Graphene supported electrocatalysts for methanol oxidation

Graphene nanosheet was prepared by modified Hummer’s chemical method and utilized as a catalyst support of PtRu nanoparticles for the electro-oxidation of methanol. Home-made graphene nanosheet was clearly characterized by Raman spectroscopy and we applied colloidal method to synthesize with high metal content of 80 wt.% Pt–Ru catalyst, which is extensively clarified by HR-TEM and XRD analysis. 80 wt.% Pt–Ru/graphene nanosheet catalyst showed superior electrochemical activity toward methanol oxidation compared to Pt–Ru/Vulcan XC-72R. It is due to the significant increase of electrochemical active surface area for better catalyst utilization.     

Influence of the surface termination on the electrochemical properties of boron-doped diamond (BDD) interfaces

The paper reports on the electrochemical study of heavily boron-doped diamond (BDD) in aqueous media. Cyclic voltammetry and Mott-Schottky analysis were used to evaluate the influence of the surface termination on the electrochemical properties of BDD electrodes. The behavior of aminated BDD (NH₂–BDD) interfaces, prepared from hydrogen-terminated BDD using NH₃ plasma and from photochemically oxidized BDD (HO–BDD) using 3-aminopropyltrimethoxysilane (APTMES), are investigated and compared to those of H–BDD and HO–BDD. While H–BDD and HO–BDD electrodes show classical semiconductor behavior, amine-terminated BDD interfaces exhibit metallic behavior at pH < 10 and a semiconductor behavior at more basic pH.     

Aqueous treatment of single-walled carbon nanotubes for preparation of Pt–Fe core–shell alloy using galvanic exchange reaction: Selective catalytic activity towards oxygen reduction over methanol oxidation

We have demonstrated a new, cost effective synthesis of single-walled carbon nanotube supported Pt–Fe core–shell alloy catalyst (Pt–Fe/SWNT) for the direct methanol fuel cell using galvanic exchange reaction. The Pt–Fe/SWNTs have shown much larger Pt active surface area (150 m²/g-Pt) than the commercial catalyst (54 m²/g-Pt). Furthermore, four-fold enhancement of catalytic activity of the Pt–Fe/SWNTs for oxygen reduction reaction (ORR) has been observed. This catalyst has also demonstrated its tolerance to methanol in ORR.     

Pd/Pt core–shell nanowire arrays as highly effective electrocatalysts for methanol electrooxidation in direct methanol fuel cells

Highly ordered Pd/Pt–core–shell nanowire arrays (Pd/Pt NWAs) have been prepared by anodized aluminum oxide (AAO) template-electrodeposition and magnetron sputtering methods. Pd/Pt NWA electrode shows a very high electrochemical active surface area and high electrocatalytic activity for the methanol electrooxidation in acid medium for direct methanol fuel cells (DMFCs). The mass specific anodic peak current density is 756.7 mA mg⁻¹ Pt for the methanol oxidation on the Pd/Pt NWA electrode, an increase by a factor of four as compared to conventional E-TEK PtRu/C electrocatalysts. The mechanism of the significant enhancement of the Pd/Pt core/shell NWA nanostructure in the efficiency and electrocatalytic activity of Pt for the methanol electrooxidation in acid medium is discussed.     

Fabrication and catalytic properties of Pt and Ru decorated TiO2⧹CNTs catalyst for methanol electrooxidation

Highly ordered anodic titania nanotube arrays provide a large surface area for electrodepositing nickel nanoparticles which are used as the catalyst for carbon nanotube growth. Pt and Ru nanoparticles, approximately 3 nm in diameter, are uniformly electrodeposited on the as synthesized titania-supported carbon nanotubes (CNTs), constructing a novel catalyst for electrocatalytic oxidation of methanol. An enhanced and stable catalytic activity is obtained due to the uniformly dispersed Pt and Ru nanoparticles, and the large CNT network facilitating the electron transfer between the adsorbed methanol molecules and the catalyst substrate. An oxidation peak current density of 55 mA/cm² is achieved at a low Pt load of 0.126 mg/cm² with a Pt/Ru mole ratio of 1:1.     

High loading of Pt–Ru nanocatalysts by pentagon defects introduced in a bamboo-shaped carbon nanotube support for high performance anode of direct methanol fuel cells

Bamboo-shaped carbon nanotubes (BCNTs), with a large amount of pentagon defects introduced in the walls, were explored as the support of high loaded Pt–Ru catalysts for the anode of direct methanol fuel cells (DMFCs) in comparison with conventional carbon nanotubes (CNTs) and Vulcan XC carbon black. By ethylene glycol reduction, Pt–Ru catalysts with a high loading (60 wt%) and uniform particle size of 2–3 nm were uniformly deposited on BCNTs; while 60 wt% Pt–Ru catalysts on CNTs resulted in significant agglomeration. The Pt–Ru/BCNT catalyst showed the highest activity on methanol oxidation in cyclic voltammetry and highest performance as the anode in a DMFC single cell. Such an enhancement was largely ascribed to an enhanced interaction of the introduced pentagon defects with Pt–Ru, which could promote a high loading and well dispersion of Pt–Ru catalysts and the charge transfer from Pt–Ru to the tubes.     

