Electrochemical Fabrication of Gold Nanoparticle Catalyst on CNTs for Glucose Fuel Cells

Abstract

Introduction Polymer electrolyte fuel cells (PEFCs) operate at low temperatures and have fast startup times, making them suitable for automobile and household power applications. However, due to their low operating temperature, PEFCs require a catalyst. In general, platinum is used as the catalyst and carbon black (CB) is used as a support. Carbon nanotubes (CNTs) have recently attracted attention as an alternative to CB due to their large specific surface area, high mechanical strength, and high electrical conductivity, which collectively would improve the durability of PEFCs. In recent years, glucose fuel cells have been attracting attention. When the diameter of gold nanoparticles is less than 10 nm, they have been reported to be effective as catalysts.1)In this study, the fabrication process for a new gold catalyst supported by CNTs as an anode for glucose fuel cells was examined. Experimental (1) Fabrication of Ni/CNT composite films 2) A Watts nickel plating bath (NiSO4·6H2O, NiCl2·6H2O, H3BO3), polyacrylic acid (MW = 5000), brightener (saccharin Na, 1.4-butynediol) and vapor grown carbon fibers (VGCFs) were used as the basic plating bath, CNT dispersant, and CNTs (Showa Denko). Electrodeposition was carried out under galvanostatic conditions. Reverse electrolysis was carried out to removing Ni deposite on the CNTs. The surface morphologies of the films were observed by field-emission scanning electron microscopy (FE-SEM). (2) Reforming of the CNT surface by plasma treatment Plasma treatment with argon was carried out for 5 min at 10, 50, 100, and 150 W on the Ni/CNT composite plating films. The surface morphologies of the plasma-treated samples were observed by FE-SEM, and the CNT defects were evaluated by Raman spectroscopy. (3) Formation of Au nanoparticles A gold sulfite bath (NaAuCl4·2H2O, Na2SO3·7H2O) was used as the plating bath. Electrodeposition of gold on the Ni/CNT films was conducted under galvanostatic conditions. The surface morphology of the plating was observed using FE-SEM and scanning transmission electron microscopy (STEM). Results and discussion (1) Fabrication of Ni/CNT composite films Ni/CNT composite films with smoother surface morphology were formed than without the addition of brightener (Fig. 1(a) and (b)). The reverse electrolysis process was effective at removing Ni deposits on the CNTs (Fig. 1(c)). The reason is thought to be due to the effect of the brightener. Fig. 2 shows a plot of the ratio of drain to gate voltages, ID/IG, vs. the power used during the plasma treatment. ID/IGincreased with increasing power, indicating that the CNT defects increased with increasing power. (2) Reforming of the CNT surface by plasma treatment Fig. 2 shows a plot of the ratio of drain to gate voltages, ID/IG, vs. the power used during the plasma treatment. ID/IGincreased with increasing power, indicating that the CNT defects increased with increasing power. (3) Formation of Au nanoparticles Compared to non-treated CNTs, smaller gold nanoparticles with sizes of about 10 nm were observed on the plasma-treated CNTs. References 1) M. Pasta, L.Hu, F. Mantia, Y. Cui, Electrochemistry Communications, 1981-84 (2012). 2) S. Arai, A. Fujimori, M. Murai, M. Endo, Materials Letters, 62 35-45 (2008). Figure 1