Improved performance of PtRu/C prepared by selective deposition of Ru on Pt as an anode for a polymer electrolyte membrane fuel cell

Ru-promoted Pt/C catalysts with different Ru/Pt ratios are prepared by selective chemical vapour deposition (CVD) of Ru onto a Pt surface. The optimum PtRu/C (Ru/Pt = 0.44) catalyst prepared using a CVD method shows improved performance as an anode for a polymer electrolyte membrane fuel cell in the presence of CO, as compared with a commercial PtRu/C (Ru/Pt = 1) catalyst and a PtRu/C (Ru/Pt = 1) catalyst prepared using a conventional impregnation (IMP) method. This observation is confirmed by the results of half-cell and single-cell tests. The CVD catalyst shows an improved CO tolerance because Ru is preferentially deposited as nano-scale particles on the Pt surface and, consequently, the number of Pt particles that are in close contact with the added Ru is greater in the CVD catalyst. An increase in the interfacial area between the Ru and the Pt facilitates the transfer of the oxygen-containing species to the CO-poisoned Pt surface such that the oxidation of CO is promoted. The Pt surface is also modified electronically due to an interaction with the added Ru, which is stronger in the CVD catalyst than in the IMP catalyst, as demonstrated by X-ray photoelectron analysis.     

Platinum-sputtered electrode based on blend of carbon nanotubes and carbon black for polymer electrolyte fuel cell

A novel Pt-sputtered electrode based on a blend layer of carbon black (CB) and carbon nanotubes (CNTs) is developed for polymer electrolyte fuel cells. The Pt is sputtered on the surface of the blend to form a catalyst layer. The CNTs generate a pore in the blend layer, and the CB provides a high surface roughness for the blend layer. At a CNT content of 50 wt.%, the maximum value (20.6 m² g⁻¹) for the electrochemical area of the Pt is obtained, which indicates that the surface area of the blend layer exposed for Pt deposition is the largest. The power density of a membrane-electrode assembly (MEA) employing the Pt-sputtered electrodes shows a linear increase with electrochemical area. The mass activity of the optimized Pt-sputtered electrode with a Pt loading of 0.05 mg cm⁻² is 8.1 times that of an electrode with a Pt loading of 0.5 mg cm⁻² prepared using a conventional screen-printing technique. Excellent mass transfer is obtained with the Pt-sputtered electrode.     

A proper amount of carbon nanotubes for improving the performance of Pt-Ru/C catalysts for methanol electro-oxidation

This study aims to improve the performance of the anode catalyst in a direct methanol fuel cell by using carbon black (XC) and mesoporous carbon (MC) as supporting materials for preparing Pt-Ru/XC and Pt-Ru/MC catalysts. This study investigates the effect of adding different amounts of bare carbon nanotubes (CNTs) or carbon nanotubes impregnated with Pt and Ru (abbreviated as Pt-Ru/CNT, containing 10 wt.% Pt and Ru) to the prepared catalysts. Experimental results reveal that 10 wt.% Pt-Ru/C with carbon black and mesoporous carbon prepared by the multiple impregnation method had smaller Pt-Ru grain sizes and a better dispersion or carbon supports due to low precursor concentrations in each impregnation. These, in turn, achieved better electro-catalytic performance for methanol oxidation. Adding CNTs or Pt-Ru/CNT to Pt-Ru/XC and Pt-Ru/MC obviously improves their electro-catalytic characteristics. The appropriate amounts of bare CNT and Pt-Ru/CNT added to Pt-Ru/XC and Pt-Ru/MC catalysts are 5% and 20%, respectively. The resulting catalysts (both containing 10 wt.% Pt and Ru) produce activities similar to those of the E-TEK Pt-Ru/C catalyst containing 20 wt.% Pt and Ru.     

