Electrocatalytic oxidation of methanol on Ni and NiCu alloy modified glassy carbon electrode

Nickel and nickel–copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV) and chronoamperometry (CA) were employed. The cyclic voltammogram of NiCu alloy demonstrates the formation of β/β crystallographic forms of the nickel oxyhydroxide under prolonged repetitive potential cycling in alkaline solution. In CV studies, in the presence of methanol NiCu alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel hydroxide increase is followed by a decrease in the corresponding cathodic current in presence of methanol. The anodic peak currents show linear dependency with the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of methanol was found to be 2 × 10⁻⁶ cm² s⁻¹ in agreement with the values obtained from CV measurements.     

Fabrication and characterization of Ni modified TiO2 electrode as anode material for direct methanol fuel cell

Highly ordered porous titanium dioxide nanotube (TiO₂-NT) surfaces were prepared with anodization method to obtain a larger specific surface area that plays a very important role in methanol oxidation. In this regard, optimum conditions such as various anodization voltages and times were determined. The largest surface area of TiO₂ occurred at anodization voltage and time of 60 V and 2 h, respectively. After obtaining the high specific surface area, very small amounts of Nickel (Ni) nanoparticles were deposited on TiO₂-NT surface and their behaviors of methanol electro-oxidation were investigated by Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) methods. Characterizations of the TiO₂-NT and Ni modified electrodes are exerted by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The average tube length and diameter are 36.32 μm and 93.6 nm according to SEM images. XRD results indicated the tetragonal structured anatase of TiO₂ and Ni (111) and (200). While methanol oxidation peak does not observe on TiO₂-NT surface, behaviors of methanol oxidation depend on the Ni content on TiO₂-NT surface. Oxidation response increases by the increasing amount of Ni nano-particles in the deposits. High surface coverage (Γ) with 3.87 × 10⁻⁹ mol cm⁻² and very low activation energy (E_a) with 11.0 kJ/mol are measured on Ni modified TiO₂-NT with the highest Ni content. Charge transfer resistance either reduced or provided long stability and durability with the deposition of Ni on TiO₂-NT. This may associate that TiO₂-NTs with the large surface areas may play a significant role in the methanol oxidation efficiency. Modification of TiO₂-NT surface with Ni particles is an effective plan for high-performance electrocatalysis. Besides, the strong electronic interaction between Ni and TiO₂ may facilitate the adsorption of methanol through the bi-functional mechanism on the electrode surface.     

Kinetics of the hydrogen evolution reaction on NiMn graphite modified electrode

The mechanism and kinetics of the hydrogen evolution reaction (HER) on graphite modified with Ni and NiMn electrode (G/Ni and G/NiMn) in 0.1 M NaOH solution were studied using the methods of steady-state polarization, electrochemical impedance spectroscopy, cyclic voltammetry and open circuit potential transient. The addition of Mn to Ni significantly increases the catalytic activity in HER due to higher real surface area and higher intrinsic activity. The simulation of the data obtained from these methods, using nonlinear fitting procedure allowed us to determine the rate constants of Volmer, Heyrovsky and Tafel steps associated with the mentioned reaction. The kinetics results indicate that HER mechanism for G/NiMn electrode at low negative potentials is a serial combination of Volmer and parallel Tafel and Heyrovsky steps. At high negative potentials where the hydrogen coverage reaches its limiting value, a Tafel line with the slope of −125 mV dec⁻¹ is obtained. In this potential region the mechanism of the HER follows Volmer-Heyrovsky while the Tafel step has negligible contribution. Open circuit potential measurements for G/Ni and G/NiMn at different charging currents show that hydrogen absorption into the electrode material occurs.     

Synthesis of ZSM-5 zeolite: Electrochemical behavior of carbon paste electrode modified with Ni (II)-zeolite and its application for electrocatalytic oxidation of methanol

In this research, we reported a novel method for synthesis of ZSM-5 zeolite. The synthesized zeolite was characterized using X-ray diffraction, scanning electronic microscopy and FT-IR techniques. The modified carbon paste electrode was prepared by incorporation of Ni (II)-zeolite in the carbon paste matrix. The electrochemical oxidation of methanol was investigated at the surface of this modified electrode in alkaline solution using cyclic voltammetry and chronoamperometry methods. It was found that methanol was oxidized by NiOOH generated with further electrochemical oxidation of nickel hydroxide on the surface of this modified electrode during the anodic potential sweep. The effect of some parameters such as scan rate of potential, concentration of methanol, amount of Ni (II)-zeolite was investigated on the oxidation of methanol at this electrode. Also, the rate constant for the catalytic reaction (k) of methanol was obtained.     

