Elsevier

Nano Energy

Volume 27, September 2016, Pages 475-481
Nano Energy

Ultralow content of Pt on Pd–Co–Cu/C ternary nanoparticles with excellent electrocatalytic activity and durability for the oxygen reduction reaction

https://doi.org/10.1016/j.nanoen.2016.07.038Get rights and content

Highlights

  • Pd–Co–Cu ternary alloy nanoparticles are prepared via a simple impregnation reduction method.

  • Ultralow Content of Pt is coated on Pd6CoCu/C nanoparticle by using a spontaneous displacement strategy.

  • The core-shell Pd6CoCu@Pt/C nanoparticles exhibit superior electrocatalyst activity and stability for ORR relative to Pt/C.

Abstract

Optimizing the utilization of Pt to catalyze the sluggish kinetics of the oxygen reduction reaction (ORR) is of vital importance in proton exchange membrane fuel cells. One of the strategies is to spread Pt atoms over the surface of a substrate to increase the surface area. Here we report a facile method to synthesize Pd6CoCu@Pt/C core-shell nanoparticles with an ultralow amount of Pt. It was found that Pt-coated layer on Pd6CoCu cores plays a vital role in enhancing the ORR activity and the cycling stability. The half-wave potential of Pd6CoCu@Pt/C positively shifts about 50 mV and 17 mV relative to Pd6CoCu/C and Pt/C, respectively. The Pt mass activity on Pd6CoCu@Pt/C was calculated to be about 27 times higher than that on Pt/C catalysts at 0.9 V. Moreover, the Pd6CoCu@Pt/C nanoparticles exhibit superior stability with almost no decay for the ORR polarization curves during 10,000 potential cycles and the core-shell structure remains with only a slight increase in the thickness of the Pt overlayer. These findings provide a methodology for synthesizing highly efficient catalytic materials for the cathodic application in fuel cells.

Graphical abstract

A facile method is reported to synthesize Pd6CoCu@Pt/C core-shell nanoparticles with an ultralow amount of Pt. It is found that Pt-coated layer on Pd6CoCu cores plays a vital role in enhancing the ORR activity and the cycling stability. The half-wave potential of Pd6CoCu@Pt/C positively shifts about 50 mV and 17 mV relative to Pd6CoCu/C and Pt/C, respectively. The Pt mass activity on Pd6CoCu@Pt/C was calculated to be about 27 times higher than that on Pt/C catalysts at 0.9 V. Moreover, the Pd6CoCu@Pt/C nanoparticles exhibit superior stability with almost no decay.

fx1
  1. Download : Download high-res image (136KB)
  2. Download : Download full-size image

Introduction

Proton exchange membrane fuel cells (PEMFCs) have long been considered as a promising energy conversion technology for transportation and stationary application owing to their high efficiency, high power and energy densities, and the lower environmental impact [1]. However, this technology is limited in part by the sluggish kinetics of the oxygen reduction reaction (ORR) and the poor long-term durability of the catalytic materials [2], [3], [4], [5]. Pt as a key electrocatalytic element for the ORR is limited by the high cost and scarcity [6], [7]. In addition, the high overpotential of the ORR and the problem of poisoning of the Pt electrode by the reactive intermediates CO, HCHO, etc. delay the practical applications [8], [9], [10]. Therefore, it is necessary to explore low-cost materials with high electrocatalytic activity and outstanding durability for the ORR.

Numerous efforts have been devoted to reducing the loading of Pt or exploring non-Pt catalysts [11], [12], [13], [14], [15]. To date, Pd-based catalysts have attracted particular attention because Pd possesses similar properties to Pt. Importantly, the cost of Pd is lower and the reserve is more abundant than that of Pt [16]. It has been reported that the activity of the alloy of Pd with selected 3d-transition metals, such as Fe, Co, Ni, Cu, V, et al., significantly enhances the ORR activity by tuning the strain and ligand effect, causing a downward shift of the D-band center and reducing the binding strength of the adsorbed intermediates [14], [17], [18], [19], [20]. However, the catalytic activity of Pd-based catalysts exhibits significant degradation after potential cycling due to the dissolution of Pd and the 3d-transition metals [21]. In this regard, fabricating core-shell structured nanoparticles with a Pt shell coated on the Pd-based core is one promising strategy to improve the catalytic activity and durability of Pd-based electrocatalysts [4], [5], [22], [23]. Previous studies demonstrated that the Pt shell can be obtained through the Cu underpotential deposition (UPD) strategy, annealing-induced segregation, as well as dealloying [16], [24], [25], [26], [27]. However, a scalable and cost-saving strategy is lacking for the synthesis of the Pt on Pd core-shell electrocatalytic materials for the ORR.

Herein, Pd6CoCu/C ternary alloy nanoparticles were prepared by using a simple impregnation reduction method followed by a high temperature treatment in H2 atmosphere to obtain a Pd-rich shell. The electrochemical results show that even though the catalytic activity and durability of Pd6CoCu/C is enhanced compared with Pd/C, further improved is needed for practical applications. To achieve the goal, Pd6CoCu/C nanoparticles were then decorated with an ultralow amount of Pt via a very simple and scalable spontaneous displacement reaction. The obtained Pd6CoCu@Pt/C core-shell nanoparticles exhibit high ORR electrocatalytic activity and long-term stability superior to those of Pt/C. The method described in the present work is designed toward producing catalytic materials with high utilization of Pt on a large scale.

