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).     

Effect of Ru addition on the structural characteristics and the electrochemical activity for ethanol oxidation of carbon supported Pt–Sn alloy catalysts

Binary Pt–Sn/C (1:1) and ternary Pt–Sn–Ru/C (1:1:0.3 and 1:1:1) catalysts were synthesized by reduction of precursors with formic acid, and their activity for ethanol oxidation was compared with that of commercial Pt/C and Pt–Ru/C catalysts. Linear sweep voltammetry measurements at 40 and 90 °C showed that for potentials higher than 0.3 V vs. RHE, the Pt–Sn–Ru/C (1:1:0.3) catalyst presents the highest activity for ethanol electro-oxidation, while the electrochemical activity of the Pt–Sn–Ru/C (1:1:1) catalyst was lower than that of both the binary Pt–Sn/C and Pt–Ru/C catalysts. Tests in a single direct ethanol fuel cell confirmed the superior performance of the Pt–Sn–Ru/C (1:1:0.3) electrocatalyst. The positive effect of the Ru presence in the Pt–Sn–Ru/C (1:1:0.3) catalyst was ascribed to the interactions between Sn and Ru oxides.     

Dealloyed carbon-supported PtAg nanostructures: Enhanced electrocatalytic activity for oxygen reduction reaction

Dealloyed PtAg/C nanostructures, prepared by selective electrochemical etching of Ag in 0.5 M H₂SO₄ from a series of alloyed Pt_mAg/C samples with atomic Pt/Ag ratio m = 0.1, 0.5, 1.0 and 1.5, were employed as cathode electrocatalysts for oxygen reduction reaction (ORR) in 0.5 M KOH. Compared with their as-prepared counterpart alloy catalysts, the dealloyed catalysts showed higher half-wave potentials (E_1/2) and significantly higher Pt mass-specific activity (MSA) data. The intrinsic activity (IA) of Pt increased more or less after the dealloying treatment but was strongly dependent on the composition (m) of the alloyed sample. The Pt IA numbers were comparable for the dealloyed catalysts derived from Pt_mAg/C of m = 0.5, 1.0 and 1.5, which were nearly twice that for E-TEK Pt/C catalyst and 3 times that for the dealloyed catalyst derived from Pt_0.1Ag/C.     

Dual-doped graphene/perovskite bifunctional catalysts and the oxygen reduction reaction

We report the first investigation of dual-doped graphene/perovskite mixtures as catalysts for oxygen reduction. Pairwise combinations of boron, nitrogen, phosphorus and sulfur precursors were co-reduced with graphene oxide and mixed with La_0.8Sr_0.2MnO₃ (LSM) to produce SN-Gr/LSM, PN-Gr/LSM and BN-Gr/LSM catalysts. In addition, the dual-doped graphenes, graphene, LSM, and commercial Pt/C were used as controls. The addition of LSM to the dual-doped graphenes significantly improved their catalytic performance, with optimised composition ratios enabling PN-Gr/LSM to achieve 85% of the current density of commercial Pt/C at − 0.6 V (vs. Ag/AgCl) at the same loading. The effective number of electrons increased to ca. 3.8, and kinetic analysis confirms the direct 4 electron pathway is favoured over the stepwise (2e + 2e) route: the rate of peroxide production was also found to be lowered by the addition of LSM to less than 10%.     

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.     

Intrinsically microporous polymer slows down fuel cell catalyst corrosion

The limited stability of fuel cell cathode catalysts causes a significant loss of operational cell voltage with commercial Pt-based catalysts, which hinders the wider commercialization of fuel cell technologies. We demonstrate beneficial effects of a highly rigid and porous polymer of intrinsic microporosity (PIM-EA-TB with BET surface area 1027 m² g^− 1) in accelerated catalyst corrosion experiments. Porous films of PIM-EA-TB offer an effective protective matrix for the prevention of Pt/C catalyst corrosion without impeding flux of reagents. The results of electrochemical cycling tests show that the PIM-EA-TB protected Pt/C (denoted here as PIM@Pt/C) exhibit a significantly enhanced durability as compared to a conventional Pt/C catalyst.     

Ultra-low platinum loading high-performance PEMFCs using buckypaper-supported electrodes

The microstructure of the catalyst layer in proton exchange membrane fuel cells (PEMFCs) greatly influences catalyst (Pt) utilization and cell performance. We demonstrated a functionally graded catalyst layer based on a double-layered carbon nanotube/nanofiber film- (buckypaper) supported Pt composite catalyst to approach an idealized microstructure. The gradient distribution of Pt, electrolyte and porosity along the thickness effectively depresses the transport resistance of proton and gas. A rated power of 0.88 W/cm² at 0.65 V was achieved at 80 °C with a low Pt loading of 0.11 mg/cm² resulting in a relatively high Pt utilization of 0.18g_Pt/kW. The accelerated degradation test of catalyst support showed a good durability of buckypaper support because of the high graphitization degree of carbon nanofibers.     

