Titanium dioxide as support material for Pt1Pd3 toward methanol oxidation

The electrocatalytic oxidation of methanol on the Pt₁Pd₃ nanoparticles supported on rutile TiO₂ in alkaline solution is investigated. The Pt₁Pd₃ nanoparticles are prepared by the chemical co-reduction of the precursors of Pt and Pd and then loaded on TiO₂. The Pt₁Pd₃ nanoparticles with sizes of about 2–4 nm and a certain degree of aggregation are dispersed on TiO₂. The position and shape of the methanol oxidation peak on Pt₁Pd₃/TiO₂ are more similar to those on Pt/TiO₂ than those on Pd/TiO₂, while Pt₁Pd₃/TiO₂ exhibits higher catalytic activity, e.g., a significantly higher peak intensity, than Pt₁Pd₃/C, Pt/TiO₂ and Pd/TiO₂. This indicates the advantage of TiO₂ as a support material and the strong synergy between the Pt₁Pd₃ and TiO₂ and between the Pt and Pd. Moreover, Pt₁Pd₃/TiO₂ has a high tolerance for the poisoning caused by CO. Rutile TiO₂ is shown to be suitable as a support material for the Pt₁Pd₃ to achieve enhanced catalytic activity and stability.     

Electrocatalytic oxidation of methanol on CoNi electrodeposited materials

Cobalt–nickel bimetallic materials electrodeposited on Si/Ti/Ni substrates were evaluated for the oxidation of methanol in alkaline media. CoNi samples were prepared potentiostatically selecting conditions adequate to achieve the desired Co/Ni ratio. All samples were characterized by X-ray fluorescence and cyclic voltammetry to determine their composition and electrochemical behaviour. The electrocatalytical performance of prepared samples was evaluated also by cyclic voltammetry using methanol solutions in alkaline media. Material composition, methanol and NaOH concentration, and temperature were the variables studied. The results indicate that a cobalt excess inhibits the methanol oxidation. In the same way, a significant enhancement of the oxidation current was observed on increasing the NaOH concentration up to 0.5 M, but for higher concentrations the electrocatalytic performance of these materials decreases. With regard to the increase of MeOH concentration or temperature, both variables are related to an improvement of the electrocatalytic performance. Finally, the effect of platinum skin on the CoNi deposits was evaluated, concluding that it favours MeOH oxidation but does not protect the substrate surface from the damage exerted by excessive NaOH concentration.     

Influence of carbon support properties on the electrocatalytic activity of PtRuCu nanoparticles for methanol and ethanol oxidation

This work set out to explore the influence of kind and surface condition of carbon supports on the electrocatalytic activity of trimetallic PtRuCu alloy nanoparticles. The structure, composition, particle size and catalyst loading were determined by XRD, EDX, XPS, TEM and ICP-AES analysis. XRD studies revealed that support physical characteristics and surface conditions have an important influence in lattice strain, while XPS pointed out that a strong electronic interaction exists between the particles and the carbon support. Electrochemical experiments showed that the activated carbon black supported PtRuCu catalyst exhibits the best performance for methanol and ethanol oxidation and the lowest poisoning rate. The superior catalytic activity of this electrode can be rationalized in terms of metal-support interaction, Pt utilization efficiency and electrical conductivity of the carbon support. Furthermore, the as-prepared electrode exhibits 13 and 7 times higher activity towards methanol and ethanol oxidation when compared with a PtRu/C commercial catalyst.     

High efficient electrocatalytic oxidation of methanol on Pt/polyindoles composite catalysts

Novel composite catalysts have been fabricated by the electrodeposition of Pt onto the glassy carbon electrode (GC) modified respectively with polyindole (PIn) and poly(5-methoxyindole) (PMI) and used for the electrooxidation of methanol in acid solution of 0.5 M H₂SO₄ containing 1.0 M methanol. As-formed composite catalysts are characterized by SEM, XRD and the electrochemical methods. The results of the catalytic activity for methanol oxidation show that the two composite catalysts exhibit higher catalytic activity and stronger poisoning-tolerance than Pt/polypyrrole/GC (Pt/PPy/GC) and Pt/GC. Electrochemical impedance spectroscopy indicates that the methanol electrooxidation on the composite catalysts at various potentials shows different impedance behaviors. At the same time, the charge-transfer resistance for electrooxidation of methanol on Pt/PIn/GC and Pt/PMI/GC is smaller than those on Pt/PPy/GC and Pt/GC. The present study shows a promising choice of Pt/PIn and Pt/PMI as composite catalysts for methanol electrooxidation.     

