Forward Peak Current Density Research Articles

Self-Supported PtAuP Alloy Nanotube Arrays with Enhanced Activity and Stability for Methanol Electro-Oxidation.

Inhibiting CO formation can more directly address the problem of CO poisoning during methanol electro-oxidation. In this study, 1D self-supported porous PtAuP alloy nanotube arrays (ANTAs) are synthesized via a facile electro-codeposition approach and present enhanced activity and improved resistance to CO poisoning through inhibiting CO formation (non-CO pathway) during the methanol oxidation reaction in acidic medium. This well-controlled Pt-/transition metal-/nonmetal ternary nanostructure exhibits a specific electroactivity twice as great as that of PtAu alloy nanotube arrays and Pt/C. At the same time, PtAuP ANTAs show a higher ratio of forward peak current density (If ) to backward peak current density (Ib ) (2.34) than PtAu ANTAs (1.27) and Pt/C (0.78). The prominent If /Ib value of PtAuP ANTAs indicates that most of the intermediate species are electro-oxidized to carbon dioxide in the forward scan, which highlights the high electroactivity for methanol electro-oxidation.

Facile synthesis of Pt nanoparticles supported on graphene/Vulcan XC-72 carbon and their application for methanol oxidation

A facile method was used for the preparation of Pt nanoparticles supported on graphene/Vulcan XC-72 carbon (denoted as Pt/Gr-C) by co-reduction of graphene oxide (GO) and H2PtCl6 with subsequent incorporation of Vulcan XC-72 carbon between graphene. The catalyst is extensively characterized by using scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. SEM and TEM observations show that aggregation of graphene is weakened through carbon insertion, which is beneficial for increase of effective contact area between catalyst and electrolyte. The electrochemical active surface area (ECSA) of Pt/Gr-C is higher than both Pt/C and Pt/Gr catalysts. The forward peak current density of Pt/Gr-C for methanol oxidation is 0.3 A mg−1 Pt, which is 1.4 and 1.7 times larger than Pt/Gr and Pt/C, respectively, due to the high utilization of Pt and large three-phase interface for methanol oxidation.

Cu Nanowires with Clean Surfaces: Synthesis and Enhanced Electrocatalytic Activity.

Low activity and high cost of electrocatalysts are the major challenge for the commercialization of the direct fuel cells (DFCs) and biofuel cells. In this work, we demonstrate the desirable "clean surfaces" effect of Cu nanocrystals in electrocatalysis. By a new reaction route of Cu2O nanospheres (Cu2O NSs), Cu nanowires (Cu NWs) with high purity and "clean surfaces" are first obtained under mild conditions. Benefiting from the path directing effects and abundant (100) facets, the as-prepared Cu NWs exhibit a lower overpotential to achieve the methanol electro-oxidation reaction (MOR) than that of analogous Cu nanoparticles (Cu NPs). Moreover, the "clean surfaces" provide more available active sites for the efficient transfer of electrons, enabling the Cu NWs to show their enhanced electrocatalytic activity. In the MOR, forward peak current density for the surface-cleaned Cu NWs is 2839 μA cm-2, which is ca. 6.45-fold higher than that of the Cu NWs with residual capping molecules on their surface. The "clean surfaces" effect can also be extended to the glucose electro-oxidation reaction (GOR), and the enhancement in specific surface area activity for the Cu NWs is 11.3-fold. This work enhances the electrocatalytic performance of Cu nanocrystals without the need for additional noble metals, which opens up new avenues for utilizing non-noble metals in the DFC or biofuel cell applications.

