Narrow Results

Potential step chronoamperospectrometry (PSCAS) measurement was carried out to investigate the one-electron transfer in the reduction of tetraphenylporphyrin cobalt(III) ([Co^IIITPP(−2)]⁺) incorporated into a Nafion or poly(4-vinylpyridine-co-styrene) (P(VP-St)) film coated on an ITO electrode. The electron transfer of the redox centers in the two systems occurred by a physical diffusion mechanism. The fraction of the electroactive complex (R_ct) was independent of the CoTPP concentration in P(VP-St) but decreased with increasing CoTPP concentration in Nafion, especially at high concentrations. In both systems the apparent diffusion coefficient D_app decreased with increasing CoTPP concentration. The D_app value in Nafion (1.6 × 10⁻⁸cm²s⁻¹ at 0.02 M) was much higher than that in P(VP-St) (1.1 × 10⁻¹⁰cm²s⁻¹ at 0.02 M). The difference in the electron transfer process in the two systems was ascribed to the interaction of the redox center with the polymer framework, the morphology of the polymer matrix, the localization of the redox species in the hydrophilic/hydrophobic region, and the counterion migration under the potential step.

Electrochemical proton reduction was catalysed by zinc phthalocyanine (ZnPc) incorporated in a Nafion or poly(4-vinylpyridine-co-styrene) (P(VP-St)) film coated on a graphite electrode. The turnover number (TN) of the complex to catalyse H₂ evolution was 10⁴ h^-1. The TN of Nafion[ZnPc] was about two times higher than that of P(VP-St)[ZnPc]. The difference was ascribed to the electron propagation in the film influenced by the interaction of the complex with the matrix and by the counterion migration between the matrix and the electrolyte solution. The electron transfer in the reduction of the ZnPc complex in the matrix was concluded to be the rate-determining step for the proton reduction. The TN was independent of the ZnPc concentration in the matrix at low concentrations although H₂ formation was regarded to be a bimolecular reaction process, which was explained by the electron transfer through the matrix via a monomolecular diffusion which was the rate-determining step.

Potential step chronoamperospectrometry (PSCAS) was carried out to analyze electron transfer in the redox reaction processes of 5,10,15,20-tetraphenylporphyrinatocobalt(II) (Co^IITPP(-2)) incorporated in a Nafion film. The reactions of Co^IITPP(-2) to [Co^IIITPP(-2)]⁺ and of [Co^IIITPP(-2)]⁺ to Co^IITPP(-2) took place through a diffusion mechanism, as confirmed by the first-order initial reaction rate with respect to the complex concentration in the matrix. However, the reaction of [Co^IIITPP(-2)]⁺ to [Co^IIITPP(-1)]²⁺ occurred by an electron-hopping mechanism, as confirmed by the second-order initial reaction rate with respect to the complex concentration. The fraction of electroactive complex (R_ct) increased with the sample time after the potential step until it reached saturation. In the reactions of Co^IITPP(-2) to [Co^IIITPP(-2)]⁺ and of [Co^IIITPP(-2)]⁺ to Co^IITPP(-2), R_ct approached 1.0, while in the reaction of [Co^IIITPP(-2)]⁺ to [Co^IIITPP(-1)]²⁺, only about 0.3 was reached. The apparent diffusion coefficient (D_app) decreased in the order of [Co^IIITPP(-2)]⁺ to Co^IITPP(-2) > Co^IITPP(-2) to [Co^IIITPP(-2)]⁺>[Co^IIITPP(-2)]⁺ to [Co^IIITPP(-1)]²⁺. The different behavior of these redox reactions was ascribed to the microenvironment of the redox species in the matrix, interaction of the redox centers, especially the product with the framework, and counter ion migration.

Concentration dependent optical properties of the various types of porphyrin compounds were studied using optical absorbance and Z-scan measurements. Enhanced absorbance width of the Soret and Q-bands have been observed by blending three different porphyrin molecules in Nafion column matrix membrane. This is an important development towards achieving efficient photon-harvesting medium for possible application in photonic devices. Moreover, new evidences have been found on the concentration dependance of the nonlinear absorption coefficient (β) of the VTPP in Nafion.

Two major reasons limit porphyrins photonic applications: (i) the difficulty of handling them in liquid solutions and (ii) their degradation with long exposure to light. This necessitates the use of appropriate solid matrices to host the porphyrin compounds such as Nafion (117), a stable and inert ion exchange polymer. The first part of this publication confirms such a possibility. In addition to their effective NLO properties, an enhancement of the Soret and Q-bands' absorbance width have been observed by blending three different porphyrin molecules in the Nafion column matrix membrane. This is an important development towards achieving efficient photon-harvesting medium for possible application in photonic devices. The second part of this contribution reports on the self-assembly/molecular recognition of a specific class of porphyrins giving rise to tubular nano-systems with potential THG nonlinear properties.

Enhancing oxygen reduction reaction (ORR) activity and simultaneously reducing usage of noble metal catalysts are significantly important both in fundamental and applied science communities for polymer electrolyte fuel cells (PEFCs). In this work, we confirm the proton conductor (perfluorosulfonic acid, containing $-$SO₃H) can promote the specific activity $(I_{\text{s}})$ of metal catalysts toward ORR. Herein, Pt nanoparticles (NPs) with a small and narrow size distribution are encapsulated with perfluorosulfonic acid through a simple colloidal route. The resulting catalyst obtains about two times $(I_{\text{s}})$ towards ORR than that of the pristine Pt/C. Significantly, the amount of $-$SO₃H groups is controlled by a heat-treatment method to investigate the influence of $-$SO₃H groups on $(I_{\text{s}})$. The results evidence the contribution of $-$SO₃H groups to elevating the ORR specific activity. The mechanism can be ascribed to the $-$SO₃H groups which effectively promote the transfer process of reaction species (e.g., H${}^{+}$, H₂O), improving the triple-phase boundary (TPB).

In order to improve the actuation stability and non-water working time (NWT) of ionic polymer-metal composites (IPMCs) in the air, polyethylene oxide (PEO) with superior water retention ability was firstly blended into the Nafion matrix to enhance the water uptake capacity of the corresponding IPMCs. The influences of molecular weight of PEO on the water uptake ration, ion exchange ability and micromorphology of PEO/Nafion membranes, and the electromechanical properties of IPMCs were investigated in detail. The results showed that the water uptake ration of the Nafion membranes and the working stability of the IPMCs in the air were greatly improved. The IPMC with 200k molecular weight of PEO exhibited the optimal deformation properties, the highest volumetric work density, and a prolonged NWT. In addition, the high content substitution of Nafion by PEO can reduce the preparation cost of IPMC to some extent. Thus, we hope that the developed PEO/Nafion-IPMCs can be promising candidates for actuation applications in the fields of bionic robotics, space explorations, and medical devices.