Non-additivity of Polarographic Diffusion Currents with Mixtures of Certain Reducible Species

Reaction Mechanism for Oxygen Reduction on Platinum: Existence of a Fast Initial Chemical Step and a Soluble Species Different from H2O2

“…Moreover, differences in j p ORR values at different ω but constant v , as in Figure A,B, can only be explained by considering the existence of, at least, two soluble species with different diffusion coefficients. Different studies have shown currents larger than those expected in LSVs owing to the coupling of the diffusional pathways by very fast reactions of species in the diffusion layer with different diffusion coefficients, as in the case of homogeneously catalyzed reactions. − In our case, the thickness of the diffusion layer of one of the species is being determined by ω (eq ) and that of the other species by v . Then, changing ω at constant v would modify the flux of the soluble species whose diffusion layer is controlled by ω, giving rise to changes in j p ORR . ,, If only one soluble species were present, or several species with equal D , identical j p ORR values would have been observed at constant v , regardless of ω, since the concentration profiles close to the surface are only controlled by the magnitude of D . − , …”

“…3Aand 3B, can only be explained by considering the existence of, at least, two soluble species with different diffusion coefficients. Different studies have shown larger currents than expected in LSVs owing to the coupling of the diffusional pathways by very fast reactions of species in the diffusion layer with different diffusion coefficients, as in the case of homogeneously catalyzed reactions[90][91][92][93]. In our case, the thickness of the diffusion layer of one of the species is being determined by ω, Eqn.…”

Electrochemical Investigations on Liquid-State Polymerizing Systems: Case of Sol−Gel Polymerization of Transition Metal Alkoxides

“…The first question raises the problem that the total current is not equal to the sum of the individual currents for each species when the solution contains a mixture of species with different diffusion coefficients due to electron exchange between small and large molecules . The problem has been previously addressed in the context of a mixture of two different reactants (see for example refs and ), including the case of interest for us, the homogeneous isotopic exchange 7 (all the electroactive species have the same standard potentials E °). In case of a fast electron exchange versus diffusion, it has been shown that the contribution of smaller species is expected to increase the current values. , In this particular case, an analytical solution can be obtained in the context of chronoamperometry in the previously nonexamined case of n species with n different diffusion coefficients D 1 .... D n .…”

“…The problem has been previously addressed in the context of a mixture of two different reactants (see for example refs and ), including the case of interest for us, the homogeneous isotopic exchange 7 (all the electroactive species have the same standard potentials E °). In case of a fast electron exchange versus diffusion, it has been shown that the contribution of smaller species is expected to increase the current values. , In this particular case, an analytical solution can be obtained in the context of chronoamperometry in the previously nonexamined case of n species with n different diffusion coefficients D 1 .... D n . Let us call Ai the oxidized species, with a bulk concentration equal to A ° i , which can be reduced in Bi at the electrode according to the reaction: Ai + e - ⇌ Bi and also exchange an electron with any of the reduced species Bj according to: …”

In Situ Mapping of H2, O2, and H2O2 in Microreactors: A Parallel, Selective Multianalyte Detection Method

“…This only works when assuming that the redox processes at the electrode are independent of each other and the resulting currents are therefore additive. This usually holds true as long as the redox processes occurring at the electrode do not produce an intermediate or product which diffuses away from the electrode and reacts with one of the other analytes, or the diffusion constants of the involved analytes differ greatly from each other. − In theory, both of these cases should not apply for the combination of H 2 , O 2 , and H 2 O 2 but the linear, additive behavior needs to be thoroughly examined in order to use the proposed subtraction method.…”