An investigation of Pt alloy oxygen reduction catalysts in phosphoric acid doped PBI fuel cells

A study of a phosphoric acid doped polybenzimidazole (PBI) membrane fuel cell using commercial carbon supported, Pt alloy oxygen reduction catalysts is reported. The cathodes were made from PTFE bonded carbon supported Pt alloys without PBI but with phopshoric acid added to the electrode for ionic conductivity. Polarisation data for fuel cells with cathodes made with alloys of Pt with Ni, Co, Ru and Fe are compared with those with Pt alone as cathode at temperatures between 120 and 175 °C. With the same loading of Pt enhancement in cell performance was achieved with all alloys except Pt-Ru, in the low current density activation kinetics region of operation. The extent of enhancement depended upon the operating temperature and also the catalyst loading. In particular a Pt-Co alloy produced performance significantly better than Pt alone, e.g. a peak power, with low pressure air, of 0.25 W cm⁻² with 0.2 mg Pt cm⁻² of a 20 wt% Pt-Co catalyst.     

Effect of carbon substrate materials as a Pt–Ru catalyst support on the performance of direct methanol fuel cells

The support effect of carbon nanotubes (CNTs) for direct methanol fuel cell (DMFC) was studied using CNTs with and without defect preparation, carbon black, and fishbone-type CNTs. The Pt–Ru/defect-free CNTs afforded the highest catalytic activity of methanol oxidation reaction (MOR) in rotating disk electrode experiments and the highest performance as the anode catalysts in DMFC single cell tests with the one-half platinum loading compared to Pt–Ru/VulcanXC-72R. CO stripping voltammograms with Pt–Ru/defect-free CNTs also revealed the lowest CO oxidation potential among other Pt–Ru catalysts using different carbon support. It is thus considered that the carbon substrates significantly affect the CO oxidation activity of anode electrocatalysts in DMFC. This is ascribed to the geometrical effect that the flat interface between CNTs and metal catalysts has a unique feature, at which the electron transfer occurs, and this interface would modify the catalytic properties of Pt–Ru particles.     

Sub-nano-Pt cluster supported on graphene nanosheets for CO tolerant catalysts in polymer electrolyte fuel cells

The carbon monoxide (CO) tolerance performance of polymer electrode fuel cells (PEFCs) was studied for a catalyst composed of graphene nanosheets (GNS) with sub-nano-Pt clusters. The Pt catalysts supported on the GNS showed a higher CO tolerance performance in the hydrogen oxidation reaction (HOR), which was significantly different from that of platinum on carbon black (Pt/CB). It is proposed that the presence of the sub-nano-Pt clusters promotes the catalytic activity and that the substrate carbon material alters the catalytic properties of Pt via the interface interactions between the graphene and the Pt.     

Aligned carbon nanotube–Pt composite fuel cell catalyst by template electrodeposition

Solution phase deposition of aligned arrays of carbon nanotubes (CNTs) in a platinum (Pt) matrix composite is demonstrated. The catalyst material is electrodeposited in an oriented manner on the nanoscale using anodised aluminium oxide (AAO) templates. The catalyst performance of the composite for the oxidation of methanol is shown. The carbon monoxide (CO) tolerance is increased and the catalyst function is improved by minimising the influence of adsorbed CO on the kinetics of the methanol oxidation reaction.     

Co-electrodeposition of Pt–Ru electrocatalysts in electrolytes with varying compositions by a double-potential pulse method for the oxidation of MeOH and CO

The co-eletrodeposition of Pt–Ru on carbon electrodes was carried out using a double-potential pulse method in electrolytes containing varying concentrations of RuCl₃ + H₂PtCl₆ in an attempt to deposit highly dispersed Pt–Ru electrocatalyst with a controlled composition. The amounts of the Pt and Ru deposited on the electrodes were analyzed using an inductively coupled plasma atomic emission spectrometer (ICP-AES). The results revealed that the Pt loading on the substrates increases linearly with H₂PtCl₆ concentrations in the bath while the Ru loading is not related to the concentration of RuCl₃, indicating that the reduction of Pt ions is the dominant reaction in the cathodic deposition of Pt–Ru clusters on the substrate. The Pt–Ru/C electrodes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optimum Ru content in the deposited Pt–Ru electrode for promoting the electro-oxidation of MeOH and adsorbed CO was found to be 25 atm%, by CO-stripping measurements in 0.5 M H₂SO₄ and by cyclic voltammography in a solution comprising CH₃OH (2.0 M) +0.5 M H₂SO₄ (0.5 M). SEM results showed that the generation of nucleation sites and growth of the deposits progresses continuously on carbon substrate and already deposited Pt–Ru particles. The particle size and loading amount of the deposits was found to increase with an increase in the number of cycles of the repeating double-potential pulse.     

