Electrooxidation Of Organic Molecules Research Articles

An amorphous Ni-Fe catalyst for electrocatalytic dehydrogenation of alcohols to value-added chemicals.

As for the hydrogen production process via electrocatalytic water splitting, the green and sustainable electro-oxidation of organic molecules at the anode is thermodynamically more favourable than the oxygen evolution reaction (OER). Here, we proposed for the first time to replace the OER process by the oxidation of N-Boc-4-piperidine methanol (BPM), via a parallel reaction, which finally leads to the green production of N-Boc-4-piperidine carboxaldehyde (BPC). The amorphous NiFeO(OH) nanospheres with rich valence states were adopted as the anode catalyst, with creation of more active sites. The gas chromatography results showed that nearly all the BPM converted to BPC after 15 h reaction. The electrochemical tests showed that the Faraday efficiency (FE) approaches nearly 100% when the charge transfer is approximately equal to the theoretical charge. This work reports a new process for the alcohol oxidation, providing a valuable green organic synthesis process.

Recent Developments of Methanol Electrooxidation Using Nickel‐based Nanocatalysts

AbstractStudies of methanol electrooxidation reactions have achieved considerable advancements in the recent years for their encouraging contributions in the exciting fields of energy conversion and storage, organic syntheses, wastewater treatment, sensing, medicinal and environmental analyses, and many others thriving fields of modern technology. Accordingly, the fabrication of less expensive, efficient and decent quality electrocatalysts with high material stability, faster electro‐oxidation kinetics, as well as less carbonation and decent corrosion inhibition activities are highly urged. Consequently, scientists around the globe are in continuous search for alternative economical smart anode‐nanocatalysts for methanol oxidations with superior electrochemical performances. In the recent years, various inexpensive and readily‐available nanocatalysts of non‐noble metals like Ni, Co, Cu, etc., in reference to electrooxidation of organic molecules have been reported. The present work highlights the recent progress accomplished by rapidly flourishing nickel‐based electrocatalysts for electrooxidation of methanol. The discussion comprehensively includes the basic mechanistic understandings and fundamentals for achieving high efficacy of methanol electrooxidation with nickel‐based electrocatalysts. Also, the current challenges faced in this emerging area have been outlined to achieve superior, productive, and commercially viable catalysts for methanol electrooxidation in the near future.

Multifunctional Noble Metal Phosphide Electrocatalysts for the Organic Molecule Electro-Oxidation

The small organic molecule electro-oxidation (OMEO) is the important anodic reaction occurring in direct liquid fuel cells (DLFCs), whose kinetics are largely hindered by the low activity and poor stability of electrocatalysts. Noble metals (e.g. Pt, Pd) are currently the state-of-the-art catalysts for the OMEO; however, for practical applications their electrocatalytic performance needs to be improved. Herein, we demonstrate that a simple phosphorization treatment at different temperatures is able to convert commercially available supported noble metal catalysts (PdNi, Pd) into multifunctional metal phosphide (PdNiP) or phosphide-metal heterostructures (PdP2-Pd/C), which exhibit substantially enhanced electrocatalytic performance toward a number of OMEO model reactions including the formic acid oxidation reaction (FAOR), methanol oxidation reaction (MOR), ethanol oxidation reaction (EOR), and ethylene glycol oxidation reaction (EGOR), in terms of not only apparent activity, but also of specific and mass activities, poisoning tolerance and catalytic stability. The improved performance and stability results from the modification of electronic structure by the introduced phosphor and synergy between of multinary structure (PdP and NiP, PdP2 and Pd), where the formed phosphide facilitates the adsorption of hydroxyl species and promotes the oxidation of poisoning intermediates giving rise to improved activity, poisoning tolerance and stability. The simple phosphorization approach reported here allows for mass production of highly-active electrocatalytic performance toward multiple OMEO reactions, holding substantial promise for their large-scale application in DLFCs.

Multifunctional Noble Metal Phosphide Electrocatalysts for Organic Molecule Electro-Oxidation

Small organic molecule electro-oxidation (OMEO) is the important anodic reaction occurring in direct liquid fuel cells (DLFCs) and requires efficient and durable electrocatalysts to promote the rea...

