Oxide (CeO2, NiO, Co3O4 and Mn3O4)-promoted Pd/C electrocatalysts for alcohol electrooxidation in alkaline media

This study investigated Pt/C, Pd/C and oxide (CeO₂, NiO, Co₃O₄ and Mn₃O₄)-promoted Pd/C for electrooxidation reactions of methanol, ethanol, ethylene glycol and glycerol in alkaline media. The results show that Pd/C electrocatalysts alone have low activity and very poor stability for the alcohol electrooxidation. However, addition of oxides like CeO₂, NiO, Co₃O₄ and Mn₃O₄ significantly promotes catalytic activity and stability of the Pd/C electrocatalysts for the alcohol electrooxidation. The Pd-Co₃O₄ (2:1, w:w)/C shows the highest activity for the electrooxidation of methanol, EG and glycerol while the most active catalyst for the ethanol electrooxidation is Pd-NiO (6:1, w:w)/C. On the other hand, Pd-Mn₃O₄/C shows significantly better performance stability than other oxide-promoted Pd/C for the alcohol electrooxidation. The poor stability of the Pd-Co₃O₄/C electrocatalysts is most likely related to the limited solubility of cobalt oxides in alkaline solutions.     

Electrochemical investigation of Pd nanoparticles and MWCNTs supported Pd nanoparticles-coated electrodes for alcohols (C1–C3) oxidation in fuel cells

Incorporation of palladium nanoparticles (PdNPs) and multi-walled carbon nanotubes (MWCNTs) into chitosan-coated glassy carbon (GC) electrode for alcohols (methanol, ethanol, and isopropanol) electrooxidation has been studied. PdNPs–chitosan and MWCNTs–PdNPs–chitosan nanocomposites are successfully prepared and characterized by transmission electron microscopy images and UV–Vis spectroscopy. Based on the results, PdNPs–chitosan nanocomposite indicates high electrochemical activity and excellent catalytic characteristic for alcohol (C₁–C₃) electrooxidation on a GC electrode in an alkaline medium. The current density of the alcohols oxidation at GC–PdNPs–chitosan electrode is investigated in optimized conditions and compared with that obtained at the GC-modified electrode by Pd with different polymers. Also, our results show that the dispersion of Pd nanoparticles on the MWCNTs significantly improved the performance of the PdNPs/chitosan composite for electrooxidation of the C₁–C₃ alcohols.     

High electrocatalysis of ethylene glycol oxidation based on nickel particles electrodeposited into poly (m-toluidine)/Triton X-100 composite

Poly (m-toluidine) (PMT) was formed by successive cyclic voltammetry in a monomer solution containing Triton X-100 (TX-100) at the surface of carbon paste electrode (CPE). Nickel was then incorporated into the polymer by electrodeposition of Ni(II) from NiSO₄ acidic solution. The electrochemical behavior of this modified electrode (Ni/PMT(TX-100)/MCPE) was investigated in the electrooxidation of ethylene glycol (EG) using cyclic voltammetry and chronoamperometry techniques. Among the electrodes [Ni/PMT(TX-100)/MCPE, Ni/PMT/MCPE, Ni/MCPE, PMT(TX-100)/MCPE, and CPE] used in this study, Ni/PMT(TX-100)/MCPE showed the most effective catalytic activity. The effects of various parameters such as film thickness, electrodepositing time, TX-100 concentration, MT concentration, and EG concentration were investigated on the electrocatalytic oxidation of EG at the surface of Ni/PMT(TX-100)/MCPE. The catalytic rate constant (k) for EG oxidation was also calculated to be 2.1 × 10⁶ cm³ mol^?1 s^?1 using a chronoamperometric method.     