Fabrication of the catalytic electrodes for methanol oxidation on electrospinning-derived carbon fibrous mats

The carbon fibrous mats with high conductivity (50 S cm⁻¹) formed by carbon nanofibers with an average diameter of ∼150 nm have been fabricated by thermally treating the electrospun polyacrylonitrile fibers. The platinum clusters are electrodeposited on the carbon nanofibrous mats (CFMs) by multi-cycle CV method. In contrast to the catalytic peak current of methanol oxidation on commercial catalyst (185 mA mg⁻¹ Pt), the catalytic peak current on optimum Pt/CFM electrode reaches to ∼420 mA mg⁻¹ Pt despite of the large size (50–200 nm) of the Pt clusters, revealing that the special structure of carbon fibrous mats is favorable to improve the performance of catalyst.     

Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

CO tolerant Pt/WC methanol electro-oxidation catalyst

Platinum supported on WC (Pt/WC) catalyst (20 wt.% Pt) was synthesized as a new methanol electro-oxidation catalyst. Particle size of 7.5 nm was obtained from X-ray diffraction results and a uniform distribution of particles was observed by transmission electron microscopy. In cyclic voltammetry (CV) measurement, the reduction peak potential of PtO increased from 0.72 V in commercial Pt/C to 0.76 V in Pt/WC. By combining the CV and CO stripping results, spill-over of H⁺ from Pt to WC was observed. Electrochemically active surface area calculated from the desorption area of H⁺ were 11.2 and 5.74 m²/g catalyst for Pt/WC and Pt/C, while those obtained from the desorption area of CO were 4.42 and 6.40 m²/g catalyst, respectively. CO electro-oxidation peak potential greatly decreased from 0.80 V in Pt/C to 0.68 V in Pt/WC. The reaction of WC with water to produce WC–OH could lower to CO electro-oxidation peak potential. Specific activity for methanol electro-oxidation increased from 144 mA/m² in Pt/C to 188 mA/m² in Pt/WC.     

Investigation of the Pt–Ni–Pb/C ternary alloy catalysts for methanol electrooxidation

This research is aimed to increase the activity of anodic catalysts and thus to lower noble metal loading in anodes for methanol electrooxidation. The Pt–Ni–Pb/C catalysts with different molar compositions were prepared. Their performance were tested by using a glassy carbon disk electrode through cyclic voltammetric curves in a solution of 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄. The performances of Pt–Ni–Pb/C catalyst with optimum composition (the molar ratio of Pt/Ni/Pb is 5:4:1) and Pt/C (E-Tek) were also compared. Their particle sizes and structures were determined by means of X-ray diffraction (XRD). The XRD results show, compared with that of Pt/C, the lattice parameter of Pt–Ni–Pb (5:4:1)/C catalyst decreases, its diffraction peaks are shifted slightly to a higher 2θ values. This indicates the formation of an alloy involving the incorporation of Ni and Pb atoms into the fcc structure of Pt. The electrochemical measurement shows the activity of Pt–Ni–Pb/C catalyst with an atomic ratio of 5:4:1 for methanol electrooxidation is the best among all different compositions. The activity of Pt–Ni–Pb (5:4:1)/C catalyst is much higher than that of Pt/C (E-Tek).     

Surface modified Pt/C as a methanol tolerant oxygen reduction catalyst for direct methanol fuel cells

A new procedure has been successfully developed by which PtN_x/C is synthesized to enhance methanol tolerance while maintaining a high catalytic activity for the oxygen-reduction reaction (ORR). The nitrogen-modified Pt surface, which is prepared using a chelating agent followed by heat treatment, exhibits considerable selectivity toward the ORR in the presence of methanol. The high methanol tolerance could be attributed to the suppression of methanol adsorption resulting from the modification of the Pt surface with nitrogen. A direct methanol fuel-cell (DMFC) test showed that a power density of up to 120 m W cm⁻² was generated when PtN_x/C was used as the cathode catalyst (1 mg cm⁻²) in 6 M methanol and oxygen at 70 °C.     

