Alcohols In Alkaline Media Research Articles

CuNi2O4/MWCNTs nanocatalyst for methanol and ethanol electro-oxidation

The widespread use of cheap and efficient catalysts in energy storage and production in electrochemical processes led our research team to the synthesis and evaluation of CuNi2O4/MWCNTs nanocatalyst for alcohol oxidation. Nanocatalyst was characterized in terms of structure and morphology by X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDAX). The ability of CuNi2O4/MWCNTs was evaluated with cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analyses in the oxidation process of methanol and ethanol alcohols in alkaline media. The optimal concentration of methanol and ethanol for CuNi2O4/MWCNTs and CuNi2O4 was obtained to investigate the methanol oxidation reaction and ethanol oxidation reaction processes. The mechanism of these processes was also evaluated in detail. The stability of both nanocatalysts was investigated by performing several consecutive CVs and in 3600 s by chronoamperometric analysis. The results showed the good stability of this catalyst. The synergistic effect of placing CuNi2O4 on the surface of carbon nanotubes improved the oxidation process of methanol and ethanol. In general, the proposed catalyst can be an efficient, stable, and cheap option and at the same time very stable for use in alcohol fuel cells.

Cobalt nickel boride as electrocatalyst for the oxidation of alcohols in alkaline media

A mixed Co and Ni boride precursor was synthesized via chemical reduction and subsequently annealed at 400 or 500 °C with or without prior addition of the monomer benzoxazine (BO). The resulting mixed CoNiB materials were investigated as electrocatalysts for three alcohol oxidation reactions (AOR) in alkaline electrolyte: the oxidation of glycerol (GOR), ethylene glycol (EGOR) and ethanol (EOR). Comparison of the rotating disk electrode (RDE) cyclic voltammograms for the different catalysts revealed that CoNiB annealed at 500 °C without the addition of BO exhibited the lowest overpotentials in AORs at 10 mA cm−2, promoting GOR at 224 ± 6 mV lower potential compared to OER. When pyrolysis was conducted at 400 °C, the BO-containing catalyst showed a significant increase in the electrocatalytic activity for the AORs compared to the CoNiB catalyst only. The product selectivity on the different catalysts was investigated in a batch-type reactor with flow recirculation revealing formate as the main oxidation product during GOR and EGOR with faradaic efficiencies (FE) in a range of 60%–80%, while acetate was obtained during EOR (FE ∼ 85%–90%). The electrode potential, electrolyte composition and the type of ionomer were explored with respect to their influence on the GOR selectivity. The use of different ionomers resulted in significant differences in the activity trends between RDE and the batch-type reactor with flow recirculation measurements, indicating a strong influence of the two different substrates used, namely glassy carbon and carbon paper on the catalyst formation and thus on the recorded electrochemical activity.

One-pot synthesis of porous Pd-polypyrrole/nitrogen-doped graphene nanocomposite as highly efficient catalyst for electrooxidation of alcohols

Herein, a ternary-nanocomposite Pd-polypyrrole/nitrogen-doped graphene (Pd-PPy/NGE) has been prepared facilely by the one-pot method. In simple terms, PPy was in-situ polymerized on the surface of NGE with PdCl42- as the oxidant, and simultaneously Pd nanopaticles were loaded on the surface of PPy or embedded in PPy particles. The obtained Pd-PPy/NGE nanocomposite exhibits promising electrocatalytic properties toward the oxidation reaction of alcohols in alkaline medium. Especially, the optimized Pd-PPy/NGE (1:50) catalyst possesses mass activity of 2176.7, 1192.7 and 498.9 mA mgPd-1 toward ethylene glycol, methanol and ethanol electrooxidation, respectively, which are 4.3, 6.7 and 2.9 times of those for commercial Pd/C catalyst. Moreover, the Pd-PPy/NGE (1:50) also shows higher anti-poisoning ability and operating stability than the Pd/C catalyst. The promising electrocatalytic performance of the Pd-PPy/NGE (1:50) for alcohols oxidation can be ascribed to the well dispersion of Pd nanoparticles, the porous and stable three dimentional structure of the composite, and the synergistic effect between different components. The structural randomness of the conducting polymer and the potential synergistic effect between the metal nanoparticles and various supports would provide broad development space for these composites as electrocatalysts in direct alcohol fuel cell.

