Noncovalently functionalized graphitic mesoporous carbon as a stable support of Pt nanoparticles for oxygen reduction

We report a durable electrocatalyst support, highly graphitized mesoporous carbon (GMPC), for oxygen reduction in polymer electrolyte membrane (PEM) fuel cells. GMPC is prepared through graphitizing the self-assembled soft-template mesoporous carbon (MPC) under high temperature. Heat-treatment at 2800 °C greatly improves the degree of graphitization while most of the mesoporous structures and the specific surface area of MPC are retained. GMPC is then noncovalently functionalized with poly(diallyldimethylammonium chloride) (PDDA) and loaded with Pt nanoparticles by reducing Pt precursor (H₂PtCl₆) in ethylene glycol. Pt nanoparticles of ∼3.0 nm in diameter are uniformly dispersed on GMPC. Compared to Pt supported on Vulcan XC-72 carbon black (Pt/XC-72), Pt/GMPC exhibits a higher mass activity towards oxygen reduction reaction (ORR) and the mass activity retention (in percentage) is improved by a factor of ∼2 after 44 h accelerated degradation test under the potential step (1.4-0.85 V) electrochemical stressing condition which focuses on support corrosion. The enhanced activity and durability of Pt/GMPC are attributed to the graphitic structure of GMPC which is more resistant to corrosion. These findings demonstrate that GMPC is a promising oxygen reduction electrocatalyst support for PEM fuel cells. The approach reported in this work provides a facile, eco-friendly promising strategy for synthesizing stable metal nanoparticles on hydrophobic support materials.     

Carbon xerogels as Pt catalyst supports for polymer electrolyte membrane fuel-cell applications

Carbon xerogels prepared by the resorcinol-formaldehyde (RF) sol-gel method with ambient-pressure drying were explored as Pt catalyst supports for polymer electrolyte membrane (PEM) fuel cells. Carbon xerogel samples without Pt catalyst (CX) were characterized by the N₂ sorption method (BET, BJH, others), and carbon xerogel samples with supported Pt catalyst (Pt/CX) were characterized by thermogravimetry (TGA), powder X-ray diffraction (XRD), electron microscopy (SEM, TEM) and ex situ cyclic voltammetry for thin-film electrode samples supported on glassy carbon and studied in a sulfuric acid electrolyte. Experiments on Pt/CX were made in comparison with commercially obtained samples of Pt catalyst supported on a Vulcan XC-72R carbon black support (Pt/XC-72R). CX samples had high BET surface area with a relatively narrow pore size distribution with a peak pore size near 14 nm. Pt contents for both Pt/CX and Pt/XC-72R were near 20 wt % as determined by TGA. Pt catalyst particles on Pt/CX had a mean diameter near 3.3 nm, slightly larger than for Pt/XC-72R which was near 2.8 nm. Electrochemically active surface areas (ESA) for Pt as determined by ex situ CV measurements of H adsorption/desorption were similar for Pt/XC-72R and Pt/CX but those from CO stripping were slightly higher for Pt/XC-72R than for Pt/CX. Membrane-electrode assemblies (MEAs) were fabricated from both Pt/CX and Pt/XC-72R on Nafion 117 membranes using the decal transfer method, and MEA characteristics and single-cell performance were evaluated via in situ cyclic voltammetry, polarization curve, and current-interrupt and high-frequency impedance methods. In situ CV yielded ESA values for Pt/XC-72R MEAs that were similar to those obtained by ex situ CV in sulfuric acid, but those for Pt/CX MEAs were smaller (by 13-17%), suggesting that access of Nafion electrolyte to Pt particles in Pt/CX electrodes is diminished relative to that for Pt/XC-72R electrodes. Polarization curve analysis at low current density (0.9 V cell voltage) reveals slightly higher intrinsic catalyst activity for the Pt/CX catalyst which may reflect the fact that Pt particle size in these catalysts is slightly higher. Cell performance at higher current densities is slightly lower for Pt/CX than the Pt/XC-72R sample, however after normalization for Pt loading, performance is slightly higher for Pt/CX, particularly in H₂/O₂ and at lower cell temperatures (50 °C). This latter finding may reflect a possible lower mass-transfer resistance in the Pt/CX sample.     

