Hydrogen evolution assisted electrodeposition of bimetallic 3D nano/micro-porous PtPd films and their electrocatalytic performance

Self-supporting PtPd bimetallic catalysts with three-dimensional (3D) porous structures and a greatly enhanced surface area are firstly fabricated at a glassy carbon electrode (GCE) by a one-step strategy of potentiostatic co-electrodeposition utilizing hydrogen bubble dynamic templates. The atomic ratio of Pt/Pd in the bimetallic catalysts is varied by changing the composition of the electrodeposition solution. The 3D porous PtPd films are characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and examined as electrocatalysts for the electro-oxidation of methanol using cyclic voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy (EIS). Experimental results demonstrate that a small amount of Pd plays the predominant role in the formation of 3D porous structure for PtPd bimetallic catalysts and is an excellent catalytically enhancing agent for the Pt catalyst towards methanol electro-oxidation. The study on electrocatalytic performance of mono and bimetallic catalysts towards formic acid electro-oxidation also reveals the better activity of 3D porous Pd film for this reaction.     

PtRu/C catalysts synthesized by a two-stage polyol reduction process for methanol oxidation reaction

Highly dispersed Ru/C catalysts are prepared using high viscosity glycerol as a reducing agent and are treated in H₂ atmosphere to ensure stability. A Pt^∧Ru/C catalyst is prepared by an ethylene glycol process based on the pre-formed Ru/C. The catalyst is tested for methanol oxidation reaction at room temperature and is compared with the activity of the as-prepared PtRu/C alloyed catalyst (prepared by co-reduction of Pt and Ru precursors) and commercial PtRu/C from E-TEK. The catalysts are extensively characterized by Transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical measurements by cyclic voltammetry (CV) showed consistently high catalytic activities and improved CO resistance for the Pt^∧Ru/C catalyst.     

Electrocatalytic properties of carbon-supported Pt-Ru catalysts with the high alloying degree for formic acid electrooxidation

A series of carbon-supported bimetallic Pt-Ru catalysts with high alloying degree and different Pt/Ru atomic ratio have been prepared by a chemical reduction method in the H₂O/ethanol/tetrahydrofuran (THF) mixture solvent. The structural and electronic properties of catalysts are characterized using X-ray reflection (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM). The electrooxidation of formic acid on these Pt-Ru nanoparticles are investigated by using cyclic voltammetry, chronoamperometry and CO-stripping measurements. The results of electrochemical measurements illustrate that the alloying degree and Pt/Ru atomic ratio of Pt-Ru catalyst play an important role in the electrocatalytic activity of the Pt-Ru/C catalyst for formic acid electrooxidation due to the bifunctional mechanism and the electronic effect. Since formic acid is an intermediate in the methanol electrooxidation on Pt electrode in acidic electrolyte, the observation provides an additional fundamental understanding of the structure-activity relationship of Pt-Ru catalyst for methanol electrooxidation.     

Methanol oxidation on hybrid catalysts: PtRu/C nanostructures promoted with cerium and titanium oxides

Hybrid catalysts comprising of ceramic, metal, and carbon phase were synthesized by incorporating titanium and cerium oxides into PtRu/C commercial catalyst using an in-situ combustion followed by heat treatment at 600 °C. The structure dependent electrochemical behavior of as-synthesized and heat-treated materials towards methanol oxidation, carbon dioxide (CO) tolerance and chemical stability was studied by XRD, HRTEM, BET, EDS, cyclic voltammetry, chronoamperometry, and CO-stripping method. As a result of heat treatment, amorphous phase of metal oxides was transformed into a crystalline phase with particle size of about 3–7 nm. Improved methanol oxidation activity of the hybrid catalysts was compared to PtRu/C catalyst as a baseline and explained by the changes in Pt electronic behavior and excess adsorption of OH-ions. When heat-treated at 600 °C, CeO₂-PtRu/C demonstrated the highest mass activity of 580 mA/mg (∼3×  that of PtRu/C) compared to TiO₂-PtRu/C (394 mA/mg). Heat-treated hybrid catalysts exhibited higher methanol oxidation activity at higher peak potentials than the corresponding as-synthesized materials. However, as-synthesized hybrid catalysts display higher CO-tolerance, lower CO-oxidation onset potentials, and better chemical stability in comparison to corresponding heat-treated catalysts. To explain the difference, a mechanism for ceramic oxide structure dependent electrochemical behavior of the hybrid catalysts is proposed and discussed.     

