Performance studies of Pd–Pt and Pt–Pd–Au catalyst for electro-oxidation of glucose in direct glucose fuel cell

Platinum is employed as anode catalyst for low temperature electro-oxidation of glucose in direct glucose fuel cell (DGFC), but it suffers from poisoning by intermediate oxidation products. In the present investigation, palladium and gold precursors are added with platinum precursor to form low metal loading (∼15–20% by wt.) carbon supported catalyst by NaBH₄ reduction technique. The prepared PtPdAu/C (metal ratio 1:1:1) and PdPt/C (metal ratio 4:1) catalysts are tested in DGFC. The Physical characterization of electro-catalysts by scanning electron microscope, transmission electron microscope, energy dispersive X-ray, X-ray diffraction and thermo-gravimetric analysis confirms the formation of nano-sized metal particles on carbon substrate with two prominent homogeneous bi- or tri-metallic crystal phases for PtPdAu/C. The cyclic voltammetry studies carried out for glucose (0.05 M) oxidation in (0.5 M KOH) alkaline medium shows the metal catalysts can efficiently electro-oxidize glucose. The catalysts tested as anode in a batch type DGFC using commercial activated charcoal as cathode produced peak power density of 0.52 mW cm⁻² for both PdPt/C and PtPdAu/C in 0.3 M glucose in 1 M KOH solution.     

Carbon supported nano-sized Pt–Pd and Pt–Co electrocatalysts for proton exchange membrane fuel cells

Nano-sized Pt–Pd/C and Pt–Co/C electrocatalysts have been synthesized and characterized by an alcohol-reduction process using ethylene glycol as the solvent and Vulcan XC-72R as the supporting material. While the Pt–Pd/C electrodes were compared with Pt/C (20 wt.% E-TEK) in terms of electrocatalytic activity towards oxidation of H₂, CO and H₂–CO mixtures, the Pt–Co/C electrodes were evaluated towards oxygen reduction reaction (ORR) and compared with Pt/C (20 wt.% E-TEK) and Pt–Co/C (20 wt.% E-TEK) and Pt/C (46 wt.% TKK) in a single cell. In addition, the Pt–Pd/C and Pt–Co/C electrocatalyst samples were characterized by XRD, XPS, TEM and electroanalytical methods. The TEM images of the carbon supported platinum alloy electrocatalysts show homogenous catalyst distribution with a particle size of about 3–4 nm. It was found that while the Pt–Pd/C electrocatalyst has superior CO tolerance compared to commercial catalyst, Pt–Co/C synthesized by polyol method has shown better activity and stability up to 60 °C compared to commercial catalysts. Single cell tests using the alloy catalysts coated on Nafion-212 membranes with H₂ and O₂ gases showed that the fuel cell performance in the activation and the ohmic regions are almost similar comparing conventional electrodes to Pt–Pd anode electrodes. However, conventional electrodes give a better performance in the ohmic region comparing to Pt–Co cathode. It is worth mentioning that these catalysts are less expensive compared to the commercial catalysts if only the platinum contents were considered.     

Durability study of Pt–Pd/C as PEMFC cathode catalyst

In this paper, Pt–Pd/C and Pt/C catalysts were evaluated and compared. The catalysts were evaluated as oxygen reduction reaction (ORR) catalysts in half cell test under potential cycling, and cathode catalysts in single cell test under dynamic loading simulating the vehicle operation. Physical and electrochemical techniques were applied to investigate the structure, performance and durability of those catalysts. The electrochemical active surface area (ECA) loss, particle size distribution, polarization behavior and electrochemistry impedance spectroscopy (EIS) suggested that the Pt–Pd/C showed a better durability than Pt/C.     

Plasma-assisted Pt and Pt–Pd nano-particles deposition on carbon carriers for application in PEM electrochemical cells

Plasma-assisted deposition of platinum and platinum-palladium nano-particles at the surface of carbonaceous electronic carriers for application in proton-exchange membrane (PEM) electrochemical cells has been carried out using a conventional DC magnetron sputtering system. Different types of carrier have been used for that purpose: carbon powder (Vulcan XC-72), carbon nanotubes and carbon nano-fibers. The interest of initial chemical pretreatment or metallization of the electronic carrier to improve surface adhesion of catalyst nano-particles has been analyzed. Nanostructured catalytic powders thus obtained have been analyzed and characterized using TGA, SEM, TEM, XRD, XRF and cyclic voltammetry. The electrochemical performances of Pt/C and Pt–Pd/C electrodes have been measured in single-cell PEM fuel cell (PEMFC), water electrolyzer (PEMWE) and unitized regenerative fuel cell (URFC). Results show a high active surface area (up to 44 m² g⁻¹) and high electrochemical activity for a number of synthesized samples. A qualitative correlation has been established between sputtering parameters, type of carbon carrier and performances as electrocatalyst.     

Enhancing the durability of multi-walled carbon nanotube supported by Pt and Pt–Pd nanoparticles in gas diffusion electrodes

This work tries to improve the durability of electrocatalysts of gas diffusion electrodes (GDEs) by using multi-walled carbon nanotube supported Pt–Pd bimetallic (Pt–Pd/MWCNT). The durability investigation of multi-walled carbon nanotube supported metals was evaluated by a repetitive potential cycling (RPC) corrosion test and by extended constant potential (ECP) experiments. Potential cycling tests were performed from −0.3 to 1.2 V at 50 mV s⁻¹ in 1 mol L⁻¹ H₂SO₄. Extended constant potential (ECP) durability test were also carried out on the GDEs by 30 h of constant potential operation at 0.8 V vs. Ag/AgCl. The smaller performance loss was observed on the GDE using Pt–Pd/MWCNT as electrocatalyst compared with GDE using Pt/MWCNT during both durability tests. ICP analysis also suggests that the dissolution of Pt nanoparticles from the carbon nanotube surface is hindered when Pd is present.     

