Facile template-free synthesis of pine needle-like Pd micro/nano-leaves and their associated electro-catalytic activities toward oxidation of formic acid
© Zhou et al; licensee Springer. 2011
Received: 27 February 2011
Accepted: 13 May 2011
Published: 13 May 2011
Pine needle-like Pd micro/nano-leaves have been synthesized by a facile, template-free electrochemical method. As-synthesized Pd micro/nano-leaves were directly electrodeposited on an indium tin oxide substrate in the presence of 1.0 mM H2PdCl4 + 0.33 M H3PO4. The formation processes of Pd micro/nano-leaves were revealed by scanning electron microscope, and further characterized by X-ray diffraction and electrochemical analysis. Compared to conventional Pd nanoparticles, as-prepared Pd micro/nano-leaves exhibit superior electrocatalytic activities for the formic acid oxidation.
Energy storage devices including fuel cell, Li-batteries etc. have been developing especially today [1, 2]. Direct formic acid fuel cell has been receiving much attention as one of the most attractive energy sources . Palladium (Pd) was found to show superior catalytic activity for formic acid electrooxidation compared with Pt-based catalysts [4, 5]. Considerable efforts have currently been directed to developing novel Pd catalysts. Due to high-surface area and other unique physicochemical properties, nano-catalysts are known to have a significant effect on promoting the electro-oxidation of formic acid. Well-controlled nanostructures are thereby essential for achieving high efficient catalysts used in fuel cells. From this prospect, Pd nanoparticles with a variety of shapes have been explored, such as microspheres , polygonal nanoparticles [7, 8], nanotubes , nanothorns , nanorods , and nanowires [12–15]. Sun et al. reported the efficiency of formic acid electro-oxidation can be improved by changing the morphology of the Pd nanostructures from nanoparticle to nanowire .
Recently, much attention has been paid to the synthesis of nanomaterials on the basis of electrochemical deposition methods because of their simple operation, high purity, uniform deposits, and easy control [17–19]. In order to obtain nano-architectural Pd catalysts directly grown on substrates by electrodeposition, templates are commonly used . However, the fabrication is relatively complicated with multiple steps. Recently, a few studies on nano-architectural Pd fabrication using direct template-free electrodeposition on an indium tin oxide (ITO) electrode have been reported [21, 22]. Park et al. reported the potentiostatic electrodeposition of Pd dendritic nanowires on an ITO electrode in a solution containing 0.2 M H3BO3 and 0.2 M PdSO4, and they did not find the formation of Pd dendritic nanowires on the ITO substrate through potentiostatic reduction of PdCl2. Kwak et al. reported the electrodeposition of Pd nanoparticles on an ITO electrode by a cyclic voltammetry method in a 0.1 M H2SO4 + 0.1 mM PdCl2 + 0.2 mM HCl solution and their catalytic properties for formic acid oxidation . Clearly, the composition of electrolytes and the different electrochemical methods employed for electrodeposition are critical to the morphology of the formed metal products. The present article provides a facile, one-step, template-free electrodeposition route of Pd micro/nano-leaves. As-formed Pd micro/nano-leaves were found to show promising activity for formic acid electro-oxidation.
Materials and apparatus
PdCl2 (Shanghai Sinopharm Chemicals Reagent Co., Ltd., China) was used as received. Formic acid, H3PO4, and H2SO4 were of analytical-grade purity. Doubly distilled water was used throughout. A 1.0 mM H2PdCl4 solution was prepared by dissolving 0.1773 g of PdCl2 in 10 mL of 0.2 M HCl solution and further diluting to 1000 mL with double-distilled water . The electrochemical experiments were carried out in a conventional three-electrode cell using a CHI 660B potentiostat/galvanostat (Shanghai Chenhua Instrumental Co., Ltd., China) at room temperature. An ITO glass substrate was used as the working electrode. The counter electrode and the reference electrode were platinum wire and saturated calomel electrode (SCE), respectively. The solutions were deaerated by a dry nitrogen stream and maintained with a slight overpressure of nitrogen during the experiments. A scanning electron microscope (SEM, S-4700, Japan) and X-ray diffraction (XRD, X' Pert-Pro MPD, PANalytical Company) were used to determine the morphology and the crystal structure of the sample nanomaterials, respectively.
