Pt Catalyst For Methanol Electrooxidation Research Articles

MOF-derived Co embedded into N-doped nanotube decorated mesoporous carbon as a robust support of Pt catalyst for methanol electrooxidation

The fabrication of a Pt-based catalyst with high activity and stability for methanol electrooxidation is both of vital importance and challenging for direct methanol fuel cells. Herein, a catalyst support based on Co embedded into N-doped nanotube decorated mesoporous carbon (Co@NCNTs-MC) derived from metal-organic frameworks (MOFs) was synthesized by a pyrolysis method at an appropriate temperature and duration using ZIF-67 as a precursor, and melamine as an additional nitrogen source. The presence of melamine ensures adequate nitrogen content at high temperature, promotes the formation of NCNTs through the help of Co nanoparticles in the pyrolysis process and forms a mesoporous carbon structure. The optimum pyrolysis condition was found to be 800 °C for 4 h. A Pt-based catalyst was synthesized with the as-prepared Co@NCNTs-MC support which was found to significantly improve the dispersion of Pt nanoparticles and enhance the transportation of electrons and mass. Co-Nx bonds are shown to provide an abundance of active sites. A Pt/Co@NCNTs-MC800-4 sample is found to show mass activities of 700.3 mA mg−1Pt for methanol electrooxidation, which is approximately 4.5 times higher than that of 20% Pt/C. This work brings new opportunities to design and prepare promising catalyst supports for direct methanol fuel cells.

Honeycomb-like mesoporous nitrogen-doped carbon supported Pt catalyst for methanol electrooxidation

A novel nitrogen-doped carbon material with honeycomb-like mesoporous structure was synthesized via carbonization of polyaniline under template and acted as support for the Pt catalyst. Pyrolysis temperature plays a significant role in enhancing electrochemical performance of Pt/mesoporous nitrogen-doped carbon (Pt/MNC) catalyst. Considering comprehensively electrocatalytic activity and stability for methanol electrooxidation, MNC-900 (MNC prepared at pyrolysis temperature of 900°C) is an appropriate support for Pt catalyst. Moreover, the electrochemical performance of Pt/MNC-900 catalyst is significantly superior to that of Pt/mesoporous carbon (Pt/MC) catalyst. The enhancement is attributed to N species introduced to the support and optimal proportion of pyridinic N, pyrrolic N and graphitic N. When the contents of pyridinic N, pyrrolic N and graphitic N achieve optimal proportion, MNC support reveals not only intense anchoring effect of Pt nanoparticles but also enhanced electric conductivity, further improving electrocatalytic activity and stability of the catalyst.

Polyaniline-functionalized TiO2–C supported Pt catalyst for methanol electro-oxidation

The hybrid support titania–carbon black (TiO2–C) is used as catalyst support and functionalized by polyaniline (PANI) to further improve the electro-catalytic activity and stability of platinum/titania–carbon black (Pt/TiO2–C) for methanol electro-oxidation for the first time. Pt nanoparticles have been successfully assembled on PANI-functionalized TiO2–C by chemical reduction method in aqueous solutions. PANI may act as a binder to fix the Pt nanoparticles on the TiO2–C support. The catalysts were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. It is observed that with the PANI functionalization, the Pt nanoparticles are smaller in size and more uniformly dispersed on the surface of TiO2–C than those of Pt/TiO2–C. Electrochemical measurements show that the electro-catalytic activity and stability of the novel platinum–polyaniline/titania–carbon black (Pt–PANI/TiO2–C) catalyst are really improved, compared to the Pt/TiO2–C catalyst. The significantly enhanced electro-catalytic activity and stability of Pt–PANI/TiO2–C are mainly ascribed to: (1) the bridging position of PANI between Pt and TiO2–C with the forming of Pt–N bonding; (2) highly dispersed Pt nanoparticles with narrowly distributed particle sizes. These studies indicate that the Pt–PANI/TiO2–C catalyst will become a new type of catalyst for methanol electro-oxidation and may be a promising electrode material for direct methanol fuel cell (DMFC).

Carbon nanotubes/tin oxide nanocomposite-supported Pt catalysts for methanol electro-oxidation

Carbon nanotubes/tin oxide nanocomposite (MWCNTs–SnO2) was obtained via the hydrolysis of SnCl4 in the presence of multi-walled carbon nanotubes (MWCNTs) and subsequent calcinations. And carbon nanotubes/tin oxide nanocomposite-supported Pt catalysts (Pt/MWCNTs–SnO2) were prepared by in-situ liquid phase reduction using H2PtCl6 as a metal precursor. As-prepared catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), and their catalytic performances were evaluated by chronoamperometry (CA) and cyclic voltammetry (CV). Desirable catalytic performance for methanol electro-oxidation was observed with a reduced size and an improved dispersion of Pt catalysts on the MWCNTs–SnO2 nanocomposite. The calcination temperature of MWCNTs–SnO2 nanocomposite was a key factor for controlling the catalytic performance of Pt/MWCNTs–SnO2 catalysts.