Palladium modified gold nanoparticles as electrocatalysts for ethanol electrooxidation

Resemblin, g core-shell electrocatalysts consisting of a Au core and Pd shell (Au@Pd) are synthesized via a Cu underpotential deposition (UPD)-Pd-displacement method. The Pd shell is non-uniform consisting of tiny Pd clusters with a coverage of 0.5–0.6. The ethanol oxidation reaction (EOR) activity of this kind of structure is much higher than Pd/C in an alkaline solution. The forward peak current density of Au@Pd is 5.4 times higher than that of Pd/C. Furthermore, the onset potential for EOR of the former is ∼100 mV more negative. An interesting particle size dependent EOR activity is also observed. With increasing the Au particle size (2.9, 5.8 and 6.5 nm), the EOR activity increases. The strain and ligand effects from the Au core, together with the bifunctional reaction mechanism in the Au–Pd system may be reasons for the enhanced activity in Au@Pd catalysts.

Effect of CeO2-ZrO2 on Pt/C electrocatalysts for alcohols oxidation

AbstractThe electrocatalytic activity and stability of Pt/C catalyst modified by using CeO2-ZrO2 mixed oxides for the alcohols electrochemical oxidation as probes were investigated. The catalyst samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties were measured by a three electrode system on electrochemical workstation (IVIUM). The results showed that the presence of CeO2-ZrO2 might be associated with the presence of Pt, which indicated that possibly there was synergistic effect between CeO2-ZrO2 and Pt nanoparticles. The electrocatalytic activity and stability of Pt-MOx/C (M=Ce, Zr) for methanol and ethanol oxidation was better than that of Pt-CeO2/C, which was attributed to that CeO2-ZrO2 composited oxides enhanced oxygen mobility and promoted oxygen storage capacity (OSC). Furthermore, the best performance was found when the molar ratio of CeO2 to ZrO2 was 2:1 for the oxidation of methanol and ethanol. The forward peak current density of Pt-MOx/C (M=Ce, Zr, Ce:Zr=2:1) towards the methanol electrooxidation was about 3.8 times that of Pt-CeO2/C. Pt-MOx/C (M=Ce, Zr) appeared to be a promising and less expensive methanol oxidation anode catalyst.

One-pot synthesis of Pt/SnO2/GNs and its electro-photo-synergistic catalysis for methanol oxidation

In this work, a simple one-pot strategy was used to synthesize an anodic electrocatalyst Pt/SnO2/GNs (EDTA) for direct methanol fuel cells (DMFCs). Under hydrothermal conditions, the reduction of H2PtCl6 and graphene oxide (GO), the oxidation of SnCl2 and the formation of SnO2 were occurred synchronously without additional reducing or oxidizing agent. The introduction of EDTA results in good dispersion and full integration of Pt and SnO2 nanoparticles, due to the complexation between Pt4+ (Sn2+) and EDTA. Electrochemical experiments show Pt/SnO2/GNs (EDTA) has much higher catalytic activity and better stability for MOR compared with the commercial Pt/C catalyst and Pt/GNs (EDTA). Furthermore, it is interesting to find that catalytic properties of Pt/SnO2/GNs (EDTA) toward MOR are significantly enhanced under external light irradiation. Especially, after UV irradiation for 30 min, Pt/SnO2/GNs (EDTA) composite shows an ultrahigh forward peak current density of 1103 mA mg−1. The remarkably improved performances under external light irradiation mainly derives from the synergistic effects between the electro-catalytic and photo-catalytic properties, which provides a novel strategy to effectively enhance the catalytic activities of Pt catalyst in DMFCs by coupling with photoresponsive metal oxides.

One-pot synthesis and electrocatalytic performance of Pd/MnOx/graphene nanocomposite for electrooxidation of ethylene glycol

In this study, low-loading palladium nanoparticles (Pd NPs) were prepared on a graphene oxide-manganese oxide (GR/MO) support using a one-pot, eco-friendly “green” process. The GR/MO-Pd nanocomposite was characterized by powder X–ray diffraction, Raman, scanning microscopy and transmission electron microscopy. The elemental composition was determined using energy dispersive X-ray spectroscopy, and the electronic state of the materials was characterized by X-ray photoelectron spectroscopy. The GR/MO-Pd nanocomposite exhibited high electrocatalytic activity towards ethylene glycol oxidation in alkaline medium. The GR/MO-Pd electrode demonstrated a forward anodic peak current density of 3.8 mA/cm2, which was higher than both MO-Pd and GR-Pd electrodes. This excellent catalytic activity, low onset potential, better intermediate tolerance and good long-term stability of the GR/MO-Pd electrode could be attributed to the uniform dispersion of Pd NPs over the GR/MO support. This work outlines a new method for simple, fast and eco-friendly fabrication of a catalyst with high electrochemical performance and potential in alcohol fuel cell applications.