Superassembly of NiCoOx solid solution hybrids with a 2D/3D porous polyhedron-on-sheet structure for multi-functional electrocatalytic oxidation

NiCoOx solid solution hybrids with a hierarchical architecture and high porosity present excellent electrocatalytic performances in the UOR and electro-oxidation of organic molecules.

Easy preparation of multifunctional ternary PdNiP/C catalysts toward enhanced small organic molecule electro-oxidation and hydrogen evolution reactions

The small organic molecule electro-oxidation (OMEO) and the hydrogen evolution (HER) are two important half-reactions in direct liquid fuel cells (DLFCs) and water electrolyzers, respectively, whose performance is largely hindered by the low activity and poor stability of electrocatalysts. Herein, we demonstrate that a simple phosphorization treatment of commercially available palladium-nickel (PdNi) catalysts results in multifunctional ternary palladium nickel phosphide (PdNiP) catalysts, which exhibit substantially enhanced electrocatalytic activity and stability for HER and OMEO of a number of molecules including formic acid, methanol, ethanol, and ethylene glycol, in acidic and/or alkaline media. The improved performance results from the modification of electronic structure of palladium and nickel by the introduced phosphorus and the enhanced corrosion resistance of PdNiP. The simple phosphorization approach reported here allows for mass production of highly-active OMEO and HER electrocatalysts, holding substantial promise for their large-scale application in direct liquid fuel cells and water electrolyzers.

The effect of CuO on a Pt−Based catalyst for oxidation in a low-temperature fuel cell

Electrocatalytic oxidation of methanol, ethanol, and formic acid has currently attracted research attention for low-temperature fuel cells. However, the efficiencies of these fuel cells mainly depend on the electrocatalytic activities of Pt-based anodic catalysts due to the problems of low kinetics for small organic molecule electro-oxidation. An anode catalyst can be developed by the addition of some metal oxides into a Pt-based catalyst, which can effectively promote the electro-oxidation of fuels based on small organic molecules. In this work, a nanocomposite catalyst consisting of multi-wall carbon nanotubes (CNTs), copper oxide (CuO) and Pt nanoparticles was synthesized and used to improve fuel cell oxidation. Due to its low cost and oxophilic character, the metal oxide can play a major role in the oxidation of CO. The synthesis of xPt−yCuO/CNT electrocatalysts was executed through two steps: supporting of CuO nanoparticles on CNTs by the alcothermal method followed by Pt loading onto the prepared CuO/CNT by chemical reduction. The as-prepared catalysts were physically characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and electrochemical measurements. The results demonstrate that CuO is well dispersed onto the CNTs and that this oxide can further interact with the active Pt present on the as-prepared catalyst composites. The activity of various xPt−yCuO/CNT electrocatalysts was determined by cyclic voltammetry (CV), where x and y are the mass ratios of Pt and CuO, respectively. The presence of CuO was found to significantly contribute to enhanced electroactivity towards oxidation reactions. The 1Pt–3CuO/CNT electrocatalyst is a capable catalyst for improving low-temperature fuel cell applications.

Mechanistic aspects of the comparative oscillatory electrochemical oxidation of formic acid and methanol on platinum electrode

The characteristics of the electrochemical oscillations that emerge along the catalytic oxidation of small organic molecules critically depend on the coverage and nature of adsorbates. Herein we report experimental results on the electro-oxidation of formic acid and methanol on platinum and platinum-modified electrodes, and under conventional, i.e., cyclic voltammetry, and oscillatory conditions. The investigation was focused on the role played by surface-free sites and the presence of a step with a short-lived specie adsorbed on electrode surface. In order to reduce the coverage of adsorbed species, and thus to increase the main reaction pathway, chronoamperometry in platinum oxide region followed by potential sweeps or the adsorption of ad atoms, like tin, to mitigate the surface poisoning was adopted. Overall, those strategies considerably improved the electrochemical oxidation of formic acid, but had no effect for methanol. Our results show that the efficiency of formic acid electro-oxidation is preferred powered, compared with methanol, on a less poisoned electrode surface, which is obtained through a self-cleaning process driven by the oscillatory electro-oxidation of organic molecules. These results are rationalized in terms of peculiarities of the reaction mechanisms of both systems.