Stable support based on highly graphitic carbon xerogel for proton exchange membrane fuel cells

Highly graphitic carbon xerogel (GCX) is prepared by the modified sol-gel polymerization process using cobalt nitrate as the catalyst, followed by high temperature treatment at 1800 °C. The as-prepared GCX is explored as a stable support for Pt in proton exchange membrane fuel cells. The results of N₂ sorption measurement and X-ray diffraction analysis (XRD) reveal that GCX has a better mesoporous structure and a preferably higher degree of graphitization, compared with the commercial XC-72 carbon black. The transmission electron microscopy (TEM) image indicates that Pt nanoparticles are well dispersed on GCX and exhibit relatively narrow size distribution. Accelerated aging test (AAT) based on potential cycling is used to investigate the durability of the as-prepared Pt/GCX in comparison with the commercial Pt/C. Electrochemical analysis demonstrates that the catalyst with GCX as a support exhibits an alleviated degradation rate of electrochemical active surface area (39% for Pt/GCX and 53% for Pt/C). The results of single cell durability tests indicate that the voltage loss of Pt/GCX at 100 mA cm⁻² is about 50% lower than that of Pt/C. GCX is expected to be a corrosion resistant electrocatalyst support.     

Low-cost and durable catalyst support for fuel cells: Graphite submicronparticles

Low-cost graphite submicronparticles (GSP) are employed as a possible catalyst support for polymer electrolyte membrane (PEM) fuel cells. Platinum nanoparticles are deposited on Vulcan XC-72 carbon black (XC-72), carbon nanotubes (CNT), and GSP via ethylene glycol (EG) reduction method. The morphologies and the crystallinity of Pt/XC-72, Pt/CNT, and Pt/GSP are characterized with X-ray diffraction and transmission electron microscope, which shows that Pt nanoparticles (∼3.5 nm) are uniformly dispersed on supports. Pt/GSP exhibits the highest activity towards oxygen-reduction reactions. The durability study indicates that Pt/GSP is 2-3 times durable than Pt/CNT and Pt/XC-72. The enhanced durability of Pt/GSP catalyst is attributed to the higher corrosion resistance of graphite submicronparticles, which results from higher graphitization degree of GSP support. Considering its low production cost, graphite submicronparticles are promising electrocatalyst support for fuel cells.     

Effect of carbon black support corrosion on the durability of Pt/C catalyst

The work intends to clarify the effect of carbon black support corrosion on the stability of Pt/C catalyst. The corrosion investigations of carbon blacks with similar structures and characteristics were analyzed by cyclic voltammograms (CV) and X-ray photoelectron spectroscopy (XPS). The results indicate that a higher oxidation degree appears on the Black Pearl 2000 (BP-2000) support, i.e. BP-2000 has a lower corrosion resistance than Vulcan XC-72 (XC-72). The durability investigation of Pt supported on the two carbon blacks was evaluated by a potential cycling test between 0.6 and 1.2 V versus reversible hydrogen electrode (RHE). A higher performance loss was observed on the Pt/BP-2000 gas diffusion electrode (GDE), compared with that of Pt/XC-72. XPS analysis suggests that higher Pt amount loss appeared in the Pt/BP-2000 GDE after durability test. X-ray diffraction (XRD) analysis also shows that Pt/BP-2000 catalyst presents a higher Pt size growth. The higher performance degradation of Pt/BP-2000 is attributed significantly to the less support corrosion resistance of BP-2000.     

Mesoporous tungsten carbide-supported platinum as carbon monoxide-tolerant electrocatalyst for methanol oxidation

This paper reports a CO-tolerant electrocatalyst, mesoporous tungsten carbide-supported platinum (Pt/m-WC), for methanol oxidation. The support m-WC was synthesized by evaporation-induced triconstituent co-assembly method in which phenol formaldehyde polymer resin was used as the carbon precursor, tungsten hexachloride as the tungsten precursor and an amphiphilic triblock copolymers (P123) as the template. Nano-sized platinum particles were loaded on the m-WC to prepare Pt/m-WC. The structure and morphology of the prepared electrocatalyst were characterized by transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray diffraction (XRD), and its activity toward methanol oxidation and its tolerance for CO were determined by cyclic voltammetry (CV) and chronopotentiometry (CP). It is found that the m-WC carburized at 900 °C(m-WC-900) has a larger specific surface area (182 m² g⁻¹) and a appropriate crystal structure compared to the m-WC carburized at 800 °C or 1000 °C, and thus is better as the support of platinum. The prepared Pt/m-WC-900 exhibits higher activity toward methanol oxidation and better tolerance for CO than Pt/Vulcan XC-72. The onset potential of CO electro-oxidation on Pt/m-WC is 0.449 V, which is more negative than that on Pt/Vulcan XC-72 (0.628 V).     