Surface Palladium rich CuxPdy/carbon catalysts for methanol and ethanol oxidation in alkaline media

Here we prepare a series of surface Pd rich CuxPdy/C catalysts with different Pd to Cu ratios which may be applied in methanol and ethanol oxidation in alkaline media. TEM images show that they are well dispersed on the carbon support and the diameters of CuxPdy nanoparticles are concentrated on 3–5nm. XPS results confirm there exist obvious interactive electron effect between Cu and Pd. Electrochemical measurements show the CuxPdy/C catalysts demonstrate better catalytic activity and stability toward ethanol than that of methanol in alkaline media. Cu1Pd2/C stands out from the four as-prepared catalysts, whose forward anodic peak current densities for methanol and ethanol oxidation are about 220mAmg−1 Pd and 520mAmg−1 Pd, respectively.

Controlled synthesis of Pt/CS/PW12-GNs composite as an anodic electrocatalyst for direct methanol fuel cells

Controlled assembly in aqueous solution was used to synthesize the well-organized Pt/CS/PW12-GNs composite. By the aid of linear cationic polysaccharide chitosan, 2-D distribution worm-like Pt nanoparticles with their length and width of 15–20 and 3–4 nm, respectively, were formed on the surface of CS/PW12-GNs using HCOOH as a reducing agent at room temperature. The introduction of CS leads to well dispersion of worm-like Pt nanoparticles, the electroactivity of H3PW12O40 (PW12) alleviates CO poisoning toward Pt particles, and graphene nanosheets (GNs) ensure excellent electrical conductivity of the composites. The combined action among different components results in significantly enhanced catalytic activity of Pt/CS/PW12-GNs toward methanol oxidation and better tolerance of CO. The as-synthesized Pt/CS/PW12-GNs exhibit the forward peak current density of 445 mA mg−1, which is much higher than that (220 mA mg−1) for Pt/C-JM (the commercially available Johnson Matthey Hispec4000 catalyst, simplified as Pt/C-JM) and some recently reported Pt/graphene-based nanomaterials. The construction of 2-D distribution worm-like Pt nanoparticles and facile wet chemical synthesis strategy provide a promising way to develop superior performance electrocatalysts for direct methanol fuel cells applications.

Enhanced methanol electro-oxidation reaction on Pt-CoOx/MWCNTs hybrid electro-catalyst

The electro-catalytic behavior of Pt-CoOx/MWCNTs in methanol electro-oxidation reaction (MOR) is investigated and compared to that of Pt/MWCNTs. The electro-catalysts were synthesized by an impregnation method using NaBH4 as the reducing agent. The morphological and physical characteristics of samples are examined by XRD, TEM, ICP and EDS techniques. In the presence of CoOx, Pt nanoparticles were highly distributed on the support with an average particle size of 2nm, an obvious decrease from 5.1nm for Pt/MWCNTs. Cyclic voltammetry, CO-stripping, Chronoamperometry, and electrochemical impedance spectroscopy (EIS) measurements are used to study the electrochemical behavior of the electro-catalysts. The results revealed a considerable enhancement in the oxidation kinetics of COads on Pt active sites by the participation of CoOx. Compared to Pt/MWCNTs, Pt-CoOx/MWCNTs sample has a larger electrochemical active surface area (ECSA) and higher electro-catalytic activity and stability toward methanol electro-oxidation. According to the results of cyclic voltammetry, the forward anodic peak current density enhances more than 89% at the optimum atomic ratio of Pt:Co=2:1. Furthermore, inclusion of cobalt oxide species causes the onset potential of methanol electro-oxidation reaction to shift 84mV to negative values compared to that on Pt/MWCNTs. Based on EIS data, dehydrogenation of methanol is the rate-determining step of MOR on both Pt/MWCNTs and Pt-CoOx/MWCNTs, at small overpotentials. However, at higher overpotentials, the oxidation of adsorbed oxygen-containing groups controls the total rate of MOR process.