Ethanol electro-oxidation on catalysts with TiO2 coated carbon nanotubes as support

Pt–TiO₂/CNTs electrocatalysts for direct ethanol fuel cells (DEFCs) were prepared by sol–gel and ethylene glycol reduction method. XRD and TEM showed that the size of the Pt particles on TiO₂/CNTs is 3.5–4 nm and with narrow particle size distribution. HRTEM revealed that a thin layer of uniform amorphous TiO₂ on CNTs was formed and the faces of the Pt crystal on Pt–TiO₂/CNTs catalysts were quite “rough” and “rounded” and some grain bounders and/or twins also appeared. The electrochemical studies using cyclic voltammetry (CV), chronoamperometry and CO stripping voltammetry indicate that Pt–TiO₂/CNTs catalysts have higher electro-catalytic activity and CO-tolerance for ethanol oxidation than Pt/C (20 wt% Pt, E-TEK) and Pt/CNTs catalyst in acid. The Pt/TiO₂ molar ratio was also optimized and proved that 1:1 was the best Pt/TiO₂ molar ratio.     

Novel synthesis of a highly active carbon-supported Ru85Se15 chalcogenide catalyst for the oxygen reduction reaction

A carbon-supported Ru₈₅Se₁₅ chalcogenide catalyst was synthesized via a microwave-assisted polyol process using RuCl₃ and Na₂SeO₃ as the Ru and Se precursors. The Ru₈₅Se₁₅ chalcogenide catalyst was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively-coupled plasma-atomic emission spectroscopy (ICP-AES). The XRD pattern for Ru₈₅Se₁₅/C clearly exhibited the characteristic reflections of metallic ruthenium. The TEM image indicated that the Ru₈₅Se₁₅ chalcogenide catalyst was well dispersed on the surface of the carbon support with a narrow particle size distribution. Rotating disk electrode (RDE) and single-cell measurements were carried out to evaluate the electrocatalytic activity of the Ru₈₅Se₁₅ chalcogenide catalyst. The oxygen reduction reaction (ORR) activity of the Ru₈₅Se₁₅/C catalyst was compared with the commercial Pt/C catalyst with the absence/presence of methanol. In the absence of methanol, the Ru₈₅Se₁₅/C catalyst showed a comparable ORR activity with the Pt/C catalyst. However, in the presence of methanol, the Ru₈₅Se₁₅/C catalyst showed a better ORR activity than the Pt/C catalyst. The performance of the membrane electrode assembly (MEA) prepared with Ru₈₅Se₁₅/C as the cathode catalyst in a single proton exchange membrane fuel cell (PEMFC) showed the maximum power density of 400 mW cm⁻² at the current density of 1300 mA cm⁻².     

Low Pt content Pt–Ru–Ir–Sn quaternary catalysts for anodic methanol oxidation in DMFC

In this communication we report our research work on low Pt content Pt–Ru–Ir–Sn quaternary catalysts for use in DMFC anodes. The carbon-supported quaternary metal alloy catalyst was synthesized according to the solution reduction method and was deposited onto a carbon fiber paper or a carbon aerogel nanofoam to form the anode for direct methanol fuel cells. The Pt loading of the electrode is 0.1 mg/cm². The testing results from a three-electrode electrochemical cell show that the simultaneous use of higher Ir (25–35 wt.%) and Sn (10 wt.%) content gives satisfactory stability and higher activity for methanol oxidation than the commercially available E-TEK anode (80%[0.5Pt 0.5Ru]/C on carbon cloth). Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscope (SEM), and Bruner–Emmett–Teller method (BET) measurements were carried out to characterize the composition, structure, morphology, and surface area of the developed catalysts.     

Platinum nanocube catalysts for methanol and ethanol electrooxidation

We prepared Pt nanocube catalyst with about 3.6 nm in size by a polyol process in the presence of PVP as a stabilizer and Fe ion as a kinetic controller. The crystal structure of Pt nanocube with {1 0 0} faces was confirmed by field-emission transmission electron microscopy. In a cyclic voltammogram, we found that the Pt nanocube catalyst showed relatively high ratio of the forward anodic peak current to the reverse anodic peak current resulting in less accumulation of residues on the catalyst. The Pt nanocube catalyst with the edge of stepped {1 0 0} faces was preferable to breakage of CH₃OH and CH₃CH₂OH compared to polycrystalline Pt nanocatalyst. In an electrochemical measurement for methanol and ethanol electrooxidation, the Pt nanocube catalyst showed an excellent catalytic activity, i.e., lower onset potential and higher current density, compared to the polycrystalline Pt nanocatalyst.     