One-step dual template synthesis of platinum on mesoporous carbon nanowires for electrocatalysts

One-step methodology has been utilized to fabricate platinum catalysts on well-aligned mesoporous carbon nanowires (Pt/MCNWs) in dual templates which are the combination of porous anodic alumina (PAA) hard template and triblock polymer ethanol solution as soft template with evaporation-induced self-assembly technique. The mesoporous nanowires structure is confirmed by transmission electron microscopy (TEM). The Pt/MCNWs has a higher electrochemical active surface area and better catalytic performance than a commercial Pt/Vulcan XC-72. It could attribute to the good dispersion of Pt and a special morphology of MCNWs. Hence, the Pt/MCNWs synthesized by the dual template method might be a promising candidate to be utilized as electrocatalyst.     

Electro-oxidation of methanol at the different carbon materials supported Pt nano-particles

Single-wall carbon nano-tubes (SWNTs), multi-wall carbon nano-tubes (MWNTs) and Vulcan XC-72 carbon (XC-72) are used as supporting carbon materials to prepare Pt/XC-72, Pt/SWNTs and Pt/MWNTs catalysts in tetrahydrofuran/water/ethanol mixture solution. Transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the type of supporting carbon material affects significantly the morphology and the electronic structure of supported Pt nano-particles (NPs). Electrochemical measurements indicate that the Pt/SWNTs catalyst exhibited the highest current density, the lowest onset oxidation potential and the best stability for methanol electro-oxidation among the three samples, indicating SWNTs are an ideal anode catalyst supporting material for the practical application of direct methanol fuel cells.     

Heat-treated platinum nanoparticles embedded in nitrogen-doped ordered mesoporous carbons: Synthesis, characterization and their electrocatalytic properties toward methanol-tolerant oxygen reduction

Fabrication of N-doped ordered mesoporous carbons containing well-dispersed and methanol-tolerant Pt nanoparticles (Pt-NOMC) via an easy route is reported in this paper. These Pt-NOMC samples invoke the pyrolysis of co-fed carbon sources and Pt precursor with various carbonization temperatures (Pt-NOMC-T) in 3-[2-(2-Aminoethylamino)ethylamino]propyl-functionalized mesoporous silicas which were simultaneously used as N sources and hard templates. A series of different spectroscopic and analytical techniques was performed to characterize these Pt-NOMC-T catalysts. Combined the results from X-ray diffraction, N₂ adsorption-desorption isotherms, transmission electron microscopy and elemental analysis show that ca. 0.7-2.2 wt% of nitrogen was successfully doped on the high surface areas of ordered mesoporous carbon rods. Further studies by X-ray photoelectron spectroscopy indicated that Pt-NOMC-T catalysts with different ratios of quaternary-N and pyridinic-N were observed. Among various Pt-NOMC-T samples, the Pt-NOMC-1073 sample, which may be due to moderate electrical conductivity of ordered mesoporous carbons, unique nanostructure between Pt nanoparticles and N-doped carbon supports, and presence of more pyridinic-N atoms, was found to possess superior electrocatalytic activity for methanol-tolerant oxygen reduction in comparison with the typical commercial electrocatalyst (Pt/XC-72).     

Preparation and characterization of nanoporous carbon-supported platinum as anode electrocatalyst for direct borohydride fuel cell

The nanoporous carbon (NPC) is synthesized by carbonization of metal–organic framework-5 (MOF-5, [Zn₄O(bdc)₃], bdc = 1,4-benzenedicarboxylate) with furfuryl alcohol (FA) as carbon source and used as the carrier of the anode catalyst for the direct borohydride–hydrogen peroxide fuel cell (DBHFC). Then the NPC-supported Pt anode catalyst (Pt/NPC) is firstly prepared by a modified NaBH₄ reduction method. The obtained Pt/NPC catalyst is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), cyclic voltammetry, chronopotentiometry, chronoamperometry and fuel cell test. The results show that the Pt/NPC is made up of the spherical Pt nanoparticles which disperse uniformly on the surface of the NPC with average size 2.38 nm, and exhibits 36.38% higher current density for directly borohydride oxidation than the Vulcan XC-72 carbon supported Pt (Pt/XC-72). Besides, the DBHFC using the Pt/NPC as anode electrocatalyst shows the maximum power density as high as 54.34 mW cm⁻² at 25 °C.     