Assessment of the beneficial combination of electrochemical and ultrasonic activation of compounds originating from biomass.

The electro-oxidation of organic molecules at the anode with simultaneous generation of hydrogen at the cathode in electrosynthesis reactors is considered as a promising and efficient process for the co-production of hydrogen and bio-sourced value-added chemicals. In this study and for the first time, we investigated the electro-oxidation of glucose and methylglucoside in 0.1molL-1 NaOH on polycrystalline Pt (real surface area=14.5±0.5cm2, roughness≈5) in the potential range [0; +1.20V vs. rhe] under silent and ultrasonic (bath, 45kHz, Pacous=11.20W) conditions. A series of linear sweep voltammograms, chronoamperograms and high-performance liquid chronoamperograms were generated. It was found that higher current densities were obtained under ultrasonic conditions over the potential range of +0.25V to +1.10V vs. rhe, indicating that higher oxidation rates were provided under ultrasonication. It was observed that the desorption of species from the Pt surface in the medium potential region was favoured, allowing free catalytic Pt sites for further adsorption and oxidation of reactants; and in the high potential region, high peak current densities in the presence of ultrasound was due to enhanced mass transport of the electroactive species from the bulk electrolyte to the Pt-polycrystalline electrode surface. HPLC studies confirmed that higher electrochemical activity was obtained in the presence of ultrasound than in the absence. In our conditions, it was also found that low frequency ultrasound did not change the selectivity of the glucose and methylglucoside electro-oxidation reactions but instead, a significant increase in the rate of conversion was observed.

High Order Cyclic Voltammograms During Electrooxidation of Ethanol Catalyzed by Gold

Under fixed limits, potential sweeps in some electrochemical systems depict current profile whose shape repeats in every n cycle (with n > 1), receiving the name of high order voltammograms (HOV). HOV have been observed during electrooxidation of organic molecules catalyzed mainly by Pt. The present study shows HOV behavior during ethanol electrooxidation reaction onto gold in alkaline media. Firstly, a strong dependence of HOV with minimum potential is remarkable in this system and has not been considered in previous numeric models. Moreover, due to high sensibility of HOV to surface conditions, it was possible to follow effects caused by cation interactions with adsorbed oxygenated species.

Facile Cu3P-C hybrid supported strategy to improve Pt nanoparticle electrocatalytic performance toward methanol, ethanol, glycol and formic acid electro-oxidation

In this study, with a uniform mixed Cu3P-C hybrid as a support, Pt/C-Cu3P composite catalysts with varied phosphide/carbon ratios are synthesized via a wet chemical reduction pathway. These catalysts have been characterized using X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), chronoamperometry (CA), electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). Among the investigated catalysts, the Pt/C-Cu3P50% catalyst presents the best enhanced catalytic performance for electro-oxidation of targeted small organic fuel molecules. Compared to state-of-the-art commercial Pt/C, it exhibits 7.26, 4.19, 5.43 and 6.76 times electrocatalytic activity promotion for methanol, ethanol, glycol and formic acid electro-oxidation, respectively. This outstanding catalytic activity promotion should be ascribed to its ideal phosphide/carbon ratio as well as the induced beneficial synergistic effect between Cu3P and Pt, such as the so-called electronic effect and bi-functional effect. The exploration of inexpensive and earth-abundant Cu3P as a promoter in Pt-catalyzed small organic molecule electro-oxidation will definitely find a broad interest in PEMFCs fields.

Electrooxidation of Ethanol and Formic Acid on Model Systems Containing Noble Metals - Combined Spectroscopic and Electrochemical Studies