The enhanced electrocatalytic activity and stability of supported Pt nanopartciles for methanol electro-oxidation through the optimized oxidation degree of carbon nanotubes

Carbon nanotubes (CNTs) with different oxidation degrees are synthesized by the modified Hummer's method and used as the support materials for platinum (Pt) catalysts. The effect of their oxidation degree on the catalytic activity and stability of the supported Pt catalysts for methanol electrooxidation is investigated for the first time. The electrocatalytic activity for methanol oxidation reaction increases with increasing the oxidation degree due to more oxygen-containing species introduced to CNTs, which improves the dispersion of Pt nanoparticles and also modifies the electronic structure of Pt catalysts. However, under more severe oxidation condition, the stability of Pt catalysts decreases due to the destruction of graphitic structure of CNTs. Therefore, the optimized treatment condition for the CNTs is mild oxidation, which provides the supported Pt catalysts with both excellent catalytic activity and stability.

One-pot synthesis of a three-dimensional graphene aerogel supported Pt catalyst for methanol electrooxidation

A Pt/graphene aerogel hybrid catalyst synthesized via a facile one-pot solvothermal method exhibits 2.86 times higher activity for methanol electrooxidation than that of Pt/graphene and the stability is improved by 10% as compared with Pt/graphene.

Boron-doped silicon carbide supported Pt catalyst for methanol electrooxidation

Boron-doped silicon carbide (B0.1SiC) synthesized by the carbothermal reduction method was used as support to prepare Pt/B0.1SiC catalyst by cyclic voltammtric deposition of Pt nanoparticles. The crystal structure, surface property and morphology of the catalysts were studied with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy techniques and N2 adsorption-desorption experiment. It is shown that B atoms have been incorporated into the SiC lattice sites by substituting Si, which increases the electrical conductivity of SiC. Pt nanoparticles uniformly dispersed on the B0.1SiC support with an average size of 2.7 nm. The prepared Pt/B0.1SiC had a larger electrochemically active area and exhibited higher electrocatalytic activity and stability for methanol oxidation than the Pt/SiC synthesized by the same method. This shows that B-doped SiC is a promising support for preparing high-performance methanol oxidation electrocatalysts.

The Platinum Catalyst Prepared from Platinum Carbonyls

Pt catalysts for methanol electro-oxidation were prepared by thermal decomposition of platinum carbonyls. [Pt3(CO)6]n2- were synthesized from inorganic platinum compounds (PtCl4 or (NH4)2PtCl4) in H2O-MeOH solutions using carbon monoxide as a reducing agent. The progress of the platinum carbonyls synthesis reaction and its performance were monitored using UV-Vis spectroscopy. The obtained results clearly indicate the possibility of using platinum carbonyls as intermediates for the synthesis of pure and finely divided platinum particles. The electrochemical tests of the platinum powders performed in the polymer-electrolyte low-temperature methanol fuel cells (DMFC) indicated good electrocatalytic properties of these materials.

Effect of Nitric Acid on Modified Mesoporous Carbon as Catalyst Support of Direct Methanol Fuel Cell

Nitric acid modified Mesoporous carbon (CMK-3) supported Pt particles have been prepared by chemical reduction with NaBH4 as a reducing agent. Energy dispersive spectrometer shows that the catalysts have some oxygenic functional groups. The activity of the composite catalysts for methanol electro-oxidation was investigated by using cyclic votammogram and chronoamperometry in acid media. The results indicated that modified mesoporous carbon can improve the catalytic ability of Pt catalyst for methanol electro-oxidation and antipoison capability for CO. The composite electrode modified by 0.23 g nitric acid has the highest electrochemical ability.

Fabrication and performance investigation of nanocrystal tungsten nitride supported Pt catalysts for methanol electrooxidation

Catalysts with high activity and stability for methanol electrooxidation are crucial for the commercialization of direct methanol fuel cells. In this work, the performance of nanocrystal tungsten nitride hybrid (WN/C) supported Pt catalyst for methanol electrooxidation is reported. X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) are adopted to investigate the physicochemical properties of WN/C and the prepared catalysts. Cyclic voltammetry, chronopotentiometry and chronoamperometry measurements are employed to study the electrocatalytic properties of the prepared catalysts. The tungsten nitride supported Pt (Pt-WN/C) catalysts exhibit significantly improved performance towards methanol electrooxidation in acidic aqueous solutions in comparison with other catalysts. The reason could predominantly originate from the synergistic effect between WN and Pt in the Pt-WN/C catalysts and the nitrogen-doping effects of the carbon supports, which could be a promising anode catalyst for direct methanol fuel cells.

