Ethylene Glycol In Alkaline Media Research Articles

RhCo alloyed nanodendrites as an efficient electrocatalyst for boosting electro oxidation of ethylene glycol in alkaline media

Since Pt- and Pd-based catalysts, as the most common anode catalysts, usually suffer from CO poisoning issue during the electro oxidation of ethylene glycol, it is essential to explore more high-efficiency Pt- and Pd-free ethylene glycol oxidation reaction (EGOR) catalysts for better service in direct ethylene glycol fuel cells (DEGFCs). In this work, RhCo alloyed nanodendritic catalysts applied on EGOR in alkaline solution are designed and synthesized by a solvothermal method. The RhCo nanodendrites consist of radially distributed pine tree shaped flakes and rod-like crystals. The mass activity for the as-prepared Rh3Co1 nanodendrites during the EGOR reaches up to 3018.7 mA mg−1, which is 2.2-folds higher than that of commercial Pt/C. Moreover, the Rh3Co1 nanodendrites exhibit better stability and CO tolerance toward the EGOR than pure Rh nanodendrites and commercial Pt/C. Experimental observations in combination with density functional theory (DFT) calculations reveal that the notably promoted catalytic performances of Rh3Co1 nanodendrites are mainly attributed to the distinct nanodendritic morphology and the synergistic effect of Rh and Co. This work provides a valuable insight for developing efficient electrocatalysts for DEGFCs.

Green synthesis of gallic acid–capped gold nanoparticles as novel electro-catalyst for electro-oxidation of ethylene glycol in alkaline media

This study reports the synthesis of gallic acid–capped gold nanoparticles (GA-AuNPs) through a simple, inexpensive, and environmentally friendly chemical method and their applications in fuel cells. In the proposed method, gallic acid acts as the reducing agent and stabilizer. The studies showed that the size and distribution of AuNPs could be controlled by controlling the molar ratio of gallic acid to gold ions. The prepared GA-AuNPs were used as an electro-catalyst to oxidize ethylene glycol (EG) molecules on the glassy carbon electrode (GCE) surface in alkaline media. The results showed that the modified electrode using GA-AuNPs with a 1:1 M ratio has a higher electrochemical active surface area (ECSA); therefore, it has improved electro-catalytic activity, increased stability, and durability for EG oxidation compared to other ratios of GA/Au and even to the bare Au electrode.

(Invited) Efficient Electrocatalysts for Alcohol Oxidation and Oxygen Reduction in Alkaline Solutions

Alkaline fuel cells have some advantages as compared with conventional acid fuel cells. Our research group has investigated the possibility of alkaline fuel cells using anion-exchange membrane as an electrolyte. In the presentation, I would like to introduce and discuss about some topics relating to alkaline fuel cells as follows: 1) Direct oxidation fuels: alcohols We have been focusing on ethylene glycol as a direct fuel in anion-exchange membrane fuel cells (AEMFCs). Ethylene glycol has superior energy density (7.56 kWh dm−3) and higher boiling point (471 K) than some typical alcohol fuels such as methanol and ethanol. The oxidation of ethylene glycol in alkaline medium is faster than that in acid medium. And, surprisingly, ethylene glycol provides larger oxidation currents than methanol and polyols such as glycerol, erythritol, and xylitol in alkaline solutions. Thus, ethylene glycol is a promising fuel for AEMFCs, which overcomes a conventional direct methanol fuel cell (DMFC). Ethylene glycol has the above-mentioned advantageous features as DAFCs’ fuel, but it has a crucial problem derived from its inherent molecular structure. Ethylene glycol is a C2 molecule having a C−C bond in its structure. C−C bond is a stumbling block for electroorganic chemists since thus C−C bond is comparatively strong and cannot be easily cleaved. As well as ethanol oxidation, ordinal Pt catalyst cannot achieve the complete oxidation of ethylene glycol, and leaves some intermediate products. Therefore, in order to increase the efficiency of fuel utilization, active catalysts, having sufficient ability to break C−C bond in ethylene glycol, are strongly required. To our best knowledge, there is no available literature concerning the oxidation of ethylene glycol to CO2from an electrocatalytical view point. Here we introduce an effective C−C bond cleavage electrocatalyst for ethylene glycol. 2) Oxygen reduction catalysts: non-precious metal catalysts Electrochemically reduction of oxygen is an essential reaction involving in fuel cells. Among the various kinds of electrocatalysts, Pt, Pt-alloy, Ag are known to be fairly active for oxygen reduction in alkaline solutions. Precious metals, however, have some serious problems to be overcome before worldwide spread of fuel cells, such as economical cost, reproducibility and limited resources. These problems motivated many researchers to study for alternative catalysts besides a standard catalyst of Pt/C. Among proposed alternative catalysts, perovskite-type oxide is one of the promising candidates as a non-precious metal catalyst. Since Meadowcroft pointed out the catalytic activity of lanthanum-cobalt oxide for oxygen reduction, perovskite-type oxides become attractive materials as electrocatalysts for many electrochemists. However, the detailed mechanism for oxygen reduction on perovskite-type oxide electrodes has not been fully clear yet. We investigated the oxygen reduction on perovskite-type oxides using thin film electrodes and single crystal electrodes, and shed lights on the catalytic roles of oxides and carbon additives.