Nickel phosphate as advanced promising electrochemical catalyst for the electro-oxidation of methanol

Mesoporous nickel phosphate nanotube (Meso NiPO NT) and mesoporous nickel phosphate nanosheet (Meso NiPO NS) are developed as catalysts for electrochemical methanol oxidation. Conventional mesoporous nickel phosphate which is composed of stacked nanocrystals (Meso NiPO), microporous VSB-5 and commercial nickel oxide (NiO) are used as control materials. Notably, both Meso NiPO NT (40.83 mA cm^?2) and Meso NiPO NS (44.97 mA cm^?2) exhibit much higher oxidation current density than VSB-5 (13.41 mA cm^?2), Meso NiPO (19.85 mA cm^?2) and commercial NiO (0.87 mA cm^?2). As for the durability test on these materials modified fluorine-doped tin dioxide transparent conductive glass (FTO) electrodes, Meso NiPO NT displays the most stable performance and still retains 91.3% electrochemical activity, which perhaps benefit from its nanotube structure and large specific surface area (99.6 m²/g). Moreover, Meso NiPO NT has higher activity and more excellent stability than many of the previously reported nickel-based materials, suggesting a potential development for direct methanol fuel cells.     

Electrochemical layer-by-layer fabrication of a novel three-dimensional Pt/graphene/carbon fiber electrode and its improved catalytic performance for methanol electrooxidation in alkaline medium

Here, we report a novel method for assembling reduced graphene oxide (RGO) and Pt nanoparticles on a carbon fiber (CF) electrode successively to form a stable Pt nanoparticle-RGO-Pt nanoparticle-RGO/CF multiple junction for electrocatalysis application. As the SEM imaging exhibited, Pt nanoparticles are uniformly deposited on the surface of each RGO sheet, performing an alternative covering structure of RGO and Pt nanoparticle multi-layer on the CF electrode. Thus, a novel three-dimensional (3D) multi-layered Pt/RGO modified CF electrode (N–Pt/RGO/CF) is obtained. Experimental results demonstrate that the prepared N–Pt/RGO/CF electrode shows good electrochemical properties and enhanced electrocatalytic activity toward methanol electrooxidation in alkaline medium as compared with the Pt/RGO/CF electrode without layer-by-layer structure or the Pt/CF electrode without RGO. It is due to the unique 3D pore structure of N–Pt/RGO/CF and the good electron transport property of RGO in the composite electrode.     

Pt-Ru-TiO2 photoelectrocatalysts for methanol oxidation

Novel photoelectrocatalysts composed of PtRuTiO₂/C are prepared by the polymeric precursor method and are characterized by scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy and cyclic voltammetry. The onset potential for methanol oxidation is similar (0.3 V vs. RHE) for all of the photoelectrocatalyst layers investigated, although the peak current density is dependent on the layer composition. Irradiation of UV light on the photoelectrocatalyst surfaces enhances the chronoamperometric responses up to 18%, which clearly demonstrates a synergistic effect between the photo- and electrocatalysts. The comparison between all the layers prepared indicates that there is an appropriate ratio of metallic nanoparticles and TiO₂ to obtain the best performance of these photoelectroactive layers. These results demonstrate that methanol oxidation is achieved by electro- and photocatalysis using a simple and affordable method. This procedure can be conveniently exploited to enhance the response of direct methanol fuel cell electrodes.     

Electrochemical impedance studies of electrooxidation of methanol and formic acid on Pt/C catalyst in acid medium

Cyclic voltammetry (CV), amperometric i − t experiments, and electrochemical impedance spectroscopy (EIS) measurements were carried out by using glassy carbon disk electrode covered with the Pt/C catalyst powder in solutions of 0.5 mol L⁻¹ H₂SO₄ containing 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄ containing 0.5 mol L⁻¹ HCOOH at 25 °C, respectively. Electrochemical measurements show that the activity of Pt/C for formic acid electrooxidation is prominently higher than for methanol electrooxidation. EIS information also discloses that the electrooxidation of methanol and formic acid on the Pt/C catalyst at various polarization potentials show different impedance behaviors. The mechanisms and the rate-determining steps of formic acid electrooxidation are also changed with the increase of the potential. Simultaneously, the effects of the electrode potentials on the impedance patterns were revealed.     

