Electrodeposition of Palladium Nanoparticles on Carbon Nanotubes Dispersed in an Ionic Liquid (2020)

Electrodeposition of palladium nanoparticles (PdNPs) was investigated on single walled carbon nanotubes (SWCNTs) or few walled carbon nanotubes (FWCNTs) dispersed in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing [PdBr 4 ] 2 - . Ionic liquids have been expected to be alternative electrolytes for electrodeposition of various metals and alloys because of such unique characteristics as wider electrochemical potential window, negligible vapor pressure, less flammability, and wider usable temperature range, compared with conventional organic electrolytes. In addition, the ionic liquids have been known to have ability to disperse nanoparticles without any additives[1]. Although several studies have reported the preparation of metal nanoparticles by electrochemical cathodic reduction in ionic liquids, there are some problems in the utilization of the nanoparticles dispersed in ionic liquids. Platinum nanoparticles (PtNPs) prepared in ionic liquids have been reported to be collected on such carbon materials as carbon nanotubes (CNTs) and carbon black with elevating temperature[2,3]. It has been reported that CNTs are dispersed in ionic liquids and act as an electrode[4]. We have already reported the electrodeposition of PtNPs is possible on CNTs dispersed in BMPTFSA containing [PtBr 4 ] 2– [5]. The average particle size of the PtNPs was 1.7 nm, which was independent on the concentration of [PtBr 4 ] 2– and the kind of CNTs. In the present study, the electrodeposition of PdNPs was investigated on SWCNTs and FWCNTs dispersed in BMPTFSA containing [PdBr 4 ] 2– in order to examine the effect of the deposition potential on the average particle size of PdNPs because the deposition potential of Pd is more positive than that of Pt[3,6]. In addition, the effect of the catalyst remaining in CNTs on electrodeposition of PdNPs was examined using high purity (&gt; 99.6% purity) FWCNT synthesized by the fluidized bed method[7]. Galvanostatic cathodic reduction was conducted in BMPTFSA containing CNTs and [PdBr 4 ] 2– at room temperature, resulted in deposition of NPs, which were identified as metallic Pd by energy dispersive X-ray analysis (EDX) and transmission electron mocroscopy (TEM). The average potential of [PdBr 4 ] 2– during the galvanostatic cathodic reduction was –1.2 V, which was close to that reported on a planar glassy carbon electrode[6]. Potentiostatic cathodic reduction at different potentials indicated that the average particle size of PdNPs decreased with lowering the potential. Pd nuclei are considered to occur and grow on the CNTs dispersed in the ionic liquid. As the potential becomes more negative, the cations of the ionic liquid are expected to be accumulated on the surface of the nuclei and CNTs in order to compensate the excess negative charge. The cations strongly attracted on the surface are considered to inhibit the growth of the PdNPs and affect their average particle size. On the other hand, the remaining catalyst in the CNTs was found to have little effect on the average particle size of PdNPs. References [1] Y. Katayama, "Electrochemical Preparation of Metal Nanoparticles in Ionic Liquids", in “ Nanocatalysis in Ionic Liquids ”, M. H. G. Prechtl Ed., John Wiley &amp; Sons, 207 (2016). [2] K. Yoshii, T. Tsuda, T. Arimura, A. Imanishi, T. Torimoto, and S. Kuwabata, RSC Adv. , 2 , 8262 (2012). [3] Y. Katayama, T. Endo, T. Miura, and K. Toshima, J. Electrochem. Soc. , 160 , D423 (2013). [4] Y. Katayama, M. Sugiyama, K. Yoshii, N. Tachikawa, and N. Serizawa, 233rd ECS Meeting, A02-0227, Seattle, May 13-17 (2018). [5] Y. Okafuji, N. Serizawa, S, Noda, and Y. Katayama, 10th Ionic Liquid Symposium, 2P13, Osaka, Nov. 21-22 (2019). [6] Y. Katayama, Y. Oshino, N. Ichihashi, N. Tachikawa, K. Yoshii, and K. Toshima, Electrochim. Acta , 830 , 37 (2015). [7] Z. Chen, D. Y. Kim, K. Hasegawa, T. Osawa, and S. Noda, Carbon , 80 , 339 (2014).