Electrocatalytic oxidation of ethylene glycol on palladium coated on 3D reduced graphene oxide aerogel paper in alkali media: Effects of carbon supports and hydrodynamic diffusion

To enhance Pd electro-catalysts in their electro-catalytic activity for C-C bond breaking and tolerance stability, Pd was electrodeposited on high-porosity 3D reduced graphene oxide (rGO) aerogel paper. For comparison, the Pd was also coated on other three different carbon material surfaces: bare carbon fiber paper (CFP), and CFP modified with either 2D graphene oxide (GO) and 2D rGO nanosheets. The Pd/3D rGO aerogel paper exhibits higher catalytic activity toward the electro-oxidation of ethylene glycol in alkaline media and higher excellent tolerance stability than other electrodes due to ultra-high porosity of the 3D rGO support leading to high active electrochemical surface area of the as-fabricated Pd catalyst electrode. In addition, the hydrodynamic diffusion of ethylene glycol to the cayalyst surface investigated in this work plays a major role to the catalytic activity of the as-prepared electrocatalyst. The Pd/3D rGO aerogel rotating disk electrode exhibits a high anodic current density of 267.8mAcm−2 at 3000rpm. This high-performance Pd/3D rGO aerogel may be practically used as the high-efficiency anode of direct ethylene glycol and other related alcohol fuel cells.

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.

Nano-Structured Pd-Sn Catalysts for Alcohol Electro-Oxidation in Alkaline Medium

The study of alcohols electrooxidation is of paramount importance not only for direct fuel cell and/or electrolysis cell applications, but also in order to gain the fundamental knowledge on reaction mechanisms for electrosynthesis applications. Tin is known to be a high performance co-catalyst of noble metal for alcohol oxidation, particularly concerning the ethanol electrooxidation reaction in acidic medium. This property of tin in association with palladium was recently confirmed for the electrooxidation of methanol, ethanol, and ethylene glycol in alkaline medium. Here, the electrocatalytic behavior of Pd1Snxcatalysts towards the electrooxidation of different C1, C2 and C3 alcohols is compared and discussed in terms of activity and reaction pathways: methanol and ethylene glycol since they are the simplest alcohol and polyol, respectively, ethanol and glycerol because they can both be produced from biomass, and isopropanol which only bears a secondary alcohol function, because it can be interesting for the development of “rechargeable” direct fuel cells. Particularly, the occurrence of two possible mechanisms, a base-catalyzed one and a mechanism based on the ability of the catalytic surface to favor the adsorption and desorption of species at low potentials, is discussed, as well as the difference in activity comparing isopropanol and glycerol oxidation reactions. For this purpose, active self-supported Pd1Snx catalysts are synthesized by the Sacrificial Support Method (SSM). Their catalytic activity towards the oxidation of C1 to C3 alcohols was determined in alkaline medium. The comparison of the activity allowed discarding a first base catalyzed deprotonation reaction of alcohols as rate determining step (rds), and spoke up for a mechanism involving a C-adsorption of carbon bearing an alcohol function. By comparing isopropanol and glycerol oxidation voltammograms, and on the basis of in situFTIR spectroscopy measurements, it has been shown that desorption of dihydroxyacetone could be the limiting step for glycerol oxidation at low potentials. Acknowledgement: Anna Zalineeva thanks the Center for Emerging Energy Technologies, Farris Engineering Center (UNM) for assistance and technical support, and the County Council of Poitou-Charentes (France) for financial support.

