Novel synthesis and characterization of nanocomposite Pt-WO3-TiO2/C electrocatalyst for PEMFC

In this study, an effective preparation of Pt-WO₃-TiO₂/C electrocatalysts has been developed for polymer electrolyte membrane fuel cell (PEMFC) application. The single cell performance of Vulcan XC-72R carbon-supported Pt-WO₃-TiO₂ electrocatalysts with various compositions (as weight percentage Pt-W-Ti 0:5:5, 2:4:4, 4:3:3, 6:2:2, and 8:1:1) as anode materials are investigated in PEMFC. These catalysts are compared with 10 % Pt/C on the same Vulcan XC-72R carbon support and 10 % Pt/C (commercial) electrocatalyst. The physical and morphological characterization of the optimized Pt-WO₃-TiO₂/C, 10 % Pt/C, and 10 % Pt/C (commercial) electrocatalysts are further investigated by X-ray diffraction (XRD), cyclic voltammetry, scanning electron microscopy with energy-dispersive X-ray analysis, and transmission electron microscopy (TEM) techniques. Among all the molar ratio of the catalysts, the Pt-W-Ti (4:3:3) molar ratio catalyst exhibited the larger electrochemical active surface area. The electrochemical performance of Pt-WO₃-TiO₂/C (with a weight percentage of Pt-W-Ti 4:3:3) as anode material is better than those of other compositions of Pt-WO₃-TiO₂/C catalysts. The amount of platinum was also reduced from 1.76 to 0.704 mg cm^?2 which exhibited higher performance in single cell tests. Platinum shows a smaller-sized crystalline structure in XRD and TEM analysis. High performance indicates that enhanced proton transport occurs through the use of this catalyst.     

Exploration of bimetallic Pt-Pd/C nanoparticles as an electrocatalyst for oxygen reduction reaction

In this study, carbon supported Pt and Pt-Pd were synthesized as oxygen reduction reaction electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs). Pt and Pt-Pd nanoparticles have been synthesized by reduction of metal precursors in presence of NaBH₄. Various techniques such as X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM) were utilized to study the prepared samples. Furthermore, electrochemical properties of the prepared samples were evaluated from cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed, the crystallite size of electrocatalysts (Pt and Pt-Pd) is below 10 nm. The higher catalytic activity was detected for Pt-Pd/C electrocatalyst for oxygen reduction reaction (ORR). In addition, it is believed that the better performance of electrocatalyst is related to the synergic effect between Pt and Pd nanoparticles, weakening of the OO bond on Pd-modified Pt nanoparticles in ORR, uniform dispersion of Pd and Pt on the carbon support and higher electrochemical active surface area (EAS) of Pt-Pd/C electrocatalyst.     

Preparation of PtSnSb/C by an alcohol reduction process for direct ethanol fuel cell (DEFC)

PtSn/C and PtSnSb/C electrocatalysts (20 wt.% metal loading) were prepared by an alcohol reduction process using H₂PtCl₆.6H₂O, SnCl₂.2H₂O, and Sb(OOCCH3) as metal sources, ethylene glycol as solvent and reducing agent, and Vulcan XC72 as carbon support. The electrocatalysts were characterized by energy dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy, while that the performance for ethanol oxidation was investigated by cyclic voltammetry and chronoamperommetry (chrono) at room temperature. The diffractograms of the PtSn/C and PtSnSb/C electrocatalysts showed four peaks associated to Pt face-centered cubic structure and two peaks that were related to a SnO₂ phase. For PtSb/C and PtSnSb/C electrocatalysts, no Sb (antimony) peaks corresponding to a metallic antimony or antimony oxide phases were observed. Transmission electron microscopy images showed that the metal particles were homogeneously distributed over the support. The PtSnSb/C (50:45:05) electrocatalyst showed an increase of performance for ethanol oxidation in relation to PtSn/C electrocatalyst at room temperature. In the tests at 100 °C on a single cell of a direct ethanol fuel cell, the maximum power density of PtSnSb/C (50:45:05) electrocatalyst was slightly higher than that of PtSn/C electrocatalyst.     

