L. Soifer

Mediation at High Potentials for the Reduction of Oxygen to Water by Cobalt Porphyrin–Quinone Systems in Porous Aerogel Carbon Electrodes

Reduced p-, m-, and o-benzoquinones: hydroquinone (HQ), resorcinol (Res), and catechol (Cat), undergo irreversible monolayer adsorption in aerogel carbon (AEC) electrodes with rates of 1.7 × 10 ―4 , 7.1 × 10 ―5 , and 1.4 × 10 ―4 s ―1 for HQ, Res, and Cat, respectively. The adsorbed species showed electrochemical quasi-reversible behavior in 1 M H 2 SO 4 with half-wave potentials (E 1/2 ) of +0.45, +0.31, and +0.58 V vs Ag/AgCl/KCl (saturated) for AEC/HQ, AEC/Res, and AEC/Cat, respectively. Upon adsorption of Co(III) tetra(p-sulfonatophenyl)porphyrin in these electrodes, a single reduction wave was observed and its E 1/2 (∼+0.45 V) was independent of the nature of the adsorbed reduced quinone. This was attributed to a metalloporphyrin/ quinone complex, which formed and stabilized at the electrode surface. This species, after being reduced, reacted with oxygen with a rate of 1.8 × 10 5 M ―1 s ―1 . Mediation of oxygen reduction by these systems occurred at a relatively high potential (∼+0.5 V) almost completely via a four-electron-transfer process.

Tautomerism in N-confused porphyrins as the basis of a novel fiber-optic humidity sensor

It is shown that N-confused porphyrins exhibit tautomerism not only in organic solvents, as already reported, but also after incorporation in dry/humid Nafion films. This allows the development of a new fiber-optic humidity sensor which exhibits long-term stability and a linear response over the humidity range 0 to at least 4000 ppm.

Preparation of a Novel Pd Hydride Electrode Based on Polymer Embedded Nanosized Pd Incorporated in Porous Carbon Substrate

A novel Pd/PdH x electrode was prepared by reducing PdCl 2 - 4 adsorbed on cross-linked poly(4-vinylpyridine) which was introduced in the pores of an aerogel carbon substrate. Nanocrystals of Pd ranging from 2.4 to 29 nm were obtained depending on the cross-linking molecule length and on whether the reduction of the palladium ions was achieved chemically or electrochemically. The maximum hydrogen capacity of the Pd particles was determined to be 165 mAh/g. The uniform particles distribution in the porous substrate structure enables to consider possible application of such electrodes loaded with a variety of catalytic metals in batteries and fuel cells.