Research on a novel Ni-doped TiN modified N-doped CNTs supported Pt catalysts and their synergistic effect for methanol electrooxidation

A novel Ni-doped TiN modified N-doped CNTs hybrid nanotubes (N-CNTs@TiNiN) is constructed and serves as hybrid support for the platinum (Pt) catalyst. We prepare the N-CNTs@TiNiN support by a solvothermal process followed by a nitriding process. It is used as anodic catalyst support to test methanol electrooxidation. By contrast, the current density of Pt/N-CNTs (0.34 A mgpt^?1) is nearly 1.31 times more than Pt/CNTs (0.26 A mgpt^?1) while Pt/TiNiN (0.56 A mgpt^?1) is almost 1.33 times as much as Pt/TiN (0.42 A mgpt^?1). What's more, among all the catalysts investigated in this work, the novel Pt/N-CNTs@TiNiN (0.86 A mgpt^?1) shows the highest reactivity for methanol oxidation, which is also much more active and durable than the commercial JM Pt/C catalyst, showing only slight activity variation even after 12 000 potential cycles. The synthetic Pt/N-CNTs@TiNiN catalyst is researched on its electrocatalytic performance toward methanol electrooxidation and the high activity and durability might be mainly attributed to the electron transfer due to the synergistic effect of the robust TiNiN NPs and N-CNTs by inducing both co-catalytic and electronic effects.     

A novel TiN coated CNTs nanocomposite CNTs@TiN supported Pt electrocatalyst with enhanced catalytic activity and durability for methanol oxidation reaction

The application of direct methanol fuel cells (DMFCs) is hampered by not only low activity but also poor stability and poor CO tolerance by the Pt catalyst. Herein, a novel titanium nitride coated multi-walled carbon nanotubes (CNTs@TiN) hybrid support was successfully synthesized by a facile solvothermal process followed by a nitriding process, and this hybrid support was used as Pt support for the oxidation of methanol. The structure, morphology and composition of the synthesized CNTs@TiN exhibits a uniform particle perfect coating with high purity and interpenetrating network structure. Notably, Pt/CNTs@TiN also showed excellent stability, experiencing only a slight performance loss after 5000 potential cycles. The onset potential (0.34 V) of CO oxidation on Pt/CNTs@TiN is obviously more negative than that on the Pt/TiN (0.38 V) and Pt/CNTs (0.48 V) in the first forward scan. In the Pt 4f XPS spectra, plentiful Pt atoms existed as Pt(II) in the Pt/CNTs and Pt/TiN catalysts, while a relatively smaller amount of Pt(II) was observed in the Pt/CNTs@TiN catalyst. The synthetic Pt/CNTs@TiN catalyst was studied with respect to its electrocatalytic activity and durability and CO tolerance toward methanol oxidation might be mainly attributed to the strongly coupled Pt–TiN and the fast electron-transport network structure. This work may provide more insight into developing novel catalyst supports of various transition metal nitrides coated CNTs for DMFCs with high activity and good durability and excellent CO tolerance.     

Titanium carbide nanoparticles supported Pt catalysts for methanol electrooxidation in acidic media

Titanium carbide (TiC) nanoparticles supported Pt catalyst for methanol electrooxidation is investigated for the first time. The resultant TiC/Pt catalysts are prepared by using a simple electrodeposition to load Pt nanoparticles on TiC nanocomposite. The electrodes are characterized by scanning electron microscopy and cyclic voltammetry. It is found that the TiC/Pt catalysts help alleviate the CO poisoning effect for methanol electrooxidation with a higher ratio of the forward anodic peak current (I_f) to the reverse anodic peak current (I_b). The improvement in the catalytic performance is attributed to the fact that TiC ameliorates the tolerance to CO adsorption on Pt nanoparticles. One possible mechanism to improve the CO tolerance of Pt taking TiC as supporting material in methanol electrooxidation is also proposed. The results suggest that TiC could be practical supporting materials to prepare electrocatalysts that are suitable for the methanol electrooxidation applications.     