Electro-oxidation of ethanol using PtRuBi/C electrocatalyst prepared by borohydride reduction

Pt/C, PtRu/C, PtBi/C, and PtRuBi/C electrocatalysts (20 wt.% metal loading) were prepared by borohydride reduction using H₂PtCl₆·6H₂O, RuCl₃·xH₂O, and Bi(NO₃)₃·5H₂O as metal sources and Vulcan XC 72 as support. The electrocatalysts were characterized by energy-dispersive X-ray analysis, X-ray diffraction, and thermogravimetric analysis. The electro-oxidation of ethanol was studied in sulfuric acid solution by cyclic voltammetry and chronoamperometry. The electrochemical studies showed that PtRuBi/C (50:40:10) electrocatalyst has superior performance for ethanol electro-oxidation at room temperature compared to the other electrocatalysts. Preliminary tests at 100 °C on a single direct ethanol fuel cell also confirm the results obtained by electrochemical techniques.     

Preparation of PtSn/C electrocatalysts using citric acid as reducing agent for direct ethanol fuel cell (DEFC)

PtSn/C electrocatalysts (Pt:Sn atomic ratios of 50:50 and 60:40) were prepared using citric acid as reducing agent, and the pH of the reaction medium was varied by the addition of OH⁻ ions. The obtained electrocatalysts were characterized by energy dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The electrocatalysts were tested on the direct ethanol fuel cell (DEFC) at 90 °C. The obtained PtSn/C electrocatalysts showed the presence of a face-centered cubic, Pt, and SnO₂ phases. In DEFC studies, the PtSn/C electrocatalysts showed a superior performance compared to a commercial PtSn/C and Pt/C electrocatalysts from E-TEK.     

Electro-oxidation of ethylene glycol on PtSn/C and PtSnNi/C electrocatalysts

A PtSn/C electrocatalyst with a Pt–Sn molar ratio of 50:50 and A PtSnNi/C electrocatalyst with a Pt–Sn–Ni molar ratio of 50:40:10 were prepared by alcohol-reduction process using ethylene glycol as solvent and reducing agent. The electrocatalysts were characterized by energy dispersive X-ray, X-ray diffraction, and cyclic voltammetry. The electro-oxidation of ethylene glycol was studied by cyclic voltammetry and chronoamperometry using the thin porous coating technique. PtSnNi/C electrocatalyst showed a superior performance compared to PtSn/C electrocatalysts in the potential range of interest for a direct ethylene glycol fuel cell.     

Electrochemical characterization of platinum-based anode catalysts for membraneless fuel cells

In the present work, carbon-supported Pt–Sn, Pt–Ru, and Pt–Sn–Ru electrocatalysts with different atomic ratios were prepared by alcohol-reduction method to study the electro-oxidation of ethanol in membraneless fuel cells. The synthesized electrocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses. The prepared catalysts had similar particle morphology, and their particle sizes were 2–5 nm. The electrocatalytic activities were characterized by cyclic voltammetry (CV) and chronoamperometry (CA). The electrochemical results obtained at room temperature showed that the addition of Sn and Ru to the pure Pt electrocatalyst significantly improved its performance in ethanol electro-oxidation. The onset potential for ethanol electro-oxidation was 0.2 V vs. Ag/AgCl, in the case of the ternary Pt–Sn–Ru/C catalysts, which was lower than that obtained for the pure Pt catalyst (0.4 V vs. Ag/AgCl). During the experiments performed on single membraneless fuel cells, Pt ? Sn ? Ru/C (70:10:20) performed better among all the catalysts prepared with power density of 36 mW/cm². The better performance of ternary Pt–Sn–Ru/C catalysts may be due to the formation of a ternary alloy and the smaller particle size.     