Study of Methanol Electro-Oxidation on Thin Nickel Films by Sampled Current Voltammetry

Nickel-based electrocatalysts have shown good catalytic activity for the electrochemical oxidation of alcohols in alkaline media, which has generated significant interest in using nickel films and nickel oxides in alcohol fuel cells. In this work, Ni films were deposited by the galvanostatic method on gold electrodes. The electrocatalytic activity for the electro-oxidation of methanol from these deposits was evaluated by cyclic voltammetry (CV) and sampled current voltammetry (SCV). Cyclic voltammetry measurements showed that depending on the Au electrode roughness, the position NiOOH formation peak of the electrodeposited Ni deposits could differ. The deposits were divided depending on whether the NiOOH formation peak was below or above 0.39 V vs. Ag|AgCl reference electrode. Sampled current voltammograms showed that the former presented greater specificity for the oxidation of methanol, and the latter, showed electrocatalytic activity for both the oxidation of methanol and for the oxygen evolution reaction.

Polyaniline Supported Atomic Gold Electrode Toward Glucose Oxidation

Gold is reported to have unique catalytic properties for oxidization of alcohols in alkaline media, and the catalytic ability is dependent on size of the gold, which enhancement in the catalytic activity is observed following reduction of the size [1]. As size of the gold reduced to atomic level, the property would vary depending on the number of atoms in a gold cluster [1, 2]. For instance, the alcohol oxidation catalytic activity is promoted when there is an even number of gold atoms in a cluster and demoted when the gold cluster contains odd number of atoms [1, 3]. Simulation results indicate that the HOMO-LUMO gap switches between conductor and semi-conductor when the atom number changes [2]. Deposition of atomic level gold clusters is realized by a cyclic atomic gold deposition process utilizing polyaniline (PANI) as the supporting substrate [1, 3]. In this study, PANI decorated with different numbers of gold atoms is prepared, and effect of the gold atom number in glucose oxidation is evaluated for application in glucose electrochemical sensor.Figure 1 shows the fabrication process of the PANI/Au electrode. The PANI was prepared by electropolymerization on a pretreated platinum electrode. The electrolyte was composed of 0.1 M aniline monomer in 2 M HBF4. Color of the surface of the Pt electrode changed from silver to blue after the polymerization process. Thereafter, KAuCl4 was used as source of the gold in the cyclic atomic gold deposition process. Figure 2 shows sequence of the cyclic atomic deposition process for gold. In one cycle of the deposition, one and only one gold ion was attracted to an amine group in the PANI, and the attracted gold ion was reduced to form a gold atom. After preparation of the PANI/Au N (N indicates the number of the deposition cycle conducted) electrode, glucose oxidase (GOD) was immobilized as an enzyme on the electrode surface by a comprehensive crosslinking method.Figure 3 shows cyclic voltammogram (CV) results of glucose oxidation on the PANI/Au2 electrode when the glucose concentration in a phosphate buffer solution (PBS) was varied from 0 to 20 mM. Anodic current generated from oxidation of the glucose was confirmed when the concentration was higher than 5 mM. In order to reveal effects of the gold atom number on oxidation of glucose, PANI/Au N electrodes with the N changed from 1 to 3 were prepared. In the CV scans, a scan rate of 50 mV/s and 10.0 mM glucose were used. Figure 4 shows the CV results when using the PANI/Au N electrode as the working electrode. Anodic current caused by oxidation of glucose was observed in all the three electrodes. The current response increased when the deposition cycle was increased from 1 to 2, and the PANI/Au3 produced current responses between those of the PANI/Au1 and PANI/Au2. This implies that the glucose oxidation is lowered when an odd number of gold atoms is deposited. [1] Alex P. Jonke, Mira Josowicz and Jiří Janata, J. Electrochem. Soc. 159 2012 40-43. [2] E. M. Fernandez, J. M. Soler, I. L. Garzon, L. C. Balbas, Phys. Rev. B 70 2004 165403. [3] J. Janata, T. Nakamoto, IEEJ Transaction 11 2016 261-267. Figure 1

Enhanced electrocatalytic performance triggered by atomically bridged boron nitride between palladium nanoparticles and carbon fibers in gas-diffusion electrodes

