Salophen-Type Ni(II) Schiff Base Complexes Derived from Naphthalene Aldehydes and Their Application as Catalysts for the Methanol Electro-Oxidation Reaction

Characterization and evaluation of Pt-Ru catalyst supported on multi-walled carbon nanotubes by electrochemical impedance

Reconstructed MgAl hydrotalcite, LDH-immobilized Ni(II)Schiff base complex composite for the electrooxidation of methanol

NiCo/C-N/CNT composite catalysts for electro-catalytic oxidation of methanol and ethanol

Structural characteristics and electrocatalytic activity in the methanol oxidation reaction in an alkaline solution of the Raney nickel promoted by a platinum-ruthenium mixture are studied with the aid of methods of scanning electron microscopy, x-ray diffraction microanalysis, BET, and measurements of cyclic voltamograms and polarization curves. Distributions of all components of the system under investigation (Al, Ni, Pt, Ru, O) at the surface of the catalyst, the average size of whose particles amounts to 20–30 µm, are established. It is shown that a number of parameters (composition and quantity of the promoting mixture, temperature and concentration of methanol and alkali, amount of the active mass of the electrode) exert an influence on the methanol oxidation rate. The catalyst on the basis of the Raney nickel promoted by 10 wt % Pt/Ru (1/9 at. %) exhibits maximum activity in the methanol electrooxidation reaction in a solution that contains 4 M CH3OH in 6 M KOH. Upon elevating temperature by 20°C in the temperature interval 40 to 80°C the reaction accelerates by 2–3 times.

Electrocatalytic oxidation of methanol on a glassy carbon disc electrode modified with Ni(II)‐hematoporphyrin IX, complex and conditioned by potential recycling in a limited range (between 100 and 600 mV vs. SCE) in 0.10 M NaOH solution, abbreviated as NiOHPME(A), was studied by cyclic voltammetry in alkaline medium. The results were compared with those obtained for a NiO modified glassy carbon electrode, NiOME, prepared in similar conditions. The findings show that the NiOHP film at NiOHPME(A) behaves as an efficient electrocatalyst for the oxidation of methanol in alkaline medium via Ni(III) species with the cross‐exchange reaction occurring throughout the layer at a low concentration of methanol and for a thin film of modifier. A plausible mechanism was proposed for catalytic oxidation of methanol at NiOHP modified electrode. Moreover, the effects of various parameters such as the scan rate, methanol concentration, thickness of NiOHP film and the real surface area of modified electrode on the oxidation of methanol were investigated. Finally, it has been shown that the NiOHPME(A) has a long‐term stability toward the oxidation of methanol.

Electrocatalytic oxidation of methanol on a glassy carbon electrode coated with Ni(II)-(1,2-phenylendiamine)2 (GC/NiOPD), conditioned by the potential recycling in a potential range of 100–650 mV (vs. SCE) is studied by cyclic voltammetry in an alkaline medium (0.10 M NaOH). The results show that the NiOPD layer formed at the surface of the electrode behaves as an efficient electrocatalyst for the oxidation of methanol in the alkaline medium via the Ni(III) species with a cross exchange reaction occurring throughout the layer at a low concentration of methanol. The effects of various parameters such as potential scan rates, methanol concentration and NiOPD surface concentration on the electro-oxidation of methanol are also investigated.

Electrocatalytic oxidation of methanol on a nickel electrode modified by nickel dimethylglyoxime complex in alkaline medium

Mechanistic study of nickel based catalysts for oxygen evolution and methanol oxidation in alkaline medium