Electrospinning-derived carbon fibrous mats improving the performance of commercial Pt/C for methanol oxidation

The carbon fibrous mats (CFMs) formed by carbon nanofibers whose average diameter is about 150 nm have been fabricated by thermally treating the electrospun polyacrylonitrile fibrous mats. The electrocatalytic activity of commercial Pt/C supported on the CFMs for methanol oxidation in a sulfuric acid solution has been investigated by cyclic voltammetry, chronoamperometry, quasi-steady state polarization, and electrochemical impedance spectroscopy (EIS) methods. The results show that the commercial Pt/C supported on the CFMs exhibits higher electrocatalytic activity, more stability, larger exchange current and smaller charge transfer resistance than that on commercial carbon papers (CPs), which reveals that the CFMs could be developed as suitably-supporting materials for Pt/C catalyst due to their special porous and continuous fibrous structures.     

Kinetic analysis of carbon monoxide and methanol oxidation on high performance carbon-supported Pt-Ru electrocatalyst for direct methanol fuel cells

The kinetic parameters of carbon monoxide and methanol oxidation reactions on a high performance carbon-supported Pt-Ru electrocatalyst (HP 20% 1:1 Pt-Ru alloy on Vulcan XC-72 carbon black) have been studied using cyclic voltammetry and rotating disk electrode (RDE) techniques in 0.50 M H₂SO₄ and H₂SO₄ (0.06-0.92 M) + CH₃OH (0.10-1.00 M) solutions at 25.0-45.0 °C. CO oxidation showed an irreversible behaviour with an adsorption control giving an exchange current density of 2.3 × 10⁻⁶ A cm⁻² and a Tafel slope of 113 mV dec⁻¹ (α = 0.52) at 25.0 °C. Methanol oxidation behaved as an irreversible mixed-controlled reaction, probably with generation of a soluble intermediate (such as HCHO or HCOOH), showing an exchange current density of 7.4 × 10⁻⁶ A cm⁻² and a Tafel slope of 199 mV dec⁻¹ (α = 0.30) at 25.0 °C. Reaction orders of 0.5 for methanol and −0.5 for proton were found, which are compatible with the consideration of the reaction between Pt-CO and Ru-OH species as the rate-determining step, being the initial methanol adsorption adjustable to a Temkin isotherm. The activation energy calculated through Arrhenius plots was 58 kJ mol⁻¹, practically independent of the applied potential. Methanol oxidation on carbon-supported Pt-Ru electrocatalyst was improved by multiple potential cycles, indicating the generation of hydrous ruthenium oxide, RuO_xH_y, which enhances the process.     

Preparation of flexible composite electrode with bacterial cellulose (BC)-derived carbon aerogel supported low loaded NiS for methanol electrocatalytic oxidation

In this study, carbon aerogel (CA) were obtained by inexpensive bacterial cellulose (BC) hydrogel freeze-dried and carbonized under N₂ atmosphere. Then nickel sulfide (NiS)/CA composite aerogel electrodes with different contents were successfully prepared by a one-step solvothermal method. The morphology, phases and surface electronic state of these electrodes were characterized by SEM/TEM, XRD and XPS, respectively, and their electrocatalytical properties for methanol oxidation were investigated by cyclic voltammetry (CV) in the alkaline media of methanol. The NiS particles dispersed uniformly on CA, and the obtained material maintained the reticulated porous structure of BC. The methanol oxidation peak current density of CNS-0.5 at 0.8 V reached 43 mA/cm² (263 mA/mg). After 1000 cycles, the peak current density retained 92% of the initial state. The composite electrode has good catalytic activity and good cycle performance for methanol catalysis. Nickel sulfide with high crystallinity transforms to nickel oxide with low crystallinity after a long cycle test, which results in excellent cycle performance of the composite. NiS/CA electrodes have the potential for application in portable or wearable devices.     

Kinetics of methanol electrooxidation on Pt/C and PtRu/C catalysts

This paper analyzes the performance of platinum and platinum:ruthenium carbon-supported catalysts modified by the application of in-situ cathodic polarizations towards the methanol oxidation reaction. These new electrodes are characterized by electrochemical techniques together with transmission electron microscopy images to envisage the dispersion of the catalyst. We measure methanol electrooxidation current transients, fitting the results with a general kinetic equation for a mixed mass and charge transfer processes for adsorbed reactant species. The kinetic equation also helps to predict the exponent of the chronoamperometric decay as directly related to the fractal dimension of the catalyst surface and to discuss the possible processes involved in the electrocatalytic reaction.     