Significant reduction of the amount of precious metals in catalysts is a major challenge. We report the synthesis of high-performance carbon paper-boron nitride-palladium (CP-BN-Pd) electrocatalytic electrodes. The nanocatalysts consist of Pd nanoparticles of 5 nm supported on an ultrathin BN film prepared by atomic layer deposition (ALD), covering the microfibers of gas-diffusion electrodes (GDL). These electrodes present significantly enhanced electrocatalytic performance towards oxygen reduction (ORR) and C2 alcohols oxidation reactions and outperform the reported data for those alcohols in alkaline media, reaching a peak current of 17 amps/mgPd in 1 M NaOH + 1 M ethanol. The ageing tests reveal excellent stability of the electrochemically active surface area even after 1000 cycles, and the ethanol oxidation activity shows negligible decay of 1% whereas commercial Pd/C show prominent decay of 44%. The use of this heterogeneous active interface opens a new route for the development of efficient and low-metal content nanocatalysts.

Enhanced electrocatalytic activity of Pd and Pd-polyaniline nanoparticles on electrochemically exfoliated graphite sheets

The catalyst support materials play an important role in improving the performance of electrocatalysts for alcohol oxidation reaction. In this work, flexible graphite sheets containing a large number of edge planes were electrochemically exfoliated by the application of large positive and negative potentials in acetonitrile medium. The process described here produces several surface functional groups on graphite sheet surface. In this work, the utility of such a functionalized surface is explored as a solid support for depositing Pd and Pd-PANI nanostructures which are studied for oxidation of alcohols in alkaline medium. The results show that these electrode materials exhibit an excellent electrocatalytic activity with very high turnover frequency and low activation energy values for ethanol oxidation reaction that has the potential to be used in low temperature polymer membrane alkaline fuel cells.

Electro-oxidation competency of palladium nanocatalysts over ceria–carbon composite supports during alkaline ethylene glycol oxidation

The effect of varying Pd–CeO2 ratios on the oxidation efficiency of ethylene glycol and low molecular weight alcohols in alkaline medium.

Unusual synergetic effect of nickel single atoms on the electrocatalytic activity of palladium for alcohol oxidation reactions in alkaline media.

Palladium nanoparticles (Pd NPs) supported on Ni single atoms encapsulated in carbon nanotubes (NiSA) show a significantly enhanced electrocatalytic activity for the oxidation reactions of methanol, ethanol and glycerol in alkaline media due to an unusual electron withdrawal effect of NiSA on Pd NPs.

Effect of Silver Modification on Glycerol Oxidation Reaction Activity of Palladium Electrode in Alkaline Medium

Introduction Biodiesel fuel (BDF) attracts attention as a carbon-neutral fuel as well as bioethanol. As the production of BDF increases, the production of the glycerol byproduct is also increasing. It is important to develop new uses for glycerol to cope with the mass production of BDF. The use of glycerol as a fuel for direct alcohol fuel cells is promising, because anodic oxidation of glycerol produced by bioprocesses occurs in carbon-neutral cycles and direct glycerol fuel cells are expected to produce electricity with a low environmental load and to be energy efficient. It is well-known that Pd is cheaper than Pt and Au, and Pd-based alloy electrodes are highly active for the oxidation of alcohols in alkaline media. We also have reported the PdAg alloys-loaded carbon exhibited higher glycerol oxidation reaction (GOR) activity and tolerance to poisoning species than Pd.1 The mechanism for GOR, however, is not so clear. In this study we prepared an Ag atomic layer-modified Pd model electrode, and investigated the potential dependence of GOR products by in situ infrared reflectance-absorption spectroscopy (IRAS). In addition, we discussed the GOR mechanism based on these data. Experimental The Ag atomic layer-loaded Pd (Ag/Pd) electrode was prepared by underpotential deposition of Cu (Cu-upd) on a Pt polycrystalline substrate and the following galvanic replacement with Ag. The coverage of Ag (θ Ag) on the Pd substrate was evaluated to be 0.5 from the charges for Cu-upd before and after the Ag modification. 1 M KOH and (1 M KOH + 0.5 M glycerol) solution were used for electrochemical measurements. In situ infrared reflection-absorption spectroscopy (IRAS) was used to qualitatively analyze the products of GOR on the Pd and Ag/Pd electrodes in alkaline solution. All electrochemical measurements were performed at room temperature. Results and Discussion The cyclic voltammograms of the Pd and Ag/Pd electrodes in a (1 M KOH + 0.5 M glycerol) solution is shown in Fig. 1. The Ag/Pd electrode had higher oxidation current and more negative onset potential of the oxidation current than the Pd electrode, clearly indicating that the GOR activity was enhanced by the modification of the Ag atomic layer. In addition, the peak potential of the oxidation current for the Ag/Pd electrode was more positive than that for the Pd electrode, suggesting that the former was superior in tolerance to poisoning species to the latter. IRAS spectra for the Pt electrode exhibited that the absorption peak at 1335 cm-1 assigned to the formation of dihydroxyacetone was mainly increased at lower potentials, but the absorption peak at 1310 cm-1 assigned to the formation of glycerate was increased at higher potentials. This suggests that the secondary OH group in a glycerol molecule is preferentially oxidized at smaller overpotentials, and the primary OH group is greatly oxidized at larger overpotentials. For the Ag/Pd electrode, the oxidation of the primary OH group occurred even at smaller overpotentials, and hydroxypyruvate was also formed at larger overpotentials. Acknowledgement This work was partially supported by JSPS KAKENHI Grant Number 15H04162. Reference 1 B. T. X. Lam, M. Chiku, E. Higuchi, H. Inoue, J. Power Sources, 297, 149 (2015). Figure 1