Controllable synthesis of efficient Ru-doped PtSn alloy nanoplate electrocatalysts for methanol oxidation reaction

Platinum (Pt) is considered as the preferred metal catalyst for methanol oxidation reactions. However, the application prospects of Pt catalysts are limited due to the inherent scarcity and cost. Enabling a trace amount of Pt to exert satisfactory catalytic activity and durability has become a key issue in designing electrocatalysts. Here, Ru-doped PtSn alloy nanoplates (PtSn@Ru NP) with an average particle size of less than 5 nm were controllably synthesized by adjusting the Pt–Sn atomic ratio. Compared with Ru-doped PtSn alloy nanospheres (PtSn@Ru NS/C, 714.7 mA/mg_Pt), PtSn bimetallic nanoplates (PtSn NP/C, 880.2 mA/mg_Pt) and commercial Pt/C (299.6 mA/mg_Pt), the prepared PtSn@Ru NP/C (1105.1 mA/mg_Pt) exhibited an extraordinary methanol oxidation mass activity. Furthermore, the peak oxidation current retention of PtSn@Ru NP/C was as high as at 87.5% after 1000 accelerated durability tests. The significantly enhanced catalytic performance and durability were attributed to the synergistic effect of the alloy components and morphological advantages. This work has led us to think more deeply about the constitutive relationship between structure and performance.     

Carbon nanotube-supported Pt-Alloyed metal anode catalysts for methanol and ethanol oxidation

To improve the electrocatalytic activity of alcohol oxidation, functionalized carbon nanotubes (CNTs) decorated with various compositions of metal alloy catalyst nanoparticles (Pt_xM_y, where M = Au and Pd; x and y = 1–3) have been prepared via reduction. The CNTs were treated with an nitric acid solution to promote the oxygen-containing functional groups and further load the metal nanoparticles. X-ray diffraction (XRD) scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to probe the formation of catalyst microstructure morphologies. A uniform dispersion of the spherical metal particles with diameters of 2–6 nm was acquired. The catalytic properties of the catalyst for oxidation were thoroughly studied by electrochemical methods that involved in the cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). To maximize the electrocatalytic performance and minimize the metal integration of the loaded CNTs, various compositions of active catalysts with large active surface areas are expected to increase the activity of the enhanced catalysts for alcohol oxidation. Most of the prepared bimetallic catalysts have better alcohol oxidation kinetics than commercial PtRu/C. Among the prepared catalysts, the PtAu/CNTs and PtPd/CNTs catalysts with high electrochemically active surface area (ECSA) show excellent activities for alcohol oxidation resulting in their low onset potentials, small charge transfer resistances and high peak current densities and I_f/I_b ratios, stability, and better tolerance to CO for alcohol oxidation. The integration of Pt and different metal species with different stoichiometric ratios in the CNTs support affects the electrochemical active surface area achieved in the catalytic oxidation reactions.     

A novel binary Pt3Tex/C nanocatalyst for ethanol electro-oxidation

The Pt₃Te_x/C nanocatalyst was prepared and its catalytic performance for ethanol oxidation was investigated for the first time. The Pt₃Te/C nanoparticles were characterized by an X-ray diffractometer (XRD), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy equipped with TEM (TEM-EDX). The Pt₃Te/C catalyst has a typical fcc structure of platinum alloys with the presence of Te. Its particle size is about 2.8 nm. Among the synthesized catalysts with different atomic ratios, the Pt₃Te/C catalyst has the highest anodic peak current density. The cyclic voltammograms (CV) show that the anodic peak current density for the Pt₃Te/C, commercial PtRu/C and Pt/C catalysts reaches 1002, 832 and 533 A g⁻¹, respectively. On the current–time curve, the anodic current on the Pt₃Te/C catalyst was higher than those for the catalysts reported. So, these findings show that the Pt₃Te/C catalyst has uniform nanoparticles and the best activity among the synthesized catalysts, and it is better than commercial PtRu/C and Pt/C catalysts for ethanol oxidation at room temperature.     

