PtCu nanoframes as ultra-high performance electrocatalysts for methanol oxidation

https://doi.org/10.1016/j.ijhydene.2019.05.072Get rights and content

Highlights

  • PtCu nanoframes (NFs) were prepared successfully using PVP as a capping agent.

  • PtCu NFs display highly-open feature and good size uniformity.

  • The PtCu NFs catalysts show remarkably enhanced activity and durability for MOR.

Abstract

Despite tremendous progress has been achieved in the past two decades, the lack of high-performance catalysts suitable for long-term operation remains a great challenge in realizing the commercial application of direct methanol fuel cell technology. Here, we reported a simple approach for one-pot synthesis of PtCu alloy nanoframes along with their exciting electro-catalytic performance for methanol oxidation. PtCu alloys with highly-open nanoframe structures have been achieved in presence of a structure-directing agent like polyvinyl pyrrolidone (PVP) and reducing solvent like sodium borohydride. Such PtCu alloy nanoframes show tremendous improvement in the methanol electrooxidation with a highest mass activity of 1.64 A mgPt −1 (much lower onset potential compared to Pt alone), which is believed to be much higher compared to that of the commercial Pt/C catalyst and most of the literature reports, indicating a better alloy formation and highly active sites created by highly open nanoframes structures.

Introduction

Platinum has been employed widely as anode electrocatalyst for the oxidation of small organic molecules (e.g. methanol [1], [2], [3], formic acid [4], [5] and dimethyl ether [6] etc.) in fuel cells (FCs). However, scarce reserves and high cost hinder its widespread application in FCs. Moreover, platinum surface is easily poisoned by the CO-like intermediates, lead to the rapid decline in catalytic activity [7], [8]. Thus, every effort needs to be made to promote the activity and durability of platinum-based catalysts. Formation of binary or multicomponent alloys by combining Pt with transition metals (e.g. Pd, Ru, Fe, Co, Ni, Cu etc. [1], [9], [10], [11], [12].) is an effective strategy to achieve a substantial improvement in the electro-oxidation performance. For example, the PtRuFe alloy nanodendrites (NDs) synthesized via a one-pot synthetic strategy exhibited excellent catalytic activity and durability toward methanol oxidation reaction (MOR) [10]. Platinum-cobalt nanowires (PtCo NWs) with high-index crystal facts and ordered intermetallic structure were prepared through a wet-chemical approach by Bu and Huang [11], which exhibited much higher mass activities for both methanol and ethanol oxidation than that of the commercial Pt catalyst. Besides, many fundamental studies revealed that the catalytic performance of platinum depends greatly on the type and concentration of exposed crystal plane and high-index crystal facets generally exhibit higher activity compared to those stable basal facets, such as {111}, {100} and {110}, since they have abundant atomic steps, ledges, and kinks that can serve as catalytically-active sites [9], [13]. Therefore, platinum-based nanostructured materials with well-defined zero-dimensional (0D) or one-dimensional (1D) shapes (e.g. tetrahedra, octahedra, rhombic dodecahedral and rods/wires/tubes [14], [15], [16], [17], [18], [19], [20]) were highly concerned because these unique nanostructures not only produce abundant high-active crystal facets of Pt, but also have excellent structural stability.

Among various Pt-based alloy catalysts, PtCu alloys are increasingly attractive for MOR because of their high activity, strong anti-poisoning capability and low cost. Those PtCu catalysts with unique shapes (for example, hollow, dendritic and cubic nanocrystals) are widely confirmed to have excellent MOR performance [4], [12], [15], [16]. Herein, we achieved a PtCu alloy nanoframes (PtCu NFs) catalyst via a facile one-step co-reaction progress using sodium borohydride as the reductant and PVP as the capping agent. When adding PVP into the reaction solution, PtCu alloy nanoframes are achieved. Instead, in the absence of PVP, chain-like PtCu nanowires (PtCu NWs) are obtained. The PtCu NFs exhibit superior activity and durability for MOR than the PtCu NWs and commercial carbon-supported Pt catalysts.

Section snippets

Materials

Sodium hexachloroplatinate hexahydrate (Sigma-Aldrich), copper chloride dehydrate (Sinopharm Chemical), polyvinyl pyrrolidone (Sinopharm Chemical), sodium borohydride (Sinopharm Chemical), N,N-dimethylformamide (Sinopharm Chemical), toluene (Sinopharm Chemical), Vulcan XC-72R carbon black (Cabot), Pt/C (20 wt%, Johnson Matthey) and Nafion ionomer solution (5 wt %, Sigma-Aldrich). All chemicals were used as received without further purification.