Hierarchical Co3O4 decorated PPy nanocasting core-shell nanospheres as a high performance electrocatalysts for methanol oxidation

In recent times, much attention has been paid to explore economic and highly active precious metal free electrocatalysts for energy conversion and storage systems due to the expensiveness of Pt-based catalysts. Here we developed a mesoporous core-shell like nanospheres composed of a metallic cobalt oxide core wrapped with a polypyrrole nanoshell (PPy/Co₃O₄) for methanol electrooxidation. The performance of the core-shell PPy/Co₃O₄ nanospheres as anodic catalyst material was measured in 1 M KOH electrolyte and the results obtained demonstrated that the hybrid possesses high catalytic activity in terms of current density and onset voltage. The core-shell PPy/Co₃O₄ delivers an oxidation current density of ～111 mA/cm² at 0.5 V with superior stability long run stability. The observed electrocatalytic performance of the porous PPy/Co₃O₄ nanospheres is attributed to the integrative effects of both Co-species and layered carbon shell and presence of exceptionally numerous mesopores. Results show evidence that the earth abundant PPy/Co₃O₄ provide a potential electrode material for methanol electrooxidation with a satisfactory reaction activity.     

The electrochemical oxidation of methanol on a Pt/TNTs/Ti electrode enhanced by illumination

A Pt/TNTs/Ti electrode is prepared by electrochemically depositing Pt using the modulated pulse current method onto high density, well ordered and uniformly distributed TiO₂ nanotubes (TNTs) on a Ti substrate. The results show that the performance and anti-poison ability of the Pt/TNTs/Ti electrode for methanol electro-oxidation under illumination is remarkably enhanced and is even better than the best bi-metallic Pt-Ru catalysts. CO poisoning is no longer a problem during methanol electro-oxidation with the Pt/TNTs/Ti electrode under illumination.     

NiFexP@NiCo-LDH nanoarray bifunctional electrocatalysts for coupling of methanol oxidation and hydrogen production

NiFe_xP@NiCo-LDH/CC nanosheet core-shell nanoarrays electrocatalysts are prepared by electrodeposition and phosphating methods for relatively low potential production of H₂ and value-added formate in methanol/water electrolysis systems. During the oxygen evolution reaction process, the over potential is 269 mA at the current density of 50 mA cm^?2 and the Tafel slope is 97 mV dec^?1. It also realizes the stable long-term electrocatalysis of methanol to formate under high current density and maintains a relatively high Faraday efficiency of 100%. Meanwhile, the energy saving is higher than 10% in the methanol oxidation and co-hydrogen production system that achieves great attention. The superior performance of NiFe_xP@NiCo-LDH/CC bifunctional electrocatalysts might be beneficial from the interaction to Ni and Fe bimetallic extranuclear electrons that exposes more active sites.     

Effective PtAu nanowire network catalysts with ultralow Pt content for formic acid oxidation and methanol oxidation

Pt is the ideal anode catalyst in fuel cells. In this paper, in order to increase the utilization of Pt, the PtAu nanowire networks (NWNs) with ultralow content of Pt are fabricated by a simple silicon monoxide (SiO) reduction method without any capping agent. PtAu NWNs supported on carbon black with Pt content of 1 wt% (Pt₀.₀₅Au NWNs) are employed as catalysts for formic acid oxidation (FAO) and methanol oxidation reaction (MOR), whose mass activities are as high as 4998.9 and 2282.3 mA∙mg_Pt⁻¹, respectively. The network structure facilitates the electron transfer and increases the stability of the catalysts. The PtAu composite experiences compressive lattice strain as confirmed by X-ray powder diffraction (XRD). The Pt₀.₀₅Au NWNs catalyst with low Pt content results in the largest strain variation compared with PtAu composited of other ratios, which may downshift the d-band center of Pt and lead to the higher electrocatalytic activity in oxidation reaction.     