Platinum nanoparticles supported on nitrobenzene-functionalised graphene nanosheets as electrocatalysts for oxygen reduction reaction in alkaline media

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O₂ reduction was 0.184 mA cm⁻², which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm⁻²) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells.     

Carbon-supported IrSn catalysts for a direct ethanol fuel cell

Carbon-supported Ir₃Sn/C and Ir/C catalysts were simply prepared with NaBH₄ as a reducing agent under the protection of ethylene glycol at room temperature. TEM and X-ray diffraction (XRD) data showed that the catalysts with small particle size exhibited the typical characteristic of a crystalline Ir fcc structure. Their electro-catalytic activities in comparison with Pt/C and Pt₃Sn/C catalysts also prepared by the NaBH₄ reduction process were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) techniques. The results indicated that Ir-based catalysts showed superior electro-catalytic activity towards ethanol oxidation to Pt/C and Pt₃Sn/C catalysts, mainly at low potential region. During single-cell tests at 90 °C, better performances of Ir-based catalysts as anodes were obtained compared to that of Pt/C catalyst. The comparable overall performance of Ir₃Sn/C to Pt₃Sn/C makes it a promising alternative choice of anode catalyst for direct ethanol fuel cells.     

Electron-deficient adduct site in the ring opening of methylcyclopentane (MCP) on tungsten-oxide-supported Pt,Ir and Pt–Ir catalysts

The activities of Pt/WO₂, Ir/WO₂ and Pt–Ir/WO₂ toward the conversion of methylcyclopentane (MCP) were investigated. The catalysts were prepared using impregnation and co-impregnation methods and were characterized by SEM, XRD, N₂-sorption and TEM investigations. The most active catalyst toward the conversion of MCP, irrespective of the temperature, was Ir/WO₂. The order of the reactivity was Ir/WO₂ > Pt–Ir/WO₂ > Pt/WO₂. Strong metal–support interactions (SMSI) were observed for all the catalysts over the entire investigated temperature range. At 400 °C, the Pt and Pt–Ir showed 100% selectivity toward ring-enlargement reactions associated with the presence of electron-deficient adduct sites on the reducible acidic WO₂ support. Ring opening occurred over all the catalysts in three positions, resulting in the formation of 2-methylpentane (2-MP), 3-methylpentane (3-MP), and n-hexane (n-H). Difficulty in breaking the secondary – tertiary carbon bonds was observed predominantly on the Ir catalyst, which opens the MCP ring via a selective mechanism.     

Reduction of aromatic compounds with Al powder using noble metal catalysts in water under mild reaction conditions

In water, Al powder becomes a powerful reducing agent, transforming in cyclohexyl either one or both benzene rings of aromatic compounds such as biphenyl, fluorene and 9,10-dihydroanthracene under mild reaction conditions in the presence of noble metal catalysts, such as Pd/C, Rh/C, Pt/C, or Ru/C. The reaction is carried out in a sealed tube, without the use of any organic solvent, at low temperature. Partial aromatic ring reduction was observed when using Pd/C, the reaction conditions being 24 h and 60 °C. The complete reduction process of both aromatic rings required 12 h and 80 °C with Al powder in the presence of Pt/C.     

Iodinated carbon materials for oxygen reduction reaction in proton exchange membrane fuel cell. Scalable synthesis and electrochemical performances

Doped graphene-based cathode catalysts are considered as promising competitors for ORR, but their power density has been low compared to Pt-based cathodes, mainly due to poor mass-transport properties. A new electrocatalyst for PEMFCs, an iodine doped grahene was prepared, characterized, and tested and the results are presented in this paper. We report a hybrid derived electrocatalyst with increased electrochemical active area and enhanced mass-transport properties. The electrochemical performances of several configurations were tested and compared with a typical Pt/C cathode configuration. As a standalone catalyst, the iodine doped graphene gives a performance with 60% lower than if it is placed between gas diffusion layer and catalyst layer. If it is included as microporous layer, the electrochemical performances of the fuel cell are with 15% bigger in terms of power density than the typical fuel cell with the same Pt/C loading, proving the beneficial effect of the iodine doped graphene for the fuel cell in the ohmic and mass transfer region. Moreover, the hybrid cathode manufactured by commercial Pt/C together with the material with best proprieties, is tested in a H₂-Air fuel cell and a power density of 0.55 W cm⁻² at 0.52 V was obtained, which is superior to that of a commercial Pt-based cathode tested under identical conditions (0.46 W cm⁻²).     