High efficient electrooxidation of formic acid at a novel Pt-indole composite catalyst prepared by electrochemical self-assembly

Self-assembly of Pt and indole into a novel composite catalyst on a glassy carbon electrode (GC) has been developed by a one-step electrodeposition in the presence of 3.0 mM H₂PtCl₆ and 0.1 mM indole. Compared to Pt/GC and Pt/C, the novel Pt-indole composite catalyst exhibits higher catalytic activity and stronger poisoning tolerance for electrooxidation of formic acid. The adsorption strength of CO on the prepared Pt-indole composite catalyst is greatly weakened as demonstrated by CO stripping voltammograms. Because of its advantageous catalytic activity and poisoning tolerance, the novel Pt-indole composite catalyst is anticipated to find interesting applications in many important fields such as energy and catalysis.     

Low Pt-loading Ni-Pt and Pt deposits on Ni: Preparation, activity and investigation of electronic properties

A unique, self-limiting, galvanostatic deposition was used to synthesize co-deposits of Ni and Pt onto nickel substrates from sonicated solutions of 0.2 M NiCl₂ in 2.0 M NH₄Cl, with a platinum blacked counter electrode as the sole platinum source. Depositions of only Pt onto the nickel substrates were also performed using this method. Cyclic voltammetry, chronoamperometry, carbon monoxide stripping voltammetry, inductively coupled plasma mass spectrometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were performed on the deposits. Results demonstrate that, due to the self-regulating nature of this deposition, the Pt-content of the co-deposits does not exceed 8 mol% loading and most of the Pt resides at or near the catalyst surface. The surface atom normalized activities of the co-deposits (Ni-Pt on Ni foam) and Pt-only deposits (Pt on Ni foam) were up to 37 times higher than platinum black towards 2-propanol electro-oxidation in base at 500 mV vs. RHE; the order of activity is Pt on Ni foam ? Ni-Pt on Ni foam > Pt black. The Ni-Pt and Pt on Ni foam catalysts are more active than Pt black at >500 mV mainly via the bi-functional mechanism and some electronic effects. The Pt on Ni foam was the most superior catalyst due to a combination of geometric and bi-functional effects.     

Simulation of nanostructured electrodes for polymer electrolyte membrane fuel cells

Aligned carbon nanotubes (CNTs) with Pt uniformly deposited on them are being considered in fabricating the catalyst layer of polymer electrolyte membrane (PEM) fuel cell electrodes. When coated with a proton conducting polymer (e.g., Nafion) on the Pt/CNTs, each Pt/CNT acts as a nanoelectrode and a collection of such nanoelectrodes constitutes the proposed nanostructured electrodes. Computer modeling was performed for the cathode side, in which both multicomponent and Knudsen diffusion were taken into account. The effect of the nanoelectrode lengths was also studied with catalyst layer thicknesses of 2, 4, 6, and 10 μm. It was observed that shorter lengths produce better electrode performance due to lower diffusion barriers and better catalyst utilization. The effect of spacing between the nanoelectrodes was studied. Simulation results showed the need to have sufficiently large gas pores, i.e., large spacing, for good oxygen transport. However, this is at the cost of obtaining large electrode currents due to reduction of the number of nanoelectrodes per unit geometrical area of the nanostructured electrode. An optimization of the nanostructured electrodes was obtained when the spacing was at about 400 nm that produced the best limiting current density.     

Investigation of Pt/WC/C catalyst for methanol electro-oxidation and oxygen electro-reduction

A Pt/WC/C catalyst is developed to increase the methanol electro-oxidation (MOR) and oxygen electro-reduction (ORR) activities of the Pt/C catalyst. Cyclic voltammetry and CO stripping results show that spill-over of H⁺ occurs in Pt/WC/C, and this is confirmed by comparing the desorption area values for H⁺ and CO. A significant reduction in the potential of the CO electro-oxidation peak from 0.81 V for Pt/C to 0.68 V for Pt/WC/C is observed in CO stripping test results. This indicates that an increase in the activity for CO electro-oxidation is achieved by replacing the carbon support with WC. Preferential deposition of Pt on WC rather than on the carbon support is investigated by complementary analysis of CO stripping, transmission electron microscopy and concentration mapping by energy dispersive spectroscopy. The Pt/WC/C catalyst exhibits a specific activity of 170 mA m⁻² for MOR. This is 42% higher than that for the Pt/C catalyst, viz., 120 mA m⁻². The Pt/WC/C catalyst also exhibits a much higher current density for ORR, i.e., 0.87 mA cm⁻² compared with 0.36 mA cm⁻² for Pt/C at 0.7 V. In the presence of methanol, the Pt/WC/C catalyst still maintains a higher current density than the Pt/C catalyst.     

