H(2), Cu, or Zn), a p-type semiconductor) were used in combination with 3,4,9,10-perylenetetracarboxyl-bisbenzimidazole (PTCBI, an n-type semiconductor), with which those photoelectrode characteristics in the water phase were investigated in terms of kinetics. Each film of the PTCBI/MPc bilayer functioned as a photoanode, where the photoinduced oxidation of thiol occurs at the MPc/water interface along with the hole conduction through the MPc layer. The holes originate on account of the photophysical events in the p/n interior, involving the charge separation of excitons at the p/n interface. The typical photoelectrochemical characteristic in the PTCBI/MPc photoanodes involved a transient photocurrent occurring in the initial stage under illumination (under potentiostatic conditions): thereafter, it attained a steady state. Moreover, both the initial spiky photocurrents and the steady-state photocurrents exhibited saturation at higher concentrations. An analysis with photoelectrode kinetics was performed by assuming an adsorption step prior to a rate-limiting charge transfer step, where equations were applied to photocurrents based on the Langmuir adsorption equilibrium. The kinetic analyses evidently showed that the photoanodic reactions are kinetically dominated by the charge transfer between MPc and thiol, where the overall kinetics for thiol oxidation decreases in the following order: H(2)Pc > ZnPc > CuPc; that is, it appeared that H(2)Pc acts as the more efficient photofunctional interface capable of oxidation in the water phase when PTCBI was concurrently employed as an electron conductor. Considering that the photocurrent generated is proportional to the surface concentration of thiol (Gamma) at the MPc as well as the intrinsic oxidation rate (cf., ZnPc > H(2)Pc approximately CuPc), the higher efficiency in the output at the H(2)Pc surface was attributed to an exceptionally high Gamma (i.e., from the kinetic analyses, the Gamma value at the H(2)Pc surface was also inferred to be 2-3 times higher than that at the other MPcs). Through the present kinetic analysis, it also revealed that the activity for thiol oxidation taking place at Pc ring is comparable to that at the conventional active catalysts (i.e., polycarboxyphthalocyaninato Co(ii) and Fe(iii)) where a central metal is an active site.

Efficient p-zinc phthalocyanine/n-fullerene organic bilayer electrode for molecular hydrogen evolution induced by the full visible-light energy

“…when similar conditions were used for photoelectrochemical H 2 evolution in both systems, in the previous system the amount of H 2 evolved was 333.5 mL in 3 h of irradiation [17]). Given that ZnPc is similar to H 2 Pc in terms of spectral shape and absorption coefficient [16,26] and that the built-in potential in ITO/ZnPc/C 60 ePt is larger than that in ITO/ H 2 Pc/C 60 ePt (cf. 250 mV [17]), the greater amount of H 2 generated in the ITO/ZnPc/C 60 ePt system is attributable to the more efficient generation of carriers, which can consequently result in a higher concentration of electron carriers available to the rate-limiting H 2 evolution reaction.…”

“…After the visiblelight absorption by the ZnPc/C 60 bilayer, the exciton formed within the bilayer needs to be separated into electrons and holes at the p/n interface, where a built-in potential (i.e., photovoltage) should be present. A procedure for measuring the photovoltage magnitude at a p/n interface has been reported elsewhere [16]. In the course of this study, the presence of a photovoltage at the ZnPc/C 60 interface (i.e., ca.…”

“…Commercially available ZnPc (TCI) was purified by sublimation prior to use, as described elsewhere [16]. The other reagents were of the extra-pure grade and were used as received.…”

Photocathode Kinetics of Phthalocyanine/Fullerene with Respect to the Base Electrode for the Bilayer Coating

“…4,5,22) In the present case, the photocurrent (J) is assumed to be proportional to the surface concentrations of the electrons (½e à 0 ) as well as of the adsorbed Fe 3þ ions (À), and it is represented as…”

Synthesis and characterization of Biphasic Vanadyl phthalocyanine and C₆₀ composite nanoparticles through a reprecipitation process

“…[3] Tang first reported in 1986 of a heterojunction composed of bilayer organic solar cell composed of CuPc and a perylene derivative. [4] We have previously studied the photoelectrochemistry of organic n/p bilayer of a perylene derivative (3,4,9,10-perylenetetracarboxyl-bisbenimidazole, PTCBI) or fullerene (C 60 ) and metal-free Pc's (H 2 Pc) in water phase, [5][6][7][8][9][10][11][12][13] wherein the evolution of O 2 from water was found to occur along with hole conduction through the p-type layer under visible light irradiation. [8] The studies indicate that the photoinduced redox reaction occur catalytically on the semiconductor surfaces and that the organic bilayer of the p/n junction lead to an efficient generation of photocurrent in comparison with the single layers of the Schottky junction.…”