High performance of carbon nanowall supported Pt catalyst for methanol electro-oxidation

The performance of Pt catalyst supported on carbon nanowall (CNW) and vertically aligned carbon nanofiber (VACNF) for methanol electro-oxidation has been compared. Pt/CNW and Pt/VACNF electrodes were fabricated by growing CNW and VACNF on carbon papers with inductively coupled plasma enhanced chemical vapor deposition, followed by sputter deposition of Pt nanoparticles using a radio-frequency magnetron sputtering system. Scanning electron microscopy and transmission electron microscopy results show that the Pt nanoparticles are homogeneously dispersed on the surface of CNW and VACNF. The histograms of Pt nanoparticle diameter for both electrodes reveal that the Pt/CNW electrode shows a broader particle size distribution. Cyclic voltammetric measurements show that the Pt/CNW electrode has a better electrochemical activity and methanol oxidation property than Pt/VACNF electrode. The unique structure of CNW ensures that Pt/CNW electrode has a faster electron transport rate and shorter electron transport path, which lead to an obvious improvement of electro-catalysis activity compared to the Pt/VACNF electrode and show a further potential application in direct alcohol fuel cells.

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.

The origin of the high performance of tungsten carbides/carbon nanotubes supported Pt catalysts for methanol electrooxidation

The Pt supported on WC modified MWCNT catalysts (PtWC/MWCNT) were synthesized by the combination of organic colloidal and intermittent microwave heating (IMH) methods for the first. The results proved the better performance of the PtWC/MWCNT catalyst than that of Pt/C for methanol oxidation in terms of the onset potential and peak current density. The synergistic effect between Pt nanoparticles and WC and the structure effect of the MWCNTs could be the reasons to result in the high activity. The CO stripping test provided the evidence that the onset potential shift for methanol oxidation is consistent with the reduction in the overpotential for the CO oxidation on PtWC/MWCNT catalyst. Therefore, the mechanism of the high performance for methanol oxidation on PtWC/MWCNT catalyst is probably the easier oxidation of CO-like species which cause high overpotential for further oxidation of methanol.

NaBH 4-assisted ethylene glycol reduction for preparation of carbon-supported Pt catalyst for methanol electro-oxidation

A carbon-supported Pt catalyst (40 wt.% loading) is prepared by a modified ethylene glycol reduction method (Pt–EG-complex). In this procedure, a complex produced by reacting ethylene glycol with sodium borohydride (NaBH 4), serves as a reducing agent for the Pt precursor and as a stabilizer for preventing the growth of Pt particles. For purposes of comparison, two types of carbon-supported Pt catalyst (40 wt.% loading) are also prepared by a NaBH 4 reduction method, in which the Pt precursor is reduced in a ethylene glycol solution (Pt–EG–NaBH 4) and in de-ionized water (Pt–H 2O–NaBH 4). Analysis by X-ray diffraction and transmission electron microscopy reveal that the Pt–EG-complex catalyst is comprised of highly-dispersed Pt nanoparticles with a uniform size (2.9–3.1 nm) on the carbon support, while large Pt particles are observed in the Pt–EG–NaBH 4 (3.3–3.6 nm) and Pt–H 2O–NaBH 4 (5.7–6.2 nm) catalysts. The Pt–EG-complex catalyst has the highest electrochemical surface area and shows the highest catalytic performance for methanol electro-oxidation.

Remarkable support effect of SWNTs in Pt catalyst for methanol electrooxidation

Carbon nanotubes have been proposed as advanced metal catalyst support for electrocatalysis. In this work, different carbon support materials including single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs) and XC-72 carbon black, were compared in terms of their electrochemical properties using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The SWNTs is found to exhibit the highest accessible surface area in electrochemical reactions and the lowest charge transfer resistance at the SWNTs/electrolytes. These carbon materials are then loaded with varying amount of Pt by the electrodeposition technique to prepare carbon supported Pt catalysts. Electrochemical measurements of methanol oxidation reveal that the SWNTs supported Pt catalyst exhibits the highest mass activity (mA/mg-Pt). In comparison with Pt-XC-72 and Pt-MWNTs, the remarkably enhanced electrocatalytic activity of the Pt-SWNTs maybe attributed to a higher dispersion and utilization of the Pt particles, which are directly related to the electrochemical characteristics of SWNTs. The high concentration of oxygen-containing functional groups, high accessible surface area, low charge transfer resistance at the carbon/electrolyte interfaces can be important for the Pt dispersing and strong metal-support interaction in the Pt-SWNTs catalyst.

Development and operation of a 150 W air-feed direct methanol fuel cell stack

A five-cell 150 W air-feed direct methanol fuel cell (DMFC) stack was demonstrated. The DMFC cells employed Nafion 117® as a solid polymer electrolyte membrane and high surface area carbon supported Pt-Ru and Pt catalysts for methanol electrooxidation and oxygen reduction, respectively. Stainless steel-based stack housing and bipolar plates were utilized. Electrodes with a 225 cm2 geometrical area were manufactured by a doctor-blade technique. An average power density of about 140 mW cm−2 was obtained at 110 °C in the presence of 1 M methanol and 3 atm air feed. A small area graphite single cell (5 cm2) based on the same membrane electrode assembly (MEA) gave a power density of 180 mW cm−2 under similar operating conditions. This difference is ascribed to the larger internal resistance of the stack and to non-homogeneous reactant distribution. A small loss of performance was observed at high current densities after one month of discontinuous stack operation.