Design and synthesis of palladium/graphitic carbon nitride/carbon black hybrids as high-performance catalysts for formic acid and methanol electrooxidation

Here we report a facile two-step method to synthesize high-performance palladium/graphitic carbon nitride/carbon black (Pd/g-C3N4/carbon black) hybrids for electrooxidizing formic acid and methanol. The coating of g-C3N4 on carbon black surface is realized by a low-temperature heating treatment, followed by the uniform deposition of palladium nanoparticles (Pd NPs) via a wet chemistry route. Owning to the significant synergistic effects of the individual components, the preferred Pd/g-C3N4/carbon black electrocatalyst exhibits exceptional forward peak current densities as high as 2155 and 1720 mA mg−1Pd for formic acid oxidation in acid media and methanol oxidation in alkaline media, respectively, far outperforming the commercial Pd-C catalyst. The catalyst also shows reliable stability, demonstrating that the newly-designed hybrids have great promise in constructing high-performance portable fuel cell systems.

Dry-grinding Synthesized Multi-walled Carbon Nanotubes Supported PdO Catalyst for Ethanol Oxidation Reaction

For the first time, it was found that dry-grinding the mixture containing technical grade PdO and multi-walled carbon nanotubes (MWCNTs) can generate a catalyst with ultrahigh electrocatalytic activity for ethanol oxidation reaction (EOR). The as-prepared catalysts were denoted as PdO/MWCNTs. For a comparison, the graphene and graphite supported PdO samples were also prepared using the same process, leading to the formation of PdO/graphene and PdO/graphite catalysts respectively. The structural details, the morphologies as well as the particle sizes of the prepared catalysts are mainly characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Although no novel diffraction peaks were observed in the XRD patterns of the resulting samples, the morphologies of the samples after the dry-grinding process have changed greatly as compared to the starting materials of PdO. The results also indicate that the PdO/MWCNTs catalysts show the smallest particle sizes among all the prepared catalysts. The catalytic activities of the prepared PdO/MWCNTs catalysts towards EOR are examined by electrochemical measurements, and the results obtained from cyclic voltammery (CV) test demonstrated that the PdO/MWCNTs catalyst delivers a forward peak current density for EOR of 5029mAmg−1 at a scan rate of 50mVs−1, which is about 2.1 times higher than the reported value (2361mAmg−1) obtained on the (Pd/C) catalyst. After detailed analysis, it is thought that the easier hydrogen evolution process on the PdO/MWCNTs catalyst is regarded as the main reason for its excellent electrochemical performance as compared to other catalysts, i.e., PdO/graphene and PdO/graphite. Most interestingly, the as-prepared catalyst has electrocatalytic activity for both methanol oxidation reaction and formic acid oxidation, which were also explored approximately in this preliminary work.

Enhanced methanol electro-oxidation activity of Pt/MWCNTs electro-catalyst using manganese oxide deposited on MWCNTs