Methanol and ethanol electrooxidation at 3D ordered silicon microchannel plates electrode modified with nickel–palladium nanoparticles in alkaline

The use of silicon microchannel plates (MCP) modified with nickel–palladium (Ni–Pd) nanoparticles by electroless plating was studied for the electrocatalytic oxidation of methanol and ethanol by cyclic voltammetry and chronoamperometry in alkaline media. The electrocatalyst was characterized by EDS, SEM and cyclic voltammetry, and the effective parameters on electrocatalytic oxidation of the alcohol, i.e. the concentration of KOH and alcohol, medium temperature and working potential limit in anodic direction were investigated. The modified electrode shows a superior electrooxidation performance with the operating temperature increasing and a strong current response to methanol and ethanol even during long-term oxidation of alcohol. All results show that the Ni–Pd/Si–MCP nanocomposite electrode is very attractive for integrated fuel cell applications.     

Ethylene Glycol Electrooxidation on Smooth and Nanostructured Pd Electrodes in Alkaline Media

The electrooxidation of ethylene glycol (EG) has been studied either in situ on a smooth Pd electrode by FTIR spectroscopy or on nanostructured Pd‐based catalysts by cyclic voltammetry. The electrooxidation on the Pd electrode is dramatically influenced by the pH. Below pH 12, CO₂ is formed and detected in the thin layer by FTIR, while at higher pH values glycolate, carbonate and oxalate are formed almost simultaneously at a potential of ca. 0.4 V versus RHE. Above 0.9 V glycolate is oxidised to oxalate and carbonate. The nanostructured electrocatalysts Pd–(Ni–Zn)/C, Pd–(Ni–Zn–P)/C and Pd/C are much more active than the smooth Pd electrode (up to 3,300 A g(Pd)^–1) and give different distributions of the oxidation products. Pd/C is the most selective catalyst yielding glycolate, while mixtures of glycolate (major>60%), oxalate and carbonate are obtained with Pd–(Ni–Zn)/C or Pd–(Ni–Zn–P)/C. Carbonate is produced by oxidation of both glycolate (major contribution) and oxalate, while the major part of oxalate seems to be produced by the direct oxidation of EG.     

Synthesis,characterization and supercapacitors of electrically conductive PPy/graphene/rare earth ions composites

PPy/graphene/rare earth ions (PPy/GR/RE³⁺) were prepared using an in situ chemical polymerization of the monomer in the presence of FeCl₃ oxidant and p-toluenesulfonic acid dopant. The PPy/GR/RE³⁺ composites were characterized by FT-IR spectroscopy, four-point probe conductivity, scanning electron microscopy and transmission electron microscopy. The maximum conductivity of PPy/GR/Gd³⁺ composites is about 9.71 S/cm found with 1 wt% GR and 2 wt% Gd³⁺ at room temperature. The capacitance of the composite electrodes was investigated with cyclic voltammetry. As results of this study, the PPy/GR/Gd³⁺ was effective to obtain fully reversible and very fast faradaic reaction. Hence, the PPy/GR/Gd³⁺ could contribute to the pseudo-capacitive charge storage. The PPy/GR/Gd³⁺ exhibited higher specific capacitance of ~238 F/g at 1 A/g current density. Thermal gravimetric analysis demonstrates an improved thermal stability of PPy in the PPy/GR/Gd³⁺ composites.     

Nano-structured PdxPt1−x/Ti anodes prepared by electrodeposition for alcohol electrooxidation

Nano-structured Pd_xPt_1−x (x = 0-1) composite catalysts supported on Ti substrate are successfully prepared by electrodeposition method, and the morphology and phase of the catalysts are analyzed by field emission scanning electron microscope (FE-SEM) and X-ray energy dispersion spectroscopy (EDS). The activity and stability of the Pd_xPt_1−x/Ti composite catalysts are assessed for the electrooxidation of alcohols (methanol, ethanol and 2-propanol) in alkaline medium using cyclic voltammetry and chronoamperometry techniques. The results show that the Pd and Pt form Pd_xPt_1−x nano-structured composite catalysts, uniformly distributed on the Ti substrate. The electrocatalytic activity and stability of the Pd_xPt_1−x nanocatalysts depend strongly on the atomic ratios of Pd and Pt. Among the synthesized catalysts, the Pd_0.8Pt_0.2/Ti displays the best catalytic activity and stability for the electrooxidation reaction of alcohols investigated in alkaline medium under conditions in this study, and shows the potential as electrocatalysts for direct alcohol fuel cells.     