Methanol Oxidation on Ru- or Ni-Modified Pd-Electrocatalysts in Alkaline Media: A Comparative Differential Electrochemical Mass Spectrometry Study

The electrochemical oxidation of methanol on electrocatalysts is intensively investigated since direct methanol fuel cells (DMFCs) were proposed as a promising alternative as power source for mobile and back-up power applications. In DMFCs, methanol is oxidized at the anode and oxygen is reduced at the cathode to convert the chemical energy of the fuels to electric power. In recent years, the electrochemical oxidation of methanol in alkaline environment is rising in interest, because other electrocatalysts than the expensive platinum are feasible as anode and cathode catalysts in alkaline DMFCs. While multiple catalysts are feasible on the cathodic site, Palladium was proven to be a suitable substitute for Pt as anode catalyst for the electrochemical oxidation of alcohols in alkaline media [1], but needs further improvement to compete with Pt especially regarding methanol oxidation reaction. The catalytic activity of Pd catalysts was improved by alloying or mixing other metals (or metal oxides) to Pd [2,3] or by controlling the size and shape of Pd particles [4]. Besides high catalytic activity, the complete oxidation of methanol to CO2is of enormous interest, because the complete oxidation results in the highest possible faradaic efficiency with six electrons transferred per methanol molecule. In contrast, two or four electrons are transferred to the anode per methanol molecule, if methanol is not completely oxidized. Differential electrochemical mass spectrometry (DEMS) is used by different research groups to quantify a catalyst’s ability to completely oxidize methanol. While the methanol electrooxidation on Pt-based catalysts was investigated intensively via DEMS in acidic media, DEMS studies on Pd-based catalysts for methanol electrooxidation in alkaline media are rare. In former studies, we reported on PdXNi/C and PdXRu/C catalysts for methanol electrooxidation in alkaline media synthesized by wet-chemical reduction with sodium borohydride [2,3]. It was possible to show that these oxophilic metals have a positive effect on the catalytic activity towards methanol oxidation of Pd-based catalysts. Taking these studies into account, we herein investigated the influence of these metals on Pd-based electrocatalysts regarding methanol oxidation reaction via DEMS. Besides analyzing the product distribution from methanol bulk oxidation on PdXNi/C or PdXRu/C, the main interest of this work is to investigate how the addition of the metals to Pd influences the methanol oxidation mechanism and catalyst poisoning. Hence, standard electrochemical tests like cyclic voltammetry, chronoamperometry, COadsstripping or methanol adsorbate stripping were conducted in the DEMS flow cell. Figure 1 shows cyclic voltammograms and corresponding MS signals for produced CO2 (m/z = 44) and methyl formate (m/z = 60) for Pd/C, Pd5Ni/C and Pd3Ru/C during methanol electrooxidation. While both modified catalysts show higher current densities and lower onset potentials than Pd/C for the electrooxidation of methanol, the product distribution differs strongly depending on the added metal. For Ni-modified catalyst the formation of CO2 is significantly lower than for Pd/C. While the addition of Ni to Pd leads to a negative effect on the ability to completely oxidize methanol, Pd3Ru/C is able to oxidize methanol more efficiently to CO2 than Pd/C. For Pd3Ru/C, the CO2 formation is shifted to lower potentials while methyl formate is produced at higher potentials. This hints to a more selective production of CO2 at low potentials on Pd3Ru/C than on Pd/C or Pd5Ni/C. Besides DEMS experiments, measurements were carried out in dependence of methanol concentration or oxidation temperature using a 3-electrode setup with stationary electrolyte to determine the rate determining step and the activation energy of methanol electrooxidation on Pd/C and the modified catalysts. Fig. 1 – Methanol bulk oxidation on Pd/C, Pd5Ni/C and Pd3Ru/C investigated via cyclic voltammetry in a DEMS flow cell at 20 mV s-1 from 0.1 to 1.2 V (vs. RHE) with 0.1 M CH3OH + 0.5 M KOH solution as electrolyte. Corresponding mass spectrometry signals for CO2 (m/z 44) and HCOOCH3(m/z 60) are displayed to evaluate the product distribution during methanol oxidation reaction.

