Electrodeposited Palladium Nanoflowers for Electrocatalytic Applications K. K. Maniam 1 , R. Chetty 1 * 1 Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai, India Received September 25, 2012; accepted August 19, 2013; published online November 25, 2013 1 Introduction Controlling the shape of noble metal nanoparticles is an interesting area of electrocatalysis research [1, 2]. Significant progress has been made over the last decade, in the develop- ment of shape controlled nanomaterials for fuel cell applica- tions, especially in the reactions of oxygen reduction and oxi- dation of small organic molecules (e.g., methanol, ethanol, and formic acid) [3, 4]. Among the noble metal electrocata- lysts, palladium in nanosized form are seen as ideal alterna- tive to Pt and has been widely used in various electrochemi- cal reactions due to the relatively abundant, less expensive resource, large surface area-to-volume ratio, and more active centers [5–8]. Platinum and palladium have very similar properties, whereas Pd is at least 50 times more abundant on the earth than Pt, and also the cost of Pd is lower than that of Pt [5]. However, the control over morphology of Pd nano- structures has been difficult, especially with the conventional synthesis methods of chemical reduction [9]. In the recent times, electrodeposition is considered as an attractive tech- nique for synthesizing shape controlled nanoparticles [10–12], which offers a feasible way to prepare metal particles directly on carbon-based substrates, widely used as support material in fuel cells [13–16]. During electrodeposition, it is important to control two major modes of particle evolution: nucleation and growth. To create shape controlled nanoparticles, growth has to be lim- ited with the encouragement of nucleation, and this can be accomplished by controlling the current/voltage or by alter- ing the electrolyte conditions with the addition of suitable additive. The combination of these two has successfully yielded shape controlled nanoparticles by various research groups [17–20]. Generally, polyethylene glycol (PEG), a nonionic surfac- tant is used as an additive to modify the morphology of Pt nanoparticles due to its selective adsorption to inhibit crystal growth [21, 22]. However, the influence of PEG concentration on the shape control of noble metal nanoparticles and facet dependent catalytic activity relation toward fuel cell reactions are not found in the reported literature. Moreover, literature on shape-control agents for direct electrodeposition of palla- dium is very limited. Thus, the study on PEG as an additive and its variable concentration on the direct electrochemical growth of palladium, to control the particle size, dispersion Abstract Palladium was electrodeposited on an electrochemically activated carbon black substrate using potentiostatic techni- que, with and without the addition of polyethylene glycol (PEG-6000) as an additive. Scanning electron micrographs showed change in morphology of Pd from spherical to flower, with increasing additive concentration. As an elec- trocatalyst for oxygen reduction reaction (ORR), formic acid oxidation and CO stripping, Pd nanoflowers displayed three- to fourfold increase in electrocatalytic activity in com- parison to the spherical Pd deposits in terms of electro- chemical surface area (ESA) and mass specific current density. X-ray diffraction (XRD) patterns showed, the intro- duction of additive with varying concentration effect the direction of Pd growth thereby changing the morphology from spherical to flower. The result demonstrates an increase in efficiency of Pd utilization achieved with the addition of PEG during electrodeposition, which could also be applicable to other precious metal electrocatalysts. A scheme for the change in Pd morphology during electro- deposition with additive is also proposed. Keywords: Electrodeposition, Formic Acid Oxidation, Fuel Cells, Oxygen Reduction Reaction, Palladium, Polyethylene Glycol – [*] Corresponding author, raghuc@iitm.ac.in 1196 © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim FUEL CELLS 13, 2013, No. 6, 1196–1204 ORIGINAL RESEARCH PAPER DOI: 10.1002/fuce.201200162