Electrocatalytic activity of platinum nanoparticles supported on different phases of tungsten carbides for the oxygen reduction reaction

Carbon-supported tungsten carbides with cubic (β-WC_1-x/C) and hexagonal (α-WC/C) are evaluated as support materials of Pt-nanoparticles, to be used as electrocatalysts for the oxygen reduction reaction (ORR) in acid media. The produced materials are characterized by X-Ray diffraction (XRD), energy dispersive X-ray spectroscopy, (EDS), X-ray photoelectron spectroscopy (XPS), in situ X-ray absorption near edge structure (XANES), and transmission electron microscopy (TEM). Cyclic voltammetry and polarization measurements on stationary and rotation disk electrodes are employed for the electrochemical investigations. It is seen that all Pt-α-WC/C catalysts present specific activity for the ORR similar to that of a standard carbon supported Pt catalyst (Pt/C), while for the Pt-β-WC_1-x/C composites the specific activitiy is 3.6 times higher than that of Pt/C, when a carbide-to-carbon load of 40 wt% is used. These differences in reactivity for the ORR may be associated to differences in the binding energy of adsorbed oxygen on Pt, introduced by the tungsten carbide substrates. Pt XANES results for the β-WC/C_1-x materials evidence a small increase in the Pt 5d band occupancy, which may lead to a weaker Pt-OH_x interaction, increasing the ORR kinetics.     

High efficiency platinum nanoparticles based on carbon quantum dot and its application for oxygen reduction reaction

1. Download high-res image (192KB)
2. Download full-size image

     

Oxygen reduction on carbon supported Pt-W electrocatalysts

The catalytic activity of Pt-W electrocatalysts towards oxygen reduction reaction (ORR) was studied. Pt-W/C materials were prepared by thermolysis of tungsten and platinum carbonyl complexes in 1-2 dichloro-benzene during 48 h. The precursors were mixed to obtain relations of Pt:W: 50:50 and 80:20%w, respectively. The Pt carbonyl complex was previously synthesized by bubbling CO in a chloroplatinic acid solution. The synthesized materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV) and a rotating disk electrode (RDE). The results show that both materials (Pt₅₀W₅₀/C and Pt₈₀W₂₀/C) have a crystalline phase associated with metallic platinum and an amorphous phase related with tungsten and carbon. The particle size of the electrocatalysts depends on the relationship between platinum and tungsten. Finally, both materials exhibit catalytic activity for oxygen reduction.     

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).     

Electrocatalytic activity of Pt nanoparticles electrodeposited on amorphous carbon-coated silicon nanocones

This study pulse-electrodeposits Pt nanoparticles on amorphous carbon-coated silicon nanocones (ACNCs) and explores them as the electrocatalyst for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) for direct methanol fuel cell applications. The work prepares silicon nanocones on the Si wafer using porous anodic aluminum oxide as the template and then deposits the amorphous carbon layer on the nanocones by microwave plasma chemical vapor deposition. According to Raman scattering and X-ray photoelectron spectroscopies (XPS), the surface of the ACNC support is composed of a nanocrystalline graphitic structure, and rich in oxygen-containing adspecies. The Pt nanoparticles pulse-electrodeposited on the highly ordered ACNC support disperses well with a large electrocatalytic surface area. The Pt/ACNC electrode exhibits excellent electrocatalytic activity and stability toward both MOR and ORR. This study suggests the abundant oxygen-containing surface species and the nanometer size of the Pt catalyst as the two major factors enhancing electrocatalytic performance of Pt/ACNC electrode. The XPS study suggests the occurrence of charge transfer from π-sites of the graphitic structure to the Pt nanoparticle, thereby improving the electrochemical stability of the electrode.     

