Electrocatalytic Oxidation of Glucose by Rhodium Porphyrin-Functionalized MWCNT Electrodes: Application to a Fully Molecular Catalyst-Based Glucose/O₂ Fuel Cell

Abstract

This paper details the electrochemical investigation of a deuteroporphyrin dimethylester (DPDE) rhodium(III) ((DPDE)Rh(III)) complex, immobilized within a MWCNT/Nafion electrode, and its integration into a molecular catalysis-based glucose fuel cell. The domains of present (DPDE)Rh(I), (DPDE)Rh-H, (DPDE)Rh(II), and (DPDE)Rh(III) were characterized by surface electrochemistry performed at a broad pH range. The Pourbaix diagrams (plots of E(1/2) vs pH) support the stability of (DPDE)Rh(II) at intermediate pH and the predominance of the two-electron redox system (DPDE)Rh(I)/(DPDE)Rh(III) at both low and high pH. This two-electron system is especially involved in the electrocatalytic oxidation of alcohols and was applied to the glucose oxidation. The catalytic oxidation mechanism exhibits an oxidative deactivation coupled with a reductive reactivation mechanism, which has previously been observed for redox enzymes but not yet for a metal-based molecular catalyst. The MWCNT/(DPDE)Rh(III) electrode was finally integrated in a novel design of an alkaline glucose/O(2) fuel cell with a MWCNT/phthalocyanin cobalt(II) (CoPc) electrode for the oxygen reduction reaction. This nonenzymatic molecular catalysis-based glucose fuel cell exhibits a power density of P(max) = 0.182 mW cm(-2) at 0.22 V and an open circuit voltage (OCV) of 0.64 V.