Preparation of the modified electrode
Before electrodeposition, ITO surface was ultrasonicated sequentially for 20 min in acetone, 10% KOH ethanol solution, and doubly distilled water. The electrodeposition process was conducted in a solution consisting of 1.0 mM H2PdCl4 and 0.33 M H3PO4 using cyclic voltammetry from -0.24 to 1.2 V with a scan rate of 50 mV s-1. The conventional Pd nanoparticles deposited on ITO were prepared by the potentiostatic method at a constant applied potential of -0.2 V in the solution as stated above. As-prepared Pd/ITO electrode was rinsed with water for three times and dried at room temperature. Before the activity test, the electrode was cycled at 50 mV s-1 between -0.3 and 0.8 V in 0.5 M H2SO4 for at least 20 scans. After that the electrode was transferred to the cell containing 0.5 M H2SO4 + 0.5 M HCOOH electrolyte solution. Subsequently, 20 scans were recorded at 50 mV s-1 in the potential range -0.3 to 0.8 V. The amount of Pd (W Pd) loaded onto ITO was analyzed by an inductive coupled plasma emission spectrometer (ICP).
Results and discussion
To pin down the related factors for the formation of Pd micro/nano-leaves, two control experiments have been carried out independently. First, replacing H3PO4 with other acids, e.g., H2SO4, HCl, HNO3, while keeping the other conditions unchanged, no Pd micro/nano-leaves were observed. It is proposed that the formation of Pd micro/nano-leaves is related to the effect driven by phosphate anions. Secondly, using a potentiostatic method instead of the cyclic voltammetry method and keeping the other conditions unchanged, featureless Pd nanoparticles (Figure 1h) were formed. Based on these observations, the existence of H3PO4 and the cyclic voltammetry method are two key factors, which are beneficial to the formation of Pd micro/nano-leaves. First, phosphate anions such as the hydrogen phosphate ion (HPO4 2-) or the dihydrogen phosphate ion (H2PO4 -) in solution are preferentially adsorbed on noble metal single crystals, which can greatly disturb the growth of the plane . The phosphate anions are known to adsorb on the (111) surface of metal electrodes with a face-centered cubic (fcc) crystal structure. Especially, they have already been observed in the adsorption of both H2PO4 - and HPO4 2- on the Pt(111) . Secondly, compared to the potentiostatic method, cyclic voltammetry is an alternating redox process, involving both electrodeposition and dissolution processes, which are critical to the formation of Pd nanoleaf structure. At the same time, varying the experimental conditions, such as the concentration, pH of the initial solution, reaction temperature, and time, may also effect the shape evolution .
Using a simple electrodeposition method, Pd micro/nano-leaves were loaded onto a clean ITO. The Pd micro/nano-leaves are demonstrated to have superior performance in electrocatalytic activity toward the oxidation of formic acid.
inductive coupled plasma emission spectrometer
indium tin oxide
saturated calomel electrode
scanning electron microscope
This work was supported by the National Natural Science Foundation of China (Grant nos. 20933007, 51073114, 51073074, and 50963002), the 'One Hundred Talents' program of Chinese Academy of Sciences (1029471301), the Opening Project of Xinjiang Key Laboratory of Electronic Information Materials and Devices, the Priority Academic Program Development of Jiangsu Higher Education Institutions.