Synthesis of PtCu NFs

Firstly, sodium borohydride (80 mg) and NaOH

Results and discussion

The TEM and HRTEM images of unsupported PtCu NFs obtained using PVP as the template are shown in Fig. 1a–c. A mean wall thickness of about 5 nm is observed for individual PtCu nanoframes (Fig. 1b). The lattice fringes with the interplanar spacing of ca. 0.21 nm indexed to the {111} planes of PtCu alloy are well discerned (the inset of Fig. 1c). The X-ray diffraction (XRD) pattern (Fig. 1d) further confirms the formation of PtCu alloy nanostructures. In addition, the PtCu nanoframes are

Conclusions

In summary, PtCu alloy nanoframes were synthesized successfully via a facile one-pot co-reduction approach. This one-pot synthetic approach can be used to synthesize other Pt-based alloy nanoframes such as PtFe and PtCo. Compared to the commercial Pt/C catalysts, PtCu nanoframes exhibit significantly improved catalytic activities for methanol electro-oxidation. This enhancement in activity is ascribed to the highly open structure of PtCu nanoframes, as well as the change in the electronic

Acknowledgements

We thank the National Natural Science Foundation of China (21573025 and 21773018), Natural Science Foundation of the Jiangsu Higher Education Institutions of China (17KJA150001), Foundation of Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology (BM2012110), Foundation of Top-notch Academic Programs Project of Jiangsu Higher Education Institutions (PPZY2015B145) and Foundation of Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, Changzhou University (

References (38)

  • W. Sugimoto et al.

    Kinetics of CH3OH oxidation on PtRu/C studied by impedance and CO stripping voltammetry

    J Electroanal Chem

    (2005)
  • F. Seland et al.

    Impedance study of methanol oxidation on platinum electrodes

    Electrochim Acta

    (2006)
  • Q. Wang et al.

    Hierarchical carbon and nitrogen adsorbed PtNiCo nanocomposites with multiple active sites for oxygen reduction and methanol oxidation reactions

    J Mater Chem

    (2016)
  • M.-X. Gong et al.

    PtCu nanodendrite-assisted synthesis of PtPdCu concave nanooctahedra for efficient electrocatalytic methanol oxidation

    Catal Sci Technol

    (2015)
  • Z. Cai et al.

    Ultrathin branched PtFe and PtRuFe nanodendrites with enhanced electrocatalytic activity

    J Mater Chem

    (2015)
  • L. Bu et al.

    Surface engineering of hierarchical platinum-cobalt nanowires for efficient electrocatalysis

    Nat Commun

    (2016)
  • X. Huang et al.

    Monodisperse Cu@PtCu nanocrystals and their conversion into hollow-PtCu nanostructures for methanol oxidation

    J Mater Chem

    (2013)
  • N. Tian et al.

    Synthesis of tetrahexahedral platinum nanocrystals with high-index facets and high electro-oxidation activity

    Science

    (2007)
  • Y. Zhang et al.

    Concave Pd-Pt core-shell nanocrystals with ultrathin Pt shell feature and enhanced catalytic performance

    Small

    (2016)
  • Cited by (29)

    • Improving the activity and CO tolerance by the nitrides-modified Pd/C electrocatalysts for methanol and formic acid oxidation reactions

      2022, International Journal of Hydrogen Energy
      Citation Excerpt :

      The EIS fitting data are obtained from the equivalent circuit (the inset of Fig. 4(f)) [74–77], which is obtained from a reaction model assuming two main reactions: the dehydrogenation reaction from CH3OH to COads and the oxidation reaction from COads to CO2 [74,75,78]. Rs represents the solution resistance of the electrolyte, CPE represents the constant phase element, Rct is the charge transfer resistance in the process of CH3OH dehydrogenation to COads, Rco is the charge transfer resistance in the process of COads oxidation to CO2, and Lco is the inductance of COads oxidation [75,77]. In Fig. 4(f), the appearance of obvious arcs indicates the existence of resistance components, where the larger capacitive arcs appear at high frequencies, and the smaller inductive arcs appear in the fourth quadrant at low frequencies.

    • One-step preparation of polyaniline-modified three-dimensional multilayer graphene supported PtFeO<inf>x</inf> for methanol oxidation

      2022, Synthetic Metals
      Citation Excerpt :

      It refers to the introduction of other substances that ionize water molecules at a lower overpotential and provide significant amounts of hydroxyl groups for the oxidation of CO toxicants [23,24]. Such as PtRu [25], PtFe [26–29], PtCo [30], PtNi [31], and PtCu [32]. In addition, doping of heteroatoms (e.g., B[33], N [34,35], P [36], and S [37]) with carbonaceous carriers and transition metal oxides [38–42], nitrides [43–46], carbides [47] and phosphides [48–50] have also been shown to be effective in enhancing the catalytic activity of Pt-based catalysts.

    • Thin layer vs. nanoparticles: Effect of SnO<inf>2</inf> addition to PtRhNi nanoframes for ethanol oxidation reaction

      2022, International Journal of Hydrogen Energy
      Citation Excerpt :

      The so-called nanoframes are the interesting variation of the polyhedral-shape nanoparticles, they not only expose specific crystal planes on their facets but also, due to their hollow interior, minimize the usage of the Pt or other precious metals [10]. Moreover, because of the open 3-D structures, nanoframes provide additional catalytically active sites for EOR [11] or other reactions [12,13]. Another important parameter that should be considered in the designing of the nanocatalysts is the size of the nanoparticles.

    View all citing articles on Scopus
    View full text