Electro-oxidation of methanol on platinum nanoparticles supported on a nanocomposite of manganese oxide (MnOx) and multi-wall carbon nanotubes (MWCNTs) is investigated. The morphology, structure, and chemical composition of the electro-catalysts are characterized by TEM, XRD, EDS, TGA, and H2-TPR. The electro-catalytic properties of electrodes are examined by cyclic voltammetry, CO-stripping, electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). Compared to Pt/MWCNTs, the Pt/MnOx-MWCNTs electro-catalyst exhibits about 3.3 times higher forward peak current density, during cyclic voltammetry, and 4.6 times higher exchange current density in methanol electro-oxidation reaction. In addition, deposition of manganese oxide onto MWCNTs dramatically increases the electrochemical active surface area from 29.7 for Pt/MWCNTs to 89.4m2g−1Pt for Pt/MnOx-MWCNTs. The results of long-term cyclic voltammetry show superior stability of Pt nanoparticles upon addition of manganese oxide to the support. Furthermore, the kinetics of formation of the chemisorbed OH groups improves upon manganese oxide incorporation. This leads to a lower onset potential of COads oxidation on Pt/MnOx-MWCNTs than on Pt/MWCNTs.

A green one-pot synthesis of Pt/TiO2/Graphene composites and its electro-photo-synergistic catalytic properties for methanol oxidation

A facile and green one-pot method was used to synthesize Pt/TiO2/Graphene composites with ethanol as a reducing agent under microwave irradiation. The as-prepared composites were characterized by SEM, TEM, EDX, XPS, XRD and Raman. Electrocatalytic performance of the Pt/TiO2/GNs composites was investigated by cyclic voltammetry (CV), chronoamperometric (CA), COad stripping voltammetry and electrochemical impedance spectrum (EIS). All experimental data have revealed that TiO2 (P25) not only enhanced the reduction ability of ethanol under microwave irradiation but also promoted Pt heterogeneous nucleation to form Pt nanoclusters which are around P25 and loaded on graphene nanosheets (GNs) surface. Electrochemical experiments showed that Pt/TiO2/GNs had much higher catalytic activity and stability toward methanol oxidation reaction (MOR) and better resistance to CO poisoning compared with Pt/GNs and the commercially available Johnson Matthey 20% Pt/C catalyst (Pt/C-JM). Especially under UV irradiation with 20min, Pt/TiO2/GNs composites showed an ultrahigh forward peak current density of 1354mAmg−1, nearly 2.5 times higher than that of Pt/C-JM, which indicated that the electrocatalytic and photocatalytic properties of Pt/TiO2/GNs had been integrated to boost the catalytic performance for MOR.

Highly dispersed Pd nanoparticles on 9-amino-1-azabenzanthrone functionalized graphene-like carbon surface for methanol electro-oxidation in alkaline medium

A simple and convenient procedure has been reported for the preparation of high dispersion Pd nanoparticles on a graphene-like carbon (GLC) surface functionalized by 9-amino-1-azabenzanthrone (AABZ). Catalyst activity for methanol electro-oxidation in fuel cells was investigated by cyclic voltammetry in alkaline medium. It was observed that the forward peak current density of Pd–AABZ/GLC catalyst is 770 A g−1Pd, which is 1.9 and 1.2 times higher than that of the Pd on commercial carbon black and reduced graphene oxide. The current at 3600 s of the chronoamperometric experiments for the Pd–AABZ/GLC catalysts is 230 A g−1Pd, which is 2.54 times higher than that of Pd/XC-72 (Pd/commercial Vulcan XC-72 carbon black). Pd–AABZ/GLC composite exhibits superior electro-catalytic activity toward methanol oxidation and is a promising candidate for application in direct methanol fuel cells. Besides, these findings will be propitious to the use of GLC as catalyst carrier for direct methanol fuel cells.

Enhanced methanol oxidation performance on platinum with butterfly-scale architectures: toward structural design of efficient electrocatalysts

Enhanced methanol oxidation performance was achieved by combining elaborate butterfly-scale architectures into platinum electrocatalysts using an electroless deposition-detemplating method. The electrochemically active surface area and the forward peak current density for methanol oxidation were dramatically increased by 5 and 5.2 times, respectively, for lamellar-ridge architectured Pt compared to its unarchitectured counterpart. Excellent mass transport properties and efficient catalytic surface accessibility were further demonstrated by finite element simulation.

