We report significant errors, resulting in the misinterpretation of the cyclic voltammetry of Ag+A monograin layers deposited on glassy carbon electrodes.' The electrochemical reduction of extraframework cations was proposed to occur while the silver cation was present within the pore and channel system of zeolite A on the basis of multiple cathodic waves. The interpretation, however, does not take into account the known ion exchange properties of zeolite A in aqueous solution and ignores previous compelling evidence that redox occurs outside of the zeolite Moreover, the data presented do not survive a detailed analysis based on site-specific redox potentials. In this brief comment we will indicate how the data of Li et al.' have been misinterpreted.The comerstone of Li et al.' is the proposition of site-specific reduction potentials. However, the data of Li et al. show quite a different behavior. Their data purport to point to the observation of four distinct extraframework cations and three types of clusters. However, the reduction potential for each is not constant. Referring to Figures 3 and 4 of the original paper, the following spans in peak potential are readily observed: peak A, 200 mV; peak B, 200 mV; peak C, 125 mV; peak D, 125 mV. The peak assignments are seemingly arbitrary. For example, Li et al. have recognized differences of 40 mV to assign site reductions to peaks A, B, and C in Figure 3 at a scan rate of 20 mV/s and x = 2.6,4.0, and 6.5, respectively. In the same figure they ignore differences of the order of 250 mV when assigning peaks to the same site reduction (peak A at 2 mV/s and x = 2.6 and 50 mV/s and x = 4.0). Clearly, the peak assignments are of an arbitrary nature dictated solely by the necessity of agreement with the hypothesis.Peaks C-E in this work are ascribed to redox processes of electrogenerated intrazeolite clusters. However, these peaks often arise before any prior reduction of silver is indicated. (See Figure 3, x = 6.5, v = 50 mV s-I, and Figure 4, x = 4.0, v = 20 mV SKI.)The authors, already claiming to demonstrate intrazeolite redox, which would open up a new vista on this field, now form clusters with no evidence of reduction. The absence of "a solution peak" (reduction of solution phase silver) is startling. In the slow scan regimes for the Ag6,sA we are asked to believe that following a 5 min immersion in 0.1 M NaC104 no silver ions are produced in solution.In all the voltammograms shown in Figures 3 and 4 of ref 1 the maximum number of peaks present is four. The authors have not considered the possibility of concentration or scan rate dependent shifts in peak potentials. It could well be that only three or four distinct reduction peaks are present. For redox couples with one insoluble species (e.g., metal deposition) the * To whom correspondence should be addressed. 0022-3654/95/2099-12367$09.00/0 reduction potentials shift to more negative potentials with decreasing concentration^.^ Although the authors leave the impression that monograin electrodes may behave differen...

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It is the goal of this work to show that the complex chronoamperometry of partially silver ion exchanged Ag3.1Na52.9Y can be understood by treating the passage of silver cations to the electrode solution interface as a diffusion-controlled reaction preceded by a feeding chemical step. This is achieved via the solution of a CE (chemical followed by electrochemical) process using simulation methods adopting a finite difference approach whereupon the zeolite is divided into a set of discrete volume elements corresponding to the large and small channels of zeolite Y. The fit with the experimentally recorded chronoamperometry of a monograin Ag3.1Na52.9Y-modified electrode covers 30 s after the application of the pulse. Using this approach, accurate determinations of intrazeolite diffusion coefficients will be possible only when exact equilibrium cation locations are known.

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