Methanol oxidation efficiencies on carbon-nanotube-supported platinum and platinum-ruthenium nanoparticles prepared by pulsed electrodeposition

Dense carbon nanotubes (CNTs, 30-50 nm in diameter, 6-8 μm in length) were grown via a thermal chemical vapor deposition process on titanium treated carbon cloths. Catalysts in the form of either nano-scale platinum (Pt) or platinum-ruthenium (Pt-Ru) particles were then deposited on the CNT surfaces by pulse-mode potentiostatic electrodeposition. Surface morphologies of the prepared electrodes were examined by scanning electron microscopy and transmission electron microscopy. Well dispersed catalysts, Pt alone (particle sizes of 7-8 nm) or Pt-Ru (particle sizes of 3-4 nm) nanoparticles, were successfully electrodeposited on the CNT surfaces in citric acid aqueous solutions. In addition, electrochemical characteristics of the specimens were investigated by cyclic voltammetry in argon saturated sulfuric acid aqueous solutions and in mixed sulfuric acid and methanol aqueous solutions. The catalytic activity of the Pt-Ru/CNTs electrode for methanol oxidation was 1038.25 A g⁻¹_Pt in a mixed solution containing 0.5 M sulfuric acid and 1.0 M methanol.     

Oxidized carbon/nano-SiC supported platinum nanoparticles as highly stable electrocatalyst for oxygen reduction reaction

Nano-SiC particles with derived carbon shells were prepared by an acid-etching method at room temperature. The mixture solutions of concentrated HF and HNO₃ were chosen to etch the nano-SiC particles, and an amorphous carbon shell absorbed by oxygen functional groups was formed on the SiC surface. The oxidized carbon/SiC (O-C/SiC) particles were used as supports for preparation of Pt electrocatalysts. The O-C/SiC supported Pt electrocatalysts showed a high catalytic activity and an excellent stability for oxygen reduction reaction. The improved stability can be ascribed to the anchoring effect of the carbon shell to Pt NPs and the high stability of nano-SiC core.     

Synthesis and characterization of platinum supported on surface-modified ordered mesoporous carbons by self-assembly and their electrocatalytic performance towards oxygen reduction reaction

Ordered mesoporous carbons (OMCs) were fabricated by an organic–organic self-assembly process. Surface-modified OMCs were also prepared via the conventional acid-oxidation, H₂O₂ oxidation and 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEPTMS) grafted routes. Pt nanoparticles (NPs) supported on OMC (Pt/OMC) and modified OMC (Pt/OMC-H₂SO₄, Pt/OMC-H₂O₂ and Pt/OMC-AEPTMS) were synthesized and characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), transmission electron microscopy (TEM) analysis. It was found that acid-oxidation (H₂SO₄/HNO₃) method led to formation of a much wider Pt distribution with mean particle size of 6.8 nm. Unlike Pt/OMC-H₂SO₄ samples, Pt NPs (ca. 2.0 nm) were supported uniformly on AEPTMS-modified OMC with low electrical conductivity. Among three surface-modified methods, the H₂O₂ treatment method was an easily controllable way for surface modification of OMC which possesses desirable electrical conductivity, well-dispersed and nanosized Pt (ca. 3 nm). Accordingly, the Pt/OMC-H₂O₂ samples were observed to have superior electrocatalytic activity for oxygen reduction reaction as compared to synthesized Pt/OMC, Pt/OMC-H₂SO₄, Pt/OMC-AEPTMS and the commercial electrocatalysts (Pt supported on XC-72).     

CoSe nanoparticles prepared by the microwave-assisted polyol method as an alcohol and formic acid tolerant oxygen reduction catalyst