Electrocatalytic activity of binary and ternary composite films of Pd,MWCNT and Ni,Part II: Methanol electrooxidation in 1 M KOH

Binary and ternary composite films of Pd, multiwalled carbon nanotubes (MWCNTs) and Ni have been obtained on glassy carbon electrodes and investigated for electrocatalysis of methanol oxidation in 1 M KOH. It is observed that small addition (1–5%) of MWCNTs to Pd increases the apparent electrocatalytic activity of the electrode considerably, the magnitude of enhancement, however, being the greatest (5–8 times) with 1% MWCNT. 1% Ni introduction to the active Pd–1% MWCNT electrode increased the apparent electrocatalytic activity by 1.4–1.7 times further. Among the electrodes investigated, the Pd–1% MWCNT–1% Ni composite electrode has the greatest apparent electrocatalytic activity. The enhanced electrocatalytic activity of the electrodes is ascribed to their improved geometrical as well as electronic properties.     

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.     

Preparation of Pd/ZnO/Ni hierarchical porous array film with enhanced electrocatalytic activity for methanol oxidation

In this study, we successfully synthesized a Pd/ZnO/Ni hierarchical porous array-film catalyst by electrodeposition and magnetron sputtering with the assistance of the monodisperse colloidal sphere template. Structural characterisation indicated that a layer of Pd nanoparticles was uniformly grown on the ZnO/Ni ordered bowl-like micro/nano array film. Electrochemical measurements in alkaline solution demonstrated that the as-grown array film had outstanding electrocatalytic activity for methanol oxidation. The specific activity of the Pd/ZnO/Ni porous array film was up to 130.1 mA cm⁻². The corresponding mass activity (812.7 mA mg⁻¹) was 6 times higher than that of commercial Pd/C catalyst (134.8 mA mg⁻¹), and the stability was also much better than the commercial one. These excellent electrochemical properties can be attributed to the unique hierarchical porous structure, which offers a high specific surface area for the methanol reaction, and ZnO intermediate layer, which effectively removes the poisoning species from the Pd sites through the strong oxidative hydroxyl radicals.     

High electrocatalytic activity and stability of PtAg supported on rutile TiO2 for methanol oxidation

Rutile TiO₂ is used as a support for the PtAg nanoparticles, and the catalytic activity and stability of PtAg/TiO₂ for the electrooxidation of methanol are investigated. The PtAg nanoparticles with a Pt:Ag atomic ratio of 1:1 are prepared by the chemical co-reduction of the precursors of Pt and Ag, and physical characterizations reveal that the PtAg nanoparticles are evenly dispersed on TiO₂. PtAg/TiO₂ shows significantly higher catalytic activity and stability than PtAg/C, Pt/TiO₂ and Pt/C for methanol oxidation in both alkaline and acidic solutions, indicating that rutile TiO₂ is superior to carbon black as supports and PtAg is superior to Pt in achieving high catalytic activity. Rutile TiO₂ is also shown to be superior to anatase TiO₂ as supports for the PtAg nanoparticles. The results of this study suggest high potential of rutile TiO₂ as a support material for electrocatalysts.     

On the essential role of current density in electrocatalytic activity of the electrodeposited platinum for oxidation of ammonia

Fabrication by electrolytic deposition of platinum (Pt) electrocatalyst provides a promising alternative for oxidation of ammonia. This work investigated the role of current density in the electrocatalytic activity of the prepared Pt electrocatalysts by cyclic voltammetry and surface characterization. The Pt loading amount is determined by inductively coupled plasma. Results demonstrated that, the electrodeposited Pt has a much higher electrocatalytic activity than the pure Pt electrode due to the high electroactive surface area of the Pt deposit. The electrocatalytic activity of the Pt catalyst is improved with the increase of the Pt loading. Moreover, the electrocatalytic activity of Pt increases with the depositing current density which results in an increasing Pt loading amount. The depositing current density also affects the surface morphology of the prepared Pt. The high depositing current density generates small Pt particles at a nanometer scale, or sheet-like dendritic structure. However, the low current density leads to large Pt particles at several hundreds of nanometer with a relatively smooth morphology. The Pt electrocatalyst with the former morphological feature exhibits a higher electrocatalytic activity than the later due to the higher electroactive surface area.     