In electrooxidation of small organic molecules, such as ethanol and formic acid, noble metals exhibit exceptional catalytic activity. However even for the most active catalysts known, both above mentioned reactions proceed with high overpotentials at room temperature. The overall low activity of known catalysts towards electrooxidation of organic molecules render the low temperature fuel cells fed with liquid organic fuels, such as direct ethanol fuel cells, far from being economically viable. Better understanding of the factors influencing catalytic activity is crucial to design new, more active catalytic systems. It is widely accepted that catalytic and electronic properties of catalyst‘s surface are strongly related. Electronic properties of catalyst can be purposely modified, for instance by modifying its lattice parameter. In general, changes of the lattice parameter of metals will induce changes in their electronic properties as degree of overlapping of band forming orbitals change . When metal lattice is contracted, the conduction band becomes broader, and when metal lattice is expanded the conduction band (d-band) shrinks. Depending of the degree of filling of the d-band, the changes in d-band width causes the shift of the d-band center in opposite directions: if the conduction band is filled in more than half the broadening of the conduction band leads to shift of the d-band center towards Fermi level; when it is filled in less than half, the d-band center shifts in the opposite direction [1]. The changes in d-band center position relative to Fermi level can be correlated to adsorption properties of the surface [1]. We used the above mechanism to purposely induce the changes in the electronic properties and to investigate how the changed electronic properties influence the catalytic activity. To study the correlation between electronic and electrocatalytic properties of catalysts we used two distinct types of model systems: i) epitaxial layers of catalytically active noble metals (platinum, palladium) on another noble metals (in form of core-shell nanoparticles) and ii) nanoalloys, where catalytically active metal was alloyed with metal inactive towards the studied reaction, such as Pt-Pd which we used for electrooxidation of ethanol in acidic conditions. In those conditions palladium is catalytically inactive, and also does not participate in so called “bi-functional mechanism”, thus it can be assumed, that the overall catalytic activity can be to a large extend attributed to changes in surface geometry and to changes of electronic properties of platinum. To confirm changes in the electronic properties of our catalysts we used X-ray Photoelectron Spectroscopy (XPS) and UV Photoelectron Spectroscopy (UPS). Valence band and core-level spectra allows for determination of the electronic properties of the material, and together with electrochemical results the relation between electronic and electrocatalytic properties can be studied.This project was funded from Polish National Science Centre budget based on decision number DEC-2013/09/B/ST4/00099[1] A. Ruban, B. Hammer, P. Stoltze, H.L. Skriver, J.K. Norskov, J. Mol. Catal. A, 1997, 115, 421-429.

Highly Active Pt-Sn/C Catalysts for Ethanol Electro-Oxidation Prepared By a Polyol-Alcohol Reduction Process

Introduction.Fuel cells are very attractive devices as power source for mobile, stationary or portable applications. In a Direct Ethanol Fuel Cell, the fuel is directly feed into the cell anode compartment without any previous chemical modification. However, alcohols are very difficult and complex to electrooxidize completely to CO2, because of the need to break C-C bonds, which results in the formation of intermediates that poison the Pt active sites. In order to overcome these issues, the efforts are focused on developing new bimetallic catalysts with higher catalytic activity and tolerance to the presence of the intermediates, mainly CO, than Pt-alone. The most efficient alternative has been to add a second metal to the composition of the catalysts used as anodes for the electrooxidation of organic molecules. Therefore, this work presents the results of a study carried out to evaluate how different synthesis variables can have an effect on the chemical reduction process of the salts, and thus, on the chemical composition of PtSn/C catalysts. Then, the chemical composition has an effect on the performance of the PtSn/C materials for the ethanol oxidation reaction in acid media.Methodology.PtSn/C anodes with Pt:Sn atomic ratio of 1:1 were prepared by the polyol method, in the presence different concentrations of ethanol and water, which were used to dissolve the Sn precursor. The structural characteristics of the catalysts were studied by XRD analysis in a Philips X’Pert diffractometer using Cu Kα Kα (λ= 1.5406 Å) radiation operating at 40 kV. The chemical composition of the catalysts was analyzed by SEM-EDS and ICP-AES.Results.Through XRD analysis, the degree of alloying of the Pt-Sn/C catalysts is evaluated with Vegard’s law. Also, the average particle size is obtained with the Scherrer equation. The results show the formation of nanocatalysts having a particle size of 2-4 nm. Chemical analysis using SEM-EDS and ICP-AES indicate the actual Pt:Sn ratio, confirming the formation of Sn oxides as a function of the concentration of ethanol and water.The electrochemical characterization indicates that the Pt-Sn/C with high degree of alloying and less Sn oxides is more active for the EOR than Pt-Sn/C anodes with a high Sn oxides formation and low degree of alloying. Moreover, the Pt-Sn/C anodes demonstrated a higher catalytic activity than Pt/C synthesized by the same method.