An electrocatalyst for methanol oxidation based on tungsten trioxide microspheres and platinum

Tungsten trioxide microspheres of 2–4 μm diameter have been prepared by controlled oxidation of tungsten carbide microspheres. These microspheres are characterized by XRD, SEM, and HRTEM. The microspheres are made of WO₃ nanoparticles with an average diameter of around 15 nm. Platinum supported on these WO₃ microspheres exhibits higher and stable electrocatalytic activity for methanol oxidation by a factor of around two, than commercial 20 wt.% Pt–Ru/Vulcan-XC72 carbon and 20 wt.% Pt–Ru/carbon microspheres even without Ru. The higher activity is attributed to the better tolerance to carbon monoxide of the Pt/WO₃ catalyst. These Pt/WO₃ microspheres appear to be a promising alternative anode material for direct methanol fuel cells. They replace Ru entirely and save a substantial amount of Pt in the Pt–Ru electrode that is presently employed in fluel cells.     

Development of a self-supported single-wall carbon nanotube-based gas diffusion electrode with spatially well-defined reaction and diffusion layers

This work reports on the development of a solvent-free method for the fabrication of a self-supported single-wall carbon nanotubes electrode, which is based on successive sedimentation of both SWCNT/surfactant and PtRu-SWCNT/surfactant suspensions followed by a thermal treatment at 130 °C. The as-prepared self-supported electrode showed sufficient mechanical strength for half-cell investigation and membrane-electrodes assembly fabrication. By using a Pt catalyst loading of 1 mg cm⁻², the overall thickness of the gas diffusion electrode reached 95 μm. Its electrochemical activity towards methanol oxidation was investigated by means of cyclic voltammetry and current-voltage polarisation measurements under half-cell and direct methanol fuel cell conditions.     

Support effect of anode catalysts using an organic metal complex for fuel cells

The carbon support effect of Pt–Ni(mqph) electrocatalysts on the performance of CO tolerant anode catalysts for polymer electrolyte fuel cells (PEFCs) was investigated using carbon black and multi-walled carbon nanotubes (MWCNTs), with and without defect preparation. 20%Pt–Ni(mqph)/defect-free CNTs showed a very high CO tolerance (75% compared to the CO-free H₂ case) under 100 ppm CO level in the half-cell system of the hydrogen oxidation reaction. On the other hand, the hydrogen oxidation current on Pt–Ni(mqph)/defective CNTs, Pt–Ni(mqph)/VulcanXC-72R and Pt–Ru/VulcanXC-72R significantly decreased with increasing concentration of CO up to 100 ppm (25–47% compared to the CO-free H₂ case). It is thus considered that the carbon support materials strongly affect the CO tolerance of anode catalysts. This is ascribed to a change in the electronic structure of the Pt particles due to the interaction with the graphene surface, leading to a reduction in the adsorption energy of CO. Ni(mqph) also mitigates CO poisoning due to its ability of CO coordination on Ni metal center.     

High loading and monodispersed Pt nanoparticles on multiwalled carbon nanotubes for high performance proton exchange membrane fuel cells

Composite electrodes consisting of Pt nanoparticles-supported on multiwalled carbon nanotubes grown directly on carbon paper (Pt/CNTs/carbon paper) have been synthesized by a new method using glacial acetic acid as a reducing agent. Transmission electron microscopy (TEM) images show that the Pt nanoparticles with high density and relative small in size (2–4 nm) were monodispersed on the surface of CNTs. X-ray photoelectron spectroscopy (XPS) analysis indicates that the glacial acetic acid acts as a reducing agent and has the capability of producing a high density of oxygen-containing functional groups on the surface of CNTs that leads to high density and monodispersion of Pt nanoparticles. Compared with standard Pt/C electrode, the Pt/CNT/carbon paper composite electrodes exhibit higher electrocatalytic activity for methanol oxidation reaction and higher single-cell performance in a H₂/O₂ fuel cell.     