High catalytic performance and stability of Pt/C using acetic acid functionalized carbon

Carbon (Vulcan XC-72, Cobat Corp.) is pretreated using acetic acid (HAC) before the Pt deposition by microwave assisted glycol method. TEM and XRD results indicate that 3 nm Pt nano-particles are uniformly dispersed on the surface of modified XC-72. In order to examine the interaction between Pt nano-particles and carbon, Pt/C-HAC and commercial Pt/C (Johnson Matthey Corp.) are calcined at 500 °C for 2 h under nitrogen atmosphere. The average Pt particle size of Pt/C-HAC after calcination is only 10–12 nm in diameter while commercial Pt particles grow up to 25–35 nm with a broad size distribution. Meanwhile, electrochemical studies of Pt/C-HAC reveal higher activity and stability for both methanol oxidation and oxygen reduction than that of Pt/C-JM. The pore structure and surface composition are investigated by BET and XPS, which implies that much microporous structure and carbonyl functional groups on carbon surface are obtained after HAC treatment. The high catalytic performance and stability might mainly be due to the strong interaction between Pt nano-particles and carbon by carbonyl functional groups. Therefore, HAC treatment is proved to be a facile and effective method for carbon as the support for Pt as fuel cell catalyst.     

Activities of Pt/Sibunit-1562 catalysts in the ORR in PEMFC: Effect of Pt content and Pt load at cathode

In this paper, a systematic investigation was carried out of activities at 80 °C of Pt supported on Sibunit-1562 graphitized carbon in the electroreduction of oxygen in the polymer electrolyte fuel cell. Pt content in the Pt/Sibunit-1562 catalysts was 20, 40, and 60 wt.% and Pt load at the cathode was varied in the 200–6.25 μg_Pt cm⁻² interval. The results were compared with the activity of commercial 20 wt.% Pt/Vulcan XC-72 catalyst. To optimize the transport properties of the cathode layer and maintain its thickness upon using Pt/Sibunit −1562 catalysts with varied Pt content and Pt loads a definite amount of Vulcan-XC-72 carbon support was added to the cathode catalytic inks. Higher activity of Pt/Sibunit-1562 catalysts was found as compared to that of commercial 20 wt.% Pt/Vulcan XC-72 with similar particle size of the active component.     

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.     

Pt/carbon nanofibers electrocatalysts for fuel cells: Effect of the support oxidizing treatment

Different Pt-based electrocatalysts supported on carbon nanofibers and carbon black (Vulcan XC-72R) have been prepared using a polymer-mediated synthesis. The electrocatalysts have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and cyclic voltammetry. The effect of carbon nanofibers treatment with HNO₃ solution on Pt particle size and electroactive area has been analyzed. Highly dispersed Pt with homogeneous particle size and an electroactive area around of 100 m² g⁻¹ is obtained in raw carbon nanofibers. The oxidizing treatment of the carbon nanofibers produces agglomeration of the platinum nanoparticles and an electroactive area of 53 m² g⁻¹. Durability studies indicate a decrease of 14% in the electroactive area after 90 h at 1.2 V in 0.5 M H₂SO₄ for platinum supported on raw carbon nanofibers and Vulcan XC-72R. The electrocatalyst supported on oxidized carbon nanofibers are stable under similar conditions.     

Pt-Ru electrocatalysts supported on ordered mesoporous carbon for direct methanol fuel cell

Pt-Ru electrocatalysts supported on ordered mesoporous carbon (CMK-3) were prepared by the formic acid method. Catalysts were characterized applying energy dispersive X-ray analyses (EDX) and X-ray diffraction (XRD). Methanol and carbon monoxide oxidation was studied electrochemically by cyclic voltammetry, and current-time curves were recorded in a methanol solution in order to establish the activity towards this reaction under potentiostatic conditions. The physicochemical and electrochemical properties of the Pt-Ru catalysts supported on CMK-3 carbon were compared with those of electrocatalysts supported on Vulcan XC-72 and commercial catalyst from E-TEK. Additionally, in order to complete this study, Pt electrocatalysts supported on CMK-3 and Vulcan XC-72 were prepared by the same method and were used as reference. Results showed that the Pt-Ru/CMK-3 catalyst presented the best electrocatalytic activity towards the CO oxidation and, therefore, good perspectives to its application in DMFC anodes. On the other hand, the activity of the Pt-Ru/CMK-3 catalyst towards methanol oxidation was higher than that of the commercial Pt-Ru/C (E-TEK) catalyst on all examined potentials, confirming the potential of the bimetallic catalysts supported on mesoporous carbons.     