Three-dimensional porous graphene supported Ni nanoparticles with enhanced catalytic performance for Methanol electrooxidation

Three-dimensional porous graphene (3D-G) is prepared by template-assembly method and employed as catalyst support for Ni nanoparticles for methanol electrooxidation. Morphology characterization confirm that Ni nanoparticles with sizes around 20 nm are uniformly scattered on the pore wall surface of the three-dimensional graphene without apparent agglomeration. Electrochemical measurements indicate that the Ni/3D-G processes higher electrocatalytic activity for methanol oxidation reaction than that of the Ni nanoparticles supported on two-dimensional graphene (Ni/2D-G) and Ni nanoparticles without graphene. The peak current density on Ni/3D-G is 64.6 mA cm^?2, which is 1.5 times higher than that on Ni/2D-G. The remarkable electrocatalytic performance of the Ni/3D-G catalyst are mainly derived from the 3D graphene. As a carrier for methanol oxidation, the 3D-G with abundant pore architecture not only hinder the agglomeration of Ni particles that is beneficial to accelerating the efficient charge transport through the whole catalyst, but also offer readily accessible channels for the diffusion of CH₃OH to the active sites of catalyst surface.     

Testing of carbon supported Pd-Pt electrocatalysts for methanol electrooxidation in direct methanol fuel cells

In the present work, a detailed characterization of the electrochemical behavior of carbon supported Pd-Pt electrocatalysts toward CO and methanol electrooxidation in direct methanol fuel cells is reported. Technical electrodes containing an ionomer in their catalyst layer were prepared for this purpose. CO and methanol electrooxidation reactions were used as test reactions to compare the electrocatalytic behavior of bimetallic supported nanoparticles in acidic liquid electrolyte and in solid polymer electrolyte (real fuel cell operating conditions). Experimental results in both environments are consistent and show that the electrochemical behavior of carbon supported Pd-Pt depends on their composition, giving the best performance in direct methanol single fuel cell with a Pd:Pt atomic ratio of 25:75 in the catalyst.     

Platinum decorated mesoporous titanium cobalt nitride nanorods catalyst with promising activity and CO-tolerance for methanol oxidation reaction

In this study, mesoporous titanium cobalt nitride nanorods (Ti_0.9Co_0.1N NRs) hybrid as non-carbon platinum supports is successfully prepared by a solvothermal process and subsequent nitridation process. The highly porous materials can provide abundant binding sites for growing well-dispersed Pt. The X-ray photoelectron spectroscopy results indicate that the cobalt element doping promoted the interaction of platinum and support. Notable, the peak current density of Pt/Ti_0.9Co_0.1N NRs catalyst is 0.85 A mgpt^?1, which 3.4-fold of Pt/C catalyst. What's more, the onset potential (0.34 V) of CO oxidation on Pt/Ti_0.9Co_0.1N NRs is lower than on the Pt/C (0.47 V) and Pt/TiN NRs (0.37 V). The results confirmed the mesoporous Pt/Ti_0.9Co_0.1N NRs catalyst unfolds a much enhanced catalytic activity and CO tolerance for methanol oxidation. The exceptional electrocatalytic properties are achieved for the Pt/Ti_0.9Co_0.1N NRs catalysts due to its unique porous structure and the electronic effect of robust Ti_0.9Co_0.1N NRs introduced by the cobalt element doping.     

Functionalization of electrochemically prepared titania nanotubes with Pt for application as catalyst for fuel cells

Titania nanotubes (TiNTs) were prepared by electrochemical anodization and were used as a support for depositing Pt. After annealing the TiNTs changed to crystalline anatase phase and were doped with carbon. The TiNTs/Pt/C was tested as electrode for electrochemical catalysis of methanol oxidation. The composite catalyst activities were measured by cyclic voltammetry in 1 M CH₃OH + 1 M H₂SO₄. The results demonstrated that TiNTs/Pt/C can greatly enhance the catalytic activity of methanol oxidation. The CO stripping led to the increase in the current peak of methanol oxidation due to activating the catalyst surface by point defect formation. Moreover, the higher ratio of the forward anodic peak current to the reverse anodic peak current indicates more effective removal of the poisonous species.     

Mesoporous Pt and Pt/Ru alloy electrocatalysts for methanol oxidation

Mesoporous Pt and Pt/Ru catalysts with 2D-hexagonal mesostructure were synthesized using a triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) copolymer (Pluronic F127^®) template, on a gold support. Large electrochemical surface areas were observed for the catalysts prepared at high overpotentials. Compared to the Pt catalyst, the Pt/Ru alloy containing 3 at% of Ru exhibited lower onset potential and more than three times the limit mass activity for methanol oxidation. This behavior is assigned to the larger pore size of the mesoporous Pt and Pt/Ru catalysts obtained with this template that seems to improve the methanol accessibility to the active sites compared to those obtained using lyotropic liquid crystals.     