Electro-deposition on carbon black and carbon nanotubes of Pt nanostructured catalysts for methanol oxidation

An electrochemical method for the Pt nanoparticles deposition on porous and high surface carbon substrates (carbon black and carbon nanotubes), as an alternative way to prepare gas diffusion electrodes for polymer electrolyte fuel cells (PEFCs), is herein described. Pt nanoparticles well distributed and localized on the electrode surface were obtained by using an electric field. The electro-catalysts were prepared by single and multiple pulse galvanostatic polarizations in 1 M sulphuric acid + 5 mM exachloroplatinic acid solution. Chemical analysis, cyclic voltammetry and field emission gun scanning electron microscopy were used to determine the electrochemical features of Pt deposits and the influence of electro-deposition method on their nano-morphology. Electro-catalytic performances were studied by investigating the methanol oxidation reaction and the results are presented in form of surface specific activity and mass specific activity to take into account the electrochemical real surface and Pt loading. A comparison with commercial E-TEK Pt/C catalysts, prepared by traditional chemical reduction and heat treatment in hydrogen, shows that the electrodeposited catalyst presents higher activity at lower Pt loading.     

Ordered silicon nanocones as a highly efficient platinum catalyst support for direct methanol fuel cells

Platinum nanoparticles were electrodeposited on ordered silicon nanocones (SNCs) and used as the catalyst for methanol electro-oxidation in direct methanol fuel cells (DMFCs). Because of uniform dispersion of Pt nanoparticles and the high surface area, the Pt-SNC electrode exhibited superior electrocatalytic properties toward the methanol electro-oxidation, with the onset potential of 0.08 V (vs. SCE). According to chronoamperometric analysis and CO stripping cyclic voltammetric (CV) study, the Pt/SNC electrode had a stable electro-oxidation activity with a very good CO tolerance. The Si surface oxide surrounding the Pt nanoparticles on the SNCs was suggested to play a key role in improving the CO tolerance via the bifunctional mechanism.     

Microfluidic direct methanol fuel cell by electrophoretic deposition of platinum/carbon nanotubes on electrode surface

Carbon nanotubes (CNTs) supported platinum (Pt) nanoparticles prepared via electrophoretic deposition are used as catalyst layer of a microfluidic direct methanol fuel cell (DMFC), to study the influence of catalyst layer materials and deposition methods on the cell performance. A Y‐shaped channel is designed and microfabricated. It is verified by cyclic voltammetric measurements that shows ca. 317.7% increase in the electrochemical active surface area for the electrode with CNTs over that without CNT. Scanning electron microscopy observations indicate the network formation within the electrode because of a 3‐D structure of CNTs, which could be beneficial to the increasing electrode kinetics and to the improvement in fuel utilization. Comparison between the DMFCs with and without CNTs as support shows that the proof‐of‐concept microfluidic DMFC with Pt/CNTs electrode is able to reach a maximum power density of 5.70 mW cm^?2 at 25 °C, while the DMFC with plain Pt electrode only has a maximum power density of 2.75 mW cm^?2. Copyright © 2015 John Wiley & Sons, Ltd.     

Silver nanowire catalysts for alkaline fuel cells

A technique for synthesizing a composite electrode structure comprised of silver nanowires and carbon nanotubes (CNTs) for use as cathode catalysts in alkaline fuel cells was developed. The Ag nanowires were produced using electroless template-based deposition and sprayed as an electrocatalytically active surface coating on CNT matrices. Four different types of electrodes were prepared; blank matrices of CNTs and PTFE, CNTs and PTFE matrices sprayed with a layer of CNTs, CNTs and PTFE matrices sprayed with a layer of CNTs and 5 wt% Ag nanowires, and CNTs and PTFE matrices sprayed with a layer of CNTs and 9 wt% Ag nanowires. The catalytic performance with respect to the oxygen reduction reaction (ORR) was determined utilizing potential step voltammetry. The electrochemical test results showed that the electrode activity increased with increasing Ag concentration when mixed with CNTs.