Section snippets

Synthesis of Pd6CoCu/C and Pd6CoCu@Pt/C nanoparticles

Carbon supported Pd6CoCu nanoparticles with 20 wt% Pd were synthesized by a facile impregnation reduction method. In detail, 67 mg of PdCl2, 14.9 mg of CoCl2·6H2O and 10.7 mg of CuCl2·2H2O were first dissolved in deionized water, and 152 mg of Vulcan XC-72 carbon were then dispersed in the solution. By interchanging magnetic stirring at 60 °C with ultrasonic blending, a smooth and thick slurry formed. After drying at 60 °C in a vacuum overnight, the resulting precursor was ground in an agate mortar,

Results and discussion

The XRD patterns of Pd6CoCu/C show typical face centered cubic (fcc) structure as Pd/C with four diffraction peaks correspond to (111), (200), (220) and (311) planes (Fig. S1, supporting information). However, the diffraction peaks position of Pd6CoCu/C shift to higher angles relative to Pd/C. The shift of diffraction peaks indicates the alloy formation between Pd and Co/Cu, causing a lattice contraction of Pd. In addition, the particle size of Pd6CoCu/C calculated to be 8 nm, which is smaller

Acknowledgment

This work was supported by the National Natural Science Foundation (21306060, 21573083), the Program for New Century Excellent Talents in Universities of China (NCET-13-0237), the Doctoral Fund of Ministry of Education of China (20130142120039), the Fundamental Research Funds for the Central University (2013TS136, 2014YQ009). We thank Analytical and Testing Center of Huazhong University of Science and Technology for allowing us to use its facilities. S/TEM work was carried out at the Center for

Sufen Liu obtained her Master's degree in the School of Chemistry and Chemical Engineering at Huazhong University of Science and Technology (HUST), under the supervision of Prof. Deli Wang. Her present research interests focus on the synthesis of Pd-based nanocatalysts and its application in proton exchange membrane fuel cells (PEMFCs).

References (28)

  • J.-N. Zheng et al.

    Electrochim. Acta

    (2014)
  • F. Garin

    Catal. Today

    (2004)
  • J. Zhao et al.

    J. Power Sour.

    (2011)
  • M.K. Debe

    Nature

    (2012)
  • B.C. Steele et al.

    Nature

    (2001)
  • J. Greeley et al.

    Nat. Chem.

    (2009)
  • M. Shao et al.

    J. Am. Chem. Soc.

    (2010)
  • K. Sasaki et al.

    Nat. Commun.

    (2012)
  • E. Antolini

    Energy Environ. Sci.

    (2009)
  • T. Yen et al.

    Appl. Phys. Lett.

    (2003)
  • G. Hoogers

    Fuel Cell Technology Handbook

    (2002)
  • D.L. Wang et al.

    ACS Nano

    (2015)
  • Z.S. Wu et al.

    Adv. Mater.

    (2012)
  • C. Wei et al.

    Chem. Commun.

    (2014)
  • Cited by (0)

    Sufen Liu obtained her Master's degree in the School of Chemistry and Chemical Engineering at Huazhong University of Science and Technology (HUST), under the supervision of Prof. Deli Wang. Her present research interests focus on the synthesis of Pd-based nanocatalysts and its application in proton exchange membrane fuel cells (PEMFCs).

    Weiping Xiao obtained her bachelor degree from Qufu Normal University. She is currently pursuing her pH. D. in the School of Chemistry and Chemical Engineering at Huazhong University of Science and Technology (HUST), under the supervision of Prof. Deli Wang. Her present research interests focus on synthesis of Pd-based nanomaterials and its application in proton exchange membrane fuel cells (PEMFCs).

    Jie Wang obtained his bachelor degree from Qingdao Agricultural University. He is currently pursuing his pH. D. in the School of Chemistry and Chemical Engineering at Huazhong University of Science and Technology (HUST), under the supervision of Prof. Deli Wang. His present research interests focus on synthesis of three-dimensional nanomaterials and its application in energy conversion and storage.

    Jing Zhu received her B.S. from Huazhong University of Science and Technology (HUST). She is currently pursuing her master's degree under the supervision of Prof. Deli Wang. Her present research interests focus on synthesis of Pt-based intermetallic nanocatalysts and its application in proton exchange membrane fuel cells (PEMFCs).

    Zexing Wu received his B.S. from Binzhou University. He is a pH. D. candidate in the School of Chemistry and Chemical Engineering at Huazhong University of Science and Technology (HUST). His present research interest mainly focus on through polymer and solvothermal methods to prepare electrocatalysts.

    Huolin Xin is a staff scientist in the Center for Functional Nanomaterials at Brookhaven National Laboratory. He is also an adjunct faculty member at Stony Brook University. His primary field of expertize lies in developing novel 3-D, atomic-resolution, and in-situ spectroscopic and imaging tools to probe the structural, chemical, and bonding changes of energy materials during chemical reactions or under external stimuli.

    Deli Wang received her pH.D. from Wuhan University in 2008. And then she joined in Nanyang Technological University working as a research fellow for 1 year. She moved to Cornell University in 2009, joined in Energy Materials Center at Cornell (EMC2) as a postdoctoral associate for 3 years. In 2012, she came back to China. She is currently a professor of School of Chemistry and Chemical Engineering, Huazhong University of Science & Technology (HUST). Her research interests mainly focused on nanomaterials for energy conversion and storage.

    View full text