Phosphorus-doped carbon nanoparticles supported palladium electrocatalyst for the hydrogen evolution reaction (HER) in PEM water electrolysis

Hydrogen production by PEM water electrolysis is one of the most efficient methods, due to the produced high purity of gases, high efficiency, and devoid of harmful emissions. In this study, phosphorus-doped carbon nanoparticles (P-CNPs) were synthesized by spray pyrolysis method in chemical vapor deposition (CVD). The synthesized P-CNPs were used as electron carrier support materials for the preparation of P-CNPs-supported palladium (Pd/P-CNPs) electrocatalyst and also used as the hydrogen evolution reaction (HER) electrode in PEM water electrolysis. These synthesized Pd/P-CNPs were characterized by field emission scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray diffraction, and cyclic voltammetry methods. The membrane electrode assemblies (MEAs) were fabricated using Pd/P-CNPs as a cathode catalyst for the HER and RuO₂ as the anode for oxygen evolution reaction (OER). The fabricated MEA electrochemical performances along with their corresponding yields of hydrogen production were evaluated in PEM water electrolyzer single cell assemblies at various experimental conditions. The obtained results showed that the synthesized Pd/P-CNPs observed a current density of 1 A cm^?2 at 2 V at 80 °C. Further, long-term stability tested for up to 500 h continuously and showed the reasonable stability with similar electrochemical activity compared to commercial Pt/CB. Hence, the synthesized Pd/P-CNPs could be used as the alternative to Pt-based catalysts for HER.     

Preparation and characterization of PtRu/C-rare earth using an alcohol-reduction process for ethanol electro-oxidation

PtRu/C (100% C) and PtRu/C-CeO₂, PtRu/C-La₂O₃, PtRu/C-Nd₂O₃, and PtRu/C-Er₂O₃ (85% C and 15% rare earth) electrocatalysts were prepared in a single step by an alcohol-reduction process using H₂PtCl₆ 6H₂O and RuCl₃ xH₂O as metal sources, ethylene glycol as solvent and reducing agent, Vulcan XC72 and rare earth (RE) as support. The electrocatalysts were characterized by energy dispersive X-ray, X-ray diffraction, and transmission electron microscopy. The performance for ethanol oxidation was investigated by cyclic voltammetry and chronoamperommetry at room temperature, and studies on the direct ethanol fuel cell were carried at 100 °C. The Pt:Ru atomic ratios were similar to the nominal used in preparation, and the average particle sizes were in the range of 2.0–3.0 nm. All PtRu/C-RE electrocatalysts showed an increase of performance for ethanol oxidation at room temperature and also on a single direct ethanol fuel cell tests in relation to PtRu/C electrocatalyst at 100 °C.     

Structural and electronic properties of PtPd and PtNi nanoalloys

The lowest-energy structures of binary (PtPd)_n, (PtNi)_m, (PtNi₃)_s, and (Pt₃Ni)_s nanoclusters, with n=2–28, m=2–20, and s=4–6, modeled by the many-body Gupta potential, were obtained by using a genetic-symbiotic algorithm. These structures were further relaxed within the density functional theory framework in order to obtain the most stable structures for each composition. Segregation is confirmed in all the (PtPd)_n clusters, where the Pt atoms occupy the cluster core and the Pd atoms are situated on the cluster surface. In contrast, for the (PtNi)_m nanoalloys, the Ni atoms are mainly found in the cluster core and the Pt atoms are segregated to the cluster surface. Likewise, for the (PtNi₃)_s nanoalloys, Ni atoms mainly compose the cluster core but there is no clear segregation of the Pt atoms to the surface. Furthermore, for the (Pt₃Ni)_s bimetallic clusters the Pt atoms concentrate in the cluster core and the Ni atoms are segregated to the surface. On the other hand, it has been experimentally found that the Pt_0.75Ni_0.25 supported nanoparticles present a higher catalytic activity for the selective oxidation of CO in the presence of hydrogen than the Pt_0.5Ni_0.5 and Pt_0.25Ni_0.75 nanoparticles. In order to understand this tendency in the catalytic activity, we also performed density functional calculations of the molecular CO adsorption on bimetallic Pt-Ni nanoclusters with the mentioned compositions.     