Controlled Synthesis of Au-Island-Covered Pd Nanotubes with Abundant Heterojunction Interfaces for Enhanced Electrooxidation of Alcohol.

Here, we, for the first time, synthesized Pd nanotubes covered by high-density Au-islands, in which abundant exposed Pd–Au heterojunction interfaces are present and the content of element Au can be easily controlled. The optimized nanostructures show remarkably enhanced activity for catalyzing different alcohols in alkaline media than commercial Pd/C. The mass activity is 9.66, 1.83, and 4.60 A mgmetal–1 toward the electrooxidation of ethanol, glycerol, and ethylene glycol in alkaline media, which is about 6, 4, and 7 times that of Pd/C, respectively. Additionally, a model was proposed to explain the relationship between the structure and the catalytic activity.

PERFORMANCE ASSESSMENT OF A POLYMER ELECTROLYTE MEMBRANE ELECTROCHEMICAL REACTOR UNDER ALKALINE CONDITIONS − A CASE STUDY WITH THE ELECTROOXIDATION OF ALCOHOLS

A novel polymer electrolyte membrane electrochemical reactor (PEMER) configuration has been employed for the direct electrooxidation of propargyl alcohol (PGA), a model primary alcohol, towards its carboxylic acid derivatives in alkaline medium. The PEMER configuration comprised of an anode and cathode based on nanoparticulate Ni and Pt electrocatalysts, respectively, supported on carbonaceous substrates. The electrooxidation of PGA was performed in 1.0M NaOH, where a cathode based on a gas diffusion electrode was manufactured for the reduction of oxygen in alkaline conditions. The performance of a novel alkaline anion-exchange membrane based on Chitosan (CS) and Poly(vinyl) alcohol (PVA) in a 50:50 composition ratio doped with a 5wt.% of poly (4-vinylpyridine) organic ionomer cross-linked, methyl chloride quaternary salt resin (4VP) was assessed as solid polymer electrolyte. The influence of 4VP anionic ionomer loading of 7, 12 and 20wt.% incorporated into the electrocatalytic layers was examined by SEM and cyclic voltammetry (CV) upon the optimisation of the electroactive area, the mechanical stability and cohesion of the catalytic ink onto the carbonaceous substrate for both electrodes. The performance of the 4VP/CS:PVA membrane was compared with the commercial alkaline anion-exchange membrane FAA −a membrane generally used in direct alcohol alkaline fuel cells- in terms of polarisation plots in alkaline conditions. Furthermore, preparative electrolyses of the electrooxidation of PGA was performed under alkaline conditions of 1M NaOH at constant current density of 20mAcm−2 using a PEMER configuration to provide proof of the principle of the feasibility of the electrooxidation of other alcohols in alkaline media. PGA conversion to Z isomers of 3-(2-propynoxy)-2-propenoic acid (Z-PPA) was circa 0.77, with average current efficiency of 0.32. Alkaline stability of the membranes within the PEMER configuration was finally evaluated after the electrooxidation of PGA.

Optical, Electrochemical and Thermoanalytical Investigations on Newly-Synthesized Perylene-3,4,9,10-Dianhydride Fluorescent Dyes.

