Electrode catalysts composed of carbon-supported PtRu nanoparticles (PtRu/C) for use as a direct methanol fuel cell anode were synthesized by the reduction of precursor ions in an aqueous solution via irradiation with a high-energy electron beam. The effect of pH control in the precursor solution on the PtRu mixing state and the methanol oxidation activity was studied in order to enhance the catalytic activity for methanol oxidation. The PtRu/C structures were characterized by transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, X-ray fluorescence spectrometry, and X-ray diffraction and X-ray absorption fine structure techniques. The methanol oxidation activity was evaluated by linear sweep voltammetry. The initial pH of the precursor solution has little influence on the average grain size for the metal particles (approximately 3.5 nm) on the carbon particle supports, but the dispersibility of the metal particles, PtRu mixing state, and methanol oxidation activity differed. The maintenance of a low pH in the precursor solution gave the best dispersibility of the PtRu nanoparticles supported on the surface of the carbon particles, whereas, a high pH gave the best PtRu mixing state and the highest oxidation current although a low dispersibility of the PtRu nanoparticles supported on the surface of the carbon particles was obtained. The PtRu mixing state strongly correlated with the methanol oxidation current. In addition, a high pH was more effective for PtRu mixing when using an electron beam irradiation reduction method, because the complexation reaction of the chelating agents was improved, which resulted in an enhancement of the catalytic activity for methanol oxidation.
Radiolytic synthesis PtRu pH control Direct methanol fuel cell Methanol oxidation activity
This study was mainly supported by Grant-in-Aid for Scientific Research A (Grant-in-Aid No. 22241023) and Grant-in-Aid for JSPS Fellows. The authors thank the staff of the Japan Electron Beam Irradiation Service, Ltd., for their assistance with the electron beam irradiation experiments. The authors are also thankful for partial support from the Ministry of Economy, Trade and Industry (R&D Project for Regional Innovation No. 22U5009).
Kageyama S, Seino S, Nakagawa T, Nitani H, Ueno K, Daimon H, Yamamoto TA (2011) Formation of PtRu alloy nanoparticle catalyst by radiolytic process assisted by addition of dl-tartaric acid and its enhanced methanol oxidation activity. J Nanopart Res 13:5275–5287. doi:10.1007/s11051-011-0513-xCrossRefGoogle Scholar
Kageyama S, Murakami A, Ichikawa S, Seino S, Nakagawa T, Daimon H, Ohkubo Y, Kugai J, Yamamoto TA (2012) Enhanced electrochemical stability of PtRuAu/C catalyst synthesized by radiolytic process. J Mater Res 27:1037–1045. doi:10.1557/jmr.2012.65CrossRefGoogle Scholar
Nitani H, Yuya M, Ono T, Nakagawa T, Seino S, Okitsu K, Mizukoshi Y, Emura S, Yamamoto TA (2006) Sonochemically synthesized core-shell structured Au–Pd nanoparticles supported on γ-Fe2O3 particles. J Nanopart Res 8:951–958. doi:10.1007/s11051-005-9048-3CrossRefGoogle Scholar
Nitani H, Nakagawa T, Daimon H, Kurobe Y, Ono T, Honda Y, Koizumi A, Seino S, Yamamoto TA (2007) Methanol oxidation catalysis and structure of PtRu bimetallic nanoparticles. Appl Catal A Gen 326:194–201. doi:10.1016/j.apcata.2007.04.018CrossRefGoogle Scholar
Ohkubo Y, Shibata M, Kageyama S, Seino S, Nakagawa T, Kugai J, Yamamoto TA (2011) Radiation induced synthesis of Au–Pd nanoparticles of random alloy structure supported on carbon particles using the high energy electron beam. Mater Lett 65:2165–2167. doi:10.1016/j.matlet.2011.04.023CrossRefGoogle Scholar
Seino S, Kinoshita T, Nakagawa T, Kojima T, Taniguci R, Okuda S, Yamamoto TA (2008) Radiation induced synthesis of gold/iron-oxide composite nanoparticles using high energy electron beam. J Nanopart Res 10:1071–1076. doi:10.1007/s11051-007-9334-3CrossRefGoogle Scholar
Watanabe M, Motoo S (1975) Electrocatalysis by ad-atoms. Part II. Enhancement of oxidation of methanol on platinum by ruthenium ad-atoms. J Electroanal Chem 60:267–273CrossRefGoogle Scholar
Yamamoto TA, Nakagawa T, Seino S, Nitani H (2010) Bimetallic nanoparticles of PtM(M = Au, Cu, Ni) supported on iron oxide: radiolytic synthesis and CO oxidation catalysis. Appl Catal A Gen 387:195–202. doi:10.1016/j.apcata.2010.08.020CrossRefGoogle Scholar
Yamamoto TA, Kageyama S, Seino S, Nitani H, Nakagawa T, Horioka R, Honda Y, Ueno K, Daimon H (2011) Methanol oxidation catalysis and substructure of PtRu/C bimetallic nanoparticles synthesized by a radiolytic process. Appl Catal A Gen 396:68–75. doi:10.1016/j.apcata.2011.01.037CrossRefGoogle Scholar