Electrochemical and impedance spectroscopy studies in H2/O2 and methanol/O2 proton exchange membrane fuel cells

This works report results of the structural and the electrochemical characterization of membrane electrode assemblies (MEA) for proton exchange membrane fuel cells (PEMFC) under various cell conditions using different MEA production processes. Electrochemical impedance spectroscopy (EIS) was applied “on-line” (in situ) as a tool for diagnosis concerning the cell performance. MEA with a 25-cm² surface area were prepared using Pt/C and Pt–Ru/C commercial electrocatalysts from E-TEK and Pt–Ru/C electrocatalysts produced by the alcohol reduction process. The catalytic ink was applied directly onto the carbon cloth or, alternatively, onto the Nafion® membrane. Two carbon cloth thicknesses were tested as diffusion layers in the MEA: 0.346 mm (common) and 0.424 mm (ELAT). An increase of the electrocatalytic activity can be obtained by pH control in the alcohol reduction process, possibly due to the better particle dispersion and the smaller particle sizes observed. In addition, a slower current decay in the ohmic region was observed using the thinner carbon cloth. This can be related to a lower resistance of the gas flow through the cloth to the catalytic active layer. Different types of methanol feed were employed in the experiments: by humidification and by evaporation. The results showed that the choice of suitable methods for catalyst preparation as well as for MEA production enhance PEMFC performance.     

Processing and characterization of ultra-thin yttria-stabilized zirconia (YSZ) electrolytic films for SOFC

Sub-micron yttria-stabilized zirconia (YSZ) electrolyte layer was prepared by a liquid state deposition method and with an average thickness of 0.5 μm to improve the performance of the anode-supported solid oxide fuel cell (SOFC). The YSZ precursors, containing yttrium and zirconium species and an additive, poly-vinyl-pyrrolidone (PVP), were spin-coated on a Ni/YSZ anode substrate. Several properties, including crystalline phases, microstructures, and current–voltage (I–V) characteristics, were investigated. The thin film of 4 mol% Y₂O₃-doped ZrO₂ (4YSZ) consisted of cubic, tetragonal, and a trace of monoclinic phases, and showed a crack-free layer after sintering at 1300 °C. The anode supported SOFC, which consists of the Ni–YSZ anode, 4YSZ electrolyte, and Pt/Pd cathode, showed power densities of 477 mW/cm² at 600 °C, and 684 mW/cm² at 800 °C. Otherwise, the surface cracks of the other YSZ-coated samples (e.g. 8YSZ) can be repaired by a multi-coating method.     

Octahedral to Cuboctahedral Shape Transition in 6 nm Pt3Ni Nanocrystals for Oxygen Reduction Reaction Electrocatalysis

Pt₃Ni stands as one of the most active electrocatalysts for the oxygen reduction reaction (ORR). The activity varies with the morphology of the nanocrystals with a high activity observed for the octahedral shape where only the high density {111} crystallographic planes are exposed. Herein, the synthesis of 6 nm Pt₃Ni octahedral nanocrystals with a Pt enriched shell or cuboctahedral nanocrystals with a Ni enriched shell is described. Interestingly, the cuboctahedral nanocrystals display a six-pointed star/skeleton of platinum, which features a very uncommon atomic distribution. In the synthesis, a decrease in the oxygen partial pressure induces the transition from octahedral to cuboctahedral morphology. The octahedral and cuboctahedral nanocrystals both demonstrate high ORR activity (1.1 mA cm⁻²_Pt and 1.2 A mg⁻¹_Pt at 0.9 V vs reversible hydrogen electrode (RHE) are the highest values obtained for PtNi-20 and PtNi-15, respectively). After exposure to oxidative conditions in the acidic electrolyte, the cuboctahedral nanoparticles with a pristine Ni-rich skin show a Pt skin and retain their cuboctahedral morphology.     

