Chapter 1 of this thesis provides a bnef introduction to the electrochemical techniques used in the study of electrode modifying matenals. A review of the synthesis, charactensation and application of redox polymers based on ruthenium and osmium poly(pyndyl) complexes is presented. Chapter 2 descnbes the synthesis, charactensation and charge transport properties of [M(N)6]2+/3+ moieties coordinatively attached to a poly(4-vinyl pyndine) backbone (where M is Ru or Os and N is pyridine ). The effect of electrolyte type and concentration on charge transport and heterogeneous electron transfer is studied using cyclic voltammetry, chronoamperometry and sampled current voltammetry For M=Ru, the effect of redox site loading is also investigated. Activation parameters are used to aid the diagnosis of rate determining steps. In Chapters 3 to 6 the Electrochemical Quartz Crystal Microbalance (EQCM) is used to probe mass transfer within modifying polymer layers An introduction to the theory and application of the EQCM is first presented. This is followed in Chapters 3 and 4 by a study of the effect of electrolyte type and concentration on the polymer morphology and resident layer mass of [Os(bipy)2(PVP)ioCl]+ films Impedance analysis of the quartz crystal \ polymer film \ electrolyte composite resonator is used to confirm the rigidity of the polymer layers and also to provide an insight into electrolyte-dependent morphology changes. The importance of the electrolyte / polymer interaction and the subsequent polymer solvation is stressed. A membrane model describing the osmotic transfer of solvent is considered. In Chapter 5, the kinetic aspects of redox-induced mass transfer through [Os(bipy)2(PVP)ioCl]+ are studied using cyclic voltammetry (under semi-infinite diffusion conditions) and potential step techniques. A correlation between the rate of charge transport and the facility for solvent transfer is established. The origins of the previously reported dependency of charge transport rates on experimental time scale for [Os(bipy)2(PVP)ioCl]+ is also explored. In Chapter 6 , the pH dependency of mass transfer for redox processes in films of [Ru(bipy)2(PVP)io(H2 0 )]2+ is used to evaluate the mechanisms for coupled proton and electron transfer Charge transport through this polymer is also considered.