High Electrochemical Active Surface Area Research Articles

Evaluation of the Durable Performance of the Pt/Marimo Carbon Catalyst in PEFC

1.IntroductionImproving the durability of polymer electrolyte fuel cell (PEFC) has been a challenge. The deterioration of carbon can be cited as a cause of reduced durability. Carbon black is considered to be easily oxidized and deteriorated, because of the low crystallinity of amorphous carbon. We applies Marimo carbon, a new carbon material comprising entangled carbon fibers.(1) There is a cavity of several hundred nanometers in Marimo carbon. The diffusion of water and fuel gas is expected to be improved compared with conventional carbon catalysts. The fibers of Marimo carbon are arranged in a cup stack structure. It is possible to easily loading platinum. We study an improvement in the power generation performance of PEFCs using Marimo carbon.(2) In this study, an accelerated degradation test of a catalyst employing Marimo carbon was performed using electrochemical measurements to evaluate changes in catalyst performance. 2.ExperimentalMarimo carbon was synthesized by chemical vapor deposition. The loading of Marimo carbon with Pt was performed using the nano colloid solution method.(3) Marimo carbon and NaOH were added to distilled water, and the mixture was stirred during ultrasonication. Citric acid and chloroplatinic acid were then added, and the mixture was stirred during ultrasonication. Next, sodium borohydride was added as a reducing agent, and the mixture was stirred during ultrasonication. Finally, centrifugation and drying were performed to prepare a Pt/Marimo carbon. Accelerated degradation tests were performed with a scan speed of 500 mV s-1, and a potential range of 1.0 - 1.5 V vs. RHE. After each test cycle, the catalyst performance was evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) with a rotating ring disc electrode (RRDE). Catalyst performance was also evaluated by I-V testing using a single cell. For comparison, similar measurements were performed using a Pt/carbon black catalyst. 3.Results and discussionLSV results before and after the accelerated degradation test are presented. The number of cycles ranged from 0 to 7200, and RRDE rotation speed was 3600 rpm. In the case of carbon black, the value of the diffusion limited current density after 7200 cycles was confirmed to become small. However, in the case of Marimo carbon, the value of the diffusion limited current density was not changed even after 7200 cycles. The lowering of the catalytic activity due to the oxidation of carbon or elimination of the catalyst from the electrode. The resistance overvoltage was compared using Tafel plots. Prior to the accelerated degradation test, no difference was found in the slopes of both catalysts. After the accelerated degradation test, the slope for Marimo carbon did not change. However, the slope for carbon black increased, and thus, the resistance increased. The electrochemically active surface area (ECSA) was calculated CV of each accelerated degradation test. The ECSA of carbon black after 7200 cycles was reduced to 34 % of its initial value. However, Marimo carbon exhibited a high ECSA value, i.e., 80 % of its initial value after 7200 cycles and 63 % of its initial value after 23400 cycles. For Marimo carbon, there was no change in the oxidation peak of carbon, before and after the accelerated degradation test. In the case of carbon black, the oxidation peak of the carbon after the accelerated degradation test increased. From these results, carbon black is easily oxidized because of its amorphous nature and low crystallinity. Marimo carbon is not easily oxidized because Marimo carbon fibers comprise laminated graphite of higher crystallinity. The durability of Marimo carbon is higher than its of carbon black.Reference (1) K. Nakagawa et al., J. Mater. Sci. 44,221-226 (2009). (2) M. Eguchi et al., Trans. Mat. Res. Soc. Japan 38, 349-352 (2013). (3) K. Baba et al., Jpn. J. Appl. Phys. 52, 06GD06 (2013).