Electro-oxidation of methanol and ethanol using PtRu/C,PtSn/C and PtSnRu/C electrocatalysts prepared by an alcohol-reduction process

PtRu/C, PtSn/C and PtSnRu/C electrocatalysts were prepared by the alcohol reduction process using ethylene glycol as the solvent and reduction agent and Vulcan Carbon XC72 as the support. The electrocatalysts were characterized by EDX, XRD and cyclic voltammetry. The electrochemical oxidation of methanol and ethanol were studied by chronoamperometry using a thin porous coating technique. The PtSn/C electrocatalyst prepared by this methodology showed superior performance compared to the PtRu/C and PtSnRu/C electrocatalysts for methanol and ethanol oxidation at room temperature.     

Fabrication and performance evaluation of graphene-supported PtRu electrocatalyst for high-temperature electrochemical hydrogen purification

The main aim of this study is to investigate the high-temperature electrochemical hydrogen purification (HT-ECHP) performances of graphene nanoplatelet (GNP) support material decorated with platinum (Pt) and platinum-ruthenium (PtRu) nanoparticles prepared by microwave irradiation technique. Prepared catalysts coupled to the phosphoric acid doped polybenzimidazole (PBI) membrane for HT-ECHP application. The structural and electrochemical properties of the catalysts were examined by thermogravimetric analysis (TGA), X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transition electron microscopy (TEM) and cyclic voltammetry (CV) analyses. The characterization results indicate that the catalysts provided the necessary properties for HT-ECHP application. The HT-ECHP performances are investigated with reformate gas mixture containing hydrogen (H₂), carbon dioxide (CO₂) and carbon monoxide (CO) in the range of 140–180 °C. The results show that the electrochemical purification performances of the catalysts increase with increasing operating temperature. The highest H₂ purification performance is obtained with PtRu/GNP catalyst. The high electrochemical H₂ purification performance of the PtRu/GNP catalyst can be attributed to the strong synergistic interactions between Pt and Ru particles decorated on the GNP. These results advocate that the PtRu/GNP catalyst is a hopeful catalyst for HT-ECHP application.     

Polyol-synthesized PtRu/C and PtRu black for direct methanol fuel cells

PtRu/C and PtRu black catalysts with nominal Pt:Ru atomic ratio of 1:1 are prepared by a modified polyol process (co-reduction of metal precursor salts) as anode catalysts for direct methanol fuel cells (DMFCs). Without the carbon support, PtRu nanoparticles tend to agglomerate, while the PtRu nanoparticles in PtRu/C have a good dispersion as shown by TEM. Both PtRu black and PtRu/C have the almost same alloy degree indicated by XRD, but PtRu supported on carbon could improve the influence of Ru on Pt toward methanol oxidization as shown by cyclic voltammetry. The microstructure of PtRu/C is further studied by high-resolution transmission electron microscopy (HRTEM), and the results indicate that the lattice constant of Pt in PtRu electrocatalyst has contracted despite a few parts of Pt not alloyed with Ru due to the lattice constant of Pt without contracting, which is further proved by the results of temperature-programmed reduction (TPR). Such parts of unalloyed Ru are further proved to have ability to reduce the methanol oxidation potential on Pt by comparing the catalytic behaviors of Pt/C and Pt + Ru/C prepared by mixing carbon with separately prepared Pt and Ru colloids. Moreover, the catalytic behaviors of PtRu black and PtRu/C are also compared with those of commercial ones.     

Effect of Ni on Pt/C and PtSn/C prepared by the Pechini method

Different compositions of Pt, PtNi, PtSn, and PtSnNi electrocatalysts supported on carbon Vulcan XC-72 were prepared through thermal decomposition of polymeric precursors. The nanoparticles were characterized by morphological and structural analyses (XRD, TEM, and EDX). XRD results revealed a face-centered cubic structure for platinum, and there was evidence that Ni and Sn atoms are incorporated into the Pt structure. The electrochemical investigation was carried out in slightly acidic medium (H₂SO₄ 0.05 mol L⁻¹), in the absence and in the presence of ethanol. Addition of Ni to Pt/C and PtSn/C catalysts significantly shifted the onset of ethanol and CO oxidations toward lower potentials, thus enhancing the catalytic activity, especially in the case of the ternary PtSnNi/C composition. Electrolysis of ethanol solutions at 0.4 V vs. RHE allowed for determination of acetaldehyde and acetic acid as the reaction products, as detected by HPLC analysis. Due to the high concentration of ethanol employed in the electrolysis experiments (1.0 mol L⁻¹), no formation of CO₂ was observed.     