Thin Film of Palladium Nanodendrites Supported on Graphite Electrode for Catalyzing the Oxidation of Small Organic Molecules

The present study describes the outcome of the electrocatalysis of small organic molecules methanol, ethanol and formic acid on palladium nanodendritic film on graphite electrode. Higher oxidation currents than commercial Pd/C catalyst and low activation energies are obtained for electro-oxidation of organic molecules, indicating that the nanodendrites are highly effective for the electro-oxidation of these molecules. The nanocomposite film is effective in alkaline medium for alcohols oxidation, and in acidic media for formic acid oxidation.

Improving the stability of Sb doped Sn oxides electrode thermally synthesized by using an acid ionic liquid as solvent

Antimony doped tin oxide electrodes were thermally synthesized over titanium substrates using three methodologies differentiated by the solvent in the preparation of the metal precursor solution, i.e.: alcoholic and sol–gel methods and a novel procedure based on the use of an acid ionic liquid. Synthesized electrodes were physically characterized and compared using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The three methods were compared in terms of activity towards dissolved organic molecule electrooxidation and electrode stability, evaluated by cyclic voltammetry, electrochemical impedance and the galvanostatic service life test. The prepared electrodes showed similar performance when working as anodes for the electrochemical oxidation of Ranitidine. However, the electrodes prepared by the proposed method, based on the use of an acid ionic liquid as solvent and structuring agent, showed the highest stability and longest service life, which regard to the properties of the ionic liquid: higher acidity and viscosity and lower volatility.

A Novel Composite Anode: The Electrooxidation of Organic Molecules via Formation of Highly Energetic Holes

This paper describes, for the first time, the electrochemical characteristics of a novel, composite electrode, comprising a thin TiO2 layer sandwiched between a silicon wafer and a metal grid. Holes thermally and/or photochemically generated near the Si/TiO2 interface in the Si are able to reach the surface of the TiO2 and oxidize water and/or species in solution. Hole transport across the TiO2 is facilitated by the application of a bias voltage across the silicon and metal grid. At low bias voltages, oxidation of water takes place at the metal grid; at higher voltages, the oxidation takes place directly at the TiO2 as surface states are accessed. The generation of holes is enhanced significantly if the TiO2 surface is irradiated with visible light. A theoretical model is presented to explain the observed data. The anodes represent a completely new area of oxidative electrochemistry with potential application across a wide range of technology, from fuel cells-on-a-chip to electroorganic chemistry.

DEMS Analysis of Small Organic Molecule Electrooxidation: A High-Temperature High-Pressure DEMS study

The electrooxidation of methanol, ethanol and ethylene glycol on a Pt/Vulcan catalyst was investigated over a wide temperature range [20 to 100oC] at 3 bar overpressure and under continuous electrolyte flow by differential electrochemical mass spectrometry [DEMS]. Oxidation of methanol, ethanol and ethylene glycol at 0.6 V at ambient temperatures yields CO2 current efficiencies of ~40, 5 and 4%, which increase to 100, 24 and 33% at 100oC, respectively. The apparent activation energies for the overall reaction and for oxidation to CO2 were found to be 58 and 64 kJ mol-1 for methanol oxidation, for ethanol / ethylene glycol they were 41 / 32 kJ mol-1 and 73 / 53 kJ mol-1, respectively. The mechanistic and kinetic implications of these data and the importance of model studies under realistic reaction conditions will be discussed.

DEMS Analysis of Small Organic Molecule Electrooxidation Products

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Structurally Modified Polymer of Carbazole with Specific Catalysis in Electrooxidation of Organic Molecules

Abstract The electrochemical oxidation of carbazole in acetonitrile containing tetra-n-butyl ammonium perchlorate produces a green film on the electrode; this film is electrocatalytic to the oxidation of 9,10-diphenylanthracene, or perylene or 9,10-dimethylanthracene or ferrocene. The spectral features of the film reveal a N-N-coupling with a total absence of—NH stretching band. It is soluble in N,N-dimethylformamide. The polymer is structurally modified compared to the film produced by carbazole oxidation in N,N-dimethylformamide.