Facile synthesis of AgPt nano-pompons for efficient methanol oxidation: Morphology control and DFT study on stability enhancement

https://doi.org/10.1016/j.jiec.2022.01.028Get rights and content

Highlights

  • N-GQDs served as morphology guiding and dispersing agents.

  • N-GQDs/AgPt NFs exhibite excellent electrocatalytic activity, CO tolerance and stability toward MOR in alkaline media.

  • The introduction of Ag into Pt-based catalysts can greatly enhance the adsorption of CO on Pt and promote the transformation of CO to COOH.

Abstract

Facile synthesis of more dendritic and uniform Pt-based nanostructures with carbon materials could greatly reduce cost and increase Pt utilization for methanol oxidation reaction (MOR) in direct methanol fuel cell (DMFC). This study reports a novel one-pot method to fabricate AgPt nano-pompons (AgPt NPs) with the guidance of N-GQDs through AA reduce the precursor of Ag and Pt. Morphology characterization describes N-GQDs as morphology guiding and dispersing agents to regulate the dendrite formation of nano-pompons. Under the optimized conditions, the AgPt NPs (Ag1Pt2) display above 11 times improvement in electrocatalytic activity and higher stability for the MOR compared with Pt/C catalysts. Density function theory (DFT) studies prove that the introduction of Ag can greatly enhance the adsorption of CO on Pt and promote the transformation of CO to COOH. The facile synthetic method and excellent MOR performance endow AgPt NPs with great application prospect in DMFCs as an anode catalyst.

Introduction

Direct methanol fuel cell (DMFC) has enormous potential as an energy conversion equipment owing to its high theoretical energy conversion efficiency (97 %), low environmental pollution, and easy storage [1], [2], [3], [4], [5]. Platinum (Pt) has been discovered as the most effective catalyst for the methanol oxidation reactive (MOR) of DMFC. However, the high price and rarity of pure Pt limit the widespread deployment of DMFC in practical application [6], [7], [8], [9], [10]. Moreover, the MOR mainly consists of continuous dehydrogenation of methanol, yielding CO species absorb onto the Pt surface (Pt-COads) and poison the Pt surface via encroaching catalytically active sites, resulting in a serious reduction in catalytic efficiency [11], [12], [13]. The development of a high active electrocatalyst that minimize the dosage of Pt necessary and enhances the CO tolerance of Pt for MOR is the pursuit of researchers.

Pt can be combined with cheaper transition metal (M) such as Ni [14], [15], Ag [16], or Co [17] et al. to improve the CO tolerance and catalytic activity for MOR [18]. There are two main effects of doping other atoms to improve the CO tolerance of Pt, one is ligand effect that doping M atoms can weaken the adsorption strength of CO on Pt. For instance, concave PtCo nanocrosses reported by Li et al. exhibited outstanding reaction kinetics of MOR, due to the ligand effect between Co and Pt atoms weakens the Pt-COads adsorption energy, which is conductive to CO desorption from Pt surface [19]. The other is bifunctional mechanism that promoted the transformation of CO to COOH. Ishikawa et al. demonstrated that doping Sn, Ru, and Ge of Pt promotes greater dissociation of H2O into ·OH than pure Pt, which facilitates that the conversion of CO to COOH [20]. Silver (Ag) as an ideal metal doped with Pt not only reduces cost of electrocatalysts but also more easily to alloy with Pt than other transition-metals (Cu, Ni, and Co et al.) [21], [22], [23]. But at the moment, there have been few studies have to research the mechanism of anti-CO poisoning on the surface of AgPt alloy for MOR.

It is known that the MOR active sites are mainly located on the surface of electrocatalysts so that the surface structure is an important factor in evaluating the performance of electrocatalytic [24]. Increasing the exposure of active sites on Pt surface via controlling the composition, size, and morphology of electrocatalysts can efficiently promote MOR activity. Hence, a variety of Pt-based nanostructures were developed, including core–shell [25], porous [26], hollow dendrites [27], and nano-pompons [28]. Among these morphologies, the nano-pompons have attracted plenty of attention owing to their higher specific surface area and low coordination number atoms at the edges, providing more reaction sites for the adsorbates involved in a close range [29]. Traditional synthesis strategies of nano-pompons are usually based on seed growth methods, which are complication and time-consuming. A facile and general method is desirable for the large-scaled preparation of novel Pt-based nano-pompons catalysts. Moreover, the introduction of carbon-based materials as the suitable morphology guiding agents and dispersing agents is an effective method to regulate the shape, size, and structure. Among the carbon-based materials, N-doped graphene quantum dots (N-GQDs) have more functional groups, effective tuning of electronic, and excellent assist in dispersing the metal nanomaterials than GQDs [30], [31]. Meanwhile, the N-GQDs have been reported that it is conducive to providing many anchoring sites for the adsorption of metal ions and supplying more active sites for the MOR [32], [33].

Herein, we develop a facile one-pot method at room temperature to fabricate silver-platinum nano-pompons (AgPt NPs) with the guidance of N-GQDs. In this process, N-GQDs as morphology guiding and dispersing agents to prepare homogeneous dendrite structures. Furthermore, the catalytic performance for MOR of AgPt NPs was evaluated in alkaline solution, and the measurements demonstrate that AgPt NPs exhibit enhanced MOR catalytic activity and long-term stability, which are better than commercial Pt/C. Density function theory (DFT) studies demonstrate that the adsorption of CO on AgPt alloy surface is enhanced compared with pure Pt surface, which is beneficial to the transformation of CO to COOH in the bifunctional mechanism.