Combinatorial screening of ternary Pt–Ni–Cr catalysts for methanol electro-oxidation

Methanol electro-oxidation activity of ternary Pt–Ni–Cr system was studied by using a combinatorial screening method. A Pt–Ni–Cr thin-film library was prepared by sputtering and quickly characterized by a multichannel multielectrode analyzer. Among the 63 different composition thin-film catalysts, Pt₂₈Ni₃₆Cr₃₆ showed the highest methanol electro-oxidation activity and good stability. This new composition was also studied in its powder form by synthesizing and characterizing Pt₂₈Ni₃₆Cr₃₆/C catalyst. In chronoamperometry testing, the Pt₂₈Ni₃₆Cr₃₆/C catalyst exhibited “decay-free” behavior during 600 s operation by keeping its current density up to 97.1% of its peak current density, while the current densities of Pt/C and Pt₅₀Ru₅₀/C catalysts decreased to 14.0% and 60.3% of their peak current densities, respectively. At 600 s operation, current density of the Pt₂₈Ni₃₆Cr₃₆/C catalyst was 23.8 A g_{noble metal}⁻¹, while that of those of the Pt/C and Pt₅₀Ru₅₀/C catalysts were 2.74 and 18.8 A g_{noble metal}⁻¹, respectively.     

Photoluminescence of La/Ti mixed oxides prepared using sol–gel process and their pCBA photodecomposition

La/Ti mixed oxides with weight ratios of 1:9, 2:8, 3:7, and 4:6 were prepared by sol–gel method. The photocatalytic activity of La/Ti oxides was evaluated based on the pCBA photodecomposition. The catalyst samples were characterized by XRD, TEM, DRS, BET, and photoluminescence (PL) spectra. Particles of the La/Ti-mixed oxides showed the diameter of about 7 nm. We found that 30% doping of lanthanum ions on the TiO₂ powders induced the highest pCBA (4-chlorobenzonic acid) photodecomposition in these experimental conditions. The order of its photoactivity was as following: 30 > 20 > 0 > 10 > 40 wt%, which was the same for PL tendency. Also, PL spectra intensity increased with calcination temperature from 500 to 600 °C, then decreased at 700 °C. Phtotcatalytic activity followed the trend of the PL spectra intensity. The modification of TiO₂ surface by lanthanum ion made it possible to enhance the photoactivity by retarding the recombination of photoexcited electron/hole pairs, in the result of the higher photoactivity in the stronger PL intensity.     

Influence of Pt and Au nanophases on electrochromism of WO3 in nanostructure thin-film electrodes

We report electrochromic properties of WO₃ in Au–WO₃ and Pt–WO₃ nanostructure thin-film electrodes prepared by co-sputtering deposition method. The nanostructure electrodes consisted of Au or Pt metallic nanophase and a tungsten oxidative phase, indicating the formation of crystalline metallic nanophases in the amorphous oxide matrix. In particular, due to metallic nanophases, the modified electrochromic properties of WO₃ were observed in the Au–WO₃ and Pt–WO₃. The nanostructure electrodes showed a reverse optical modulation with respect to applied potentials in H₂SO₄ solution compared to that of pure WO₃ electrode. However, due to an excellent electrocatalytic activity of platinum for methanol electrooxidation at 25 °C, the electrochromism of the Pt–WO₃ in contrast with that of the Au–WO₃ was affected by the potentials for methanol electrooxidation in 2 M CH₃OH and 0.5 M H₂SO₄.     

Study of CuZnMOx oxides (M = Al,Zr, Ce,CeZr) for the catalytic hydrogenation of CO2 into methanol

CuO–ZnO–Al₂O₃ catalysts were synthesized by two methods, sol–gel and co-precipitation syntheses. Al₂O₃ was then substituted with other supports, such as ZrO₂, CeO₂ and CeO₂–ZrO₂ in order to have a better understanding of the support's effect. These catalysts containing 30 wt% of Cu were then tested for CO₂ hydrogenation into methanol. The effect of reaction temperature and GHSV on the catalytic behaviour was also investigated. The best results were obtained with a 30 CuO–ZnO–ZrO₂ catalyst synthesized by co-precipitation and calcined at 400 °C. This catalyst presents a good CO₂ conversion rate (23%) with 33% of methanol selectivity, leading to a methanol productivity of 331 g_MeOH.kg_cata⁻¹·h⁻¹ at 280 °C under 50 bar and a GHSV of 10,000 h⁻¹.     

A novel MEA architecture for improving the performance of a DMFC

Direct methanol fuel cell (DMFC) consisting of a double-catalytic layered membrane electrode assembly (MEA) provide higher performance than that with the traditional MEA. This novel structured MEA includes a hydrophilic inner catalyst layer and a traditional electrode with an outer catalyst layer, which was made using both catalyst coated membrane (CCM) and gas diffusion electrode (GDE) methods. The inner catalyst was PtRu black on anode and Pt black on cathode. The outer catalyst was carbon supported Pt–Ru/Pt on anode and cathode, respectively. Thus in the double-catalytic layered electrodes three gradients were formed: catalyst concentration gradient, hydrophilicity gradient and porosity gradient, resulting in good mass transfer, proton and electron conducting and low methanol crossover. The peak density of DMFC with such MEA was 19 mW cm⁻², operated at 2 M CH₃OH, 2 atm oxygen at room temperature, which was much higher than DMFC with traditional MEA.