In the present work, an attempt has been made to evaluate activation energy, electro-active surface area, kinetics, quantity of reacted methanol molecules, and catalytic activity relationship over the newly developed non-noble metal alloy decorated Schiff's base based conjugated conductive polymer composite electrodes for fuel cell applications. Typically, a new type of catalysts was developed using nickel and nickel-tin decorated conjugated Schiff's base based conductive polymer-palm flower carbon composites to utilize them in the form of possible high-performance catalysts. The bimetallic composition with different weight percentage concentrations of NiSn10/CSP-PC, NiSn20/CSP-PC, NiSn30/CSP-PC, and Ni/CSP-PC nanoparticles decorated Schiff's base based conductive polymer-palm carbon (CSP-PC) composite electrode materials are developed through the facile chemical reduction route. Structure, composition, morphology, electro-active surface area, kinetics, activation energy, quantity of molecules reacted, and the electrocatalytic activity are evaluated by using different analytical techniques. The electrochemical studies indicate that the nickel nanoparticles deposited Schiff's base based conductive polymer-palm flower carbon composite electrode developed in the present work shows the enhanced electro-oxidation current, reduced onset potential, lower activation energy, higher electro-active surface, and improved stability than those of other Schiff's base based conductive polymer and palm flower carbon. Electrochemical characterization studies also indicate that the appropriate amount of tin doping (10%) improved not only the catalytic activity but also enhanced the long-term anti-poisoning ability than that of Ni/CSP-PC catalyst. The onset potential of the NiSn10/CSP-PC catalyst for methanol oxidation is lower when compared with that of other catalysts having varied weight percentage compositions. With the best of our knowledge, this is considered to be the first report in the field of development of conjugated Schiff's base based conductive polymer-palm flower carbon composite as new support for efficient, low cost, and non-noble metal electrocatalysts for direct methanol fuel cell (DMFC) applications.

Nickel and zinc salen complexes were simultaneously encapsulated in the supercages of the mesoporous zeolite A by using the flexible ligand method. This heterogeneous catalyst NiZnsalenA was characterized by X-ray diffraction, infrared spectroscopy, diffuse reflectance UV-vis spectroscopy, elemental analysis, and N2 adsorption/desorption experiments. The techniques of cyclic voltammetry (CV) and chronoamperometry (CA) were employed to investigate the electrochemical behavior and electrocatalytic activity toward the oxidation of methanol on NiZnsalenA glassy carbon electrode (GCE) in 0.1-M NaOH solution. The CV results presented a pair of redox peaks associated with the Ni2+(salen)(OH)2/Ni3+(salen)O(OH) redox couple. NiZnsalenA also showed the superior electrocatalytic activity to the oxidation of methanol than pure Ni-modified electrode, mainly due to a synergetic effect in NiZnsalenA. This synergetic effect may originate from the interaction of Ni(salen) and Zn(salen) and/or the formation of dinuclear salen complexes via the lattice oxygen of the zeolitic host. The effects of the scan rate, methanol concentration, and OH− concentration on methanol oxidation are investigated, and a possible mechanism is proposed that the oxidation of methanol is done by reaction with Ni3+(salen)O(OH) and also direct electrooxidation reaction. The kinetic parameters such as the electron transfer coefficient α and the rate constant k s of the electrode reaction were estimated to be 0.39 and 1.59 s−1, respectively. In both the CA and CC studies, the process of methanol oxidation followed a Cottrellian behavior, and the diffusion coefficients D CA and D CC of methanol represented the similar tendency, where an initial sharp drop was terminated to a very slow change as the concentration of methanol was approaching 0.7 M. The catalytic rate constant k cat increased rapidly until the concentration of methanol was increased above 0.7 M, and then the values of k cat remained almost constant.

Electrocatalytic oxidation of methanol on a glassy carbon disc electrode modified with Ni(II)-1-(2-pyridylazo)-2-naphthol (Ni-PAN) complex and conditioned by potential recycling in a limited range (between 100–600 mV) in 0.1 M NaOH solution, abbreviated as NiPANME, is studied by cyclic voltammetry in alkaline medium. The results are compared with those obtained for a NiO modified glassy-carbon electrode, NiOME, prepared in similar conditions. The findings show that the NiPAN film behaves as an efficient electrocatalyst for the oxidation of methanol in alkaline medium via Ni(III) species with the cross-exchange reaction occurring throughout the layer at a low concentration of methanol and for a thin film of modifier. Effects of the scan rate and methanol concentration on the methanol oxidation are investigated. The cyclic voltammetry and amperometry methods are used to investigate the methanol electrooxidation at the modified electrode.