A series of dyes using tetrachloroperylene dianhydride as fluorescent chromophore was synthesized by the substitution of suitable aliphatic and alicyclic alcohols in alkaline medium, and evaluation of dyes was done for their optical, electrochemical and thermal properties. These dyes exhibited absorption maxima λmax in the range of 440-460nm in aqueous medium due to the presence of highly-conjugated framework. Fluorescence spectra of these dyes in water showed sharp emission peaks with small bandwidths and large fluorescence rate constants, i e., 1.36 × 10(8) to 2.25 × 10(8)S(-1). Redox potential E1/2 and band gap energy Eg were observed in the range of -0.689 to -0.784 and 2.530 to 2.610eV, respectively. Thermal stability was noticed up to 300°C on the basis of TG and DTA findings. The structures of perylene-azo dyes were confirmed by FTIR and NMR spectroscopy. Graphical Abstract Optical, electrochemical and thermoanalytical investigations on newly-synthesized perylene-3,4,9,10-dianhydride fluorescent dyes.

Microwave-Assisted Solvothermal Synthesis of Pd-MnO2 Hybrid at Onion-like Carbons: Electrocatalytic Oxidation of Alcohols in Alkaline Media

The use of less toxic glycerol, (a non-flammable, volatile, and little-valued residue of biodiesel production), ethanol as well as ethylene glycol (EG) as fuel may be an interesting alternatives to methanol for Direct Alcohol Fuel Cell (DAFC) technology. The volumetric energy densities of glycerol, ethanol and EG are 5.80, 6.31 and 5.97 kW h L-1 compared to 5.81 kW h L-1for methanol makes them good fuel cell candidates [1-2]. The secret to the efficient electrocatalysis of alcohols is the use of efficient nanocatalyst. Palladium-based catalysts have emerged as the most viable electrocatalysts for alcohol in alkaline electrolytes. To harness the great catalytic potential offered by Pd, and to reduce cost, Pd-based alloys supported on different carbon supports are constantly used in direct alcohol fuel cells (DAFCs). In this work, palladium-manganese oxide nanoparticles supported on carbon nano onions (Pd-MnO2/OLC) were synthesized using the microwave-assisted solvothermal technique. Palladium-manganese oxide nanoparticles supported on Vulcan carbon (Pd@MnO2/XC–72) were also synthesized using the same technique for comparison. The catalysts were characterized using XRD, XPS, FESEM and HRTEM techniques. Electroxidation of the alcohols was performed in 0.5 M alcohol / 0.5 M KOH via cyclic and linear sweep voltammetry, chronoamperometric and elelctrochemical impedance spectroscopy. Results obtained show that the catalyst supported on OLC exhibited the highest current density and least charge transfer resistance relative to the catalyst supported on XC–72. Pd-MnO2/OLC gave the best result amongst the catalyst synthesized with respect to the current density, and electrochemical stability as well as exhibited the least charge transfer resistance in all the alcohols studied. For instance, the onset oxidation potential and current density of the glycerol oxidation process were -0.5386 V and 5.58mAcm-2, respectively. The implications of these results relative to methanol oxidation using the best catalyst system synthesized are discussed.

Hydroxyapatite wrapped multiwalled carbon nanotubes composite, a highly efficient template for palladium loading for electrooxidation of alcohols

A new electrocatalyst is introduced by loading palladium nanoparticles on the unique structured composite of hydroxyapatite and multiwalled carbon nanotubes. The structure and morphology of the designed electrocatalyst are characterized by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The efficiency of the resulted nanostructure is explored toward the electrooxidation of some common alcohols in alkaline media. The electrooxidation of ethylene glycol (EG) is explored more extensively which provides a large peak current density (more than 1810 mA mg−1Pd). Surprisingly, the efficiency of oxidation is maintained even for relatively high concentrations of EG. In terms of the current density and the onset potential, significant improvements are observed for the proposed structure versus hydroxyapatite free catalyst. The high efficiency of the proposed electrocatalyst is explained via the presence of hydroxyl rich surface of hydroxyapatite which causes a more effective oxidation of alcohols over the loaded Pd nanoparticles.