Synthesis and characterization of Pt nanoparticles on sulfur-modified carbon nanotubes for methanol oxidation

Pt nanoparticles supported on carbon nanotubes (Pt/CNTs) have been synthesized from sulfur-modified CNTs impregnated with H₂PtCl₆ as Pt precursor. The dispersion and size of Pt nanoparticles in the synthesized Pt/CNT nanocomposites are remarkably affected by the amount of sulfur modifier (S/CNT ratio). The results of X-ray diffraction and transmission electron microscopy indicate that an S/CNT ratio of 0.3 affords well dispersed Pt nanoparticles on CNTs with an average particle size of less than 3 nm and a narrow size distribution. Among different catalysts, the Pt/CNT nanocomposite synthesized at S/CNT ratio of 0.3 showed highest electrochemically active surface area (88.4 m² g⁻¹) and highest catalytic activity for methanol oxidation reaction. The mass-normalized methanol oxidation peak current observed for this catalyst (862.8 A g⁻¹) was ∼ 6.5 folds of that for Pt deposited on pristine CNTs (133.2 A g⁻¹) and ∼ 2.3 folds of a commercial Pt/C (381.2 A g⁻¹). The results clearly demonstrate the effectiveness of a relatively simple route for preparation of sulfur-modified CNTs as a precursor for the synthesis of Pt/CNTs, without the need for tedious pretreatment procedures to modify CNTs or complex equipments to achieve high dispersion of Pt nanoparticles on the support.     

Pt catalyst supported on titanium suboxide for formic acid electrooxidation reaction

Pt catalysts supported on titanium suboxide (Ti₄O₇), commercial TiO₂ and carbon black were prepared by a borohydride reduction method, respectively, and used as electrocatalysts for direct formic acid fuel cells (DFAFCs). Transmission electron microscopy (TEM) images show that Pt nanoparticles have a poorer dispersion on Ti₄O₇ compared to that on TiO₂ and carbon black due to the hydrophobicity and high density of Ti₄O₇. Nevertheless, according to cyclic voltammetry (CV) and chronoamperometry (CA) results, it is found that the Pt/Ti₄O₇ catalyst possesses better catalytic activity and stability. Besides the high electrical conductivity, it is suggested from X-ray photoelectron spectroscopy (XPS) analyses that the higher content of metallic Pt caused by the Ti₄O₇ support material also contributes to the better catalytic performance of Pt/Ti₄O₇.     

Pt and PtRu nanoparticles deposited on single-wall carbon nanotubes for methanol electro-oxidation

Platinum (Pt) and platinum–ruthenium (PtRu) nanoparticles supported on Vulcan XC-72 carbon and single-wall carbon nanotubes (SWCNT) are prepared by a microwave-assisted polyol process. The catalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The PtRu nanoparticles, which are uniformly dispersed on carbon, have diameters of 2–6 nm. All the PtRu/C catalysts display the characteristic diffraction peaks of a face centred cubic Pt structure, excepting that the 2θ values are shifted to slightly higher values. The results from XPS analysis reveal that the catalysts contain mostly Pt(0) and Ru(0), with traces of Pt(II), Pt(IV) and Ru(IV). The electrooxidation of methanol is studied by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. Both PtRu/C catalysts have high and more durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a single direct methanol fuel cell using the SWCNT supported PtRu alloy as the anode catalyst delivers high power density.     

Pd nanoparticles supported on copper phthalocyanine functionalized carbon nanotubes for enhanced formic acid electrooxidation

The hydrothermal synthesis of a novel Pd electrocatalyst using copper phthalocyanine-3,4′,4″,4′″-tetrasulfonic acid tetrasodium salt (TSCuPc) functionalized multi-walled carbon nanotubes (MWCNTs) composite as catalyst support for Pd nanoparticles is reported. The prepared nanocomposites were characterized by UV–vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical tests. It is found that Pd nanoparticles are uniformly deposited on the surface of TSCuPc-MWCNTs, and their dispersion and electrochemical active surface area (ECSA) are significantly improved. Studies of cyclic voltammetry and chronoamperometry demonstrate that the Pd/TSCuPc-MWCNTs exhibits much higher electrocatalytic activity and stability than the Pd/AO-MWCNTs catalyst for formic acid oxidation. This study implies that the as-prepared Pd/TSCuPc-MWCNTs will be a promising candidate as an anode electrocatalyst in direct formic acid fuel cell (DFAFC).     

