Current Nanoscience, 2007, 3, 215-221 215 1573-4137/07 $50.00+.00 © 2007 Bentham Science Publishers Ltd. Deposition of Ru-Ni-S Nanoparticles on Carbon by Spray-Pyrolysis: Effects of Solvent and other Processing Parameters Kalyana C. Pingali, Shuguang Deng* and David A. Rockstraw Department of Chemical Engineering, New Mexico State University, P.O. Box 30001, MSC 3805, Las Cruces, NM 88003, U.S.A. Abstract: Nanoparticles of Ru-Ni-S were synthesized in a single-step spray-pyrolysis process as potential catalysts for fuel cells and other applications. The liquid precursors containing ruthenium, nickel, and sulfur were nebulized by an ultra-sonic atomizer to generate aerosol droplets, which were subsequently decomposed to form uniformly distributed nanoparticles for deposition on a carbon thin film. It was observed that the application of methanol as solvent has a strong effect on the particle morphology, size, and composition. The morphology of the Ru-Ni-S nanoparticles changed from spherical with water as solvent, to dendrites upon increase in the methanol con- centration in the precursor solution. It was also found that the pyrolysis temperature strongly affected the particle morphology when methanol was used as solvent. High temperatures promote dendrite formation. When a water/methanol mixture was used as solvent, crys- talline ternary nanoparticles of Ru-Ni-S on a carbon layer were formed at lower temperatures. A very interesting and unique structure of spherical clusters of crystalline particles attached by a chain of crystalline nanoparticles was synthesized. Elemental analysis obtained with EDS attached to the SEM used for particle characterization has confirmed the existence of all elements of interest, and X-ray map- ping showed all elements were distributed uniformly in the nanoparticles. Key Words: Nanoparticles, spray-pyrolysis, particle morphology, solvent effect, dendrite. 1. INTRODUCTION Spray-pyrolysis processing is a versatile technique for produc- tion of inorganic materials of a wide range of composition, size, and morphology. It typically consists of several steps that may include: precursor preparation, precursor atomization, droplet evaporation, droplet precipitation, droplet drying, droplet coagulation, thermoly- sis, and sintering. An review on spray-pyrolysis processing by Messing et al. [1] has discussed the fundamental process parame- ters enabling the formation of particles with controlled morphology and composition. Among the important process parameters in spray-pyrolysis processing, the effects of precursor properties on particle size, composition, and morphology are probably the least understood. Synthesis of electrocatalysts in a spray-pyrolysis process for different types of fuel cells is a relatively new application of the spray-pyrolysis technique. Tolerance to small amounts of carbon monoxide and sulfur is important for proton exchange membrane fuel cells operating on hydrogen obtained by reforming carbon- based fuels. Conventional nanoparticles (2-5 nm) of platinum-based metal alloys are used as both anode and cathode catalysts for proton exchange membrane fuel cells due to the high activity for both hy- drogen oxidation and oxygen reduction [2]. However the platinum- based catalysts used today suffer high polarization losses, reducing performance and fuel efficiency due to particle agglomeration, car- bon monoxide and sulfur poisoning [2, 3]. The search for carbon monoxide and/or sulfur-tolerant non-platinum electrocatalysts for fuel cell applications have been a very active research endeavor [4- 10]. Only a few researchers have studied the platinum- and ruthe- nium-based nanoparticles for methanol oxidation in fuel cell appli- cations. The binary and ternary crystalline nanoparticles were sup- ported on carbon nanofilm as fuel cell catalysts. Waszczuk et al. [11] studied the methanol adsorption on platinum-ruthenium sur- faces and observed that the decomposition of methanol is quite different at ultra-high vacuum. It was observed that the behavior of simple molecules would be different under ultra-high vacuum. Con- trol of size, morphology, and composition of nanoparticles is im- portant in the synthesis processing of ceramic powders. It was *Address correspondence to this author at the Department of Chemical Engineering, New Mexico State University, P.O. Box 30001, MSC 3805, Las Cruces, NM 88003, U.S.A.; Tel: (505)646-4346; Fax: (505)646-7706; E-mail: sdeng@nmsu.edu believed that nanoparticle structure changes in the presence of sta- bilizing agents. Cordente [12] observed that chemisorption led to various shapes of nickel nanoparticles. It was found that the expo- sure of nickel nanoparticles to carbon monoxide or methanol re- duced their magnetization. Both crystalline and amorphous struc- tures of nanoparticles were found to be of considerable interest [13- 18]. Synthesis of binary and ternary nanoparticles has seldom been reported to date. Spicer et al. [19] used water-like solutions with minimum energy in a novel process to synthesize liquid crystalline nanoparticles. The structural properties of crystalline nanoparticles can vary with the particle size. A similar view was expressed by Huignard et al. [20] showing crystalline nanoparticles exhibiting ellipsoidal form with two characteristic dimensions of around 15 and 30 nm. Such particles are 2-D according to the study by Dragieva et al. [21]. Presence of crystalline nanoparticles can en- hance the mechanical properties as studied by Bertran et al. [22] where the crystalline particles were synthesized by chemical vapor deposition. Structural, mechanical, and surface properties were studied. Several crystalline nanoparticles were synthesized and their op- erating conditions and solvent effects were investigated leading to such structures [23-31]. Dendrite structures have been synthesized in the past by some researchers. Afify et al. [32] prepared dendritic structures by spray-pyrolysis at temperatures ranging from 425 to 525˚C. Dendrites were also observed in the carbon nanotube forma- tions. Cao et al. [33] observed carbon nanotubes dendrites, where nanotubes grow from the outer wall. The continuous feeding of catalyst particle during the nanotube growth process resulted in the dendritic structure. Combination of crystallization and dendrite formation was a matter of interest [34-36]. Dendrites structures were also formed at various temperatures. It was found that the temperature and decomposition had an impact on the whisker growth [35, 36]. However, it was observed that the whisker varied with the temperature and resulted in dendrite structures. Experimental parameters can explain the structure and mor- phology of many crystalline structures of nanoparticles. From the above discussions, it can be said that one can control the crystalline structure of nanoparticle by controlling processing conditions. Mono metallic crystalline nanoparticles have been synthesized over the years and their morphologies have been studied. The study of binary and ternary nanoparticles of Ru-Ni and Ru-Ni-S supported Not For Distribution