Impact of the Alkali Cation on the Oscillatory Electro-Oxidation of Ethylene Glycol on Platinum

We report the effect of alkali cation (Li+, Na+, and K+) on the oscillatory electro-oxidation of ethylene glycol in alkaline media. As experimentally verified, the nature of the alkali cation strongly impacts the waveform and frequency of the potential oscillations. The oscillation frequencies decrease in the order KOH > NaOH > LiOH, which also corresponds to the ascending order of the surface blockage due to the noncovalent interactions. On the other hand, the estimated rate constant of poison formation, kp, under oscillatory regime is higher in the presence of KOH rather than NaOH, both acting as the supporting electrolytes. In order to shed light on the relationships between the kinetic and dynamical features, we performed numerical simulations based on a generic model which includes the time evolution of cation coverage. Overall, we were able to reproduce the major features observed experimentally; kp was assigned to the electrochemical steps of C–C bond breaking instead of direct noncovalent interact...

Electrocatalytic Performance of Pd/SnO2-TiO2/MWCNT Catalyst for Oxidation of Ethylene Glycol in Alkaline Media

A novel Pd/SnO2-TiO2/multiwalled carbon nanotube (MWCNT) catalyst was synthesized using a facile and controllable in situ chemical method. Pretreated TiO2 was anchored to a functional MWCNT template, which was used as a support material to enhance the stability and electrical conductivity of the Pd nanoparticles. The Sn(II) ions adsorbed on the surface of the TiO2 precursor acted as reducing agents and ensured that Pd reduction only occurred on the precursor surface. The physicochemical properties of the catalyst were determined by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results showed that small metallic Pd nanoparticles were evenly dispersed over the catalyst surface. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were used to evaluate the electrocatalytic properties of the Pd/SnO2-TiO2/MWCNT catalyst in an alkaline solution containing 0.5 M NaOH and 1.0 M ethylene glycol. The high dispersion of the metallic Pd nanoparticles caused by the presence of the SnO2-TiO2 precursor significantly enhanced the electrocatalytic activity and tolerance of the catalyst to the accumulation of carbonaceous species. This new Pd/SnO2-TiO2/MWCNT catalyst is a promising candidate for use in the oxidation of ethylene glycol under alkaline conditions.

Ethylene Glycol Oxidation at Pt/TiO2/Carbon Hybrid Catalysts Modified Glassy Carbon Electrodes in Alkaline Media