Carbon nanotubes supported Pt-Co-P ultrafine nanoparticle electrocatalysts with superior activity and stability for methanol electro-oxidation

The Pt-Co-P ultrafine nanoparticles supported on carbon nanotubes (Pt-Co-P/CNT) have been successfully synthesized by a hypophosphite-assisted one-pot reduction strategy and used as the electrocatalysts for methanol oxidation reaction (MOR). Transmission electron microscope observation clearly indicates that the Pt-Co-P nanoparticles are highly dispersed onto the surface of CNT with a narrow particle size distribution. The average diameter of the Pt-Co-P nanoparticles with the different P contents can be controlled from 1.5nm to 2.7nm, probably by the assistance of in-situ phosphate capping agent for nanoparticle growth, which generated from simultaneous oxidation of sodium hypophosphite. The electrochemical measurement data indicate that the Pt-Co-P/CNT with the average particle diameter of 1.5nm possesses superior electrocatalytic activity, outstanding tolerance against CO-like intermediates and excellent electrochemical stability, which is better than those of Pt-Co/CNT and commercial Pt/C. The improved electrochemical performance of Pt-Co-P/CNT can be attributed to the high electrochemical active surface area and rapid removal of CO-like intermediates arising from the ultrafine features of Pt-Co-P nanoparticles as well as the strong interaction among Pt, Co, and P. Therefore, the Pt-Co-P/CNT electrocatalysts prepared by a hypophosphite-assisted one-pot reduction strategy can be considered as a promising candidate for high performance MOR electrocatalyst.

Ultra-fine Pt nanoparticles supported on 3D porous N-doped graphene aerogel as a promising electro-catalyst for methanol electrooxidation

Three dimensional porous nitrogen-doped graphene aerogel (3D-NGA) was successfully fabricated via a combined hydrothermal self-assembly, thermal treatment and template-removing process. The as-synthesized Pt/3D-NGA catalysts exhibit an interconnected 3D porous structure, high N-doped level and uniform dispersion of Pt NPs. In studying the electrocatalytic performance of samples towards methanol electrooxidation, we found that Pt/3D-NGA hold a high electrochemical active surface area (ECSA) of 90.7m2g−1 and better catalytic activity as well as stability compared to Pt/G and Pt/3D-GA catalysts. Our studies provide a simple approach to synthesize 3D metal or metal oxide/graphene-based composites, holding great potential for fuel cell applications.

Free-Surfactant Synthesis of Graphene-Layered Carbon Composite and Its Utilization for Electrocatalysis

Abstract We synthesized a characteristic graphene-layered carbon particle composite using pyrolysis of hydrocarbon in an electric field and consecutive activation treatment under CO2 atmosphere. TEM, N2 adsorption isotherm, Raman spectroscopy, and XPS revealed structural features of this unique composite. Graphenes and carbon particles in the resultant composite are combined homogeneously in nanoscale with a mesoscale structure and with high carbon purity. When Pt nanoparticles are loaded on the composite, they show high performance as an electrocatalyst because of their higher electrochemical active surface area and higher durability against the sintering of Pt nanoparticles. Resulting material is a multifunctional composite by virtue of its nanostructural features.

The reduction of benzylbromide at Ag-Ni deposits prepared by galvanic replacement

A two-step procedure was applied to prepare bimetallic Ag-Ni glassy carbon supported catalysts (Ag-Ni/GC). First Ni layers were prepared by means of electrodeposition in an aqueous deaerated nickel chloride+nickel sulfamate+boric acid solution. Second, the partial replacement of Ni layers by Ag was achieved upon immersion of the latter in solutions containing silver nitrate. Three different pretreatment protocols were used after preparation of the Ag/Ni deposits; as prepared, cathodised in alkali and scanned in acid. After the pretreatment the surface was characterised by means of spectroscopy techniques (scanning electron microscopy and energy dispersive x-ray) and electrochemically in an alkali NaOH solution through cyclic voltammetry (CV). Afterwards the modified electrodes were tested for the reduction of benzylbromide in acetonitrile solutions by using CV and were found to show improved activity compared to bulk Ag electrode. The highest activity towards benzylbromide reduction was observed for pre-cathodised Ag-Ni electrodes. A final stage of the research focuses on the development of a practical Ag/Ni foam catalyst for the reduction of benzylbromide. Due to the high electrochemical active surface area of Ag/Ni foam, a higher conversion of benzyl bromide was obtained in comparison with bulk Ag.