Direct methanol fuel cells: The influence of methanol on the reduction of oxygen over Pt/C catalysts with different particle sizes

Two Pt/C catalysts with different particle sizes (Pt/C: 2.5 nm, Pt/C-700Ar: 5.1 nm) were investigated by applying a half-cell configuration —rotating disk electrode (RDE) technique in H₂SO₄ aqueous solutions in the absence of or in the presence of methanol with different concentrations. Pt/C catalyst exhibited higher mass activity in H₂SO₄ aqueous solution without methanol and slightly lower mass activity in H₂SO₄ plus 0.1 mol/L CH₃OH in comparison with that of Pt/C-700Ar catalyst. On the contrary,single direct methanol fuel cell (DMFC) tests showed that Pt/C exhibited higheroxygen reduction reaction (ORR) activity and better cell performance, mainly due to the different kinds of electrolyte properties. Furthermore, it suggested that a better single DMFC performance could be obtained with a smaller particle size Pt-based cathode catalyst. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 — 18, 2004.     

Pt/CNTs电催化剂制备的UV-Vis、FTIR和XRD光谱分析

采用在乙二醇溶液中添加十二烷基硫酸钠(SDS)作为稳定剂的调变乙二醇还原法,制备了高分散的碳纳米管(CNTs)负载Pt电催化剂Pt/CNTs。利用紫外-可见(UV-Vis)、傅里叶变换红外(FTIR)和X射线衍射(XRD)光谱研究了催化剂的制备过程和结构,考察了Pt/CNTs制备过程中SDS的添加对其结构和甲醇电催化氧化活性的影响。结果表明,在乙二醇溶液中PtCl2-₆与SDS形成了配合物,PtCl2-₆能够被乙二醇完全还原;超声处理后的CNTs表面接上了含氧基团,有利于Pt粒子的吸附,催化剂上不残留有SDS;Pt/CNTs电催化剂具有典型的面心立方结构,添加SDS制备的Pt/CNTs-2电催化剂Pt高度分散,粒径更小,达4.5 nm。循环伏安(CV)测试结果表明,添加SDS制备的Pt/CNTs-2电催化剂比传统乙二醇还原法制备的Pt/CNTs-1具有更高的甲醇电催化氧化活性。     

An effective electrocatalyst for ethanol oxidation: Pt-modified IrCu alloy nanoparticle

There is a growing interest in ethanol oxidation electrochemistry as it plays an important role in renewable energy technologies. The goal of this work was to develop active multifunctional catalyst materials for ethanol oxidation. Here, a carbon-supported Pt-modified IrCu alloy electrocatalyst (Pt–IrCu/C) was prepared by a two-step method. X-ray diffraction and transmission electron microscope showed that the Pt–IrCu/C has a two-phase structure: Pt nanoparticle-modified IrCu alloy. The Pt–IrCu/C catalyst was found to have not only a large electrochemically active specific area (S _EAS) but also good CO oxidation ability for oxidation of ethanol compared to the commercial Pt/C electrocatalyst using cyclic voltammetry. Furthermore, the Pt current density of Pt–IrCu/C was more than 1.6 times as high as that of Pt/C for ethanol oxidation. The Pt–IrCu/C catalyst also exhibited more efficient usage of Pt and enhanced the stability of ethanol electro-oxidation compared with a Pt/C catalyst.     