CoSe catalyst supported on nanoporous carbon was synthesized by microwave heating of glycerol solutions of Co(II) acetate and sodium selenite. The electrocatalytic behavior of the CoSe/C for oxygen reduction reaction (ORR) and its tolerance to several alcohols and formic acid were investigated by rotating disk electrode voltammetry and the results were compared with those of Pt/C. The results indicate that CoSe/C is a highly selective electrocatalyst towards ORR and shows a very high degree of tolerance to the presence of formic acid, methanol, ethanol, 2-propanol and ethylene glycol in acid medium. For a 20 wt.% CoSe/C, the onset potential and the magnitude of the current for ORR were almost the same with or without the presence of these fuels. In contrast, the Pt/C catalyst exhibited a mixed potential due to the simultaneous oxidation of the fuels and reduction of oxygen, which in turn caused the onset potential for the ORR to shift cathodically by ca. 500 mV in the presence of these fuels. Electrochemical measurements showed that the synthesized CoSe/C catalyst had a four-electron transfer mechanism for ORR. It is expected that this low cost electrocatalyst with its almost full tolerance and multi-fuel capability can find application in conventional and mixed-reactant fuel cells fueled with low molecular weight alcohols or formic acid.     

Platinum nanoparticles decorated Nb2CTx MXene as an efficient dual functional catalyst for hydrogen evolution and oxygen reduction reaction

Here, a dual functional Nb₂CT_x@Pt nanocomposite has been synthesized by in situ reduction method. The Pt loading in the composite has been optimized to get minimum overpotential (141 mV at 10 mA/cm²) for hydrogen evolution reaction (HER) along with a promising Tafel slope of 46.3 mV/dec, while Pt/C shows an overpotential and Tafel slope of 104 mV and 32.4 mV/dec, respectively. The Pt mass activity for Nb₂CT_x@Pt3.8 composite at 100 mV overpotential was 3.44 A g^?1 while the Pt mass activity for conventional Pt/C was 0.7 A g^?1, which shows that the activity of Nb₂CT_x@Pt3.8 composite is approximately 5 times higher than Pt/C. In addition, the catalyst was found to be stable for continuous 500 cycles without any binder molecules. The oxygen reduction reaction (ORR) capability of the material was also evaluated and found that the catalyst exhibited a current density of ?4.28 mA/cm² in the diffusion limiting region in comparison with the current density of ?5.82 mA/cm² for Pt/C at 2600 revolutions per minute (RPM). The Pt mass activity of Nb₂CT_x@Pt3.8 composite for ORR is approximately 10 times higher than Pt/C. The Nb₂CT_x@Pt3.8 composite was able to reduce O₂ completely using the 4-electron pathway with very little peroxide production. From these results, the dual functionality of the Nb₂CT_x@Pt3.8 composite for both HER and ORR has been established.     

Oxygen reduction on platinum electrode coated with Nafion

The kinetics of the reduction of oxygen on platinum covered by a Nafion^® film in sulfuric acid (0.5 M) has been studied in order to determine to what extent the solid polymer electrolyte modifies this reaction. As electrode we used a rotating electrode which is particularly well adapted to the measurement of the permeability D_fC_f (product of the diffusion coefficient and of the oxygen concentration in the film) of oxygen in the Nafion^® film. This product is of the order of 6×10⁻¹² M cm⁻¹ s⁻¹ whatever the state of division of the platinum, and is of the same order of magnitude as the permeability D_sC_s of oxygen in the adjacent sulfuric acid solution. It is shown, moreover, that the oxygen concentration in the film is very high, about five times that in the solution.     

Impact of SO2 poisoning of platinum nanoparticles modified glassy carbon electrode on oxygen reduction

An extraordinary recovery characteristic of Pt-nanoparticles from SO₂ poisoning is introduced in this study. Platinum nanoparticles (nano-Pt) modified glassy carbon electrode (nano-Pt/GC) has been compared with polycrystalline platinum (poly-Pt) electrode towards SO₂ poisoning. Two procedures of recovery of the poisoned electrodes were achieved by cycling the potential in the narrow potential range (NPR, 0-0.8 V vs. Ag/AgCl/KCl (sat.)) and wide potential range (WPR, −0.2 to 1.3 V). The extent of recovery was marked using oxygen reduction reaction (ORR) as a probing reaction. SO₂ poisoning of the electrodes changed the mechanism of the oxygen reduction from the direct reduction to water to the stepwise reduction involving the formation of H₂O₂ as an intermediate, as indicated by the rotating ring-disk voltammetry. Using the WPR recovery procedure, it was found that two potential cycles were enough to recover 100% of the activity of the ORR on the nano-Pt/GC electrode. At the poly-Pt electrode, however, four potential cycles of the WPR caused only 79% in the current recovery, while the peak potential of the ORR was 130 mV negatively shifted as compared with the fresh poly-Pt electrode. Interestingly, the NPR procedure at the nano-Pt/GC electrode was even more efficient in the recovery than the WPR procedure at the poly-Pt electrode.     