Support Effect in the Electrocatalytic Activity of Cu@Pd Core-Shell toward Electrooxidation of Short Chain Alcohols in Alkaline Media

Cu@Pd core-shell particles were synthesized by a chemical method using ethylene glycol as reaction media. Carbon nanofibers (CNFs) and Vulcan carbon were employed as supports and added during the catalyst synthesis procedure. According to transmission electron microscopy, Cu@Pd core-shell particles were prepared with two different morphologies regardless of support: semi-spherical and rod-shaped nanoparticles with sizes of 6 and 10 nm, respectively. X-ray diffraction patterns were typical of a face-centered cubic structure with crystallite sizes of 8.2 and 8.8 nm for Cu@Pd/C and Cu@Pd/CNF, respectively. X-ray fluorescence analyses revealed a composition (% mass) of 60/40 for the Cu@Pd materials. Electrocatalytic activity was evaluated by cyclic voltammetry (CV) at alcohol concentrations of 0.1, 0.5, 1 and 3 M for methanol, ethanol, ethylene glycol and glycerol. The highest current densities (at least 3-fold) and the most negative potentials (at least 0.2 V of difference) were found through the use of nanofibers instead of Vulcan carbon. Evaluation of the electrocatalyst/support stability was performed by cyclic voltammetry (1000 cycles), showing superior stabilities for the CNF materials compared to the Vulcan supported systems, with metal losses of approximately 30%. The enhancement of the electrocatalytic activity and stability is related to the Cu@Pd metal-metal and Cu@Pd/CNFs metal/support interaction.

Preparation of a Carbon-Platinum-Polyaniline Support for Atomic Metal Deposition

A low-cost, thin, graphitized carbon electrode with electrodeposited platinum and polyaniline has been characterized for electrochemical oxidation of aliphatic alcohols in alkaline medium and for possible further incorporation of atomic metals and alloys. Our previously developed atomic metal polyaniline composites used solid platinum as the electrode material. The replacement of this solid platinum with a small amount of electrochemically annealed Pt on a carbon support was optimized for alcohol oxidation. An HPLC procedure for analysis of oxidation products of 1-propanol has also been utilized for the characterization of the composite electrode.

Increased Electrochemical Oxidation Rate of Alcohols in Alkaline Media on Palladium Surfaces Electrochemically Modified by Antimony, Lead, and Tin

Several adatoms (M=Sb, Sn, or Pb) were added to Pd nanoparticles and examined for the electrochemical oxidation of ethanol, 1-propanol, 2-propanol, ethylene glycol, propylene glycol, and glycerol. We observed a significant increase in oxidation rate on Pd-M for each of the adatoms in each of the fuels. For example, the oxidation rate of ethanol was 1.5 times greater on Pd-Pb and Pd-Sn as compared with the oxidation rate on Pd after 10minutes of oxidation. However, even more notable is the behavior observed by the polyhydric alcohols that exhibit sluggish reaction kinetics even in alkaline media. For example, the oxidation rate of propylene glycol on Pd-Pb was observed to be 21 times greater than the oxidation rate on Pd after 10minutes, and it was still 7.1 times greater after 12hours. These results show particular promise for the potential of efficiently oxidizing bulkier and higher energy density alcohols in the alkaline direct liquid fuel cell. All three bimetallic surfaces induced an increase in oxidation rate with all alcohols as compared to the monometallic Pd. Based on analysis of our results, we attribute a significant amount of the increase in oxidation rate to the bifunctional effect and suggest a lesser role is played by the electronic effect.

Pt catalysts modified with Bi: Enhancement of the catalytic activity for alcohol oxidation in alkaline media

Recent developments on anion-exchange membranes for fuel cell application renewed the interest in the study of alcohol oxidation at high pHs for applications in anion-exchange membrane direct alcohol fuel cells (AEM-DAFC). Although platinum is still the most studied catalyst for oxidation of alcohols in alkaline media, the introduction of one or more metals in order to increase the oxophilicity of the catalyst is a common approach in the development of improved materials for these reactions. In this manuscript, we report the enhancement of the catalytic activity of Pt/C toward ethanol, methanol, and propanol oxidation in alkaline media by simple adsorption of Bi surface. The activity was checked by cyclic voltammetry, and the reaction products and intermediates were analyzed by “in situ” infrared spectroscopy. The presence of Bi was shown to increase the activity of Pt toward the oxidation of the referred alcohols by acting as a third body (impeding surface poisoning) and also by an electronic effect (on water adsorption at the surface).