Electrocatalytic activity of Pt/C catalysts for methanol electrooxidation promoted by molybdovanadophosphoric acid

A Pt/C catalyst modified by the Keggin-structure molybdovanadophosphoric acid (PMV) is prepared by cyclic voltammetry and the modified Pt/C catalyst is studied for methanol electrooxidation. The results show that the PMV modified Pt/C catalyst has increased the electron transfer coefficient of the rate-determining step and diminished the adsorption of CO on Pt/C catalysts. Significant improvements in the catalytic activity and stability for methanol electrooxidation are observed, and it indicates that the PMV combined with Pt/C catalyst can be considered as a good electrocatalyst material for potential application in direct methanol fuel cells.     

Electrochemical Characteristics and Performance of Platinum Nanoparticles Supported by Vulcan/Polyaniline for Oxygen Reduction in PEMFC

We report a Pt/Vulcan carbon–polyaniline (VC–PANI) catalyst for the oxygen reduction reaction (ORR). This electrocatalyst was prepared from Pt nanoparticles supported by a VC–PANI composite substrate. Electrochemical performance was measured using potentiostat/galvanostats technique and a proton exchange membrane fuel cell (PEMFC) test station. The electrochemical properties of the electrodes were characterized using linear sweep voltammetry, AC impedance spectroscopy and chronoamperometry. Electrochemical characterization by hydrogen adsorption/desorption cyclic voltammetry and CO stripping voltammetry indicates that the electrochemical active surface areas of the Pt/VC–PANI are comparable to the commercial catalyst. The performance of the Pt/VC–PANI and Pt/C(E‐TEK) + PANI electrocatalysts were found to be 1.82 and 1.33 times higher than of the Pt/C(E‐TEK) electrode. The surface morphologies of the electrodes were characterized by using scanning electron microscopy (SEM). PANI has a fibrous structure and the improved performance was attributed to the PANI effect and synergistic effects between the carbon Vulcan and the PANI fiber. These results indicate that Pt/VC–PANI is a promising catalyst for the ORR in PEMFCs using an H₂/O₂ feed.     

Synthesis of Novel Submicrometer‐Scale Flat Carbon Fibers and Application in the Electrooxidation of Methanol

Novel submicrometer‐scale flat carbon fibers (SFCF) have been synthesized by catalytic chemical vapor deposition of acetylene over an Ni‐Al layered double hydroxide (NiAl‐LDH) compound, and the electrochemical activity of Pt supported on as‐synthesized SFCF for methanol oxidation has been investigated. The materials were characterized by power X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, and cyclic voltammetry tests. The results reveal that the active crystal facets of the NiAl₂O₄ spinel phase derived from NiAl‐LDH can deposit carbon atoms to grow SFCF, and that the co‐growing Ni nanoparticles are not catalytically active for the formation of SFCF. Furthermore, after support with Pt, the resultant Pt/SFCF electrocatalyst shows much higher activity for methanol oxidation than the Pt/C one in both acid and alkaline media, which is attributed to the combined beneficial effects of the microstructure of the SFCF support, improved electrical conductivity originating from the NiAl₂O₄ spinel catalyst embedded in SFCF, and improved dispersion of Pt particles through exposed Ni nanoparticles adhering intimately to the SFCF.     

Methanol-tolerant PdPt/C alloy catalyst for oxygen electro-reduction reaction

A carbon-supported Pd-based PdPt catalyst (PdPt/C) with a small amount of Pt was prepared by borohydride reduction method and its activity in the oxygen electro-reduction reaction (ORR) was investigated in acidic conditions both with and without methanol. For comparison, carbon-supported Pt (Pt/C) and Pd (Pd/C) catalysts were prepared and the ORR activities were compared. Results revealed that the PdPt/C catalyst showed slightly lower ORR activity in terms of onset potential of oxygen reduction than Pt/C catalyst in 0.1M HClO₄. However, PdPt/C catalyst exhibited enhanced activity toward selective ORR with methanol-tolerant characteristics in 0.1M HClO₄ in the presence of methanol. The PdPt/C catalyst prepared here is suitable for use as a cathodic electrocatalyst in direct alcohol fuel cells after addition of small amount of expensive Pt metal.     