Electrooxidation of aliphatic alcohols on palladium oxide catalyst prepared by pulsed electrodeposition technique

Palladium film can be deposited on gold polycrystalline electrodes, from a deoxygenated alkaline solution containing 50 mM NaOH plus 0.5 mM K₂Pd(CN)₄. A multipulse sequence of potentials of equal amplitude and duration was used for the palladium deposition process. In particular, an optimized waveform of potentials of E₁ = 1.0 V vs. SCE and E₂ = −1.0 V vs. SCE for the relevant pulse duration of t₁ = 0.05 s and t₂ = 0.05 s, for 30 s, was used. Cyclic voltammetry and scanning electron microscopy (SEM) were employed to characterize the gold-palladium modified electrode (Au-Pd) towards the electrooxidation of aliphatic alcohols in alkaline solutions. The voltammetric study suggests that the kinetics involved in the alcohol electrooxidation at the Pd-Au electrode are sensibly higher than those observed on the bare Pd and Au electrodes. In addition, the most interesting aspect of the electrooxidation of aliphatic alcohols at the Au-Pd electrode was that as the number of methylene groups on the homologous series of aliphatic alcohols increased, the molar response also increased. Under pulsed chronoamerometric conditions (PCC), using an optimized triple pulse waveform of potentials the modified electrode exhibits interesting catalytic currents without any apparent poisoning effects during the oxidation of aliphatic alcohols.     

A highly active Pd coated Ag electrocatalyst for oxygen reduction reactions in alkaline media

We synthesized and characterized a highly active electrocatalyst for oxygen reduction reactions (ORRs) in alkaline media by coating carbon-supported silver nanoparticles with Pd (Pd@Ag/C) via a galvanic displacement method. The electrochemical measurements were carried out using an ultrathin film rotating disk electrode. Compared to the Pt/C electrocatalyst, the specific and mass activities of the Pd@Ag/C were enhanced by a factor of 3 and 2.5, respectively. The potentiostatic measurements showed that the Pd@Ag/C is less stable than the Pt/C at the potential of −0.1 V vs. Hg/HgO/OH⁻ in alkaline media. The Pd@Ag/C is insensitive to alcohol, and, as a cathode electrocatalyst of a direct alcohol fuel cell, can resist poisoning by the possible alcohol crossover from the anode.     

Electrocatalytic oxidation of 2-chlorophenol on a composite PbO2/polypyrrole electrode in aqueous solution

The electrocatalytic oxidation of 2-chlorophenol on a composite PbO₂/polypyrrole (PPy) electrode was carried out in 0.1 m H₂SO₄ solution. The composite PbO₂/PPy electrode was developed by the codeposition of polypyrrole and PbO₂ microparticles on the PbO₂/SnO₂/Ti substrate. The PbO₂ microparticles and polypyrrole in the composite electrode were observed to be hydrophilic active-sites and hydrophobic inactive-sites, respectively. The results indicated that the conversion of 2-chlorophenol and the efficiency of electrooxidation were improved on the hydrophobic-modified PbO₂/PPy electrode. The performance for electrooxidation of 2-chlorophenol on the composite PbO₂/PPy electrode was better than that on Pt or PbO₂/SnO₂/Ti electrodes. The thicker the composite (PbO₂/PPy) layer, the more active-sites in the composite electrode and the more 2-chlorophenol could be oxidized.     