Investigation of grain boundary formation in PtRu/C catalyst obtained in a polyol process with post-treatment

The grain boundary formation in PtRu/C catalyst obtained in a polyol process with post-treatment was investigated by scanning transmission electron microscopy, transmission electron microscopy (TEM) and High resolution TEM. The crystalline structure and surface composition of the PtRu/C catalysts were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical activities were evaluated by CO stripping voltammetry and linear sweep voltammetry measurements in combination with in situ IR reflection-absorption spectroscopy. As-prepared isolated spherical nanoparticles on the carbon support started to interconnect after washing procedure, and the interconnection between the particles was greatly promoted by reduction post-treatment at 80 °C; grain boundary formation occurred in the interconnected particles with increasing reduction temperature to 200 °C, and the particles reconstructed severely with further increasing reduction temperature to 400 °C. The defects at the grain boundary served as active sites for methanol electro-oxidation by weakening CO_ads adsorption on Pt sites and facilitating OH_ads formation, and the PtRu/C catalyst treated in 5% H₂/Ar at 200 °C for 10 h had the greatest catalytic activity for methanol electro-oxidation among the PtRu/C catalysts treated under various atmospheres and temperatures.     

Anodic oxidation of ethanol on core-shell structured Ru@PtPd/C catalyst in alkaline media

The direct ethanol fuel cell has been attracting increased attention due to its safety and the wider availability of ethanol as compared with methanol. The present work investigates the anodic oxidation of ethanol on a core-shell structured Ru@PtPd/C catalyst in alkaline media. The catalyst shows high activity toward the anodic oxidation of ethanol; with 18 wt.% ruthenium as the core and 12 wt.% PtPd (Pt:Pd = 1:0.2) as the active shell, its activity in terms of PtPd loading is 1.3, 3, 1.4, and 2.0 times as high as that of PtPd/C, PtRu/C, Pd/C, and Pt/C, respectively, indicating high utilization of Pt and Pd. The ratio of forward peak current density to backward peak current density (I_f/I_b) reaches 1.5, which is 1.9 times that of PtPd/C catalyst, revealing high poisoning tolerance to the intermediates in ethanol electrooxidation. In addition, the stability of Ru@PtPd/C is higher than that of Pt/C and PtPd/C, as evidenced by chronoamperometric evaluations. The catalyst is extensively characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy. The core-shell structure of the catalyst is revealed by XRD and TEM.     

Methanol oxidation by pEDOT-pSS/PtRu in DMFC

Direct methanol fuel cells (DMFCs) are attracting more and more attention because of their operating temperature and easy fuel management. While carbons are the most widely used supports for both metal catalysts, i.e. PtRu for methanol oxidation and Pt for oxygen reduction, conducting polymers also can act as suitable supports for catalyst particles because of their conductive and stable three-dimensional structure. We thus chemically synthesized poly(3,4-ethylenedioxythiophene)-polystyrene-4-sulfonate (pEDOT-pSS) with different (3,4-ethylenedioxythiophene):styrene-4-sulfonate (EDOT:SS) molar ratios and prepared the electrocatalytic systems pEDOT-pSS/PtRu and pEDOT-pSS/Pt, the former by both electrochemical and chemical deposition of PtRu and the latter by chemical deposition of Pt. The results of the electrocatalytic activity tests of the pEDOT-pSS/PtRu composite electrodes performed in 0.1 M H₂SO₄–0.5 M CH₃OH liquid solution and in passive, air-breathing DMFC configuration with Nafion^® 115 protonic membrane and 1 M CH₃OH are reported and discussed.     

Surfactant-free room temperature synthesis of PdxPty/C assisted by ultra-sonication as highly active and stable catalysts for formic acid oxidation

Formic acid oxidation is usually catalyzed on PdPt bimetallic catalysts, which are synthesized by co-reduction of noble metal precursors in the presence of high molecular capping agents. In this work, surfactant-free Pd_xPt_y/C catalysts are synthesized by H₂ reduction in ethylene glycol assisted with ultrasonication vibration at room temperature. Nanoparticle agglomeration in the course of preparation has been sufficiently curbed by strong mechanical ultrasonication instead of traditionally-employed surfactants. As a result, “clean” surfactant-free Pd_xPt_y/C catalysts necessitate only simple washing before collection. The catalysts are characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The compositionally optimized Pd₁₀₀Pt₁/C catalyst registers a mass activity of 3171 A g⁻¹ (Pt + Pd) for formic acid oxidation in 0.5 M H₂SO₄+0.5 M HCOOH, which lists one of the best results reported so far and surpasses that of a commercial Pd/C by 5.6 times. Stability of the catalysts is investigated by cyclic voltammetric as well as chronoamperometric evaluations. This work offers a convenient and environmentally benign room-temperature route to synthesize highly active and stable catalysts for formic acid oxidation.     