Investigation of PtNi/C as methanol tolerant electrocatalyst for the oxygen reduction reaction

Platinum–nickel electrocatalysts prepared by a simple and cost-effective procedure have been investigated for the oxygen reduction reaction (ORR) in direct methanol fuel cells (DMFCs). The formic acid method was used to deposit well-dispersed PtxNiy nanoparticles (x:y=3:2) on the surface of a carbon black support (Ketjenblack). Carbothermal reduction of the as-prepared catalyst in an inert gas (Ar) at 900°C produced an alloy and a partial modification of the crystalline structure from the face centered cubic, typical of Pt, to a tetragonal structure of PtNi alloy. An acid leaching treatment was carried out to partially remove unalloyed surface nickel atoms in the outermost layers, leading to an enrichment of Pt concentration (x:y=2:1). Cyclic voltammetry analysis in acidic medium indicated a relatively high electrochemical active surface area (>70m2g−1) for both untreated and thermally treated PtxNiy catalysts. The activity towards the ORR was evaluated in half-cell configuration (0.5M H2SO4) using the rotating disk electrode technique. Similar behavior towards the ORR was found for the untreated and thermally treated PtNi/C catalysts, with an increase in activity compared to a commercial Pt/C catalyst. A remarkably better tolerance to methanol was observed for both PtNi/C cathode catalysts compared to the commercial Pt/C catalyst.

Hydrogen production in single chamber microbial electrolysis cells with stainless steel fiber felt cathodes

Microbial electrolysis cell (MEC) is a promising technology for sustainable production of hydrogen from biodegradable carbon sources. Employing a low-cost and high efficient cathode to replace platinum catalyzed cathode (Pt/C) for hydrogen generation is a challenge for commercialization of MEC. Here we show that a 3D macroporous stainless steel fiber felt (SSFF) with high electrochemical active surface area has an excellent catalytic activity for hydrogen generation, which is comparable to Pt/C cathode and superior to stainless steel mesh (SSM) cathode in the single-chamber MEC. The SSFF cathode (mean filter rating 100 μm) produces hydrogen at a rate of 3.66 ± 0.43 m3 H2 m−3d−1 (current density of 17.29 ± 1.68 A m−2), with a hydrogen recovery of 76.37 ± 15.04% and overall energy efficiency of 79.61 ± 13.07% at an applied voltage of 0.9 V. The performance of SSFF cathode improves over time due to a decrease in overpotential which caused by corrosion. These results demonstrate that SSFF can be a promising alternative for Pt catalytic cathode in MEC for hydrogen production.

Nanostructured Transition Metal Nitride (MN) As a Potential Support for Pt(Ru) Anode Electro-Catalyst for Direct Methanol Fuel Cells (DMFCs)