Nickel phthalocyanine-tetrasulfonic acid as a promoter of methanol electro-oxidation on Pt/C catalyst

This paper describes an investigation of the role of nickel phthalocyanine-tetrasulfonic acid (NiPcTs) for methanol electro-oxidation on a Pt/C catalyst. Cyclic voltammetry (CV) revealed that NiPcTs has no catalytic activity in methanol or CO electro-oxidation. However, methanol electro-oxidation occurs faster on a Pt/C catalyst modified with NiPcTs than on the original Pt/C catalyst. CO stripping results demonstrated that NiPcTs promotes electro-oxidation of adsorbed CO (CO_ads) on the Pt/C catalyst, which is likely to be responsible for the enhancement of the methanol electro-oxidation rate. The promotion effect of NiPcTs is attributable to its ability to modify the electron density of the Pt surface. The electron deficiency of Pt⁰ in the NiPcTs-Pt/C catalyst is shown by the shift of the Pt⁰ 4f peak to higher binding energies in the X-ray photoelectron spectrum.     

Enhanced activity and stability of Pt/C fuel cell anodes by the modification with ruthenium-oxide nanosheets

Ruthenium-oxide nanosheet (RuO₂ns) crystallites with thickness less than 1 nm were prepared via chemical exfoliation of a layered potassium ruthenate and deposited onto carbon supported platinum (Pt/C) as a potential co-catalyst for fuel cell anode catalysts. The electrocatalytic activity towards carbon monoxide and methanol oxidation was studied at various temperatures for different RuO₂ns loadings. An increase in electrocatalytic activity was evidenced at temperatures above 40 °C, while little enhancement in activity was observed at room temperature. The RuO₂ns modified Pt/C catalyst with composition of RuO₂:Pt = 0.5:1 (molar ratio) exhibited the highest methanol oxidation activity. CO-stripping voltammetry revealed that RuO₂ns promotes oxidation of adsorbed CO on Pt. In addition to the enhanced initial activity, the RuO₂ns modified Pt/C catalyst exhibited improved stability compared to pristine Pt/C against consecutive potential cycling tests.     

微波法制备的Pt/C催化剂对甲醇和CO的电催化氧化

用微波间断升温法制备了3种Pt/C催化剂,运用循环伏安和线行扫描方法测试甲醇和吸附态CO在不同方法制备的Pt/C催化剂上的电催化氧化情况。发现在酸性溶液中,对于相同Pt载量的Pt(2)和Pt(3)催化剂,Pt(3)具有较小的Pt平均粒径及较高的电催化活性;对于具有较高Pt载量的Pt(1)催化剂,具有最小的平均粒径和最高的电催化活性。     

Investigation of carbon-supported Pt and PtCo catalysts for oxygen reduction in direct methanol fuel cells

Carbon-supported Pt and Pt₃Co catalysts with a mean crystallite size of 2.5 nm were prepared by a colloidal procedure followed by a carbothermal reduction. The catalysts with same particle size were investigated for the oxygen reduction in a direct methanol fuel cell (DMFC) to ascertain the effect of composition. The electrochemical investigations were carried out in a temperature range from 40 to 80 °C and the methanol concentration feed was varied in the range 1-10 mol dm⁻³ to evaluate the cathode performance in the presence of different conditions of methanol crossover. Despite the good performance of the Pt₃Co catalyst for the oxygen reduction, it appeared less performing than the Pt catalyst of the same particle size for the cathodic process in the presence of significant methanol crossover. Cyclic voltammetry analysis indicated that the Pt₃Co catalyst has a lower overpotential for methanol oxidation than the Pt catalyst, and thus a lower methanol tolerance. Electrochemical impedance spectroscopy (EIS) analysis showed that the charge transfer resistance for the oxygen reduction reaction dominated the overall DMFC response in the presence of high methanol concentrations fed to the anode. This effect was more significant for the Pt₃Co/KB catalyst, confirming the lower methanol tolerance of this catalyst compared to Pt/KB. Such properties were interpreted as the result of the enhanced metallic character of Pt in the Pt₃Co catalyst due to an intra-alloy electron transfer from Co to Pt, and to the adsorption of oxygen species on the more electropositive element (Co) that promotes methanol oxidation according to the bifunctional theory.     