Enhanced catalytic activity of nanoshell carbon co-doped with boron and nitrogen in the oxygen reduction reaction

The use of carbon cathode catalysts in polymer electrolyte fuel cells instead of the current platinum catalysts is attracting increasing attention. We claim that two factors are important for enhancing the activity of carbon cathode catalysts in the oxygen reduction reaction (ORR): the formation of a nanoshell structure and co-doping with boron and nitrogen. Herein, we investigate the preparation and characterization of active ORR carbon catalysts that combine the above factors. Boron and nitrogen (BN)-doped nanoshell-containing carbon (BN-NSCC) was prepared by carbonizing a mixture of poly(furfuryl alcohol), cobalt phthalocyanine, melamine, and a trifluoroborane–methanol complex at 1000 °C. Transmission electron microscopy and X-ray photoelectron spectroscopy revealed the formation of nanoshell structures with distorted graphitic layers and the introduction of boron and nitrogen atoms, respectively. The ORR activity was evaluated in oxygen-saturated 0.5 mol dm^?3 H₂SO₄ using Koutecky–Levich analysis. The BN-NSCC showed an eight to ten times higher ORR activity than undoped NSCC, with an increased number of electrons participating in the reaction. Tafel analysis revealed a change in the rate-determining step caused by BN-doping. Thus, the combination of a nanoshell structure and co-doping with boron and nitrogen was found to improve the ORR activity of carbon catalysts.     

Electrochemical activity and durability of platinum nanoparticles supported on ordered mesoporous carbons for oxygen reduction reaction

A facile procedure for synthesizing platinum nanoparticles (NPs) studded in ordered mesoporous carbons (Pt–OMCs) based on the organic–organic self-assembly (one-pot) approach is reported. These Pt–OMCs, which can be easily fabricated with controllable Pt loading, were found to possess high surface areas, highly accessible and stable active sites and superior electrocatalytic properties pertinent as cathode catalysts for hydrogen–oxygen fuel cells. The enhanced catalytic activity and durability observed for the Pt–OMC electrocatalysts are attributed to the strengthened interactions between the Pt catalyst and the mesoporous carbon that effectively precludes migration and/or agglomeration of Pt NPs on the carbon support.     

Carbon-coated tungsten oxide nanowires supported Pt nanoparticles for oxygen reduction

Carbon-coated tungsten oxide nanowires were grown directly on carbon fiber of a carbon paper (C–W₁₈O₄₉ NWs/carbon paper) by chemical vapor deposition method and Pt nanoparticles were deposited on the nanowires (Pt/C–W₁₈O₄₉ NWs/carbon paper) to form the composite electrode. The microstructure and electrochemical behavior of the resultant Pt/C–W₁₈O₄₉ NWs/carbon paper composites are characterized by a transmission electron microscope (TEM) and cyclic voltammetry, respectively. The electrocatalytic activities of these composite electrodes for oxygen reduction reaction (ORR) were investigated and higher mass and specific activities in ORR were exhibited as compared to commercial Pt/C electrode.     