Improved methanol electro-oxidation reaction on PdRh-PVP/C electrodes

Here we report on the organometallic synthesis of polyvinylpyrrolidone (PVP)-stabilized palladium-rhodium nanostructures that display high electrochemical properties when used as carbon-supported electrodes (Pd_xRh_1-x-PVP/C) for methanol oxidation reaction (MOR). These nanostructures were synthesized by hydrogenation of the tris(dibenzylideneacetone)dipalladium(0) (Pd₂(dba)₃) and tris(allyl) rhodium (Rh(η³-C₃H₅)₃) complexes, in tetrahydrofuran (THF) under mild reaction conditions (room temperature and 3 bar H₂) and in the presence of PVP as stabilizer. The influence of methanol concentration (0.5, 1.0 and 2.0 M) as well as different scan rates (5–100 mV s^?1) was evaluated to determine changes in the stability and catalytic activity. The organometallic approach and the use of PVP for the preparation of PdRh electrode materials promoted the formation of highly dispersed nanostructures, that led to a remarkably enhanced methanol electro-oxidation in alkaline medium. This high catalytic behavior can reasonably arise from a synergistic effect between Pd and Rh metals as, under the applied conditions, Rh is expected to enhance the Pd ability to oxidize methanol to CO₂ (oxophilic character) as well as the catalyst stability. From all the evaluated electrode materials, Pd₈Rh₂-PVP/C electrode showed the highest mass activity at high methanol concentration (2.0 M) and low scan rate (10 mV s^?1). This catalyst showed a performance up to 26 times higher than that of Pd-PVP/C and interestingly an electroactivity superior to that of previously reported PdRh catalysts.     

Parametric study on electrochemical deposition of hair shaped PtRu as methanol oxidation catalyst

In this article we report a method for synthesis of hair shaped PtRu and investigation of its catalytic ability towards methanol oxidation reaction. Hair shaped PtRu electrochemically was deposited on electrode from an electrolyte with high acidity containing anionic surfactant, sodium dodecylsulfate (SDS). The PtRu modified gold film electrodes were characterized by scanning electron microscopy (SEM). The effect of Pt:Ru composition; electrodeposition time and SDS concentration on catalyst morphology were investigated in terms of electrocatalytic response of as-fabricated electrode. The amount of the Pt loaded on the electrode, in the best electroreduction condition, was analyzed using ICP-AES technique.     

Electrodeposition of platinum microparticle interface on conducting polymer film modified nichrome for electrocatalytic oxidation of methanol

A simple and “green” approach for fabrication of platinum microparticle interface on conducting polymer film modified nichrome matrix (Pt/PAn/Nc) for methanol oxidation was investigated. The Pt microparticles were grown directly on the polyaniline precursor film modified nichrome matrix (PAn/Nc) in dilute chloroplatinic acid solution by cyclic voltammetry. The SEM revealed that the deposits were composed of spherical Pt microparticles. Cyclic voltammetry and chronoamperometry were used for characterization of the electrode properties. Results showed that the spherical Pt/PAn/Nc electrode enhanced the catalytic activity and promoted methanol electrooxidation. The catalytic activity of Pt/PAn/Nc electrode was 15 times higher than that obtained from pure platinum under the same conditions. Moreover, the deposited Pt microparticles improved the electrochemical properties of nichrome and reduced the dosage of noble metal platinum, remarkably. The cost could be reduced dramatically by decreasing the contents of platinum. The Pt/PAn/Nc are likely a promising electrocatalyst for methanol electrooxidation.     

Gold nanoparticle-coated Ni/Al layered double hydroxides on glassy carbon electrode for enhanced methanol electro-oxidation

We report a facile electrochemical strategy for the synthesis of Ni/Al layered double hydroxides (LDHs) and gold nanoparticle (AuNPs)-coated glassy carbon electrode (GCE). The new electrode is named LDH/AuNPs/GCE. The new electrode is named LDH/AuNPs/GCE. The electrocatalytic activity of LDH/AuNPs toward methanol electro-oxidation was studied by cyclic voltammetry and chronoamperometry. Compared to the Ni/Al-LDH modified GCE without AuNPs film (LDH/GCE), the LDH/AuNPs/GCE exhibits remarkably higher catalytic activity for methanol electro-oxidation, e.g. the lower oxidation potential (0.57 V vs. SCE) and the higher current density (6-fold). The enhancement may be attributed to the higher electrocatalytic activity of Ni/Al-LDHs in the presence of AuNPs, the synergy effect between them, or both. The results presented here may be of broad interest not only for developing fuel cells but also for understanding of OH⁻ electro-generated on noble metal surfaces.