Influence of Sn content on the electrocatalytic activity of NiSn alloy nanoparticles-incorporated carbon nanofibers toward methanol oxidation

Improvement of the electrocatalytic activity of nickel toward methanol oxidation can be conducted by exploiting the synergetic influence of a co-catalyst and/or utilizing a proper support. In this study, utilizing tin as a co-catalyst and supporting on carbon nanofibers are proposed to enhance methanol oxidation in the alkaline media. Typically, NiSn nanoparticles alloy-incorporated carbon nanofibers could be prepared by calcination of electrospun nanofibers composed of poly (vinyl alcohol), nickel acetate tetrahydrate and tin chloride under argon atmosphere at a high temperature. The influence of the co-catalyst content and the calcination temperature on the morphology, composition and electrocatalytic activity of the proposed nanofibers was investigated. Smooth electrospun nanofibers can be prepared regardless the tin chloride content up to 35 wt%, and the calcination process did not distinctly affect the nanofibrous morphology. Mostly, Ni₃Sn and Ni₃Sn₂ nanoparticles-incorporated amorphous carbon nanofibers were obtained at all the utilized calcination temperatures (700, 850 and 1000 °C) and examined SnCl₂ contents. However, at 10 wt% SnCl₂ content and 850 °C calcination temperature, single metallic compound (Ni₃Sn₂)-incorporated carbon nanofibers were synthesized. Electrochemical measurements indicated that the electrocatalytic activity depends strongly on the tin content as well as the calcination temperature. The nanofibers obtained from electrospun solution containing 10 wt% SnCl₂ and calcined at 850 °C showed very good performance compared to the other formulations. Typically, the corresponding onset potential of the methanol oxidation reaction using these nanofibers catalyst is 315 mV (vs. Ag/AgCl) while it was 405 mV for the nanofibers obtained from electrospun solution containing 0, 5, 15, 25 and 35 wt% SnCl₂. Moreover, the best nanofibers reveal the highest current density. Kinetic study indicated that the corresponding activation energy is 15.6 kJ/mol.     

Coverage-dependent electro-catalytic activity of Pt sub-monolayer/Au bi-metallic catalyst toward methanol oxidation

The coverage-dependent catalytic properties of a Pt nanofilm formed on a Au substrate were investigated for the electro-oxidation of methanol. The coverage of Pt nanofilm was precisely fabricated by the formation of coverage-controlled under potential deposition of Cu adlayer and followed by the surface limited redox replacement reaction with different Pt complex ions. The STM images exhibit the formation of Pt nano-film on Au substrate with different coverage. It was clearly shown that the activity of Pt nanofilm deposited on Au substrate toward the methanol electro-oxidation was highly sensitive to its surface coverage. Pt–Au bimetallic catalyst was found to become active at the Pt surface coverage near 0.2 and reached its maximum around 0.6. The electro-catalytic activity as well as CO tolerance on Pt–Au bimetallic system was found higher than those on a Pt electrode.     

Influence of support’s oxygen functionalization on the activity of Pt/carbon xerogels catalysts for methanol electro-oxidation

Highly mesoporous carbon xerogels (CXs) were synthesized using two different resorcinol to catalyst, R/C, molar ratios and functionalized with different oxidation treatments. The synthesized carbon materials were used as supports for Pt particles, deposited by impregnation and reduction in formic acid. Both carbon supports and the catalysts prepared were characterized by means of N₂ physisorption, scanning and transmission electron microscopy, temperature programmed desorption and X-ray diffraction. The electrochemical activity of the catalysts towards the oxidation of carbon monoxide and methanol was assayed by means of cyclic voltammetry and chronoamperometry. Textural characterization of the materials prepared evidenced more developed and mesopore-enriched porous structure for the carbon xerogel prepared using the highest R/C molar ratio. Enhanced textural properties of this material led to the preparation of highly active Pt-catalysts, which showed increased tolerance to CO and higher activity in methanol electro-oxidation, in comparison to Pt-E-TEK and the catalysts prepared in an analogous way using Vulcan XC-72R carbon black as support. Functionalization treatments resulted in enhanced dispersion, lower Pt crystal size and improved catalytic performance in the case of the catalysts prepared using the carbon xerogel possessing a less developed porous structure. Pt agglomeration was found to strongly determine the activity of the catalysts prepared. At high potentials, i.e. 1 V vs. RHE, the catalyst prepared using the carbon xerogel submitted to the most stringent oxidation treatment showed the highest specific peak activity towards methanol electro-oxidation, probably due to the positive influence of the presence of oxygen surface groups in Pt-carbon interaction, in spite of the higher agglomeration extent confirmed by TEM. On the other hand, at 0.60 V vs. RHE, highest activity towards methanol electro-oxidation was determined for the catalysts prepared using the non-functionalized carbon xerogel which can be explained in terms of enhanced reactant/product diffusion together with intrinsic higher catalytic activity due to lower Pt crystal size. In any case, the activity of this catalyst prepared using a carbon xerogel as support was found to be more than 2 times higher than the one determined for Pt/E-TEK, confirming the considerable improvement of the electrocatalytic system by means of optimization of the carbon support employed.     