Synthesis,characterization and electrocatalytic activity for ethanol oxidation of carbon supported Pt,Pt–Rh,Pt–SnO2 and Pt–Rh–SnO2 nanoclusters

Nanoclusters of Pt, Pt–Rh, Pt–SnO₂ and Pt–Rh–SnO₂ were successfully synthesized by polyol method and deposited on high-area carbon. HRTEM and XRD analysis revealed two phases in the ternary Pt–Rh–SnO₂/C catalyst: solid solution of Rh in Pt and SnO₂. The activity of Pt–Rh–SnO₂/C for ethanol oxidation was found to be much higher than Pt/C and Pt–Rh/C and also superior to Pt–SnO₂/C. Quasi steady-state measurements at various temperatures (30–60 °C), ethanol concentrations (0.01–1 M) and H₂SO₄ concentrations (0.02–0.5 M) showed that Pt–Rh–SnO₂/C is about 20 times more active than Pt/C in the potential range of interest for the fuel cell application.     

Pt nanocrystallines/TiO2 with thickness-controlled carbon layers: Preparation and activities in CO oxidation

Pt nanocrystallines (~3 nm) covered with controllable carbon layers were synthesized by photochemical reduction method which exhibited extraordinary anti-sintering properties and different CO oxidation activities.     

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.     

Oxygen reduction reaction activities of Ni/Pt(111) model catalysts fabricated by molecular beam epitaxy

Oxygen reduction reaction (ORR) activities were evaluated for clean Pt(111) and Ni/Pt(111) model catalysts fabricated by molecular beam epitaxy. Exposure of clean Pt(111) to 1.0 L CO at 303 K produced linear-bonded and bridge-bonded CO-Pt IR bands at 2093 and 1858 cm^? 1. In contrast, 0.3-nm-thick Ni deposited on Pt(111) at 573 K (573 K-Ni_0.3 nm/Pt(111)) produced broad IR bands for adsorbed CO at around 2070 cm^? 1; the separation of reflection high-energy electron diffraction (RHEED) streaks is slightly wider for 573 K-Ni_0.3 nm/Pt(111) than for the clean Pt(111). For 823 K-Ni_0.3 nm/Pt(111), the separation of the RHEED streaks is the same as that for the Pt(111), and a single sharp IR band due to adsorbed CO is located at 2082 cm^? 1. The results suggest that for the 823 K-Ni_0.3 nm/Pt(111), a Pt-enriched outermost surface (Pt-skin) was formed through surface segregation of the substrate Pt atoms. ORR activities for the 573 K- and 823 K-Ni_0.3 nm/Pt(111) as determined from linear sweep voltammetry curves were five times and eight times higher than that for clean Pt(111), respectively, demonstrating that Pt-skin generation is crucial for developing highly active electrode catalysts for fuel cells.     

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.     

Controlled deposition of Pt on Au nanorods and their catalytic activity towards formic acid oxidation

Platinum submonolayer decorated gold nanorods with controlled coverage were prepared by the addition of Au nanorods into the growth solution of Pt in the presence of NH₂OH · HCl as the growth agent. The properties of Au nanorods decorated by Pt submonolayer were investigated by various techniques including transimission electron microscopy, X-ray diffraction, and electrochemical methods. The Pt decorated Au nanorods on carbon black showed significantly higher activity on formic acid electrooxidation than the conventional Pt/C catalysts. They showed different reaction path of formic acid electrooxidation by suppressing the formation of poisoning intermediate CO.     

A novel route for preparation of PtRuMe (Me = Fe,Co, Ni) and their catalytic performance for methanol electrooxidation

PtRuMe (Me = Fe, Co, Ni) catalysts dispersed on multi-wall carbon nanotubes (MWCNTs) were prepared by ultrasonic-assisted chemical reduction. X-ray diffraction (XRD) showed that Pt existed as face-centered cubic structure, while Ru and Me alloyed with Pt. The calculated particle sizes from XRD data are of 3.40, 3.40, 2.61 and 3.06 nm for PtRu, PtRuFe, PtRuCo and PtRuNi, respectively, and are consistent with TEM results. The electrochemical measurements showed that the addition of Me to PtRu enhances the electrocatalytic properties for methanol oxidation and PtRuNi has the best catalytic activity and stability.     

Nitrogen-doped carbon nanotubes as a cathode catalyst for the oxygen reduction reaction in alkaline medium

A new approach to synthesize nitrogen-doped carbon nanotubes (NCNTs) as catalysts for oxygen reduction by treating oxidized CNTs with ammonia is presented. The surface properties and oxygen reduction activities were characterized by cyclic voltammetry, rotating disk electrode and X-ray photoelectron spectroscopy. NCNTs treated at 800 °C show improved electrocatalytic activity for oxygen reduction as compared with commercially available Pt/C catalysts.