The rapid depletion of fossil fuels and increased environmental pollution due to vast fossil-fuel consumption is a thrust for efficient use of energy and exploration of renewable and clean energy sources.1 Generation of electricity from renewable energy sources, such as solar, wind without producing carbon dioxide-an undesired green house pollutant, offers enormous potential for meeting future energy demands. In this direction, fuel cell technology has gained special attention as it provides promising and sustainable approach for the production of continuous power with reduced greenhouse gas emissions and higher efficiencies compared to combustion based technologies. In particular, direct methanol fuel cells (DMFCs) have got attention as power sources due to advantages like use of methanol as fuel which has higher energy density (3800 kcal/l) than hydrogen (658 kcal/l, used as a fuel in proton exchange membrane fuel cells), safety and ease of handling the fuel (than H2) and low operating temperature. This offers quick start-up and extended durability of system components. The simple system design would be reflected as an ease in operation, reduced cost and high reliability. Hence, they are considered to be an ideal energy source for applications like automobile, portable devices, stationary systems, etc.2One of the major constraints in the development of high performance DMFCs is the low power density of the system due to poor catalytic performance at the electrodes and high capital cost due to use of expensive noble metal electro-catalysts. Hence, it is important to explore new electro-catalyst with reduced noble metal content at both anode and cathode to enhance the efficiency and power density of DMFC. Currently, Pt(Ru) alloy has been identified as a most active anode electro-catalyst for methanol electro-oxidation in DMFC. The synthesis of high surface area Pt(Ru) electro-catalyst is important to improve the reaction kinetics. In addition, efficient utilization of electro-catalyst by achieving high electrochemical active surface area is important, which can be accomplished by dispersing Pt(Ru) electro-catalyst on support with high surface area and superior electrical conductivity. The present study explores highly conductive nanostructured transition metal nitride (MN) as a potential support for Pt(Ru) electro-catalyst for methanol eletcro-oxidation. High surface area Pt(Ru)/MN (~125 m2/g) has been synthesized by wet chemical approach employing non-halide precursors of Pt and Ru. The electrochemical characterization has been carried out in 1 M methanol and 0.5 M sulfuric acid, used as fuel and electrolyte, using Pt wire as counter electrode and Hg/Hg2SO4 as reference electrode (+0.65 V with respect to NHE) and Pt loading of 0.3 mg/1cm2 at 400C. Pt(Ru)/MN shows promising performance for methanol oxidation, showing ~52% improved catalytic activity at ~0.65 V (vs NHE) in half-cell configuration and ~56% higher maximum power density in single DMFC study (Fig. 1) than that of commercial JM-Pt(Ru). This is attributed to well-dispersion of Pt(Ru) on MN (support of surface area of ~125 m2/g) offering high utilization of noble metals Pt and Ru, along with superior electrochemical active surface area and low charge transfer resistance for Pt(Ru)/MN than that of JM-Pt(Ru). Pt(Ru)/MN also shows superior electrochemical stability in half-cell configuration and single DMFC study than JM-Pt(Ru) electro-catalyst. Thus, the present study demonstrates the potential of MN as a support in improving the electrochemical activity of Pt(Ru) electro-catalyst, in the aim of achieving superior electrochemical performance and stability with reduced noble metal content for the electro-catalyst of DMFC. This portends significant reduction in the overall capital cost of DMFC system. Results of the synthesis, structural characterization and electrochemical activity of these electro-catalysts will be presented and discussed.

High performance and durable nanostructured TiN supported Pt50–Ru50 anode catalyst for direct methanol fuel cell (DMFC)

The design of high performance and durable electro-catalyst has been of particular interest for DMFC anodes. Pt(Ru) has been considered the most active DMFC anode catalyst. In this work, the reaction kinetics of Pt(Ru) electro-catalyst has been improved by synthesizing high active surface area Pt50(Ru50) catalyst supported on highly conductive nanostructured titanium nitride, TiN. The Pt(Ru)/TiN has been synthesized by a complexed sol-gel (CSG) process using non-halide precursors of Pt and Ru. High surface area Pt(Ru)/TiN shows promising electrochemical performance for methanol oxidation, showing ∼52% improved catalytic activity at ∼0.65 V (vs NHE) and stability/durability in comparison with commercial JM-Pt(Ru). Single cell DMFC performance shows 56% improved maximum power density and superior electrochemical stability for CSG-Pt(Ru)/TiN compared to that of commercial JM-Pt(Ru). This is attributed to the uniform dispersion of Pt(Ru) achieved on the nanostructured TiN (support) yielding higher electrochemical active surface area and lower charge transfer resistance than commercial JM-Pt(Ru). Thus, the present study demonstrates the potential of nanostructured TiN as a support for Pt(Ru) based anode electro-catalyst for DMFC applications.

