347 J. Electroanal. Chem., 360 (1993) 347-349 Elsevier Sequoia S.A., Lausanne JEC 03022 Reply to the comment on “zeolite matrix effects on the electrochemistry of metal hexacyanoferrates” S. Bharathi, K.L.N. Phani, J. Joseph, S. Pitchumani, D. Jeyakumar and G. Prabhakara Rao Central Electrochemical Research Institute, Karaikudi (India) (Received 22 December 1992; in revised form 20 June 1993) The objective of our paper [ll was to provide the evidence for the participation of the zeolitic cations in the electrochemistry of metal hexacyanoferrates (MHCFs, M = Ni/Co). The first objection raised by Baker and Senaratne is that the complexes exist only on the external surface of the zeolite and/or the conductive part of the electrode under our experimental conditions based on the ion exchange property of the zeolite Y. We agree with Baker and Senaratne that these com- plexes also exist on the external surface of zeolite Y. Here we provide various observations in our study which show evidence for both intra- and extra-crystalline presence of MHCFs. Our contention is that MHCFs exist both inside and outside zeolite crystals and the currents result from the electrochemistry of both. The intrazeolitic presence of MHCFs has been inferred from our experiments on the effect of tetrabutylammonium ions (which are size excluded from the zeolite Y cages) in solution with Z (Na/K) MHCFs. At ths juncture, it should be recalled that the redox activity of MHCFs depend very much on the solution cation and this is reflected in the form of changes in the redox potential/change in current magnitudes depending on the cation [2]. Accordingly, the GC-NiHCF and GC- CoHCF show complete blocking of the redox activity in the TBA+ medium resulting from the hindered transport of the charges in the film. While in contrast, redox activity of Z(Ni/Co)HCF electrodes in the presence of TBA+ ions in solution is retained without a change in the redox potential but with a slight decrease in the current magnitudes. This implies that the TBA+ ion because of its size selectivity “silences” only the surface confined complexes and the observed redox activity is attributed only to the intrazeolitic presence of the complex. It may be noted that Scherzer in his papers [3,4] observes the formation of MHCFs throughout the zeolite Y crystals and only upon the post treatment (calcination) the Fe(B) and Fe010 conversion and subsequent migration of these 0022-0728/93/$06.00 0 1993 - Elsevier Sequoia S.A. All rights reserved