Satoru Kageyama

Carbon-supported AuPd bimetallic nanoparticles synthesized by high-energy electron beam irradiation for direct formic acid fuel cell

Nanoparticle catalysts of carbon-supported Pd (Pd/C) and carbon-supported AuPd (AuPd/C) for the direct formic acid fuel cell (DFAFC) anode were synthesized by the reduction of precursor ions in an aqueous solution irradiated with a high-energy electron beam. We obtained three kinds of nanoparticle catalysts: (1) Pd/C, (2) AuPd/C of the core–shell structure, and (3) AuPd/C of the alloy structure. The structures of AuPd nanoparticles were controlled by the addition of citric acid as a chelate agent, and sodium hydroxide as a pH controller. The structures of nanoparticle catalysts were characterized using transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, the techniques of X-ray diffraction and X-ray absorption fine structure. The catalytic activity of the formic acid oxidation was evaluated using linear sweep voltammetry. The oxidation current value of AuPd/C was higher than that of Pd/C. This indicated that the addition of Au to Pd/C improved the oxidation activity of the DFAFC anode. In addition, the AuPd/C of the alloy structure had higher oxidation activity than the AuPd/C of the core–shell structure. The control of the AuPd mixing state was effective in enhancing the formic acid oxidation activity.

Preparation of carbon-supported PtCo nanoparticle catalysts for the oxygen reduction reaction in polymer electrolyte fuel cells by an electron-beam irradiation reduction method

We prepared carbon-supported PtCo bimetallic nanoparticles (PtCo/C) as electrode catalysts for the oxygen reduction reaction (ORR) at the cathodes in polymer electrolyte membrane fuel cells (PEFCs) by an electron-beam irradiation reduction method (EBIRM). An EBIRM allows nanoparticles to be easily prepared by the reduction of precursor ions in an aqueous solution irradiated with a high-energy electron beam. The structures of PtCo/C were characterized by transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, and the techniques of X-ray diffraction and X-ray absorption near edge structure. It found for the first time that both PtCo alloy and Co oxide were prepared simultaneously on the carbon support by an EBIRM. The catalytic activity and durability of PtCo/C were evaluated by linear-sweep voltammetry and cyclic voltammetry, respectively. The addition of Co to Pt/C not only enhanced the catalytic activity for the ORR but also improved the catalytic durability. As the Co concentration increased, both behaviors became pronounced. These improvements are explained by the effects of both PtCo alloy and Co oxide. We demonstrated that an EBIRM can not only synthesize the alloy and oxide simultaneously on the carbon support but also mass-produce the electrode catalysts for PEFC cathodes.

Mass production of highly loaded and highly dispersed PtRu/C catalysts for methanol oxidation using an electron-beam irradiation reduction method

An electron-beam irradiation reduction method (EBIRM) is a technique to reduce metal ions in an aqueous solution via irradiation with a high-energy electron beam. In this study, an EBIRM is improved to develop a technique for the mass production of highly loaded and highly dispersed PtRu/C catalysts for use as direct methanol fuel cell anodes. An increase in the Pt and Ru input concentrations increased the loading weight from 9 to 37 wt%; however, the dispersibility of the PtRu nanoparticles on the carbon particles decreased. To improve the low dispersibility, sodium phosphinate was added to the precursor solution and the input amount of carbon particles was decreased. These changes resulted in not only highly loaded but also highly dispersed PtRu/C catalysts. The catalytic activity of the highly loaded and highly dispersed PtRu/C catalysts for methanol oxidation was at least 1.6 times higher than that of the lowly loaded and lowly dispersed PtRu/C catalysts in all voltage range. More than 6000 mg of highly loaded and highly dispersed PtRu/C catalysts were relatively easily obtained, and the average particle size of the PtRu nanoparticles was 1.8 nm. These results demonstrated that the improved EBIRM is effective for the mass production of carbon-supported, highly loaded, and highly dispersed metal nanoparticles.