- Liu J, Xue D: Hollow Nanostructured Anode Materials for Li-Ion Batteries. Nanoscale Res Lett 2010, 5: 1525. 10.1007/s11671-010-9728-5View Article
- Liu J, Xia H, Xue D, Lu L: Double-Shelled Nanocapsules of V 2 O 5 -Based Composites as High-Performance Anode and Cathode Materials for Li Ion Batteries. J Am Chem Soc 2009, 131: 12086. 10.1021/ja9053256View Article
- Rice C, Ha S, Masel RI, Waszczuk P, Wieckowski A, Barnard T: Direct formic acid fuel cells. J Power Sources 2002, 111: 83. 10.1016/S0378-7753(02)00271-9View Article
- Capon A, Parsons R: The oxidation of formic acid on noble metal electrodes: II. A comparison of the behaviour of pure electrodes. J Electroanal Chem 1973, 44: 239. 10.1016/S0022-0728(73)80250-5View Article
- Hoshi N, Kida K, Nakamura M, Nakada M, Osada K: Structural Effects of Electrochemical Oxidation of Formic Acid on Single Crystal Electrodes of Palladium. J Phys Chem B 2006, 110: 12480. 10.1021/jp0608372View Article
- Qiu CC, Zhang JT, Ma HY: Fabrication of monometallic (Co, Pd, Pt, Au) and bimetallic (Pt/Au, Au/Pt) thin films with hierarchical architectures as electrocatalysts. Solid State Sci 2010, 12: 822. 10.1016/j.solidstatesciences.2010.02.011View Article
- Lee YW, Han SB, Park KW: Electrochemical properties of Pd nanostructures in alkaline solution. Electrochem Commun 2009, 11: 1968. 10.1016/j.elecom.2009.08.030View Article
- Tian N, Zhou ZY, Yu NF, Wang LY, Sun SG: Direct Electrodeposition of Tetrahexahedral Pd Nanocrystals with High-Index Facets and High Catalytic Activity for Ethanol Electrooxidation. J Am Chem Soc 2010, 132: 7580. 10.1021/ja102177rView Article
- Steinhart M, Jia Z, Schaper AK, Wehrspohn RB, Gösele U, Wendorff JH: Palladium Nanotubes with Tailored Wall Morphologies. Adv Mater 2003, 15: 706. 10.1002/adma.200304502View Article
- Meng H, Sun SH, Masse JP, Dodelet JP: Electrosynthesis of Pd Single-Crystal Nanothorns and Their Application in the Oxidation of Formic Acid. Chem Mater 2008, 20: 6998. 10.1021/cm8014513View Article
- Wang XG, Wang WM, Qi Z, Zhao CC, Ji H, Zhang ZH: Electrochemical catalytic activities of nanoporous palladium rods for methanol electro-oxidation. J Power Sources 2010, 195: 6740. 10.1016/j.jpowsour.2010.03.098View Article
- Taşaltın N, Öztürk S, Kılınç N, Yüzer H, Öztürk ZZ: Fabrication of vertically aligned Pd nanowire array in AAO template by electrodeposition using neutral electrolyte. Nanoscale Res Lett 2010, 5: 1137. 10.1007/s11671-010-9616-zView Article
- Fukuoka A, Araki H, Sakamoto Y, Inagaki S, Fukushima Y, Ichikawa M: Palladium nanowires and nanoparticles in mesoporous silica templates. Inorg Chim Acta 2003, 350: 371.View Article
- Ksar F, Surendran G, Ramos L, Keita B, Nadjo L, Prouzet E, Beaunier P, Hagège A, Audonnet F, Remita H: Palladium Nanowires Synthesized in Hexagonal Mesophases: Application in Ethanol Electrooxidation. Chem Mater 2009, 21: 1612. 10.1021/cm803492jView Article
- Yoo Y, Seo K, Han S, Varadwaj K, Kim HY, Ryu JH, Lee HM, Ahn JP, Ihee H, Kim B: Steering Epitaxial Alignment of Au, Pd, and AuPd Nanowire Arrays by Atom Flux Change. Nano Lett 2010, 10: 432. 10.1021/nl903002xView Article
- Wang JJ, Chen YG, Liu H, Li RY, Sun XL: Synthesis of Pd nanowire networks by a simple template-free and surfactant-free method and their application in formic acid electrooxidation. Electrochem Commun 2010, 12: 219. 10.1016/j.elecom.2009.11.029View Article
