Zdenek Samec

Molecular electrocatalysis for oxygen reduction by cobalt porphyrins adsorbed at liquid/liquid interfaces.

Molecular electrocatalysis for oxygen reduction at a polarized water/1,2-dichloroethane (DCE) interface was studied, involving aqueous protons, ferrocene (Fc) in DCE and amphiphilic cobalt porphyrin catalysts adsorbed at the interface. The catalyst, (2,8,13,17-tetraethyl-3,7,12,18-tetramethyl-5-p-amino-phenylporphyrin) cobalt(II) (CoAP), functions like conventional cobalt porphyrins, activating O(2) via coordination by the formation of a superoxide structure. Furthermore, due to the hydrophilic nature of the aminophenyl group, CoAP has a strong affinity for the water/DCE interface as evidenced by lipophilicity mapping calculations and surface tension measurements, facilitating the protonation of the CoAP-O(2) complex and its reduction by ferrocene. The reaction is electrocatalytic as its rate depends on the applied Galvani potential difference between the two phases.

Proton-Coupled Oxygen Reduction at Liquid−Liquid Interfaces Catalyzed by Cobalt Porphine

Cobalt porphine (CoP) dissolved in the organic phase of a biphasic system is used to catalyze O(2) reduction by an electron donor, ferrocene (Fc). Using voltammetry at the interface between two immiscible electrolyte solutions (ITIES), it is possible to drive this catalytic reduction at the interface as a function of the applied potential difference, where aqueous protons and organic electron donors combine to reduce O(2). The current signal observed corresponds to a proton-coupled electron transfer (PCET) reaction, as no current and no reaction can be observed in the absence of either the aqueous acid, CoP, Fc, or O(2).

H2O2 Generation by Decamethylferrocene at a Liquid|Liquid Interface

Hydrogen peroxide generation at a liquid|liquid interface occurs with a yield of 20 % with respect to the concentration of reducing agent (decamethylferrocene). The liquid|liquid interface supplies electrons from the reducing agent and protons from the aqueous phase to drive the reduction of O2 into H2O2, which is extracted into the aqueous phase during the course of reaction (see picture; DCE=1,2-dichloroethane).

Charge-transfer processes at the interface between hydrophobic ionic liquid and water

This article provides a brief review of theoretical and methodological concepts in the area of the charge-transfer processes at the interface between a hydrophobic ionic liquid (IL) and an electrolyte solution in water (W). Electrochemical methods of study of the W|IL interfaces are described, current experimental problems are indicated, and the most important experimental results are summarized. The relevance of electrochemistry at the W|IL interfaces to the extraction behavior of ILs is outlined.

Cyclic voltammetry of highly hydrophilic ions at a supported liquid membrane

Cyclic voltammetry has been used to study the coupling of ion transfer reactions at a liquid membrane. The liquids are either supported by a porous hydrophobic membrane (polyvinylidene difluoride, PVDF) when the organic solvent is non-volatile (o-nitrophenyloctylether) or are merely a free standing organic solvent layer such as 1,2-dichloroethane comprised between two hydrophilic dialysis membranes supporting the adjacent aqueous phases. The passage of current across the liquid membrane is associated with two ion transfer reactions across the two polarised liquid I liquid interfaces in series. It is shown that it is possible to study the transfer of highly hydrophilic ions at one interface by limiting the mass transfer of the other ion transfer reaction at the other interface. Indeed, for systems comprising an ion M in one aqueous phase and a reference ion R partitioned between the membrane and the other aqueous phase, the observed and simulated cyclic voltammograms have a half-wave potential determined by the Gibbs energy of transfer of M transferring at one interface and by the limiting mass transfer of R at the other interface. This new methodology opens a way to measure the Gibbs energy of transfer of highly hydrophilic or hydrophobic ions, which usually limits the potential window at single liquid \ liquid interfaces (ITIES)

Oxygen and proton reduction by decamethylferrocene in non-aqueous acidic media

Experimental studies and density functional theory (DFT) computations suggest that oxygen and proton reduction by decamethylferrocene (DMFc) in 1,2-dichloroethane involves protonated DMFc, DMFcH(+), as an active intermediate species, producing hydrogen peroxide and hydrogen in aerobic and anaerobic conditions, respectively.

Evidence of tetraphenylporphyrin monoacids by ion-transfer voltammetry at polarized liquid|liquid interfaces

We present a simple methodology to illustrate the existence of tetraphenylporphyrin monoacid based on ion-transfer voltammetry at a polarized water|1,2-dichloroethane interface and organic pK values are also estimated.

Dioxygen Reduction by Cobalt(II) Octaethylporphyrin at Liquid|Liquid Interfaces

Oxygen reduction catalyzed by cobalt(II) (2,3,7,8,12,13,17,18-octaethylporphyrin) [Co(OEP)] at soft interfaces is studied by voltammetry and biphasic reactions. When Co(OEP) is present in a solution of 1,2-dichloroethane in contact with an aqueous acidic solution, oxygen is reduced if the interface is positively polarized (water phase versus organic phase). This reduction reaction is facilitated when an additional electron donor, here ferrocene, is present in excess in the organic phase.

Photochemical transfer of tetraaryl ions across the interface between two immiscible electrolyte solutions

Abstract Illumination of solutions of tetraarylborate and tetraarylarsonium ions in 1,2-dichloroethane in contact with an aqueous electrolyte solution leads to the onset of a photocurrent at the interface between the two immiscible electrolyte solutions. These photocurrents have been attributed to ion transfer reactions. Analysis of the data shows that the transferring ion is an intermediate in the photochemical decomposition of the tetraarylborate/arsonium ions. The present communication demonstrates how measurement of photocurrents at liquid/liquid interfaces can be used to measure the lifetimes of intermediates in photochemical reactions.