Effect of Dispersion Methods on Oxygen Reduction and Ammonia Oxidation Reactions for Multiwall Carbon Nanotube Supported Pt

Abstract

When the activity of a catalyst was estimated by a rotating ring disk electrode (RRDE) method, the modified glassy carbon (GC) electrode was generally fabricated by casting catalyst suspension prepared by various methods, followed by drying under various conditions. There are many preparation methods for catalyst suspension. And it is known that the dispersivity of the catalyst on the GC electrode, which affects collection efficiency of H2O2as well as current density, depends on the above methods and conditions. Since an optimum method and condition often varies with the kinds of catalysts, researchers have to find them. However, it is difficult to evaluate the dispersivity on the electrode and reproducibility quantitatively. In this study, the dispersivity of multi wall carbon nanotube supported Pt catalyst (Pt/MWCNT) on the modified electrode prepared by various methods was estimated by digitizing height data of the electrode using a laser surface roughness meter. 30 wt% Pt/MWCNT (Pt particle size: 4.26 ± 0.09 nm) catalyst was synthesized by a microwave polyol process. 2 mg/mL of 30 wt% Pt/MWCNT-0.1 wt% various alcohol (MeOH, EtOH, and 2-PrOH) suspensions were prepared by ultrasonication for 10 min. 10 μL of the suspensions cast on a GC electrode, and the electrode allowed to dry by three method: 1) in air for 1 h (abbreviated as Air), 2) in saturated ethanol vapor pressure for 1 h (EV), and 3) in air with infrared irradiation for 10 min at 60 °C (IR). The samples were named as [solvent] – [drying method]. The modified electrodes were observed with a digital microscope (MSP-3080, PANRICO). And the surface height data of the modified electrodes were digitized with a laser surface roughness meter (SV-C4500 CNC, Mitutoyo), and the data were analyzed by a software "Roughness Analyzer" developed by our laboratory. The software detects secondary particles of the catalyst (clusters) on the electrode and the user can obtain the volumes, the average height, and the area of the clusters as well as the distribution of the catalysts from the center of the electrode. Fig. 1 (a) shows cumulative cluster volume distribution for MeOH–Air, 2-PrOH-Air and EtOH–EV. The electrode surface prepared by the EtOH-EV method had the clusters up to 1.9×10-3 mm3, whereas those prepared by MeOH-Air and EtOH-EV had the clusters up to 6.7×10-4 mm3 and 1.9×10-3 mm3, respectively, suggesting that the EtOH-EV method tend to be aggregated to produce large secondary particles. Fig. 1 (b) shows the average cluster heights of the samples. The standard deviation of the average cluster height for 2-PrOH-Air was the smallest of the three methods, indicating that the 2-PrOH-Air method is the most reproducible casting method of the three methods. Some quantification methods will be reported in the meeting. Figure 1