Mesopore-functional carbon sphere nanochains and their integration with alloy nanoparticles for enhanced electrochemical performances

One of novel porous 1-D architectures, mesopore-functional carbon sphere nanochains (MCSNs), with highly interrelated networks have been directly evolved from the colloidal carbon sphere nanochains (CCSNs) through a unique Li2CO3-molten salt strategy. The PtRu/MCSNs hybrid system, achieved by rational integration of 2.5-nm-size PtRu alloy NPs into the mesopores of MCSNs were prepared, and for comparison, the solid carbon sphere nanochain (SCSN)-supported PtRu NPs (PtRu/SCSN) and benchmark carbon (Vulcan XC-72)-supported PtRu (PtRu/C) were also prepared. It is demonstrated that the PtRu/MCSN hybrid system exhibited superior catalytic properties toward methanol oxidation with specially enhanced catalytic activity and desirable stability. The forward peak current density of PtRu/MCSNs (437mAmg−1) was obviously much higher than those of PtRu/SCSNs (265mAmg−1) and PtRu/C (310mAmg−1). The onset potential of PtRu/MCSNs (0.24V) is much earlier than those of PtRu/SCSNs (0.38V) and PtRu/C (0.37V). This attractive efficiency can be ascribed to the functionalities of mesoporous carbon support, which affords more efficient electron transfer and better mass transport, maximizing the availability of nano PtRu catalysts.

Electrocatalytic Activity of Graphene-supported Pt-Cu Catalysts Prepared by an Impregnation Method for Methanol and Ethanol Oxidations

In this study, platinum (Pt) and Pt-copper (Cu) nanoparticles were synthesized on graphene sheets by an impregnation method, and their electrocatalytic activity for methanol and ethanol oxidations was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Experimental results demonstrate that, in comparison to graphene-supported Pt, graphene-supported Pt-Cu catalyst possesses enhanced efficiency for both methanol and ethanol electro-oxidations, which is reflected by a higher forward oxidation peak current density and a lower transfer resistance. This study indicates that Pt-Cu catalyst could be desirable catalyst candidates for both direct methanol and ethanol fuel cells.

A ternary Pt/MnO2/graphene nanohybrid with an ultrahigh electrocatalytic activity toward methanol oxidation

Ultrafine Pt nanoparticles with an average diameter of only 1.7 nm are uniformly dispersed onto MnO2-functionalized graphene sheets by a facile and cost-effective method. In such a ternary Pt/MnO2/graphene sheets (Pt/MnO2/GS) nanohybrid, each component provides unique and critical function to achieve optimized utilization of metallic platinum, allowing it to express ultrahigh electrocatalytic activity ability in methanol oxidation (the forward anodic peak current density is up to 1224 mA mg−1) in comparison with Pt/graphene sheets (Pt/GS), Pt/Vulcan XC-72 (Pt/XC-72) and Pt/MnO2/XC-72 catalysts. This work could provide new insights into the fabrication of the next generation high-performance electrocatalyst and promote their practical application in fuel-cell technologies.

N-doped graphene-supported Pt and Pt-Ru nanoparticles with high electrocatalytic activity for methanol oxidation

In this work, Pt and Pt-Ru nanoparticles were synthesized on both graphene and nitrogen (N)-doped graphene sheets, and their effects on electrocatalytic activity for methanol oxidation were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. Experimental results show that, in comparison to pure graphene as catalyst support, N-doped graphene-supported Pt and Pt-Ru nanoparticles demonstrate enhanced characteristics for methanol electro-oxidations with regard to oxidation potential, forward peak oxidation current density, and charge transfer resistance. For instance, the forward peak current densities of graphene-supported Pt and Pt-Ru nanoparticles were 9.5 mA/cm2 and 7.3 mA/cm2, respectively; however, the current densities of N-doped graphene-supported Pt and Pt-Ru nanoparticles were 19.9 mA/cm2 and 16.2 mA/cm2, respectively. The doping of nitrogen into graphene can effectively improve the currently density by twice. Our findings suggest the use of N-doped graphene sheets as promising catalyst supports for direct methanol fuel cells.