CHARACTERIZATION OF CARRAGEENAN HYDROGEL ELECTRODE COATINGS WITH IMMOBILIZED CATIONIC METAL-COMPLEX REDOX COUPLES

The redox behavior of cationic metal complexes immobilized in a kappa-carrageenan hydrogel matrix, which acts as a cation-exchange polymeric electrode coating, is described. Ru(bpy)3(2+), Ru(cn)3(3+), Ru(NH3)6(3+), and Co(bpy)3(3+) (bpy = 2,2'-bipyridine; en = ethylenediamine) were immobilized singly and in pairs (Ru(bpy)3(2+) and Co(bpy)3(3+)) on the surface of a Pt electrode and were characterized by cyclic voltammetry. The redox couples were selected on the basis of their structural similarity and wide range of electron self-exchange rate constants (10(1)-10(9) M-1 s-1). The surface-modified carrageenan hydrogel electrode was found to exhibit superior electrolyte diffusion properties when compared with more commonly used cation-exchange immobilization matrices such as Nafion, and to be stable with respect to leakage of cations into the solution. The carrageenan hydrogel film was also found to be permeable to anionic redox couples such as Fe(CN)6(3-/4-). All immobilized redox couples exhibited quasi-reversible electrochemical behavior. Evidence supporting a dual-mode mechanism involving physical diffusion and electron hopping for charge propagation through the carrageenan hydrogel is presented.