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.     

Enhanced electrocatalytic activity of high Pt-loadings on surface functionalized graphene nanosheets for methanol oxidation

Here we report a simple one-pot microwave-polyol reduced method to anchor platinum nanoparticles on graphene with the aid of poly (diallyldimethylammonium chloride) (PDDA), forming a Pt/PDDA–G hybrid (Pt/PDDA–G). High Pt metal loadings, up to 85 wt.% with a mean size of 1.4 nm, were densely in situ decorated on PDDA-modified graphene surfaces. The electrochemical tests showed that the activity and stability of Pt supported on PDDA–graphene hybrid substrates for methanol oxidation were better than that of Pt supported on graphene sheets, also better than the widely used Pt/carbon black electrocatalysts with the same Pt content on the electrode. This improved activity indicates that PDDA plays a crucial role in the highly dispersion and stabilization of Pt nanoparticles on graphene and PDDA–G are able to an alternative support for Pt immobilization in direct methanol fuel cells.     

Electrosynthesis of dendritic palladium supported on Ti/TiO2NTs/Ni/CeO2 as high-performing and stable anode electrocatalyst for methanol electrooxidation

Liquid-fueled direct methanol fuel cell (DMFC) is highly promising for low-carbon transportation, but is hindered by high cost and short lifespan of conventional Pt-based electrocatalysts. Herein, we propose a new Pt-free catalyst strategy to exploit high-performing and stable electrocatalyst of DMFC, achieving enhanced electrocatalytic activity and high stability for methanol oxidation reaction (MOR) in alkaline media. A new Pt-free anode catalysts consisting of titanium/reduced-titanium dioxide nanotubes/nickel/cerium dioxide (Ti/r-TiO₂NTs/Ni/CeO₂) nanosupport and uniformly-dispersed Pd dendrites is successfully prepared by a facile three-step electrodeposition route without applying any template or surfactant. Noticeably, the as-prepared Ti/r-TiO₂NTs/Ni/CeO₂–Pd as an anode electrode exhibits superior activity than commercial Pd/C and other electrodes. The obtained large mass activity for Ti/r-TiO₂NTs/Ni/CeO₂–Pd electrode is 1752 mA mg_Pd^?1 for MOR. After successive CV tests of 1000 cycles, Ti/r-TiO₂NTs/Ni/CeO₂–Pd electrode still retained 88.9% of its initial current. The superior performance of Ti/r-TiO₂NTs/Ni/CeO₂–Pd attributes to the large surface area and excellent conductivity, as well as the synergistic effects among nanosupport and Pd dendrites. Therefore, this study will open a new door for high-performance fuel cell applications.     

Study on anodic oxidation of magnesium in 6 M KOH solution by alternative current impedance

The result obtained from linear potential sweep indicates that magnesium in 6 M KOH solution behaves like an active–passive metal. The anodic oxidation process of magnesium and the interface structure between magnesium and solution were investigated by alternative current impedance analysis. It is found that when anodized, magnesium experiences active dissolution, passivation and secondary oxidation. In active region, magnesium dissolves actively, which is controlled by charge transfer step. In passive region, magnesium is passivated by the deposited Mg(OH)₂ but its oxidation controlled by charge transfer step still happens. In the secondary oxidation region, magnesium is oxidized directly to MgO, which is mix-controlled by charge transfer step and diffusion of water.     

