Effect of Anode Microporous Layer on the Performance of Direct Methanol Fuel Cell Using Carbon Nanocoil-Supported PtRu Catalyst

Direct methanol fuel cell (DMFC) is a promising energy source for portable and automotive applications, mainly due to their low operating temperature, direct use of liquid fuel, and simple structure without the stringent need for a reformer. Nevertheless, issues such as water management and methanol crossover still limit the widespread commercial application of DMFC. In our previous study, we analyzed the use of carbon nanocoils (CNCs) as a catalyst support in DMFC [1]. Due to their three dimensional structure, CNC is considered to be a unique support material for electrocatalyst materials. However, when CNC-supported PtRu catalyst was used in the anode of DMFC, it resulted in poor DMFC performance. Therefore, to utilize the advantages of CNC as an anode catalyst support, we applied the anode microporous layer (MPL) to DMFC for improving the efficiency of utilization of the CNC-supported PtRu catalyst [2]. The anode MPL is expected to play a crucial role in preventing the permeation of methanol across CNCs in the anode catalyst layer (CL). Carbon nanoballoon (CNB) and Vulcan were used as the anode MPL materials. CNB is a unique material because of its hollow structure and high electrical conductivity, while Vulcan has a high surface area and high electrical conductivity. CNCs were synthesized using an automatic chemical vapor deposition system with a consecutive substrate transfer mechanism [1]. As seen in the transmission electron micrograph, the fiber diameter of the CNCs is ~300 nm, the coil diameter is ~1000 nm, and the coil length is ~10 μm. Hydrogen hexachloroplatinate (IV) hexahydrate (H 2 PtCl 6 ·6H 2 O) and ruthenium trichloride (RuCl 3 ) were used as the Pt and Ru precursors, respectively. The molar ratio of Pt and Ru was set at 1:1. Each of the carbon nanomaterials (200 mg) was dispersed in 500 mL of deionized water by sonication for 20 min. H 2 PtCl 6 ·6H 2 O and RuCl 3 were stirred in 50 mL of deionized water at 60 rpm for 10 min. The solutions were mixed and stirred at 600 rpm for 10 min. Next, a 30-fold molar excess of sodium borohydride (NaBH 4 ) with respect to the metal precursors was added to 400 mL deionized water. This NaBH 4 solution was added to the metal precursor and carbon nanomaterial mixture and stirred. The solution was then filtered, washed and dried to obtain the supported catalyst. A Nafion ® 115 membranes (Du Pont, K.K., Tokyo, Japan) were cleaned several times with deionized water, hydrogen peroxide solution, and sulfuric