High-Performance Pt Catalysts Supported on Polybenzimidazole-Grafted XC72 for Pemfcs

The performance of a polymer electrolyte membrane fuel cell (PEMFC) is limited by the sluggish oxygen reduction reaction (ORR) and the poor durability of the catalyst. Typically, most common catalysts are chemically deposited Pt nanoparticles on the surface of carbon nanoparticles (XC-72). A functionalized carbon support allows better dispersion of the catalyst nanoparticles, which can reduce the aggregation of metal nanoparticles and, consequently, improve the catalyst performance.1 Polybenzimidazole (PBI) is one kind of conducting polymer with excellent thermal stability and proton conductivity upon acid doping.2 Therefore, polybenzimidazole has been widely studied as proton conducting membrane in high-temperature fuel cells.3Recently, several studies have been reported the use of physically-adsorbed polybenzimidazole on carbon as the stable Pt catalyst support. In this work, covalently-functionalized carbon black XC-72 with polybenzimidazole was prepared as the catalyst support. The Pt nanoparticles were uniformed deposited onto PBI/XC-72 due to a strong interaction between PBI and Pt. Such Pt catalyst supported on the PBI grafted XC-72 will be expected to possess better proton conductivity, higher stability and better mass transport. The synthesized catalysts were characterized using rotating disk electrode (RDE) as well as membrane electrode assembly (MEA). The Cyclic voltammetry (CV) curves of PBI-grafted XC-72 supported Pt catalyst at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4 is shown in Figure 1. The electrochemical active surface area (ECSA) was calculated to be about 74 m2 Pt/gPt, which is much higher with that of commercial E-TEK Pt/C catalyst (58 m2 Pt/gPt). This high ECSA value suggests the uniform distribution of Pt on the surface of PBI/XC-72. Accelerated degradation tests (ADT) were also evaluated by monitoring the changes in electrochemical surface area during voltage cycling between 0.6 V and 1.2 V at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4. After 1000 cycles, a relatively surface area loss of more than 34% was observed in commercial catalyst. In comparison, the relative surface area loss of graphene/PBI supported Pt catalyst was only 14%. The increase in the stability of catalyst may result from the strong binding of Pt nanoparticles on PBI and the electrochemical stability of PBI-grafted XC-72. This catalyst was further compared with commercial Pt/C catalyst in MEA. It is shown that the peak power density of MEA made with was about 1400 mW/cm2, much higher than that of the commercial Pt/C catalyst (970 mW/cm2). Besides, the IR-drop of Pt/PBI-grafted XC-72 was lower than Pt/XC-72 mainly due to an enhanced proton transport. It is known that the MEA performance at high current densities is limited by the proton and mass transport. It is believed that the proton transport can be signifantly improved at the triphase interface (PBI-grafted XC-72 surfaces, Pt nanoparticles, and Nafion). Proton conducitivity tests are current being carried out in our group to elucidate our assumptions. In conclusion, the excellent electrochemical performance and better durability of PBI-grafted XC72 supported Pt catalyst illustrates the advantage of polybenzimidazole-grafted XC-72 as a catalyst support in PEMFCs. Figure 1. (a) CV curves of PBI/XC72 supported Pt catalyst between 0 and 1 V vs RHE at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4; (b) ECSA retention during ADT; and (c) MEA performance. Reference (1) Xu, F.; Wang, M.-x.; Sun, L.; Liu, Q.; Sun, H.-f.; Stach, E. A.; Xie, J. Electrochim. Acta 2013, 94, 172-181. (2) He, R.; Li, Q.; Xiao, G.; Bjerrum, N. J. Journal of Membrane Science 2003, 226, 169-184. (3) Xiao, L.; Zhang, H.; Scanlon, E.; Ramanathan, L. S.; Choe, E.-W.; Rogers, D.; Apple, T.; Benicewicz, B. C. Chem. Mater. 2005, 17, 5328-5333. Figure 1

Effect of ethylene glycol on electrochemical and morphological features of platinum electrodeposits from chloroplatinic acid