Durability investigation of carbon nanotube as catalyst support for proton exchange membrane fuel cell

Electrochemical surface oxidation of carbon black Vulcan XC-72 and multiwalled carbon nanotube (MWNT) has been compared following potentiostatic treatments up to 168 h under condition simulating PEMFC cathode environment (60 °C, N₂ purged 0.5 M H₂SO₄, and a constant potential of 0.9 V). The subsequent electrochemical characterization at different treatment time intervals suggests that MWNT is electrochemically more stable than Vulcan XC-72 with less surface oxide formation and 30% lower corrosion current under the investigated condition. As a result of high corrosion resistance, MWNT shows lower loss of Pt surface area and oxygen reduction reaction activity when used as fuel cell catalyst support.     

Platinum and palladium nano-particles supported by graphitic nano-fibers as catalysts for PEM water electrolysis

Platinum and palladium nano-particles supported by graphitic nano-fibers (GNFs) have been prepared and used as cathodic electrocatalysts in proton-exchange membrane (PEM) water electrolysis cells for the hydrogen evolution reaction (HER). Raw GNF structures have been synthesized by chemical vapor deposition (CVD). Noble metal nano-particles have been deposited at the surface of GNFs using an impregnation-reduction method. Structural properties and electrochemical performances of the GNF-supported catalysts have been determined using TEM analysis and cyclic voltammetry. Current-voltage polarization curves have also been recorded using a PEM cell (7 cm²). The performances obtained with GNF-supported catalysts were found more efficient than those obtained with catalysts supported with conventional carbon black (Vulcan^® XC-72). In particular, a reduced electrolysis cell voltage (1.67 instead 1.72 V at 1 A.cm⁻² and 90 °C) has been obtained using Pt/GNF cathodes in place of Pt/XC-72 at the cathode and with similar platinum contents (40 wt.%).     

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.     

Methanol oxidation on MoO3 promoted Pt/C electrocatalyst

MoO₃ is incorporated into Vulcan carbon XC-72R by solid-state reaction under intermittent microwave heating (IMH) method. The Pt nanoparticles are dispersed by microwave-assisted polyol process. The physicochemical characterization reveals that MoO₃ and Pt nanoparticles are evenly deposited on Vulcan carbon XC-72R. The non-conducting MoO₃ is electrochemically reduced to nonstoichiometric and electroconductive hydrogen molybdenum bronze (H_xMoO₃) in acidic solution. The peak current for methanol electrooxidation is about 128% higher on Pt-MoO₃/C electrode than Pt-Ru/C electrode. Also, there is a significant increase in the electrode response toward stability test which can be attributed to hydrogen molybdenum bronze phase and its direct role in the conversion of CO to CO₂. Intermittent microwave heating method is effective for incorporating oxide materials in Vulcan XC-72R in a short span of time which is evidenced by the formation of hydrogen molybdenum bronze phase during the CV measurements.     

Preparation of Pt/NiO-C electrocatalyst and heat-treatment effect on its electrocatalytic performance for methanol oxidation

Pt catalyst supported on Vulcan XC-72R containing 5 wt% NiO (Pt/NiO–C) showed larger electrochemical active surface area and higher electrochemical activity for methanol oxidation than Pt catalyst supported on Vulcan XC-72R using polyol method without NiO addition. Prepared Pt/NiO–C electrocatalyst was heat-treated at four temperatures (200, 400, 600, and 800 °C) in flowing N₂. X-ray diffraction and temperature-programmed desorption results indicated that NiO was reduced to Ni in inert N₂ during heat-treatments at temperatures above or equal to 400 °C, while oxygen from NiO reacted with carbon support due to the catalytic effect of Pt. The reduced Ni formed an alloy with Pt, which, according to the X-ray photoelectron spectroscopy data, resulted in a shift to a lower binding energy of Pt 4f electrons. The Pt/NiO–C electrocatalyst heat-treated at 400 °C showed the best activity in methanol oxidation due to the change in Pt electronic structure by Ni and the minimal aggregation of Pt particles.