Water-in-Supercritical CO2 Microemulsion for Synthesis of Carbon-Nanotube-Supported Pt Electrocatalyst for the Oxygen Reduction Reaction

• Published in: Energy & fuels 2008-07, Vol.22 (4), p.2543-2549
• Main Authors: Shimizu, Kenichi, Cheng, I. Francis, Wang, Joanna S, Yen, Clive H, Yoon, Byunghoon, Wai, Chien M
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel Cells
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef800052b

Four electrocatalysts, including a commercial Pt on carbon black (Pt-CB), were compared for performance in the reduction of oxygen. Three of the catalysts were prepared on the basis of the deposition of Pt onto carbon nanotubes using (i) water-in-supercritical CO2 microemulsion (Pt-CNT SCME), (ii) direct supercritical CO2 fluid deposition (Pt-CNT SC), and (iii) water-in-hexane microemulsion (Pt-CNT ME). Cyclic voltammetric studies yielded an electrochemically active surface area for Pt-CNT SCME at 31.1 m2/g, which was the largest among all electrocatalysts tested in this work. Hydrodynamic polarization curves for oxygen reduction exhibited that the cell potential of the Pt-CNT SCME catalyst was over 350 mV more positive than the commercial Pt-CB system at 10 A/g of Pt. In chronoamperometric analyses, Pt-CNT SCME catalyst (6.6 × 103 A/g of Pt) generated 2.5 times more specific activity at 30 s than Pt-CNT ME (2.6 × 103 A/g of Pt) and 5 times more than the commercial Pt-CB (1.3 × 103 A/g of Pt). Tafel analysis indicated the exchange current density of 7.87 µA/cm2 for Pt-CNT SCME that was significantly higher than the commercial Pt-CB (1.37 µA/cm2).