Biomass-based fuels in conjunction with direct alcohol alkaline fuel cells are an emerging technology that may be able to wean us of our dependency of fossil fuels. However, their adoption is stalled by their high production costs (i.e., precious metal loading) and low electrocatalytic efficiencies. In this study, the platinum loading of 20 % Pt/C catalyst for use in ethylene glycol electrooxidation was reduced by mixing with TiO2 nanopowder in different mass ratios. This was followed by surface activation and cyclic voltammograms of the hydrogen adsorption and Pt oxide potential regions in 0.1 M KOH showed peak potential changes that are attributed to platinum interactions with TiO2. The catalysts were further tested for the electrochemical oxidation of ethylene glycol in alkaline media, where the titanium-modified catalysts showed a maximum increase in peak current density by 91 %, when compared to the commercial Pt/C catalyst. When the peak current was normalized by Pt surface area and mass, a maximum increase of 322 % was found. Tafel plot analysis showed increased exchange currents for the rate determining step of ethylene glycol oxidation at Pt/TiO2/C hybrid catalysts up to 7.35 × 10−7A/cm2. This is nearly 8.7 times larger than, 8.47 × 10-8A/cm2, the ethylene glycol exchange current density for the rate determining step in commercial Pt/C catalysts. Finally, chronoamperometric studies showed that the hybrid catalysts possessed increased stability and activity for ethylene glycol electrooxidation in 0.1 M ethylene glycol in 0.1 M KOH at an applied potential of −0.350 V vs. Ag/AgCl. This study shows that TiO2 can modify the platinum surface catalyst activity without the need of a TiO2 support. This avoids loss in electrical conductivity of the catalyst and lowers the total catalyst mass without sacrificing catalytic mass activity.

Facile synthesis of reduced graphene oxide supported PtAg nanoflowers and their enhanced electrocatalytic activity

In this work, a simple and facile method is developed in the synthesis of well-dispersed PtAg nanoflowers on reduced graphene oxide nanosheets (PtAg/RGOs) under solvothermal conditions, using ethylene glycol as a reducing agent and hexadecyl trimethyl ammonium bromide (CTAB) as capping and stabilizing agents. The as-prepared nanocomposites show a superior electrocatalytic activity, good tolerance, and better stability toward the oxidation of formic acid and ethylene glycol in alkaline media, compared with the commercial Pt/C (10 wt%) catalyst. For the oxidation of formic acid, the PtAg nanoflowers own thirty times higher of the catalytic currents than those of the commercial Pt/C catalyst. Meanwhile, for the oxidation of ethylene glycol, the ratio of forward current (jF) to reverse current (jR) is high up to 8.4, which is almost four times higher than that of the commercial Pt/C catalyst. This strategy provides a promising platform for direct formic acid and ethylene glycol fuel cells.

Facile synthesis of Pt–Pd nanodendrites and their superior electrocatalytic activity

Porous Pt–Pd nanodendrites were fabricated by a co-chemical reduction method using both PVP and urea as the co-stabilizing and co-structure-directing agents. The Pt–Pd nanodendrites displayed high catalytic activity and stability toward the electrooxidation of methanol and ethylene glycol in alkaline media.

Alkyne-functionalized palladium nanoparticles: Synthesis, characterization, and electrocatalytic activity in ethylene glycol oxidation

1-Octyne-stabilized palladium nanoparticles (PdHC8, core dia. 2.50±0.28nm) were prepared by a simple reduction procedure. FTIR studies showed that the self-assembly of 1-octyne onto the Pd nanoparticle surfaces involved the effective breaking of the terminal HC bonds and the formation of Pd–vinylidene interfacial linkages by a tautomeric rearrangement process. With this conjugated metal–ligand interfacial bond, the nanoparticles exhibited unique photoluminescence properties that were analogous to those of diacetylene derivatives. Furthermore, thermogravimetric analysis showed that there were about 150 ligands per nanoparticle, with an average footprint of ca. 13Å2 per capping ligand on the nanoparticle surface, consistent with a head-on configuration of the alkyne ligands on the Pd surface. Interestingly, the PdHC8 nanoparticles exhibited apparent electrocatalytic activity in the oxidation of ethylene glycol in alkaline media that was about twice that of commercial Pt/C, as manifested in cyclic voltammetric and chronoamperometric studies. Such an apparent improvement of the electrocatalytic activity was most probably ascribed to the partial removal of the alkyne capping ligands whereby the remaining molecules provided a relatively hydrophobic chemical environment and hence facilitated the removal of water generated from the oxidative dehydration reaction of ethylene glycol. Additionally, the enhanced electron density within the Pd metal cores as a result of the intraparticle charge delocalization between the particle-bound acetylene moieties might also facilitate the formation of PdC bonds in Pd-[C2H3(OH)2]ads, which was presumed to be the rate-determining step in ethylene glycol oxidation on Pd surfaces.