The aim of this work was to investigate the morphology, average size, and the electrochemical behavior of platinum nanoparticles electrodeposited from water and mixed water–ethylene glycol solutions of the electrolyte of H2PtCl6 and H2SO4 at a rotating disk electrode coated with Vulcan XC-72 carbon powder. Cyclic voltammetry and linear sweep voltammetry were used to determine the electrochemically active surface area (ESA) and oxygen reduction reaction (ORR) activity of the prepared Pt/C materials, respectively. XRD and scanning electron microscopy were used to study the influence of the electrodeposition methods applied on the morphology of platinum particles deposited in water and mixed water–ethylene glycol solutions. The average size of Pt crystallites was in the range of ca. 6–10 nm, and the average size of deposited Pt particles was in the range of ca. 30–150 nm. It was found that the presence of ethylene glycol in the electrolyte solution increased the overpotential of electrodeposition and it also strongly affected the morphology of Pt deposits when constant current electrodeposition was employed. Moreover, it was shown that pulse current electrodeposition is a more effective method compared to constant current electrodeposition method for the preparation of the Pt/Vulcan electrode with high ESA of Pt and enhanced catalytic activity toward ORR. The results obtained concerning the morphology and the spatial distribution of platinum particles electrodeposited on the surface of carbon support at different conditions demonstrate new possibilities to improve synthesis of Pt/C by electrodeposition methods.

Gold film supported nanostructured Cu/Pt catalyst with high electrochemical surface area and enhanced electrocatalytic activity for methanol oxidation

The rough Cu film was prepared by electrochemical reduction of copper ions at the surface of gold film electrode (GFE). Nanostructured Cu/Pt catalyst was prepared by partially galvanic replacement of Cu with platinum by simply immersion of Cu-coated gold film electrode in a K2PtCl6 aqueous solution. The structure and nature of the fabricated Cu and Cu/Pt species were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Cu-/Pt-coated gold film electrode exhibits really high electrochemical active surface area and remarkable electrocatalytic activity toward methanol oxidation. The effect of electrodeposition potential on the stability of the catalyst during the formation of Cu layer was comparatively investigated by performing methanol oxidation using voltammetry methods.

Microwave Activation of Palladium Nanoparticles for Enhanced Ethanol Electrocatalytic Oxidation Reaction in Alkaline Medium

AbstractThe impact of microwave irradiation on the structure and electrochemistry of monodispersed palladium nanoparticles is reported for the first time. When compared to the Pd that was not subjected to microwave treatment, the microwaved Pd nanocatalyst gave higher electrochemical active surface area (EASA≈67 m2 g−1), aggregation/uniformity of dispersion, showed higher amount of the palladium oxides, and showed remarkable electrocatalytic behaviour towards ethanol oxidation reaction in alkaline medium (in terms of high mass activity, stability and fast reaction kinetics). The remarkable microwave‐induced properties on the Pd catalyst promise to revolutionize the use of microwave for catalyst activation for enhanced heterogeneous catalysis and fuel cell chemistry.

Electrochemical performance and biosensor application of TiO2 nanotube arrays with mesoporous structures constructed by chemical etching.

Novel mesoporous TiO2 nanotube arrays (TiO2 NTAs) were synthesized by an anodization method combined with chemical etching in HF solution, and the electrochemical performance was studied. Glucose oxidase (GOx) was immobilized on the mesoporous TiO2 NTAs to achieve an efficient biosensor for amperometric detection of glucose. The morphology, structure, component and electrochemical performance of mesoporous TiO2 NTAs were characterized by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectrometry and an electrochemical workstation, respectively. The influence of the mesoporous structure on the electrochemical performance is discussed in detail by comparing the cyclic voltammograms and electrochemical impedance spectrum of TiO2 and mesoporous TiO2 NTAs in different conditions. High electrochemical active surface area and electron transfer rate play key roles in enhancing the electrochemical performance of mesoporous TiO2 NTAs. When used as the basis of a biosensor, the amperometric response of glucose on a GOx/TiO2-0.5 NTAs electrode is linearly proportion to the glucose concentration in the range from 0.1 to 6 mM with a sensitivity of 0.954 μA mM(-1) cm(-2), which is 14.3 times that of un-etched GOx/TiO2 NTAs.

Platinum nanoparticles on porphyrin functionalized graphene nanosheets as a superior catalyst for methanol electrooxidation.

