Fast microwave-assisted solvothermal synthesis of metal nanoparticles (Pd, Ni, Sn) supported on sulfonated MWCNTs: Pd-based bimetallic catalysts for ethanol oxidation in alkaline medium

Abstract

The preparation of metal nanoparticles (Pd, Ni, Sn) supported on sulfonated multi-walled carbon nanotubes (SF-MWCNTs) using a very rapid microwave-assisted solvothermal strategy has been described. Electrocatalytic behavior of the SF-MWCNT-Pd and its 'mixed' bimetallic electrocatalysts (i.e., SF-MWCNT-PdSn mix and SF-MWCNT-PdNi mix ) towards ethanol oxidation in alkaline medium was investigated. The result shows that the mixed Pd-based catalysts (obtained by simple ultrasonic-mixing of the individual MWCNTmetal nanocomposites) gave better electrocatalytic activity than their alloy nanoparticles (obtained by co-reduction of metal salts) or Pd alone. The SF-MWCNT platform gave better electrocatalytic performance compared to the unsulfonated and commercial Vulcan carbons. Detailed electrochemical studies (involving cyclic voltammetry, chronoamperometry, chronopotentiometry, and impedance spectroscopy) prove that the electrocatalytic oxidation of ethanol at the SF-MWCNT-PdNi mix platform is more stable, occurs at lower potential, gives lower Tafel slopes, with faster charge-transfer kinetics compared to its SF-MWCNT-PdSn mix counterpart. Also, result revealed that SF-MWCNT-PdNi mix is more tolerant to CO poisoning than the SF-MWCNT-PdSn mix . The results provide some important insights into the electrochemical response of microwavesynthesised Pd-based bimetallic catalysts for potential application in direct ethanol alkaline fuel cell technology. Instruments and ProceduresThe transmission electron microscope (TEM) micrographs were obtained using a JEOL 2010 TEM system operating at 200 kV. The Results and discussion Significance of the microwave synthetic methodScheme 1 summarises the synthetic process adopted in this work.To our knowledge, this is the first instance microwave-assisted synthetic strategy has been employed to support Pd, Ni and Sn nanoparticles onto sulfonate-functionalized MWCNTs. Microwave method is highly advantageous over the conventional borohydride reduction methods; the reaction mechanism of microwave methodology is described elsewhere [28,30]. The MWAS method provides a uniform nucleation environment and offers highly crystalline monodispersed metal nanoparticles. In this method, ethylene glycol (EG) was used as the solvent, as it can be rapidly heated by microwave radiation, provides the reducing environment for the reaction to prevent the oxidation of the metal catalysts, acts as a stabiliser, limiting particle growth, and prohibiting agglomeration. The metal ions coordinate with the functional groups (i.e., -COOH, -C=O, and -SO 3 H) on the MWCNTs, functioning as a nucleation precursors that are finally reduced to produce metal 12 nanoparticles on the MWCNTs. The pH of the synthesis solution greatly influences the stability and size of metal particles. EG is believed to be oxidized to acetic acid at high pH which then acts as a stabilizer. Thus, in this work, the synthesis pH was increased to ~7.4 as reported by Zhao et al.[31]. forms. In addition, figure 4b shows the detailed spe...

Preparation of cobalt silicide on graphene as Pt electrocatalyst supports for highly efficient and stable methanol oxidation in acidic media

“…At the same time, CoSi supported on graphene can prevent the aggregation of nanosheets and produce much more nanoparticle dispersion and utilization on its surface, therefore, nanoparticles can be loaded on both sides of graphene, which can also played an important role in the improvements of the electrocatalytic performance. We also found that the anodic peak current density of the Pt/CoSi-graphene is 5-20 times higher than other reported Pt-base electrocatalysts at the similar electrochemical reaction conditions [35][36][37][38][39][40][41][42].…”

Electrochemical behavior of electrodeposited Pd and PdNi coatings for the ethanol oxidation reaction in alkaline solution

“…The results of the Tafel polarization study corroborate the findings of CV. Nearly the same values of Tafel plots were obtained on graphene supported NiPd binary catalysts [6], binary composite films of Pd and Ni on multiwalled carbon nanotubes (MWCNT) [36], carbon supported PdNi nanoparticles [35,37] and rather higher on PdNi nanoparticles supported on sulfonated MWCNT [38]. Figure 6 shows the CVs obtained at Pd 0.74 Ni 0.26 catalyst in 1 M NaOH +1.0 M C 2 H 5 OH solution at different scan rates.…”

Electrocatalytic oxidation of ethylene glycol at palladium-bimetallic nanocatalysts (PdSn and PdNi) supported on sulfonate-functionalised multi-walled carbon nanotubes

“…showed enhanced electrocatalysis towards alcohol than that by co-reduction of the metals [22,24]. In this work, we use XPS as a further proof for the formation of alloy.…”

“…To our knowledge the only known work is that by Sun et al [23] where the authors used Pd nanoparticles supported on sulfonate-functionalised multi-walled carbon nanotubes (SF-MWCNTs). Recently, it was shown that Pd bimetallic catalysts on SF-MWCNTs exhibit better performance towards ethanol electro-oxidation compared to monodispersed Pd nanoparticles [22,24]. Thus, motivated by the paucity of literature on EG electro-oxidation on Pd alloy catalysts in alkaline media, and the poor performance of monodispersed Pd nanocatalysts compared to the Pd bimetallic catalysts, we decided to investigate the electrocatalytic behavior of the Pd bimetallic catalysts (SF-MWCNT-PdNi and SF-MWCNT-PdSn) towards the oxidation of EG in alkaline medium.…”