Rac-2-[(2-Chloro-phen-yl)(4-chloro-phen-yl)meth-yl]-1,3-dioxolane.

The title compound, C16H14Cl2O2, is a chiral mitotane derivative that contains a dioxolane ring and crystallizes from methanol as a racemic mixture. It was obtained in high yield from mitotane and ethyl­eneglycol in alkaline medium, followed by neutralization with sulfuric acid and extraction with ethyl acetate. The mol­ecular structure is stabilized by an intra­molecular C— H⋯ O hydrogen bond. The dihedral angle between the aromatic rings is 80.1 (2)°. The dioxolane ring adopts a puckered envelope conformation with an O atom as the flap.

Catalytic Activity of Pt/MWCNT for the Electro-Oxidation of Ethylene Glycol in Alkaline Media

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Electrocatalytic oxidation of ethylene glycol (EG) on supported Pt and Au catalysts in alkaline media: Reaction pathway investigation in three-electrode cell and fuel cell reactors

Carbon supported Pt and Au nanoparticles with small sizes (2.4nm for Pt/C, and 3.5nm for Au/C) and narrow size distributions were prepared though a modified solution-phase reduction method, and served as the working catalysts for an investigation of electrocatalytic oxidation of EG in alkaline media. Our three-electrode cell with an on-line sample collection system showed that with applied potential increasing, glycolic acid, oxalic acid and formic acid were sequentially produced from EG oxidation on Pt/C, while only glycolic acid and formic acid were detected on Au/C. Oxalic acid is a fairly stable product, and Pt/C is inactive to its further oxidation reaction. On Au/C, glycolic acid is the primary product, and no oxalic acid was found at specified test conditions. We clarified that formic acid was produced preferably from direct CC bond cleavage of EG not glycolic acid on both Pt/C and Au/C catalysts. The single anion exchange membrane-direct EG fuel cell (AEM-DEGFC) with Pt/C and Au/C anode catalysts showed consistent results with the three-electrode cell tests. The AEM-DEGC with Pt/C anode catalyst demonstrated a peak power density of 71.0mWcm−2, which is much higher than that with the Au/C (only 7.3mWcm−2) at 50°C. With the fuel cell operation voltage decreasing (anode overpotential increasing), deeper-oxidized products oxalic acid and formic acid were generated in the Pt/C anode AEM-DEGFC with higher selectivity. No formic acid was detected in the Pt anode AEM-DEGFC when glycolic acid was employed as fuel. On Au/C anode catalyst, very high selectivity to glycolic acid (>98%) was achieved. The AEM-DEGFC results confirmed the EG electro-oxidation pathways proposed by using an on-line sample collection system.

PdNi-decorated manganite nanocatalyst for electrooxidation of ethylene glycol in alkaline media

PdNi bimetallic nanoparticles coated onto manganite (MN) nanocatalyst was used for ethylene glycol (EG) and glycerol (Gly) electrooxidation in alkaline media. The MN nanorods were prepared by hydrothermal method, and the PdNi was coated on the rods by an in situ reduction method. The prepared nanocomposite was characterized by scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), Energy dispersive X-ray spectroscopy (EDS), and electrochemical methods. The SEM and TEM images exhibit the formation of nanorods of 10 nm and also show the formation of nanocrystalline PdNi on the walls of the MN nanorods. This study shows that the MN nanorods can be excellent support material and they supply oxygen to the catalyst, by which the catalytic activity is enhanced. The electrooxidation reactions in strong alkaline condition containing various concentrations of EG have been studied. Among the different concentrations, 9 M KOH/6 M EG exhibits the highest activity. PdNi/MN nanocatalyst exhibits better activity even in higher electrolytic concentrations of EG and alkali.