Pd nanoparticles on mesoporous tungsten carbide as a non-Pt electrocatalyst for methanol electrooxidation reaction in alkaline solution

We demonstrate Pd nanoparticles on well-defined mesoporous tungsten carbide (Pd/meso-WC) for methanol electrooxidation in alkaline solution. The meso-WC exhibits mesoporous structure with ∼8.5 nm in average pore size and ∼47 m² g⁻¹ in specific surface area. The Pd nanoparticles with size of ∼3.3 nm are highly dispersed on the meso-WC. The electron transfer from W to Pd due to the difference of electronegativity is confirmed by X-ray photoelectron spectroscopy. The improved electrocatalytic activity and stability for methanol electrooxidation of Pd/meso-WC is likely to be mainly attributed to a strong interaction between Pd nanoparticles and mesoporous tungsten carbide structure.     

Tungsten carbide as supports for Pt electrocatalysts with improved CO tolerance in methanol oxidation

One anti-CO-poisoning Pt-WC/C catalyst for methanol electro-oxidation is prepared in this work, through depositing platinum on tungsten carbide support using an intermittent microwave heating (IMH) method. The catalyst presents an improved methanol oxidation performance evidenced by a negative shift in onset potential, and increase of peak current density, compared with a commercial Pt/C one. CO stripping experiments indicate that the adsorbed CO is able to be oxidized and removed from the Pt-WC/C catalyst more easily, attesting the enhanced capability of anti-poisoning to CO-like species. Theoretical calculation further provides evidence that the surface electronic structure in Pt-WC/C and Pt/C catalysts is likely different. WC supports could lead to much stronger negative electronic property, which is beneficial for avoiding CO adsorption on the Pt-WC/C catalyst. In the mean time, the electron donating effect generated by WC supports also promotes the ability to oxidize the adsorbed CO-like species on catalysts. In good agreement with experimental results, the theoretical calculation proves the anti-CO-poisoning nature of the Pt-WC/C catalyst, and well explains the origin of the improvement in the electrochemical catalytic performance for effectively accelerating the oxidation of CO to CO₂ in methanol oxidation.     

Performance of Pt/C catalysts prepared by microwave-assisted polyol process for methanol electrooxidation

Pt nanoparticles catalysts supported on the Vulcan XC-72 carbon black with different mean sizes have been synthesized by microwave-assisted polyol process and characterized by energy dispersive analysis of X-ray (EDAX), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results of physical examinations show that Pt nanoparticles have a narrow size distribution and are highly dispersed on the surface of carbon support, and Pt loading in Pt/C catalyst is the similar with the theoretical value. The results of cyclic voltammetry and chronoamperometry demonstrate that the Pt/C catalyst prepared by microwave-assisted polyol process at the pH value of about 12 exhibits the highest catalytic activity for methanol electrooxidation. The activity of Pt/C catalyst is also related to the microwave heating time, and the optimal heating time is 40 s in this work.     

Ethanol electrooxidation on carbon-supported Pt nanoparticles catalyst prepared using complexing self-reduction method

A novel self-reduction of Pt-complex method is used to prepare Vulcan XC-72 carbon-supported Pt nanoparticles (Pt/C) catalysts by employing ethylenediamine-tetramethylene phosphonic acid (EDTMP) as a complexing reagent. During the preparation of Pt/C catalysts, the particle size of Pt nanoparticles (Pt-NPs) can be controlled effectively in the range of 1.7-13.5 nm by adjusting reaction solution pH values. TEM images demonstrate that the Pt-NPs well disperse on the Vulcan XC-72 carbon support with a relatively narrow particle size distribution by using the complex self-reduction method. Therefore, the Pt/C catalysts prepared by the same method are suitable for evaluating the size effect of the Pt-NPs on electrocatalytic performance for ethanol electrooxidation. A correlation between the electrocatalytic activity of ethanol oxidation and particle size of the Pt/C catalysts indicates that Pt-NPs with mean particle size of ca. 2.5 nm possesses the highest electrocatalytic performance for ethanol electrooxidation.     