Preparation and characterisation of carbon-supported palladium nanoparticles for oxygen reduction in low temperature PEM fuel cells

Pd nanoparticles have been synthesised using different reducing agents, including ethylene glycol (EG), formaldehyde and sodium borohydride and their activity for the oxygen reduction reaction (ORR) evaluated. The use of EG led to the best morphology for the ORR and this synthetic method was optimised by adjusting the system pH. Carbon-supported Pd nanoparticles of approximately 7 nm diameter were obtained when reduction took place in the alkaline region. Pd synthesised by EG reduction at pH 11 presented the highest mass activity 20 A g^?2 and active surface area 15 m² g^?1. These synthetic conditions were used in further synthesis. The effect of heat treatment in H₂ atmosphere was also studied; and increased size of the palladium nanoparticles was observed in every case. The Pd/C catalyst synthesised by reduction with EG at pH 11 was tested in a low temperature H₂/O₂ (air) PEMFC with a Nafion^® 112 membrane, at 20 and 40 °C. Current densities at 0.5 V, with O₂ fed to the cathode, at 40 °C were 1.40 A cm^?2 and peak power densities 0.79 W cm^?2, approximately; which compared with 1.74 A cm^?2 and 0.91 W cm^?2, respectively for a commercial Pt/C.     

Synthesis and electrochemical properties of graphene oxide/nanosulfur/polypyrrole ternary nanocomposite hydrogel for supercapacitors

A method for synthesizing Graphene oxide (GO)/nano‐sulfur/polypyrrole (PPy) ternary nanocomposite hydrogel is depicted. The higher surface area of GO, PPy porous structure and their excellent conductivity are utilized, and the GO hydrogel can be made easily. The products are characterized by field‐emission scanning electron microscopy (FESEM), X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, and electrochemical workstation. The results demonstrated that GO/nano‐S/PPy ternary nanocomposite hydrogel is successfully synthesized. The electrochemical properties are investigated by cyclic voltammetry, galvanostatic charge/discharge measurements, and cycling life in a three‐electrode system in 1M Li₂SO₄ electrolyte solution. The GO/nano‐S/PPy ternary nanocomposite hydrogel exhibit a high specific capacitance of 892.5 F g^?1 at scan rates of 5 mV s^?1 and the capacitance retain about 81.2% (594.8 F g^?1) of initial capacitance (732.5 F g^?1) after 500 cycles at a current density of 1 A g^?1. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40814.     

In situ FTIR spectroscopic studies of electrooxidation of ethanol on Pd electrode in alkaline media

Electrooxidation of ethanol on a polycrystalline Pd disk electrode in alkaline media was studied by in situ Fourier transform infrared (FTIR) reflection spectroscopy. The emphasis was put on the quantitative determination of intermediates and products involved in the oxidation. It has revealed that most of ethanol was incompletely oxidized to acetate. The selectivity for ethanol oxidation to CO₂ (existing as CO₃²⁻ in alkaline media) was determined as low as 2.5% in the potential region where Pd electrode exhibited considerable electrocatalytic activity (−0.60 to 0.0 V vs. SCE). Nevertheless, the ability of Pd for breaking C-C bond in ethanol is still slightly better than that of Pt under the same conditions. Besides, a very weak band of adsorbed intermediate, bridge-bonded CO (CO_B) was identified on the Pd electrode for the first time, suggesting that CO₂ and CO₃²⁻ species may also be generated through CO pathway (i.e., indirect pathway).     

Ni0.3Co2.7O4 spinel particles/polypyrrole composite electrode:: Study by X-ray photoelectron spectroscopy

In this work we have studied the multilayered polypyrrole/oxide composite electrode on glassy carbon having the structure GC/PPy/PPy(Ni_0.3Co_2.7O₄)/PPy, in which the spinel oxide Ni_0.3Co_2.7O₄ is known to be an electrocatalyst of the oxygen reduction reaction in alkaline medium. The successive GC/PPy, GC/PPy/PPy(Ni_0.3Co_2.7O₄) and GC/PPy/PPy(Ni_0.3Co_2.7O₄)/PPy parts of the electrode were examined by X-ray photoelectron spectroscopy. The results indicate that the electronic structure of the PPy is independent of the thickness of the PPy used to prepare the electrodes. The XPS data also show that cobalt is present in both divalent and trivalent states. The PPy doping degree by Cl⁻ ions (in terms of the Cl⁻/N) and the oxide/PPy mass ratio observed by XPS were 19 and 4.5%, respectively.     