Concentration Dependence of the Electro-Oxidation of Ethanol and Ethylene Glycol at Platinum in Alkaline Medium

In the present work, the electro-oxidation of ethanol and ethylene glycol in alkaline medium is studied depending on their concentration by cyclic voltammetry, chronoamperometry and differential electrochemical mass spectrometry (DEMS). It is shown that in the case of ethanol, carbon dioxide as product of the oxidation can only be found during cyclic voltammetry. Within the investigated concentration range, potentiostatic experiments do not indicate bulk oxidation of ethanol to carbon dioxide. For ethylene glycol, the oxidation in cyclic voltammetry as well as in chronoamperometric experiments leads to significant carbon dioxide formation with the tendency that low concentrations and low potentials yield high carbon dioxide current efficiencies. Furthermore, comparatively higher current densities in cyclic voltammetry and chronoamperometric experiments indicate that with respect to ethanol, ethylene glycol is more active and the poisoning effect on platinum in alkaline medium is less severe.

Electrochemical investigations on carbon supported palladium catalysts

Highly dispersed palladium catalysts on carbon were prepared by reduction of their salts with various reducing agents. The crystallite parameters and metal surface area were evaluated by XRD and electrochemical techniques. The electrochemical activity for the oxidation of hydrogen, methanol, formaldehyde and ethylene glycol and reduction of oxygen was evaluated in alkaline solutions by making PTFE bonded carbon electrodes. The electrochemical activity was correlated with the catalyst properties. Pd dispersed catalysts on carbon supports exhibit high activity for the oxidation of hydrogen and ethylene glycol in alkaline medium. Their electrochemical activity is dependant upon the crystallite properties like surface area, dispersion and crystallite size. For oxygen reduction reaction, the activity can be increased by alloying with other elements.

Electrocatalytic oxidation of ethylene-glycol Part II. Behaviour of platinum-ad-atom electrodes in alkaline medium

Seven different foreign metal ad-atoms (Bi, Cd, Cu, Pb, Re, Ru, Tl) were investigated as activity modifiers of a platinum electrode for the electrocatalytic oxidation of ethylene-glycol in alkaline medium. None of these metal ad-atoms has an inhibiting behaviour at the optimum concentration of the precursor salt in solution. Among them, Pb, Bi and Tl greatly enhance the electrocatalytic activity of platinum, leading to current densities as high as 100 mA cm −2 for 0.1 M ethylene-glycol at room temperature; Cd shifts the whole polarization curve towards negative potentials; and Cu, Ru and Re leave the electrocatalytic activity of platinum practically unaffected. A qualitative explanation is suggested, based on the modification (due to the presence of the metal ad-atom) of the coverage of the electrode surface both by the organic adsorption residue and adsorbed hydroxyl.

Electrocatalytic oxidation of ethylene-glycol: Part II. Behaviour of platinum-ad-atom electrodes in alkaline medium

Seven different foreign metal ad-atoms (Bi, Cd, Cu, Pb, Re, Ru, Tl) were investigated as activity modifiers of a platinum electrode for the electrocatalytic oxidation of ethylene-glycol in alkaline medium. None of these metal ad-atoms has an inhibiting behaviour at the optimum concentration of the precursor salt in solution. Among them, Pb, Bi and Tl greatly enhance the electrocatalytic activity of platinum, leading to current densities as high as 100 mA cm −2 for 0.1 M ethylene-glycol at room temperature; Cd shifts the whole polarization curve towards negative potentials; and Cu, Ru and Re leave the electrocatalytic activity of platinum practically unaffected. A qualitative explanation is suggested, based on the modification (due to the presence of the metal ad-atom) of the coverage of the electrode surface both by the organic adsorption residue and adsorbed hydroxyl.