Elsevier

Journal of Power Sources

Volume 301, 1 January 2016, Pages 160-169
Journal of Power Sources

Ultrafast synthesis of flower-like ordered Pd3Pb nanocrystals with superior electrocatalytic activities towards oxidation of formic acid and ethanol

https://doi.org/10.1016/j.jpowsour.2015.09.114Get rights and content

Highlights

  • Pd3Pb nanocrystals with different morphologies were synthesized by various methods.

  • Ordered flower-like Pd3Pb obtained within 10 s by polyol method.

  • Superior catalytic activities in formic acid and ethanol oxidation compared to Pd/C.

  • Pd3Pb catalysts were found to be more stable compared to commercial Pd/C.

Abstract

Ordered intermetallic nanocrystals with high surface area are highly promising as efficient catalysts for fuel cell applications because of their unique electrocatalytic properties. The present work discusses about the controlled synthesis of ordered intermetallic Pd3Pb nanocrystals in different morphologies at relatively low temperature for the first time by polyol and hydrothermal methods both in presence and absence of surfactant. Here for the first time we report surfactant free synthesis of ordered flower-like intermetallic Pd3Pb nanocrystals in 10 s. The structural characteristics of the nanocrystals are confirmed by powder X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. The as synthesized ordered Pd3Pb nanocrystals exhibit far superior electrocatalytic activity and durability towards formic acid and ethanol oxidation over commercially available Pd black (Pd/C). The morphological variation of nanocrystals plays a crucial role in the electrocatalytic oxidation of formic acid and ethanol. Among the catalysts, the flower-like Pd3Pb shows enhanced activity and stability in electrocatalytic formic acid and ethanol oxidation. The current density and mass activity of flower-like Pd3Pb catalyst are higher by 2.5 and 2.4 times than that of Pd/C for the formic acid oxidation and 1.5 times each for ethanol oxidation.

Graphical abstract

A facile and ultrafast method was employed for the synthesis of ordered Pd3Pb. The material showed outstanding catalytic activity towards ethanol and formic acid oxidation compared to the commercial Pd on carbon support.

  1. Download : Download high-res image (274KB)
  2. Download : Download full-size image

Introduction

Direct liquid fuel cells such as direct formic acid fuel cell (DFAFCs), direct ethanol fuel cell (DEFCs) have attracted a considerable attention as new generation power sources [1], [2], [3]. The design of efficient anode catalyst for the oxidation of small organic molecules (SOMs), like formic acid (HCOOH), ethanol (EtOH) and methanol (MeOH) has become an active area of research [4], [5], [6], [7]. In general, Pt [8] and Pt based alloys and intermetallics (PtPb [9], [10], Pt3Pb [11], [12], PtSn [13], PtBi [9], PtCo [14], PtZn [15], AuPt [16] PtM [M = Ni, Cu, Mn, Cr, V, Co] [17], [18], [19], [20]) are mostly considered as efficient anode materials in the fuel cells. But, one of the major problems for Pt based catalysts is carbon monoxide (CO) poisoning [21]. Alternatively, Pd nanoparticles (NPs) are found to be more active than the commonly used Pt catalysts in catalyzing formic acid oxidation (FAO) reaction in polymer electrolyte membrane fuel cells [22]. The enhancement in the adsorption/dissociation of HCOOH on Pd surface is believed to be the limiting step for the improvement of FAO activity [23]. The desired enhancement of adsorption/dissociation properties can be achieved through alloying Pd with oxophilic metals (M) like Co and Cu through so called ligand effect, which basically needs manipulating Pd-M bonding [21]. Alloys [24], bimetallics [25] and intermetallics [26], [27] based on Pd have exhibited excellent catalytic activity for formic acid oxidation as compared to Pt due to their ability to oxidize HCOOH to carbon dioxide (CO2) in direct pathway by avoiding the formation of CO [21].

Along with HCOOH, EtOH is also considered as a promising alternative fuel. Alkaline membrane DEFCs have already been considered as promising power source for different electronics and automobiles due to enhanced kinetics of electro-oxidation in alkaline medium [11]. Although Pt based NPs are considered as the best catalysts for Ethanol Oxidation Reaction (EOR) [11], [28], Pd based catalysts have also been widely studied in recent times as an alternative to Pt because of its low cost, greater abundance, good resistance to CO poisoning and high catalytic activity [29], [30]. Many alloys and oxide supported Pd-M (M = Ru, Cu, Au, Ni, Ag, Sn, Ir, Co and Pb) binary electrocatalysts have exhibited improved electrocatalytic activity for ethanol oxidation [14], [31], [32], [33], [34], [35], [36], [37], [38]. Shape tailored Pd and Pd based alloy nanocrystals are also found to exhibit enhanced electrocatalytic activity [39], [40]. Although alloys and bimetallics are promising materials, they suffer from surface segregation of metal atoms and surface poisoning by CO due to insufficient quantities of bimetallic elements on the surface [11]. In contrast to disordered alloy/bimetallic, ordered intermetallic compounds, such as PtPb, PtBi, Pt3Ti, Pt3V have shown excellent electrocatalytic performance towards HCOOH, EtOH, MeOH oxidation in terms of current density and CO tolerance [41], [42]. The advantage of ordered structure comes from its uniform surroundings of active sites. The number and distance between active sites play an important role in the catalytic activity. However it is very difficult to synthesize ordered intermetallic nanomaterial by low temperature solution based synthesis. Usually it requires post synthetic high temperature heat treatment to achieve ordered structure [42].

