Fabrication of a highly conductive ordered porous electrode by carbon-coating of a continuous mesoporous silica film

A mesoporous silica film (MSF, 20 × 20 mm in size) with 3D accessible mesopores (Fmmm symmetry) was synthesized on a current collector substrate, and then the entire pore surface was coated with an extremely thin carbon layer. The resulting carbon-coated mesoporous silica film (C/MSF), which well retains the continuous silica phase with its ordered mesopore network intact, has many advantages over conventional MSFs, porous carbons, or carbon electrodes. Thanks to the continuous carbon-coated layer, C/MSF is electrically conductive, and besides, it has remarkably better stability in an aqueous solution than MSFs. These features enable C/MSF to be used as a stable electrode in aqueous electrolyte solutions. In addition, C/MSF exhibits a much higher rate of performance as an electrode of an electric double layer capacitor than conventional powdery electrodes, indicating that the C/MSF electrode has excellent electrical conductivity, which can be ascribed to the continuous film shape of C/MSF. Another noticeable feature of C/MSF is light transmittance (67.9% at a wavelength of 1000 nm). Thus, C/MSF can be a transparent porous electrode unlike any porous carbon electrodes ever reported. Furthermore, due to the uniform mesopores (2 nm in diameter), C/MSF showed a large capability of immobilizing a giant active species such as iron-porphyrin molecules. Indeed, a much larger current was detected for the charge transfer from C/MSF to the iron-porphyrin than in the case of the iron-porphyrin loaded on a conventional graphite electrode. C/MSF is therefore a promising candidate as an effective electrode in various fields.