Enhancement of electrocatalytic activity of platinum for hydrogen oxidation reaction by sonochemically synthesized WC1−x nanoparticles

Two types of composite materials composed of Pt and WC_1−x nanoparticles supported on multiwalled carbon nanotubes (MWNT) are synthesized and evaluated in terms of their electrochemical properties, especially for the hydrogen oxidation reaction (HOR). The Pt nanoparticles are prepared by reduction of H₂PtCl₆ with NaBH₄, and the WC_1−x nanoparticles by a sonochemical method with a W(CO)₆ precursor. One of the composites is synthesized by forming WC_1−x nanoparticles on Pt-loaded MWNT and the other by physically mixing Pt-loaded MWNT with WC_1−x-loaded MWNT. The sonochemical synthesis of WC_1−x on Pt-loaded MWNT forms WC_1−x preferentially on Pt nanoparticles, which makes intimate contact between WC_1−x and Pt nanoparticles. The cyclic voltammograms of these composite materials show evidences for H⁺-spill-over from Pt to WC_1−x, thereby increasing the electrochemically active surface area (ECA). The composite in which WC_1−x is deposited on Pt shows a remarkable increase in ECA probably because the intimate contact between WC_1−x and Pt enhances the H⁺-spill-over. These materials exhibit enhanced HOR characteristics with Pt-specific mass activities about twice that of pure Pt nanoparticles.     

Platinum-decorated palladium-nanoflowers as high efficient low platinum catalyst towards oxygen reduction

A three-dimensional, low platinum (Pt) catalyst was prepared by decorating platinum on the palladium nanoflowers (PdNF) by an underpotential deposition (UPD) method. The PdNF was synthesized by a solvothermal approach, using oleic acid as the template and benzyl alcohol as the solvent-reducing agent. The obtained Pd with a morphology of uniform nanoflowers is composed of plentiful nanosheets. After decorating with platinum, the catalyst PdNF@Pt exhibits much higher activity for the oxygen reduction reaction (ORR) compared to commercial Pt/C (Pt 20 wt%). The interaction between deposited Pt and PdNF was revealed by XPS analysis, and the high performance of the PdNF@Pt catalyst was attributed to following two aspects: the increased of dispersion of platinum based on PdNF substrate, and the increased intrinsic activity of the active sites caused by the interaction of Pt and Pd NF.     

Carbon-supported Pd nanocatalyst modified by non-metal phosphorus for the oxygen reduction reaction

A carbon-supported palladium catalyst modified by non-metal phosphorus (PdP/C) has been developed as an oxygen reduction catalyst for direct methanol fuel cells. The PdP/C catalyst was prepared by the sodium hypophosphite reduction method. The as-prepared Pd nanoparticles have a narrow size distribution with an average diameter of 2 nm. Energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results indicate that P enters into the crystal lattice of Pd and forms an alloy. The PdP/C catalyst has an oxygen reduction reaction (ORR) activity comparable to the commercial Pt/C catalyst and a higher activity than the Pd/C catalyst synthesized by the conventional NaBH₄ reduction method. Its high catalytic activity can be attributed to its small size, lower relative crystallinity, and the formation of PdP alloy.     

One-step synthesis of carbon-encapsulated nickel phosphide nanoparticles with efficient bifunctional catalysis on oxygen evolution and reduction

As a promising and cost-efficient alternative to noble metal catalysts, transition metal phosphides (TMPs) show highly catalytic performance toward oxygen reduction and evolution reactions (ORR and OER). Mesoporous carbon-coated nickel phosphide (NiP) nanoparticles were successfully synthesized by thermal decomposition at 500 °C under N₂/H₂ (95:5) atmosphere. The NiP/C hybrid exhibits excellent OER/ORR activity. It can generate an OER current density of 10 mA cm^?2 at the overpotential of 0.26 V with a low Tafel slope of 43 mV dec^?1, and produce a limited ORR current density of 5.10 mA cm^?2 at 1600 rpm with a half-wave potential of 0.82 V via a 4-electron pathway. In addition, the OER/ORR catalytic currents remain considerable stable without significant loss for more than 25 h polarization. This work will open up a new avenue to design a bifunctional catalyst with a superior OER/ORR activity and stability, and this cost-efficient strategy will pave the way for the industrial application of the renewable energy technologies.