Voltammetric behavior of carboxyl hydrogel particles on a cavity electrode surface

A platinum electrode with two-dimensional ordered arrays of hemispherical cavities was fabricated via the inverted crystal template technique. Due to the overlap of the diffusion zones, voltammetric response of ferricyanide at the cavity platinum (CPt) electrode was almost the same as that at a flat platinum (FPt) electrode. Uniformly sized poly(N-isopropylacrylamide-co-acrylic acid) (NIPA/AA) hydrogel particles were synthesized and modified into the cavities of the CPt electrode. Voltammograms of the NIPA/AA-CPt electrode showed a cathodic peak at −0.38 V in the negative potential range. The peak was attributed to the reduction of H+ which supplied from the dissociation of carboxyl groups of the absorbed particles. Compared with the peak observed at NIPA/AA-FPt electrode, the peak potential was shifted in the positive direction by 0.19 V. The peak current was increased linearly with the loaded amount of the particles, and was controlled by the participation of diffusion, adsorption and dissociation. The electron-transfer rate constant between dissociated H+ and the CPt electrode was estimated to be one order smaller than that between ferricyanide and the FPt electrode.