Synthesis of mesoporous silica (SBA-16) nanoparticles using silica extracted from stem cane ash and its application in electrocatalytic oxidation of methanol

In this work, a new catalyst based on modified mesoporous silica SBA-16 is proposed and used for electrochemical oxidation of methanol. Mesoporous silica SBA-16 nanoparticles are synthesized hydrothermally under the acidic medium using SiO₂/F127/BuOH/HCl/H₂O gel. Pure SiO₂ powder is prepared from inexpensive and environmentally friendly silica source of stem cane ash (SCA). The synthesized SBA-16 is characterized using X-ray diffraction, scanning electronic microscopy, transmission electron microscopy, Brumauer–Emmett–Teller (BET) and FT-IR techniques. The synthesized SBA-16 is modified with Ni(II) by dispersion in a 0.1 M nickel chloride solution. A modified carbon paste electrode (CPE) is prepared by mixing of NiSBA-16 to carbon paste (NiSBA-16CPE). The electrocatalytic oxidation of methanol was studied on modified electrode by cyclic voltammetry and chronoamperometry. From cyclic voltammetry, it is observed that the oxidation current is extremely increased by using NiSBA-16CPE compared to the nonmodified CPE. The incorporation of Ni²⁺ into SBA-16 channels provides the active sites for catalysis of methanol oxidation. Also, the rate constant for the catalytic reaction (k) of methanol is obtained.     

NiPt sinter as a promising electrode for methanol electrocatalytic oxidation

Methanol is one of the chemical compounds utilized in fuel cells. The direct methanol fuel cell (DMFC) can be applied in many devices such as light electric vehicles and field equipment. Such a fuel cell is characterized by its high fuel energy density and low pollution. Despite many advantages of DMFCs, they are not commercially available, as the most efficient catalyst, which can be used in this process, has not been developed yet. Traditionally, it was platinum that was used in these fuel cells which is expensive and susceptible to CO poisoning. The solution to this is the use of bimetallic catalysts such as a NiPt system. In this study, we used a sintered NiPt electrode as the anode for the electrocatalytic oxidation of methanol. Based on our results, the sintered NiPt electrodes exhibited much higher activity in the oxidation of methanol, when compared with some conventional anodes.     

Oxidation of methanol on perovskite-type La2-xSrxNiO4 (0 ≤ x ≤ 1) film electrodes modified by dispersed nickel in 1 M KOH

Finely-dispersed nickel particles are electrodeposited on high surface-area perovskite-type La_2-xSr_xNiO₄ (0 ≤ x ≤ 1) electrodes for possible use in a direct methanol fuel cell (DMFC). The study is conducted by cyclic voltammetry, chronoamperometry, impedance spectroscopy and anodic Tafel polarization techniques. The results show that the apparent electrocatalytic activities of the modified oxide electrodes are much higher than those of unmodified electrodes under similar experimental conditions; the observed activity is the greatest with the modified La_1.5Sr_0.5NiO₄ electrode. At 0.550 V (vs. Hg|HgO) in 1 M KOH + 1 M CH₃OH at 25 °C, the latter electrode delivers a current density of over 200 mA cm⁻², whereas other electrodes of the series produce relatively low values (65–117 mA cm⁻²). To our knowledge, such high methanol oxidation current densities have not been reported on any other non-platinum electrode in alkaline solution. Further, the modified electrodes are not poisoned by methanol oxidation intermediates/products.     

Effect of deposition potential on the structure and electrocatalytic behavior of Pt micro/nanoparticles

In fuel cells, Pt is often employed as an electrode material to facilitate electrochemical reaction processes, in which morphology plays an important role. In this work, three kinds of Pt flowers have been prepared on a glassy electrode substrate via a facile electrochemical deposition in a solution of H₃PO₄; by controlling work potentials at −0.1 V, −0.2 V and −0.3 V, cauliflower-like, needle-like and rose-like shapes of Pt micro/nanoparticles as confirmed by SEM and XRD are obtained, respectively. Taking methanol oxidation as a model reaction and using CO stripping voltammogram in an acid medium, the electrocatalytic performance of as-prepared three Pt flowers has been evaluated. The three Pt flowers show different electrocatalytic activities, and the needle-like Pt flowers present the highest catalytic activity for electrooxidation of methanol and CO.