- Tsai MC, Yeh TK, Tsai CH: An improved electrodeposition technique for preparing platinum and platinum-ruthenium nanoparticles on carbon nanotubes directly grown on carbon cloth for methanol oxidation. Electrochem Commun 2006, 8: 1445. 10.1016/j.elecom.2006.07.003View Article
- Chen X, Li N, Eckhard K, Stoica L, Xia W, Assmann J, Muhler M, Schuhmann W: Pulsed electrodeposition of Pt nanoclusters on carbon nanotubes modified carbon materials using diffusion restricting viscous electrolytes. Electrochem Commun 2007, 9: 1348. 10.1016/j.elecom.2007.01.034View Article
- Sun M, Zangari G, Shamsuzzoha M, Metzger RM: Electrodeposition of highly uniform magnetic nanoparticle arrays in ordered alumite. Appl Phys Lett 2001, 78: 2964. 10.1063/1.1370986View Article
- Xu CW, Wang H, Shen PK, Jiang SP: Highly Ordered Pd Nanowire Arrays as Effective Electrocatalysts for Ethanol Oxidation in Direct Alcohol Fuel Cells. Adv Mater 2007, 19: 4256. 10.1002/adma.200602911View Article
- Song YJ, Kim JY, Park KW: Synthesis of Pd Dendritic Nanowires by Electrochemical Deposition. Cryst Growth Des 2009, 9: 505. 10.1021/cg8007574View Article
- Kim BK, Seo D, Lee JY, Song H, Kwak J: Electrochemical deposition of Pd nanoparticles on indium-tin oxide electrodes and their catalytic properties for formic acid oxidation. Electrochem Commun 2010, 12: 1442. 10.1016/j.elecom.2010.08.004View Article
- Wang DW, Li T, Liu Y, Huang JS, You TY: Large-Scale and Template-Free Growth of Free-Standing Single-Crystalline Dendritic Ag/Pd Alloy Nanostructure Arrays. Cryst Growth Des 2009, 9: 4351. 10.1021/cg900217tView Article
- Moraes IR, Nart FC: Vibrational study of adsorbed phosphate ions on rhodium single crystal electrodes. J Electroanal Chem 2004, 563: 41. 10.1016/j.jelechem.2003.08.018View Article
- He QG, Yang XF, Chen W, Mukerjee S, Koel B, Chen SW: Influence of phosphate anion adsorption on the kinetics of oxygen electroreduction on low index Pt(hkl) single crystals. Phys Chem Chem Phys 2010, 12: 12544.View Article
- Xu J, Xue D: Five branching growth patterns in the cubic crystal system: A direct observation of cuprous oxide microcrystals. Acta Mater 2007, 55: 2397. 10.1016/j.actamat.2006.11.032View Article
- Zhang SX, Qing M, Zhang H, Tian YN: Electrocatalytic oxidation of formic acid on functional MWCNTs supported nanostructured Pd-Au catalyst. Electrochem Commun 2009, 11: 2249. 10.1016/j.elecom.2009.10.001View Article
- Zhang HM, Zhou WQ, Du YK, Yang P, Wang CY: One-step electrodeposition of platinum nanoflowers and their high efficient catalytic activity for methanol electro-oxidation. Electrochem Commun 2010, 12: 882. 10.1016/j.elecom.2010.04.011View Article
- Zhou WJ, Lee JY: Highly active core-shell Au@Pd catalyst for formic acid electrooxidation. Electrochem Commun 2007, 9: 1725. 10.1016/j.elecom.2007.03.016View Article
- Liu ZL, Hong L, Tham MP, Lim TH, Jiang HX: Nanostructured Pt/C and Pd/C catalysts for direct formic acid fuel cells. J Power Sources 2006, 161: 831. 10.1016/j.jpowsour.2006.05.052View Article
- Guo S, Dong S, Wang E: Pt/Pd bimetallic nanotubes with petal-like surfaces for enhanced catalytic activity and stability towards ethanol electrooxidation. Energy Environ Sci 2010, 3: 1307. 10.1039/c0ee00053aView Article
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