Pd–Co/MWCNTs Catalyst for Electrooxidation of Hydrazine in Alkaline Solution

Multiwall carbon nanotubes supported Pd–Co electrocatalysts (Pd–Co/MWCNTs) for hydrazine electrooxidation in alkaline electrolytes were prepared. Their morphology and structure were characterized by scanning electron microscopy, transmission electron microscope, and X‐ray diffraction. The effect of the mass ratio of Pd to Co on the catalytic performance was examined via cyclic voltammetric and chronoamperometric measurements. The Pd–Co/MWCNTs with a mass ratio of 1:1 for Pd:Co shows higher catalytic performance than both Pd/MWCNTs and Co/MWCNTs and it has good stability for catalyzing the electrooxidation of hydrazine. The gas collection measurements indicated that hydrazine electrooxidation on Pd–Co/MWCNTs proceeded via a near 4‐electron pathway.     

Potentiostatically deposited polypyrrole/graphene decorated nano-manganese oxide ternary film for supercapacitors

A simple method based on potentiostatic polymerization was developed for the preparation of ternary manganese oxide-based nanocomposite films. The ternary nanocomposites, which were characterized using x-ray diffraction spectroscopy and x-ray photoelectron spectroscopy, showed that the manganese oxide within the film consisted of MnO₂ and Mn₂O₃. Electrochemical measurements showed that the ternary nanocomposite electrode exhibited high specific capacitance (up to 320.6 F/g), which was attributed to the morphology of a polypyrrole/graphene/manganese-oxide (PPy/GR/MnO_x) ternary nanocomposite. The experimental approach maximized the pseudocapacitive contribution from redox-active manganese oxide (MnO_x) and polypyrrole (PPy), as well as the electrochemical double layer capacitive (EDLC) characteristic from graphene (GR) sheets. Long cyclic measurements indicated that the specific capacitance of the ternary nanocomposite film could retain 93% of its initial value over 1000 charge/discharge cycles, in the potential range of −0.2 to 0.7 V versus silver/silver chloride electrode (Ag/AgCl).     

A novel nanocomposite of Pd nanocluster/poly(N-acetylaniline) nanorod modified electrode for the electrocatalytic reduction of oxygen

A novel nanocomposite of palladium nanoclusters/poly(N-acetylaniline) nanorods was electrodeposited on to a glassy carbon electrode by cyclic voltammetry (CV). This electrode, Pd/PAANI/GCE, was characterized by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), CV and chromoamperometry. It was demonstrated that the ball-shaped Pd nanoclusters were mainly growing on the ends of the nanorods, forming a novel nanocomposite. The preliminary study also demonstrated that the electrode modified with this nanocomposite matrix had high electrocatalytic activity toward 4-e⁻ oxygen reduction.     

Electrooxidation of Methanol and Ethylene Glycol Mixture on Platinum and Palladium in Alkaline Medium

The performance of mixture of methanol and ethylene glycol (EG) oxidation has been studied on both Pt and Pd electrodes in alkaline medium. The activity of EG oxidation is better than that of methanol oxidation and the stability of EG oxidation is better than that of methanol and ethanol oxidation on the Pd electrode. The onset potential for ethanol oxidation is more negative 200 mV than that of EG, however the stability of EG oxidation on the Pd electrode is better than that of ethanol oxidation. The performance of methanol oxidation improves pronouncedly by adding a small amount of EG on both Pt and Pd electrodes. The onset potential and peak potential of mixture of methanol and EG oxidation are close to or more negative than that of sole methanol and EG oxidation on the Pd electrode. The mixture of methanol and EG is more easily to be electrochemically oxidized and gives a better performance than sole methanol and EG on the Pd electrode. The results show that the mixture of methanol and EG is a promising candidate as fuel in direct alcohol fuel cells.     