Methanol electrooxidation on a nickel electrode modified by nickel–dimethylglyoxime complex formed by electrochemical synthesis

Multi-walled carbon nanotubes (MWNTs)-supported palladium (Pd) nanoparticles (NPs) catalyst (Pd/MWNTs) for methanol oxidation was prepared by a novel one-pot bottom-up method, i.e., direct reduction of palladium acetylacetonate (Pd(AcAc)2) in the refluxing xylene solution in the presence of carboxylic groups functionalized MWNTs without any assistance of reduction agents. Transmission electron microscope (TEM) micrographs revealed that Pd NPs with an average size of 14.0 nm were uniformly grown onto MWNTs surface, confirming a successful synthesis of the catalysts. The loading of Pd was calculated to be 24.1% from the thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) results. Raman spectroscopy and X-ray diffraction (XRD) results indicate an obvious interaction between Pd NPs and MWNTs. The electrocatalytic activity of the Pd/MWNTs catalyst was evaluated for methanol oxidation in KOH solutions. Parameters including the concentration of methanol and KOH were investigated. Experimental A facile one-pot solution-based reduction method was developed to synthesize the composite catalyst with Pd NPs decorated on MWNTs. Briefly, 100.0 mg MWNTs was dispersed with 50 mL xylene in a 100 mL beaker under ultra-sonication for 1 hour, after which the MWNTs/xylene mixture was transferred into a 250 mL 3-neck flask. Then, the solution was heated to reflux ( ~140 °C) after 20 min. At the meantime, 304.0 mg Pd(AcAc)2was dispersed with 20 mL xylene in a 50 mL beaker under magnetic stirring for 10 min, and the mixture was then transferred into the 3-neck flask. The whole solution was then kept refluxing for an additional 3 hours to complete the reaction. After that, the final solution was cooled down to room temperature naturally, filtered under vacuum and rinsed with ethanol and distilled water 3 times, respectively. The final product (black powders) was collected after vacuum drying at 50 °C for 24 hours. Results and Discussion Pd NPs are successfully synthesized and uniformly dispersed on the MWNTs support with no obvious agglomeration, Pd NPs are strongly insert into the MWNTs, implying an intensively chemical interaction between Pd NPs and MWNTs due to the promoting function of carboxylic groups on the surface of MWNTs.The peak current increase when the KOH concentration increases from 0.2 M to 0.5 M, a further increase of the KOH concentration to 1.0 M leads to an obvious decrease in peak current, the peak potential has a continuous negative – shift with the increase of KOH concentration, the negative-shift in the peak potential suggests that increasing KOH concentration has a favorable effect on the oxidation of methanol, the changes of peak current and peak potential clearly illustrate that the optimum peak current can only be achieved by a balance between the methanol and hydroxyl adsorbates coverage. Conclusion In this work, Pd/MWNTs catalyst has been successfully prepared by a facile one-pot bottom-up method. The electrocatalytic activities of the Pd/MWNTs catalyst for methanol oxidation are evaluated by varying the concentration of methanol and alkaline and changing the temperature. The reaction of the adsorbed intermediate species with the adsorbed hydroxyl is found to be the rate-determining step and an optimum peak current can only be achieved by a balance between methanol and hydroxyl adsorbates coverage. A pronounced influence of temperature on the Pd/MWNTs is manifested, implying greater tolerance of the catalyst towards poisoning residues at high temperatures. Acknowledgments The financial supports from Seeded Research Enhanced Grant (REG) and College of Engineering at Lamar University are kindly acknowledged. Figure 1. Cyclic voltammograms of the methanol oxidation reaction on the Pd/MWNTs electrode in solutions containing 3.0 M methanol with various KOH concentrations of (a) 0.2 M, (b) 0.5 M, and (c)1.0 M at a scan rate of 50 mV s-1at room temperature. Inset shows TEM image of the Pd/MWNTs.

Elaboration of new electrodes with carbon paste containing polystyrene functionalized by pentadentate nickel(II)-Schiff base complex – Application to the electrooxidation reaction of methanol and its aliphatic analogs.

Pt–Ag/C catalyst for methanol oxidation and alcohol tolerant cathode in different electrolytes