Unexpected facilitation of the pyrolysis products of potassium ferrocyanide to the electrocatalytic activity of a PdO based palladium iron composite catalyst towards ethanol oxidation reaction (EOR)

It was found, for the first time, that the pyrolysis products of potassium ferrocyanide (K₄[Fe(CN)₆]) could significantly promote the electrocatalytic activity of the PdO based palladium iron composite catalyst towards ethanol oxidation reaction (EOR). In this work, huge carbon spheres (abbreviated as HCSs) were prepared firstly via a pyrolysis method using glucose and 1-butyl-3-methylimidazolium tetrafluoroborate as the starting materials. Secondly, PdO based palladium iron composites supported on HCSs (noted as PdO–Pd–Fe/HCSs) were successfully fabricated through a pyrolysis procedure employing PdO·H₂O, HCSs and K₄[Fe(CN)₆] as the initial materials. When preparing PdO–Pd–Fe/HCSs, four different amounts of K₄[Fe(CN)₆] were respectively added in the preparation system producing four kinds of samples. The sample prepared in the absence of K₄[Fe(CN)₆] was nominated as sample b-0. And the samples prepared in the presence of 5, 10 and 20 mg K₄[Fe(CN)₆] were, respectively, labeled as sample b-5, b-10 and b-20. It was indicated by the XRD and XPS patterns that the metallic Pd particles were the main crystalline materials of above four samples. SEM images of all synthesized samples substantially demonstrated that the added amount of K₄[Fe(CN)₆] was a pivotal factor which could significantly affect the morphologies of the prepared samples. For sample b-0, besides some nanoparticles with a size close to 30 nm, a larger number of pores were created on the surface of the HCSs producing a honeycomb-shaped surface. Interestingly, aniseed shaped particles, cauliflower-like particles and irregular particles with a diameter more than 150 nm were, respectively, anchored on the HCSs surface of sample b-5, b-10 and b-20. Most of all, as indicated by CV and CA measurements, all the samples prepared in the presence of K₄[Fe(CN)₆] delivered much better electrocatalytic activities towards EOR when compared to the sample prepared with no addition of K₄[Fe(CN)₆]. For example, in the CV curves, the peak current density of the peak appearing in the positive potential scanning (peak f) for EOR on sample b-10 was nearly 6.4 times greater than that on sample b-0 (16.6 mA cm^?2 vs. 2.6 mA cm^?2). The significantly decreased charge transfer resistance and the remarkably enlarged electrochemical surface area were analyzed to be the main reasons for sample b-10 to exhibit the best electrocatalytic performance among all prepared samples. In general, a novel electrocatalyst consisting of PdO, Pd and the pyrolysis products of K₄[Fe(CN)₆] for EOR was developed in this work, which, due to its very lower preparation cost and its satisfied electrocatalytic activity towards EOR, was very helpful to the development of Pd-based EOR electrocatalyst.     

An ionic liquid-present hydrothermal method for preparing hawthorn sherry ball shaped palladium (Pd)-based composite catalysts for ethanol oxidation reaction (EOR)

For the first time, a hawthorn sherry ball shaped Pd-based composite catalyst for EOR was prepared via an ionic liquid-present two-step hydrothermal method in this work. In the first hydrothermal step, micron-scale solid carbon spheres (MSCS) were fabricated in the presence of glucose, an ionic liquid of 1-butyl-3-methyl tetrafluoroboric acid and one kind of surfactant. And in the second hydrothermal process, sesame like Pd particles were immobilized on the surface of MSCS forming a hawthorn sherry ball shaped Pd-based composite catalyst (denoted as Pd/MSCS) using PdO as the source of Pd. In the course of preparing MSCS, four kinds of surfactants were respectively employed desiring to study the influence of surfactant type on the physicochemical properties of the produced samples. The prepared MSCS and Pd/MSCS were examined majorly by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It was addressed by SEM images that in the presence of SDS and EDTA, hawthorn sherry ball shaped Pd-based composite catalysts were successfully prepared. XRD and XPS analysis substantially documented that metallic palladium was the main component of the synthesized Pd/MSCS catalysts. The electrocatalytic abilities of the Pd/MSCS catalysts for EOR were examined in 1 M C₂H₅OH alkaline solution mainly utilizing cyclic voltammetry (CV) and chronoamperometry (CA), illustrating that all produced Pd/MSCS catalysts had an electrocatalytic activity towards EOR, and the forward peak current density of EOR on the catalyst of Pd/MSCS (prepared in the presence of SDS) was 7 times larger, along with 60 mV decrease in the onset potential of EOR, than that on the Pd/MSCS (prepared with CATB) catalyst. Summarily, a very cost-effective and facile method for fabricating hawthorn sherry ball shaped Pd-based composite catalysts towards EOR was created in this work, which was very meaningful not only to the further development of EOR catalysts but also to the exploration of micron-devices.     

Using PdO and PbO as the starting materials to prepare a multi-walled carbon nanotubes supported composite catalyst (PdxPby/MWCNTs) for ethanol oxidation reaction (EOR)

For the first time, a novel composite catalyst, namely, a multi-walled carbon nanotubes (MWCNTs) supported palladium and lead catalyst (denoted as Pd_xPb_y/MWCNTs), was prepared through a hydrothermal method using PdO, PbO and MWCNTs as the starting materials. The electrocatalytic activities of the resultant catalysts towards EOR in 1M KOH were examined mainly by using CV, CA and EIS. The electrochemical measurement results indicated that the peak current of EOR in the forward potential scan on the catalyst of Pd₁Pb₁/MWCNTs was almost 9 times larger, plus about 100 mV decrease in the onset potential value of EOR, than that on the Pb-free catalyst. A very simple, cost-effective and scalable way to synthesize Pd and Pb composite electrocatalyst for EOR was presented in this work, which was very meaningful to the further commercialization of EOR.     