Catalyst development for viability of electrochemical hydrogen purifier and compressor (EHPC) technology

Considering the disadvantages of conventional compressors, which are widely used in the world, it is thought that the electrochemical hydrogen purifier and compressor system (EHPC) to be developed will provide great advantages in hydrogen technologies. The electrocatalyst, which is one of the main components of the EHPC system, is critical for both the performance and applicability of the system. In this study, commercial carbon black supported Pt and Pd containing catalysts were prepared for the EHPC system by using microwave heating method. The synthesized catalysts were mono and bimetallic and were named as Pt/C, Pd/C and PtPd/C, respectively. By characterizing the prepared catalysts with ICP-MS, SEM-EDS, TEM, XRD and XPS, information about the distribution, amount, morphology and composition of metal nanoparticles on the support material was obtained. In addition, electrochemical properties of the catalysts were determined by CV analysis. The physical characterization results revealed that the catalysts were successfully synthesized by microwave method and that different ratios of metals and bimetallic could be loaded on the support material. It was also seen that the electrochemical activity of the PtPd/C bimetallic catalyst was better than the others.     

Ethanol electro-oxidation on Pt/C and PtSn/C catalysts in alkaline and acid solutions

Carbon supported Pt and PtSn were prepared by a modified polyol method. The electrocatalytic activities and stabilities of the Pt/C and PtSn/C catalysts towards ethanol electro-oxidation reactions (EORs) were investigated by potentiodynamic and potentiostatic methods in a 0.1 M NaOH solution (or 0.5 M H₂SO₄) containing 0.01 M ethanol. On both catalysts, the EOR currents in the alkaline solutions were much higher than those in the acid solutions, and the onset potentials of the EOR in alkaline solutions were less positive than those in acid solutions, indicating that the kinetics of the EOR improve in alkaline solutions. Even though a significant improvement was observed in acid media on PtSn/C, compared with Pt/C, only negligible improvement was observed in alkaline media. The apparent activation energies of the EOR on the PtSn/C catalyst varies from 21 to 33 kJ mol⁻¹, depending on the potentials, which are slightly lower than the corresponding values on the Pt/C catalyst (25∼42 kJ mol⁻¹) under the same conditions. The Tafel slopes are divided into two parts–at low overpotentials, Tafel slopes on both catalysts are close to 120 mV dec⁻¹, which is in agreement with the proposed mechanism–Temkin-type adsorption for both OH_ad and ethoxi at low overpotentials; in contrast, at high overpotentials, Tafel slopes on both catalysts are over 300 mV dec⁻¹ due to the oxide formation on the surface.     

CeO2 nanoparticles improved Pt-based catalysts for direct alcohol fuel cells

We developed an ultrasonic co-deposition technique to enhance the activity of Pt/C catalyst (and Pt/CNT, PtRu/C catalysts) for direct alcohol fuel cells (DAFCs) by CeO₂ nanoparticles. The composite catalyst architecture is obtained by an ultrasonically mixing commercial Pt/C catalyst and CeO₂ nanoparticles. Both Pt and CeO₂ are dispersed uniformly in the electrodes resulting in a great deal of CeO₂–Pt–C triple junction interfaces. Unlike traditional preparation of metal oxide supported Pt catalysts, CeO₂ will not cut the connection between Pt and C in this composite catalyst structure. Electrochemical measurements confirm that CeO₂ can improve almost all Pt based catalysts (Pt/C, Pt/CNT, and PtRu/C) for almost all small molecular alcohols (methanol, ethanol, ethylene glycol, and glycerol) electro-oxidation. EIS measurement shows that reaction resistance between Pt and alcohols is decreased much by adding small CeO₂ nanoparticles. Besides, these composite catalysts have high stability. It proves CeO₂ a very promising co-catalyst of Pt based catalysts for DAFCs.