A novel nanostructured catalyst of platinum nanoparticles supported on 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP) functionalized graphene (TMPyP-graphene) is synthesized by the hydrothermal polyol process. The as-synthesized nanocomposites are characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis absorption spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical tests. It has been found that Pt nanoparticles of ca. 3.4 nm are uniformly dispersed on the surface of TMPyP-graphene, and hold a high electrochemical active surface area (ECSA) of 126.2 m(2) g(-1). The results demonstrate that the Pt/TMPyP-graphene catalyst exhibits a much higher electrocatalytic activity and stability than the Pt/graphene and commercial Pt/C catalysts for methanol oxidation, which is of significant importance in improving the efficiency of Pt-based electrocatalysts for DMFCs applications.

Carbon-embedded carbon nanotubes as supports of polymer electrolyte membrane fuel cell catalysts.

Carbon shells embedded carbon nanotubes can facilitate Pt nanoparticles loading and dispersing on the core-shell nanostructural support. Carbon shells are prepared by coating polyaniline layers on the core (carbon nanotubes) with in-situ polymerization and subsequent carbonization. The carbon shell embedded carbon nanotube supported Pt catalyst reveals high electrochemical active surface area and mass activity, which are the factors of 1.4 times and 2.2 times higher than that of the pristine carbon nanotube supported Pt, respectively. In addition, the carbon shell embedded carbon nanotube supported Pt catalyst has a higher stability than the carbon nanotube supported Pt catalyst. The improved catalytic activity and stability of our new catalyst can be ascribed to the improved dispersion of Pt nanoparticles on surfaces of carbon nanotubes and the interaction between Pt nanoparticles and carbon shells.

Pt Catalysts Supported on Polybenzimidazole-Grafted Graphene for PEMFCs

The performance of a PEMFC is dominated by its catalyst performance, which depends on the size and distribution of the catalyst on the surface of the carbon support. A functionalized carbon support allows better dispersion of the catalyst nanoparticles, which can reduce the aggregation of metal nanoparticles and, consequently, improve the catalyst performance.1 Graphene is single-atomic-layer-thick carbon atoms arranged in a hexagonal lattice, which is the thinnest catalyst support for Pt catalyst nanoparticles. Graphene has many advantages over conventional carbon black catalyst support, like high electronic conductivity, surface area, mechanical strength, and excellent stability.2 All of these unique properties make the graphene as an ideal candidate for Pt catalyst support in polymer electrolyte fuel cells (PEFCs).3 In this work, covalently-functionalized graphene with polybenzimidazole (PBI) was employed as the catalyst support. The Pt nanoparticles were uniformed deposited onto graphene/PBI due to a strong interaction between PBI and Pt. Such Pt catalyst supported on the PBI grafted graphenes will benefit the MEA for PBI membrane based PEMFCs. The synthesized catalysts were characterized using rotating disk electrode (RDE) for their elctrocatalytic performance. The Cyclic voltammetry (CV) curves of graphene/PBI supported Pt catalyst at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4 is shown in Figure 1. The electrochemical active surface area (ECSA) was calculated to be about 55 m2 Pt/gPt, which is comparable with that of commercial E-TEK Pt/C catalyst (58 m2 Pt/gPt). The high ECSA value suggests the uniform distribution of Pt on the surface of graphene/PBI. Accelerated degradation tests (ADT) were also evaluated by monitoring the changes in electrochemical surface area during voltage cycling between 0.6 V and 1.2 V at a scan rate of 20 mV/s in N2-saturated 0.1 M HClO4. After 1000 cycles, a relatively surface area loss of more than 81% was observed in commercial catalyst. In comparison, the relative surface area loss of graphene/PBI supported Pt catalyst was 57%. The increase in the stability of catalyst may result from the strong binding of Pt nanoparticles onto PBI-grafted graphene. In conclusion, the high ECSA and excellent durability of graphene/PBI supported Pt catalyst illustrates the advantage of polybenzimidazole-grafted graphene as a catalyst support in PEMFCs.