Graphitized carbon nanocages/palladium nanoparticles: Sustainable preparation and electrocatalytic performances towards ethanol oxidation reaction

Graphitized carbon (GC) nanocages have been successfully prepared via a sustainable carbon powder buried-type Ni catalysis-growth technology from Tween-80 molecule precursor. The GC nanocages are used as support for the further construction of GC/Pd electrocatalyst towards ethanol oxidation reaction. The material structures and surface morphologies are studied by XRD, SEM and TEM techniques. The electrochemical properties are investigated by CV, LSV, EIS and CP techniques. The results showed that GC nanocages have good graphited structure and plentiful opening gaps, and the Pd nanoparticles were evenly distributed on the inner and outer surfaces of GC nanocages. The GC/Pd electrocatalyst exhibits excellent electrocatalytic performance towards ethanol oxidation. The positive scanning peak current density of GC/Pd electrode is up to 1612 A/g Pd in 1.0 mol/L NaOH +1.0 mol/L ethanol electrolyte, which is much higher than those (500–1100 A/g Pd) of traditional Pd electrodes supported with carbon nanotubes or graphene nanosheets.     

Preparation of graphite carbon/Prussian blue analogue/palladium (GC/PBA/pd) synergistic-effect electrocatalyst with high activity for ethanol oxidation reaction

In this paper, newly graphite carbon/Prussian blue analogue/palladium (GC/PBA/Pd) synergistic-effect electrocatalyst for ethanol oxidation reaction were developed, with Co-based PBA (Co₃[Co(CN)₆]₂) as a co-catalyst. Structural analysis shows that the Co₃(Co(CN)₆)₂ nanoparticles were highly dispersed and inlaid on surface of GC nanosheets with outstanding structural stability. The GC/Co₃(Co(CN)₆)₂/Pd electrocatalyst exhibits significantly enhanced electrocatalytic activity towards ethanol oxidation with a maximum mass activity of 2644 A g^?1 Pd GC/Pd, which is more than double that of GC/Pd electrocatalyst (1249 A g^?1). Excellent electrochemical stability is also demonstrated for this GC/Co₃(Co(CN)₆)₂/Pd electrocatalyst. The enhanced electrocatalytic activity can be attributed to the synergistic effects of GC support and Co₃(Co(CN)₆)₂ promoter on the Pd electrocatalysts, in which Co₃(Co(CN)₆)₂ acts as a co-catalyst and GC acts as a conductive support.     

Facile-synthesis and shape-adjustment of irregular gravel-like PtPd nanocatalysts by three-dimensional hyperbranched polyamide (HBPA) with enhanced activity in ethanol oxidation

Direct ethanol fuel cells (DEFCs) technology as a promising clean-energy, is obstructed by unsatisfactory activity of ethanol oxidation reaction (EOR) nanocatalysts. Traditional shape-controllers usually lead to regular nanoparticles. Three-dimensional dendrimers, like hyperbranched polyamide (HBPA), however, have superiorities to form irregular morphologies, due to their multitudinous terminal functional groups and irregular interior cavities. Considering the lack of researches, herein, a novel HBPA was utilized to facilely and controllably synthesize irregular gravel-like PtPd nanoparticles (g-PtPd-NPs) with rich active sites. The synthetic mechanism was studied by both experiments and density functional theory calculations. N atoms of HBPA were proven essential. In EOR tests, the activity of g-PtPd-NPs was 2.05-fold of commercial Pt/C, and higher than PtPd catalysts of control sets and reports. The durability was excellent, too. This study is promotive for DEFCs into practice, and may enlighten more nanomaterials' synthesis.     

Methanol oxidation reaction on Ti/RuO2(x)Pt(1−x) electrodes prepared by the polymeric precursor method

In this work, ruthenium oxide films containing platinum nanoparticles were prepared using the polymeric precursor method on Ti substrates with several molar ratios. This paper aims at presenting the characterization of the Pt content effect in the methanol electrochemical oxidation reaction. The films were physically characterized using X-ray diffraction and both Pt and RuO₂ (rutile) phases were observed. The mean crystallite sizes were 6 nm for Pt and 25 nm for RuO₂. The X-ray photoelectronic results indicated that on the electrodes surfaces, depending on the substrate, there was RuO₂, Ru metal and Pt metal. Besides, it was not observed the formation of PtRu alloys. The atomic force microscopy images of the films showed highly rough surfaces. A decrease in the roughness mean square values is observed as the Pt content increases. These last results are similar to electroactive surface area values calculated by redox-couple (K₄FeCN₆/K₃FeCN₆). There was an increase in the globular size observed on the electrode surface and lower particle dispersion as the Pt content is increased from 12.5 to 75 mol%. Regarding the eletrode electrocatalytical behavior for methanol oxidation, it was observed that the onset oxidation overpotential is displaced towards more negative values as Pt content is decreased. Besides, an increase has been shown in the current density for methanol oxidation of 600% using a Ti/RuO₂-Pt (87.5:12.5) electrode compared to polycrystalline Pt.