Bimetallic Pt-M electrocatalysts supported on single-wall carbon nanotubes for hydrogen and methanol electrooxidation in fuel cells applications

A series of PtRu and PtMo bimetallic catalysts were prepared via a chemical reduction method by bubbling CO to form carbonyl compounds as metal precursors. In both cases the PtRu and PtMo bimetallic electrocatalysts achieved the maximum activity when the amount of Ru and Mo in the material was 50%wt. The physicochemical characterization of the electrocatalytic materials through X-ray diffraction (XRD) and transmission electron microscopy (TEM) has determined the presence of bimetallic structures. The electrochemical characterization using cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and polarization curves in Proton Exchange Membrane Fuel Cells (PEMFC) and Direct Methanol Fuel Cell (DMFC) allowed to systematically investigate the electrocatalytic activity of the synthesized materials for the electrooxidation of hydrogen and methanol. The PtRu/SWCNT electrocatalysts showed a higher current density at least 7-fold and 3-fold compared with Pt/SWCNT and PtMo/SWCNT electrocatalysts, respectively. Besides, the Pt50%–Ru50%/SWCNT exhibited a shifting to negative values in the onset potential reaction for the electrooxidation of methanol of 200 mV in comparison with Pt100%/SWCNT and Pt50%–Mo50%/SWCNT electrocatalysts. The experimental and simulated polarization curves obtained from DMFC show that PtRu/SWCNT and PtMo/SWCNT electrocatalysts exhibited higher power and current densities values compared with the Pt/SWCNT electrocatalyst. The membrane-electrode assembly (MEA) with Nafion^® and the PtRu/SWCNT electrocatalysts showed an open-circuit voltage value of 0.730 V, significantly higher than that the values for the MEAs with Pt/SWCNT (0.663 V) and PtMo/SWCNT (0.633 V), respectively.     

Influence of metal oxides on Pt catalysts for methanol electrooxidation using electrochemical impedance spectroscopy

Carbon nanotubes used as supports for platinum catalysts deposited with metal oxides (CeO₂, TiO₂, and SnO₂) were prepared for their application as anode catalysts in a direct methanol fuel cell. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements were carried out in a solution of 0.5 M CH₃OH and 0.5 M H₂SO₄. Catalysts with the addition of CeO₂, TiO₂, and SnO₂ presented higher catalytic activity than pure platinum catalysts, and the catalysts with CeO₂ were the best among them. Electrochemical impedance spectra indicated that methanol electrooxidation on these catalysts had different impedance behaviors at different potential regions. The mechanism of methanol electrooxidation changed with increases of the potential. The promotion effect of the metal oxides lies in the oxidation of intermediate CO_ads on Pt at low potential regions.     

A polyoxometalate-deposited Pt/CNT electrocatalyst via chemical synthesis for methanol electrooxidation

Polyoxometalate anion PMo₁₂O₄₀³⁻ (POM) is chemically impregnated into a Pt-supported carbon nanotubes (Pt/CNTs) catalyst that is prepared via a colloidal method. The POM-impregnated Pt/CNTs catalyst system (Pt/CNTs-POM) shows at least 50% higher catalytic mass activity with improved stability for the electrooxidation of methanol than Pt/CNTs or POM-impregnated Pt/C (Pt/C-POM) catalyst systems. The enhancement in electrochemical performance of the Pt/CNTs-POM catalyst system can be attributed to the combined beneficial effects of improved electrical conductivity due to the CNTs support, highly dispersed Pt nanoparticles on the CNTs, and increased oxidation power of the polyoxometalate that can assist oxidative removal of reaction intermediates adsorbed on the Pt catalyst surface.     

Platinum nanoparticles supported on activated carbon fiber as catalyst for methanol oxidation

Activated carbon fiber (ACF) with high specific surface area has been used as support in the preparation of Pt nanoparticles electrocatalyst (Pt/ACF) for direct alcohol fuel cells. It is found that the Pt nanoparticles on ACF are highly and homogeneously dispersed with a narrow size distribution in the range of 1.5–3.5 nm with an average size of 2.4 nm. In comparison with the commercial E-TEK Pt/C catalyst, the Pt/ACF catalyst exhibits much higher catalytic activity for methanol, ethanol and isopropanol oxidation, which are about 2.4 times as high as that of the former. The Pt/ACF catalyst is observed to be significantly more stable during the constant current density polarization and continuous cyclic voltammetry in comparison with Pt/C catalyst. Both the uniform dispersion of Pt nanoparticles and strong interactions between Pt nanoparticles and ACF are of benefit to achieve the performance improvement of Pt/ACF catalyst.