Inspired by the good catalytic activity of Pd, promoting effect of Pb [10], [11], [38], [43] and effect of ordered structure on the electrooxidation of alcohols and other organic fuels, herein, for the first time we report a facile ultrafast synthesis of flower-like and interconnected network type ordered Pd3Pb intermetallic nanocrystals at low temperature by solution based methods (hydrothermal, polyol). To the best of our knowledge, this is the first report on the surfactant free synthesis of flower-like ordered nanomaterials within 10 s. Interestingly, Pd3Pb has formed within 10 s by polyol method, which could presumably be due to ultrafast diffusion of constituent elements leading to the formation of an ordered intermetallic compound. We have studied the electrochemical oxidation of HCOOH in acidic medium and EOR in alkaline medium using the Pd3Pb catalysts synthesized at different conditions. The increase in catalytic activity for the compound formed by polyol method in ultrafast condition clearly indicates that the morphology of the nanoparticles plays a crucial role in the electrocatalysis. The electrocatalytic activity of all the different shaped Pd3Pb nanomaterials exhibited superior performance to the commercial Pd/C.

Section snippets

Chemicals

Potassium tetrachloropalladate (K2PdCl4), palladium acetylacetonate (Pd(acac)2), sodium borohydride (NaBH4) and nafion binder (5 wt%) were purchased from Sigma–Aldrich, lead acetate trihydrate (Pb(OAc)2·3H2O) and polyvinyl pyrrollidone (PVP) were purchased from SDFCL and tetra ethylene glycol (TEG) was purchased from Alfa Aesar. All the chemicals (more than 99% purity) were used as purchased without further purification. Millipore water of resistivity 18.2 MΩcm was used for the synthesis and

Structure, synthesis, shape and morphology

The compound Pd3Pb is a primitive cubic system having Cu3Au structure type with Pm3¯m space group [44]. A typical representation of the unit cell of the Pd3Pb crystal structure in comparison with Pd structure is shown in Fig. 1d. Pure palladium metal has a face centered cubic crystal structure (Fm3¯m) where all the corners and faces are occupied by the Pd atoms (Wyckoff no. 4a). Whereas, in Pd3Pb the Pb atoms occupy the corner positions (Wyckoff no. 1a) and the Pd atoms occupy half of the

Conclusion

A facile and ultrafast synthetic method has been employed for the preparation of Pd3Pb intermetallic nanoparticles in different morphologies for the first time. The synthesis methods can be extended for the formation of other Pd and group IV metal based intermetallics by choosing appropriate precursor salts. The electrochemical oxidation of formic acid and ethanol were studied on Pd3Pb nanocrystals of different shapes and morphologies in different supporting electrolytes (KOH, HClO4). Among all

Acknowledgments

We thank Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Sheikh Saqr Laboratory and Department of Science and Technology, India (DST) for financial support. R. K. J. thanks Council of Scientific and Industrial Research (CSIR), JNCASR and DST for research fellowship, U. S. thanks CSIR for research fellowship, and S. C. P thanks DST for Ramanujan Fellowship (Grant SR/S2/RJN-24/2010). We are grateful to Prof. C. N. R. Rao, F.R.S for his constant support and encouragement.

References (76)

  • S. Badwal et al.

    Appl. Energy

    (2015)
  • S. Sharma et al.

    J. Power Sources

    (2012)
  • X.W. Yu et al.

    J. Power Sources

    (2008)
  • X. Zhou et al.

    J. Power Sources

    (2013)
  • Z. Yan et al.

    J. Power Sources

    (2015)
  • Z. Liu et al.

    J. Power Sources

    (2008)
  • T. Gunji et al.

    J. Power Sources

    (2015)
  • D.-H. Kwak et al.

    J. Power Sources

    (2015)
  • L.-k. Tsui et al.

    J. Power Sources

    (2015)
  • M. Liao et al.

    J. Power Sources

    (2015)
  • E. Lee et al.

    J. Power Sources

    (2015)
  • Q.-S. Chen et al.

    J. Power Sources

    (2015)
  • M.A. Matin et al.

    J. Power Sources

    (2014)
  • Y.-H. Qin et al.

    J. Power Sources

    (2012)
  • D. Sun et al.

    J. Power Sources

    (2015)
  • L. Li et al.

    J. Power Sources

    (2014)
  • L. Ma et al.

    J. Power Sources

    (2013)
  • H. Na et al.

    J. Power Sources

    (2015)
  • Y.-Y. Feng et al.

    J. Power Sources

    (2013)
  • H. Yang et al.

    J. Power Sources

    (2014)
  • C. Peng et al.

    J. Power Sources

    (2015)
  • S. Shen et al.

    Electrochim. Acta

    (2010)
  • Y. Wang et al.

    J. Power Sources

    (2010)
  • G.C. Li et al.

    Electrochim. Acta

    (2006)
  • M. Ellner

    J. Less Common Met.

    (1981)
  • R. Larsen et al.

    J. Power Sources

    (2006)
  • S. Ha et al.

    J. Power Sources

    (2005)
  • Z. Liang et al.

    Electrochim. Acta

    (2009)
  • Z.-Y. Zhou et al.

    Electrochim. Acta

    (2010)
  • Z.L. Liu et al.

    J. Power Sources

    (2008)
  • U.B. Demirci

    J. Power Sources

    (2007)
  • J. Greeley et al.

    Surf. Sci.

    (2005)
  • B. Habibi et al.

    Int. J. Hydrogen Energy

    (2011)
  • N. Kakati et al.

    Chem. Rev.

    (2014)
  • H. Meng et al.

    Catalysts

    (2015)
  • Y. Wang et al.

    Catalysts

    (2015)
  • C. Roychowdhury et al.

    Chem. Mater.

    (2006)
  • Y.J. Kang et al.

    ACS Nano

    (2012)
  • Cited by (0)

    View full text