Preparation and characterization of lead dioxide electrode with three-dimensional porous titanium substrate for electrochemical energy storage

Lead dioxide electrodes with three-dimensional porous titanium as substrate (3D-Ti/PbO2) were prepared by galvanostatic electrodeposition. The structure, morphology and electrochemical performances of 3D-Ti/PbO2 were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry and galvanostatic charge-discharge techniques. The electrochemical performances of 3D-Ti/PbO2 were optimized by adjusting the applied deposition current density. Results reveal that the 3D-Ti/PbO2 prepared at 1mAcm−2 had nanoparticles on its surface with abundant crystal orientations. It had a high capacity of 132 mAh g−1 with an active material utilization of 57% at discharge current density of 0.9 A g−1. With the same condition, the lead dioxide electrode with planar titanium substrate (Ti/PbO2) only had a capacity of 20.8 mAh g−1. The high electrochemical active surface area and small charge transfer resistance resulted in the high capacity of 3D-Ti/PbO2. The possible factors, which affected the electrochemical performances of 3D-Ti/PbO2, were interpreted in detail with voltammetric charge analysis and electrochemical impedance spectroscopy.

Synthesis of ordered mesoporous carbon doped with carbon nanotubes and a new strategy to use it as a support for Pt electrocatalysts

Our work pivots around modified mesoporous materials as supports for Pt electrocatalysts. Carbon nanotubes–ordered mesoporous carbon (CNTs–OMC) composite materials have been successfully fabricated through a hard template method. Firstly, carbon nanotubes–ordered mesoporous silica (CNTs–OMS) composites were prepared by using P123 as an organic template for directing the formation of mesoporous silica. Ordered mesoporous carbon doped with CNTs (designated as CNTs–OMC) has been successfully replicated from the above-synthesized CNTs–OMS template by using sucrose as a carbon precursor. We find that the addition of appropriate CNTs has no effect on the ordered mesoporous structure of carbon and can make the mesoporous structure more stable. The TEM images of the CNTs–OMC show highly ordered parallel channels and CNTs can be uniformly embedded in the ordered mesoporous carbon matrix. The OMC after doping shows a higher electrical conductivity of 26.4 S m−1 while that of the OMC (before doping) is only 4.3 S m−1, which is due to the nature of its graphitic framework as well as its lower interfacial resistance. Then the CNTs–OMC and OMCs were used as fuel cell catalyst supports for loading Pt nanoparticles prepared via a microwave synthesis process. The conductivity and plumbaginous degree of the CNTs–OMC composite are higher than those of OMC, which is beneficial for loading Pt nanoparticles. The Pt/CNTs–OMC catalyst has a higher electrochemical active surface area of 113.4 m2 g−1 than that of the Pt/OMC catalyst, which indicates that the addition of an appropriate amount of CNTs to OMC significantly improves the performance of Pt nanoparticles.

Low loading platinum nanoparticles on reduced graphene oxide-supported tungsten carbide crystallites as a highly active electrocatalyst for methanol oxidation

In this study, low loading platinum nanoparticles (Pt NPs) have been highly dispersed on reduced graphene oxide-supported WC nanocrystallites (Pt-WC/RGO) via program-controlled reduction-carburization technique and microwave-assisted method. The scanning electron microscopy and transmission electron microscopy results show that WC nanocrystallites are homogeneously decorated on RGO, and Pt NPs with a size of ca. 3nm are dispersed on both RGO and WC. The prepared Pt-WC/RGO is used as an electrocatalyst for methanol oxidation reaction (MOR). Compared with the Pt/RGO, commercial carbon-supported Pt (Pt/C) and PtRu alloy (PtRu/C) electrocatalysts, the Pt-WC/RGO composites demonstrate higher electrochemical active surface area and excellent electrocatalytic activity toward the methanol oxidation, such as better tolerance toward CO, higher peak current density, lower onset potential and long-term stability, which could be attributed to the characterized RGO support, highly dispersed Pt NPs and WC nanocrystallites and the valid synergistic effect resulted from the increased interface between WC and Pt. The present work proves that Pt-WC/RGO composites could be a promising alternative catalyst for direct methanol fuel cells where WC plays the important role as a functional additive in preparing Pt-based catalysts because of its CO tolerance and lower price.