Preparation of PtSnRh/C-Sb2O5·SnO2 electrocatalysts by an alcohol reduction process for direct ethanol fuel cell

PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts with different Pt/Sn/Rh atomic ratios (90:05:05, 70:25:05, and 50:45:05) were prepared by an alcohol reduction process using H₂PtCl₆·6H₂O, SnCl₂·2H₂O, RhCl₃·xH₂O as metal sources, ethylene glycol as solvent and reducing agent, and a physical mixture of Vulcan XC72 (85?wt%) and Sb₂O₅·SnO₂ (15?wt%) as support. The electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. The electro-oxidation of ethanol was studied by cyclic voltammetry and chronoamperometry at 25 and 50?°C and in single direct ethanol fuel cell (DEFC) at 100?°C. The diffractograms of PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts showed the peaks characteristic of Pt face-centered cubic structure and several others peaks associated with ·SnO₂ and Sb₂O₅·SnO₂. Transmission electron micrographs of PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts showed the metal nanoparticles distributed on the supports with particle sizes of about 2?C3?nm. The electrochemical measurements and the experiments in a single DEFC showed that PtSnRh/C-Sb₂O₅·SnO₂ (90:05:05) and PtSnRh/C-Sb₂O₅·SnO₂ (70:25:05) electrocatalysts exhibited higher performance for ethanol oxidation in comparison with PtSnRh/C electrocatalyst.     

Ultrasound assisted synthesis of highly active nanoflower-like CoMoS4 electrocatalyst for oxygen and hydrogen evolution reactions

Rapid technological development requires sustainable, pure, and clean energy systems, such as hydrogen energy. It is difficult to fabricate efficient, highly active, and inexpensive electrocatalysts for the overall water splitting reaction: the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The present research work deals with a simple hydrothermal synthesis route assisted with ultrasound that was used to fabricate a 3D nanoflower-like porous CoMoS₄ electrocatalyst. A symmetric electrolyzer cell was fabricated using a CoMoS₄ electrode as both the anode and cathode, with a cell voltage of 1.51 V, to obtain a current density of 10 mA/cm². Low overpotentials were observed for the CoMoS₄ electrode (250 mV for OER and 141 mV for HER) at a current density of 10 mA/cm².     

Improved resolution in HREELS using maximum-entropy deconvolution: CO on PtxNi1−x(111)

High-resolution electron energy loss spectroscopy (HREELS) has been used to study stretch vibrations of CO chemisorbed at low coverage on Pt_xNi_1−x(111). Bayesian probability theory along with the entropic prior (Maxent) has been employed to deconvolve the apparatus function and to improve the apparent energy resolution. Maxent has proven very successful in a wide range of inversion problems. Here the resolution enhancement enables the positions of CO on the PtNi surface to be identified. It appears that CO is predominantly on top of Ni with the Ni atoms coordinated threefold laterally and with Ni in linear chains or on top of Pt. Furthermore, the ratio of the Pt to the Ni peak is used to study the dependence of the Pt concentration in the first layer on the annealing temperature.     

Nafion/mordenite hybrid membrane for high-temperature operation of polymer electrolyte membrane fuel cell

Nafion/mordenite hybrid membranes for the operation of polymer electrolyte membrane fuel cells (PEMFCs) above 100 °C were prepared by mixing of H⁺-form mordenite powder and perfluorosulfonylfluoride copolymer resin. PEMFC operation above 100 °C reduces CO poisoning as well as passivation of the Pt anode electrocatalyst by other condensable species. The physico-chemical properties of hybrid membranes were investigated by tensile strength and proton conductivity measurements. As the mordenite content increases at the high temperature region, the proton conductivity of hybrid membranes increased due to the late dehydration rate of existent water in the mordenite. Also, from the results of current–voltage relationship for single cells under 130 °C of operation condition, the hybrid membrane cell with 10 wt.% mordenite showed better performance than that of the others over the entire current density range. This result indicated that the existent water in the hybrid membrane containing 10 wt.% mordenite was higher than that with the others, thereby maintaining its conductivity. The Nafion/mordenite hybrid membrane prepared by this present method is thought to be a satisfactory polymer electrolyte membrane for PEMFC operation above 100 °C.