A highly cross-linked polyviologen hydrogel, poly(tripyridiniomesitylene) (PTPM), has been designed as an anode-active material. It displays a reversible two-electron redox capability at -0.4 and -0.8 V vs Ag/AgCl in an aqueous electrolyte. The PTPM layer coated on a current collector by electropolymerization via a 4-cyanopyridinium electro-coupling reaction demonstrates a rapid charging-discharging reaction with a redox capacity comparable to that obtainable using the formula weight-based theoretical density, because of the combination of the redox-active viologen moieties built into the hydrogel. A test cell that has been fabricated using the developed PTPM anode, a poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl acrylamide) (PTAm)-based cathode, and an aqueous electrolyte exhibits a discharging voltage of 1.1 and 1.5 V, and has proven its ability to be recharged more than 2000 times.

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Reactivity of redox-active molecules for heterogeneous electron-transfer processes at the surface of doped zinc oxide substrates depended on their energy levels. The redox-active molecules with negative redox potentials displayed a reversible electrochemical response but those with positive redox potentials were characterized by slow electrode kinetics, which was attributed to more than three times larger heterogeneous electron-transfer rate constant for the former redox-active molecules. A photovoltaic cell using methyl viologen as an acceptor molecule, TEMPOL as a donor molecule, and the doped ZnO as the transparent conducting substrate gave high photovoltage, which was ascribed to the reactivity of the redox-active molecules at the doped ZnO surface.