Section snippets

Chemicals

All reagents used in this work were of analytical grade and all solutions were prepared using secondary distilled water. Silver nitrate (AgNO3), chloroplatinic acid hexahydrate (H2PtCl6·6H2O), citric acid, urea, ascorbic acid (AA) were purchased from Aladdin.

Synthesis of N-GQDs

The N-GQDs were synthesized by referring to previous study [34], 1.7 g urea and 2.0 g citric acid were dissolved into 50 mL secondary distilled water at room temperature. Then, the above solution was transferred into 100 mL Teflon lined

Characterization

The morphologic and crystalline structures of the AgPt NPs were characterized with transmission electron microscopy (TEM). Typical TEM image (Fig. 1a) of N-GQDs shows that they are dispersed uniformly with an average diameter of 2.67 ± 0.7 nm. The ultraviolet–visible (UV–vis) absorption spectra of N-GQDs (Fig. S1) displays two clear absorption peaks at 234 nm (π->π* of C = C) and 328 nm (n->π* of C = O) [34]. The TEM images of AgPt NPs, Fig. 1b and c, exhibit clear spiny dendrites and lots of

Conclusions

In summary, the AgPt NPs with abundant dendrites have been synthesized by a facile one-pot strategy. Due to the high surface active areas and electronic effects, the optimized AgPt NPs electrocatalysts show above 11 times increase in mass activity for MOR and excellent stability compared to commercial Pt/C catalysts. N-GQDs with high specific surface area and high electron mobility increase the catalytic activity of AgPt alloy. The introduction of Ag facilitates the chemical desorption of

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

Financial was sponsored by the National Natural Science Foundation of China (21165016, and 21265018), the Science and Technology Support Projects of Gansu Province (Nos.1011GKCA025, and 1208RJZM289), the Postgraduate Research Funding Projects of Northwest Normal University (2020KYZZ001163) and Outstanding Graduate Student Innovation Star project of Gansu (2021CXZX-292).

Reference (58)

  • U.B. Demirci

    J. Power Sources

    (2007)
  • L. Gong et al.

    J. Energy Chem.

    (2018)
  • X.H. Yan et al.

    J. Power Sources

    (2016)
  • M.G.F. Sales et al.

    Biosens. Bioelectron.

    (2017)
  • P. Majidi et al.

    Electrochim. Acta

    (2016)
  • N. Bhuvanendran et al.

    Int. J. Hydrogen Energy

    (2020)
  • F. Shao et al.

    Int. J. Hydrogen Energy

    (2017)
  • G. Sheng et al.

    J. Colloid Interface Sci.

    (2018)
  • R. Baronia et al.

    Int. J. Hydrogen Energy

    (2017)
  • M.-S. Liao et al.

    Surf. Sci.

    (2000)
  • F.Q. Shao et al.

    J. Colloid Interface Sci.

    (2017)
  • J. Lv et al.

    Electrochim. Acta

    (2014)
  • A. Shafaei Douk et al.

    Int. J. Hydrogen Energy

    (2018)
  • Y. Yang et al.

    Chem

    (2018)
  • Y. Hu et al.

    J. Power Sources

    (2015)
  • H. Xu et al.

    J. Colloid Interface Sci.

    (2017)
  • Y. Yang et al.

    Biosens. Bioelectron.

    (2017)
  • Z. Li et al.

    J. Electroanal. Chem.

    (2017)
  • S.-S. Chen et al.

    Sens. Actuators, B

    (2017)
  • F. Shao et al.

    Electrochim. Acta

    (2016)
  • A. Muthurasu et al.

    Int. J. Hydrogen Energy

    (2018)
  • A.B. Yousaf et al.

    Electrochim. Acta

    (2016)
  • J. Cao et al.

    J. Power Sources

    (2015)
  • M.R. Kim et al.

    Appl. Catal. B

    (2011)
  • Q. Liu et al.

    J. Colloid Interface Sci.

    (2018)
  • L. Liu et al.

    Electrochim. Acta

    (2016)
  • L. Hong et al.

    Comput. Theor. Chem.

    (2012)
  • D. Ma et al.

    Appl. Surf. Sci.

    (2016)
  • X. Liu et al.

    Appl. Surf. Sci.

    (2014)
  • Cited by (8)

    • Electrodeposited Pd nanoparticles on polypyrole/nickel foam for efficient methanol oxidation

      2023, International Journal of Hydrogen Energy
      Citation Excerpt :

      Correspondingly, more effective catalysts in terms of electrocatalyst activity and stability are vital to boost the performance of DMFCs and further large-scale commercialization, as well [12]. In that propose, numerous studies on the electrooxidation of methanol on platinum (Pt) based materials have been conducted to consider it as a promising materials for DMFCs [13–21]. Yet, the low abundance, high cost and high carbon monoxide (CO) poisoning restrict their widespread applications in DMFCs [22,23].

    View all citing articles on Scopus
    View full text