Pt–NiO/C anode electrocatalysts for direct methanol fuel cells

Pt catalyst was supported on Vulcan XC-72R containing 5 wt.% NiO using NaBH₄ as a reducing agent. The prepared catalyst was heat-treated at 400 °C. XRD, TEM and EDX analyses were applied to characterize Pt–NiO/C electrocatalyst. The introduction of NiO reduces the particle size of Pt crystallites. The electrocatalytic activity of Pt–NiO/C electrocatalysts was examined towards methanol oxidation reaction in 0.5 M H₂SO₄ solution using cyclic voltammetry and chronoamperometry techniques. A three fold increment in the oxidation current density was gained at Pt–NiO/C electrocatalyst compared to Pt/C one. The corresponding chronoamperograms showed high steady state current density values suggesting better stability of Pt–NiO/C electrocatalyst towards the carbonaceous poisoning species. The enhanced electrocatalytic performance and the long-term cycle durability of Pt–NiO/C electrocatalyst are attributed to the strong interaction between Pt and NiO and the formation of small Pt crystals.     

Graphitized mesoporous carbon supported Pt-SnO2 nanoparticles as a catalyst for methanol oxidation

A mesostructured composite catalyst, Pt-SnO₂ supported on graphitized mesoporous carbon (GMC), has been prepared and its electrochemical activity for methanol oxidation has been investigated. The materials were characterized by XRD, FESEM, TEM, EDX spectrum and N₂ sorption techniques. Cyclic voltammetry, chronoamperometry and steady-state polarization tests were adopted to characterize the electro-catalytic activities of the materials for methanol oxidation. The results show that, the overall methanol electro-oxidation catalytic activity of the mesostructured composite catalyst, 20 wt.% PtSnO₂ (1:1, mass ratio)/GMC, is obviously higher than that of 20 wt.% PtSnO₂/C with commercial carbon black as support under the same loading amount of Pt-SnO₂ catalysts, and is also much higher than that of commercial catalyst 20 wt.% Pt/C at half Pt using amount.     

Preparation and the physical/electrochemical properties of a Pt/C nanocatalyst stabilized by citric acid for polymer electrolyte fuel cells

Pt/C nanocatalysts were prepared by the reduction of chloroplatinic acid with sodium borohydride, with citric acid as a stabilizing agent in ammonium hydroxide solution. These nanocatalysts were obtained by altering the molar ratio of citric acid to chloroplatinic acid (CA/Pt) from 1:1, 2:1, 3:1 to 4:1. Transmission electron microscopy and X-ray diffraction analyses indicated that the well-dispersed Pt nanoparticles of around 3.82 nm in size were obtained when the CA/Pt ratio was maintained at 2:1. X-ray photoelectron spectroscopy measurements revealed that the 2:1, 3:1 and 4:1 molar ratio catalysts had a relatively higher amount of Pt in their metallic state than did the 1:1 molar ratio catalyst. Cyclic voltammetry results demonstrated that the Pt/C nanocatalysts annealed at 400 °C in an N₂ atm provided higher electrocatalytic activity. Among all the molar ratio catalysts, the 2:1 molar ratio catalyst exhibited the largest electrochemical active surface (EAS) area, and its methanol oxidation reaction current was superior to the E-TEK catalyst. The oxygen reduction reaction of the catalysts studied by linear sweep voltammetry and tested in a fuel cell indicated that the catalytic activity of the 2:1 molar ratio catalyst was comparable to that of an E-TEK catalyst.     

Investigations of Compositions and Performance of PtRuMo/C Ternary Catalysts for Methanol Electrooxidation

PtRuMo/C catalyst was prepared by impregnation reduction method and characterised. Comparison is made between a home‐made PtRu/C prepared by similar method and Pt/C (E‐Tek Co., Pt/C‐ET) catalysts. One glassy carbon disc electrode for ternary alloy catalyst was used to evaluate the catalytic performances by cyclic voltammetric, chronoamperometric, amperometric i–t curves, and electrochemical impedance spectra (EIS). The electrochemical measurement results indicated that the performance of PtRuMo/C with a molar ratio of 6:3:1 was the highest among 15 Pt_xRu_yMo_10–x–y/C catalysts with different molar ratios. The composition, particle size, lattice parameter and morphology of the PtRuMo(6:3:1)/C catalyst were determined by means of X‐ray energy dispersive analysis, X‐ray diffraction (XRD) and transmission electron micrographs (TEM). The result of XRD analysis exhibits that PtRuMo(6:3:1)/C has the fcc structure with the smaller lattice parameter than the home‐made PtRu/C and Pt/C‐ET. Its typical particle sizes is only about 5 nm. With respect to the catalytic activity and stability, the PtRuMo(6:3:1)/C catalyst is superior to PtRu/C despite their comparable active areas. Though the electrochemically active surface area of Pt/C‐ET is the biggest, its performance is the lowest. EIS results also indicate that the reaction resistances for methanol electrooxidation on the PtRuMo(6:3:1)/C catalyst are smaller than those of PtRu/C at different polarisation potentials.     