Green bio-synthesis of Ni/montmorillonite nanocomposite using extract of Allium jesdianum as the nano-catalyst for electrocatalytic oxidation of methanol

In this work, synthesis of Ni nanoparticles was carried out successfully by water extract of Allium jesdianum as a biochemical reducing agent in the presence of montmorillonite clay (MMT) as a natural solid support for the first time. Then the electrochemical activity of the synthesized nanocomposite was investigated in methanol electrocatalytic oxidation. MMT with high cation exchange capacity and nano layer structure was exposed to ion exchange conditions in nickel solution. Then Ni²⁺ ion exchanged form was used in this process as a source of ions and also capping agent. Water extract of Allium jesdianum used as a reducing agent due to abundant availability of phenolic and flavonoid contents. The synthesized Ni/MMT nanocomposite was characterized using UV–Vis spectroscopy (UV–Vis), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM) and Energy-dispersive X-ray spectroscopy (EDX). The surface of prepared modified electrode has been characterized using SEM to evaluate the morphology, showing uniform dispersion of Ni nanoparticles with mean diameter of 12 to 20 nm. The modified carbon paste electrode was then used in methanol electrocatalytic oxidation reaction. Methanol oxidation on the proposed modified electrode surface occurs at 0.6 V and 0.3 V in alkaline and acidic medium respectively. Also, the results showed the better performance of modified electrode toward methanol electrocatalytic oxidation in comparison with carbon paste electrode that is modified by ion exchanged MMT. Charge transfer coefficients and apparent charge transfer rate constant for the modified electrode in the absence of methanol in alkaline medium were respectively found as: α_a = 0.53, α_c = 0.37 and k_s = 1.6 × 10⁻¹ s⁻¹. Also, the average value of catalytic rate constant for the electrocatalytic oxidation of methanol by the prepared nano-catalyst was estimated to be about 0.9 L·mol^-1·s^-1 by chronoamperometry technique. The prepared electrode was also effective for electrocatalytic oxidation of ethanol and formaldehyde in alkaline medium.     

Manganese oxide embedded polypyrrole nanocomposites for electrochemical supercapacitor

MnO₂ embedded PPy nanocomposite (MnO₂/PPy) thin film electrodes were electrochemically synthesized over polished graphite susbtrates. Growing PPy polymer chains provides large surface area template that enables MnO₂ to form as nanoparticles embeded within polymer matrix. Co-deposition of MnO₂ and PPy has a complimentary action in which porous PPy matrix provides high active surface area for the MnO₂ nanoparticles and, on the other hand, MnO₂ nanoparticles nucleated over polymer chains contribute to enhanced conductivity and stability of the nanocomposite material by interlinking the PPy polymer chains. The MnO₂/PPy nanocomposite thin film electrodes show significant improvement in the redox performance as cyclic voltammetric studies have shown. Specific capacitance of the nanocomposite is remarkably high (∼620 F g⁻¹) in comparision to its constituents MnO₂ (∼225 F g⁻¹) and PPy (∼250 F g⁻¹). Photoelectron spectroscopy studies show that hydrated manganese oxide in the nanocomposite exists in the mixed Mn(II) to Mn(IV) oxidation states. Accordingly, chemical structures of MnO₂ and PPy constituents in the nanocomposite are not influenced by the co-deposition process. The MnO₂/PPy nanocomposite electrode material however shows significantly improved high specific capacitity, charge-discharge stability and the redox performance properties suitable for application in the high energy density supercapcitors.