Effect of heat treatment on PtRu/C catalyst for methanol electro-oxidation

The effect of heat treatment on a commercial PtRu/C catalyst was investigated with a focus on the relationship between electrochemical and surface properties. The heat treated PtRu/C catalysts were prepared by reducing the commercial PtRu/C catalyst at 300, 500, and 600 °C under hydrogen flow. The maximum mass activity for the methanol electro-oxidation reaction (MOR) was observed in the catalyst heat treated at 500 °C, while specific activity for the MOR increased with increasing heat treatment temperature. Cyclic voltammetry (CV) results revealed that the heat treatment caused Pt rich surface formation. The increase in surface Pt was confirmed by X-ray photoelectron spectroscopy; the surface (Pt:Ru) ratio of the fresh catalyst (81:19) changed to (87:13) in the 600 °C heat treated catalyst. Quantitative analysis of the Ru oxidation state showed that the ratio of metallic Ru increased with an increase in heat treatment temperature. On the other hand, RuO_xH_y completely reduced at 500 °C and the ratio of RuO₂ slightly decreased with increasing heat treatment temperature.     

Electrochemical characterization of the electrooxidation of methanol,ethanol and formic acid on Pt/C and PtRu/C electrodes

Methanol, ethanol and formic acid electrooxidations in acid medium on Pt/C and PtRu/C catalysts were investigated. The catalysts were prepared by a microwave-assisted polyol process. Cyclic voltammetry and chronoamperometry were employed to provide quantitative and qualitative information on the kinetics of methanol, ethanol and formic acid oxidations. The PtRu/C catalyst showed higher anodic current densities than the Pt/C catalyst and the addition of Ru reduced the poisoning effect.     

Electrocatalytic activity of Pt nanoparticles deposited on porous TiO2 supports toward methanol oxidation

Porous TiO₂ thin films were prepared on the Si substrate by hydrothermal method, and used as the Pt electrocatalyst support for methanol oxidation study. Well-dispersed Pt nanoparticles with a particle size of 5–7 nm were pulse-electrodeposited on the porous TiO₂ support, which was mainly composed of the anatase phase after an annealing at 600 °C in vacuum. Cyclic voltammetry (CV) and CO stripping measurements showed that the Pt/TiO₂ electrode had a high electrocatalytic activity toward methanol oxidation and an excellent CO tolerance. The excellent electrocatalytic performance of the electrode is ascribed to the synergistic effect of Pt nanoparticles and the porous TiO₂ support on CO oxidation. The strong electronic interaction between Pt and the TiO₂ support may modify CO chemisorption properties on Pt nanoparticles, thereby facilitating CO oxidation on Pt nanoparticles via the bifunctional mechanism and thus improving the electrocatalytic activity of the Pt catalyst toward methanol oxidation.     

Carbon-supported Pt(Cu) electrocatalysts for methanol oxidation prepared by Cu electroless deposition and its galvanic replacement by Pt

Bimetallic Pt–Cu carbon-supported catalysts (Pt(Cu)/C) were prepared by electroless deposition of Cu on a high surface area carbon powder support, followed by its partial exchange for Pt; the latter was achieved by a galvanic replacement process involving treatment of the Cu/C precursor with a chloroplatinate solution. X-ray diffraction characterization of the Pt(Cu)/C material showed the formation of Pt-rich Pt–Cu alloys. X-ray photoelectron spectroscopy revealed that the outer layers are mainly composed of Pt and residual Cu oxides, while metallic Cu is recessed into the core of the particles. Repetitive cyclic voltammetry in deaerated acid solutions in the potential range between hydrogen and oxygen evolution resulted in steady-state characteristics similar to those of pure Pt, indicating the removal of residual Cu compounds from the surface (due to electrochemical treatment) and the formation of a compact Pt outer shell. The electrocatalytic activity of the thus prepared Pt(Cu)/C material toward methanol oxidation was compared to that of a commercial Pt/C catalyst as well as of similar Pt(Cu)/C catalysts formed by simple Cu chemical reduction. The Pt(Cu)/C catalyst prepared using Cu electroless plating showed more pronounced intrinsic catalytic activity toward methanol oxidation than its counterparts and a similar mass activity when compared to the commercial catalyst. The observed trends were interpreted by interplay between mere surface area effects and modification of Pt electrocatalytic performance in the presence of Cu, both with respect to methanol oxidation and poisonous CO removal.     

Pt-CeO2/C anode catalyst for direct methanol fuel cells

In order to develop a cheaper and durable catalyst for methanol electrooxidation reaction, ceria (CeO₂) as a co-catalytic material with Pt on carbon was investigated with an aim of replacing Ru in PtRu/C which is considered as prominent anode catalyst till date. A series of Pt-CeO₂/C catalysts with various compositions of ceria, viz. 40 wt% Pt-3–12 wt% CeO₂/C and PtRu/C were synthesized by wet impregnation method. Electrocatalytic activities of these catalysts for methanol oxidation were examined by cyclic voltammetry and chronoamperometry techniques and it is found that 40 wt% Pt-9 wt% CeO₂/C catalyst exhibited a better activity and stability than did the unmodified Pt/C catalyst. Hence, we explore the possibility of employing Pt-CeO₂ as an electrocatalyst for methanol oxidation. The physicochemical characterizations of the catalysts were carried out by using Brunauer Emmett Teller (BET) surface area and pore size distribution (PSD) measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques. A tentative mechanism is proposed for a possible role of ceria as a co-catalyst in Pt/C system for methanol electrooxidation.     

Study of Methanol‐tolerant Oxygen Reduction Reaction at Pt–Bi/C Bimetallic Nanostructured Catalysts

The nanostructured platinum–bismuth catalysts supported on carbon (Pt₃Bi/C, PtBi/C and PtBi₃/C) were synthesised by reducing the aqueous metal ions using sodium borohydride (NaBH₄) in presence of a microemulsion. The amount of metal loading on carbon support was found to be 10 wt.‐%. The catalyst materials were characterised by X‐ray diffraction (XRD), X‐ray fluorescence (XRF), transmission electron microscope (TEM) and electroanalytical techniques. The Pt₃Bi/C, PtBi/C and PtBi₃/C catalysts showed higher methanol tolerance, catalytic activity for oxygen reduction reaction (ORR) than Pt/C of same metal loading. The electrochemical stability of these nano‐sized catalyst materials for methanol tolerance was investigated by repetitive cycling in the potential range of –250 to 150 mV_MSE. Bi presents an interesting system to have a control over the activity of the surface for MOR and ORR. All Pt–Bi/C catalysts exhibited higher mass activities for oxygen reduction (1–1.5 times) than Pt/C. It was found that PtBi/C catalyst exhibits better methanol‐tolerance than the other catalysts.     

Polyaniline–13X zeolite composite‐supported platinum electrocatalysts for direct methanol fuel cell applications

We successfully synthesized 13X zeolite using a hydrothermal method. Then, composites of polyaniline (PANI) with 13X zeolite and PANI–13X with platinum were prepared by chemical oxidative polymerization and chemical reduction, respectively. Field emission scanning electron microscopy, X‐ray diffraction, Raman spectroscopy and Brunauer–Emmett–Teller techniques were used to characterize the PANI–Pt and PANI–Pt–13X composites. Further, the electrocatalytic activity towards methanol oxidation of the synthesized catalysts was explored using cyclic voltammetry in 1 mol L^?1 CH₃OH + 0.5 mol L^?1 H₂SO₄ solution. From the obtained results, PANI–Pt–13X shows superior performance compared to PANI–Pt towards methanol oxidation and electrical conductivity. Hence, the 13X zeolite‐incorporated PANI–Pt composite could be an efficient catalyst for direct methanol fuel cell applications. © 2019 Society of Chemical Industry     

Preparation of supported PtRu/C electrocatalyst for direct methanol fuel cells

In this work, high-surface supported PtRu/C were prepared with Ru(NO)(NO₃)₃ and [Pt(H₂NCH₂CH₂NH₂)₂]Cl₂ as the precursors and hydrogen as a reducing agent. XRD and TEM analyses showed that the PtRu/C catalysts with different loadings possessed small and homogeneous metal particles. Even at high metal loading (40 wt.% Pt, 20 wt.% Ru) the mean metal particle size is less than 4 nm. Meanwhile, the calculated Pt crystalline lattice parameter and Pt (2 2 0) peak position indicated that the geometric structure of Pt was modified by Ru atoms. Among the prepared catalysts, the lattice parameter of 40-20 wt.% PtRu/C contract most. Cyclic voltammetry (CV), chronoamperometry (CA), CO stripping and single direct methanol fuel cell tests jointly suggested that the 40-20 wt.% PtRu/C catalyst has the highest electrochemical activity for methanol oxidation.