A DMFC stack operating with hydrocarbon blend membranes and Pt–Ru–Sn–Ce/C and Pd–Co/C electrocatalysts

Direct methanol fuel cell (DMFC) stacks consisting of 5 cells and 20 cells were assembled with low-cost hydrocarbon blend membranes and new electrocatalysts with better methanol tolerance and stability. The hydrocarbon blend membranes consisting of an acidic polymer (sulfonated poly (ether ether ketone), SPEEK) and a basic polymer (polysulfone-2-amide-benzimidazole, PSf-ABIm) exhibited low methanol crossover, high conductivity, and good mechanical stability. The Pt–Ru–Sn–Ce/C anode catalyst exhibited better stability than the commercial PtRu/C catalyst, while the cathode catalyst Pd–Co/C showed better methanol tolerance than the commercial Pt/C catalyst. A maximum power of around 20 W was achieved with a DMFC stack consisting of 20 membrane-electrode assemblies (MEAs) fabricated with the above membranes and electrocatalysts. The results demonstrate the feasibility of utilizing these acid-base blend membranes and novel catalysts for DMFC applications.     

In-situ investigation on the CO tolerance of carbon supported Pd–Pt electrocatalysts with low Pt content by electrochemical impedance spectroscopy

Carbon supported Pd–Pt electrocatalysts (Pd–Pt/C) with low Pt content were investigated in proton exchange membrane fuel cells (PEMFCs) with pure H₂ and CO/H₂ as the feeding fuels, respectively. The Pd–Pt/C catalysts showed high activity for hydrogen oxidation reaction (HOR) and improved CO tolerance. Electrochemical impedance spectroscopy (EIS) was employed to probe the in-situ information of the improved CO tolerance. The dependence of Nyquist plots and Bode plots on current density and feeding gas was investigated in low polarization region. The results of EIS analysis indicated that the improved CO tolerance of Pd–Pt/C catalysts can be attributed to the lower coverage of CO on the Pd–Pt bimetal than that on the pure Pt.     

Electrocatalytic oxidation of formic acid on Pt–Pd decorated polyfluorenes with hydroxyl and carboxyl substitution

A series of novel Pt–Pd/polyfluorenes (PFs) composite catalysts were facilely prepared based on Pt/Pd precursor and PFs with hydroxyl and carboxyl substitution at the C-9 position by electrochemical method and their electrocatalytic performance toward formic acid oxidation were studied. Electrocatalytic experiments demonstrate that the Pt–Pd nanoparticles immobilized on poly(9-fluorenecarboxylic acid) (PFCA)-decorated glassy carbon (GC) electrode (Pt–Pd/PFCA/GC) show larger electrochemical active surface area, higher catalytic activity and stability toward formic acid oxidation than that of other Pt–Pd/PFs/GC, Pt–Pd/GC, as well as the commercial JM 20% Pt/C/GC electrodes, which can be attributed to the small-sized and well-dispersed Pt–Pd nanoparticles on PFCA matrix and the special electronic interaction between the metal nanoparticles and the polymer substrate. Moreover, the electron-withdrawing carboxyl substitution rather than the electron-donating hydroxyl on the polymer main chain is of great benefit to the removal of poison CO as well as the enhancement of catalytic activity of Pt–Pd toward formic acid oxidation.     

Pd,Pd–Ni and Pd–Ni–Fe nanoparticles anchored on MnO2/Vulcan as efficient ethanol electro-oxidation anode catalysts

Pd–Ni–Fe nanoparticles supported on MnO₂/Vulcan XC-72 R (carbon black powder) as the electrocatalyst for the anodic oxidation of ethanol in a direct ethanol alkaline fuel cell (DEAFC) has been conducted. Electrocatalyst structures and morphologies are investigated by XRD, FE-SEM, EDX and elemental mapping techniques and subsequently electrochemical performance of electrocatalysts for ethanol oxidation reaction (EOR) are studied by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). Pd/MnO₂/Vulcan, Pd–Ni/MnO₂/Vulcan and Pd–Ni–Fe/MnO₂/Vulcan efficiently advanced ethanol electro-oxidation reaction under alkaline conditions. Pd/MnO₂/Vulcan revealed best potential window and low charge transfer resistance (R_ct) for EOR. Pd–Ni/MnO₂/Vulcan and Pd–Ni–Fe/MnO₂/Vulcan electrocatalysts have a good anti CO-poisoning capability. Pd–Ni–Fe/MnO₂/Vulcan has significantly high current density, excellent catalyst durability and cyclic stability for ethanol oxidation which encourage researchers for application of such exceptional materials as anode electrocatalysts in DEFC.     

Evaluation of Pt–Ru–Ni and Pt–Sn–Ni catalysts as anodes in direct ethanol fuel cells

In this study, the electrooxidation of ethanol on carbon supported Pt–Ru–Ni and Pt–Sn–Ni catalysts is electrochemically studied through cyclic voltammetry at 50 °C in direct ethanol fuel cells. All electrocatalysts are prepared using the ethylene glycol-reduction process and are chemically characterized by energy-dispersive X-ray analysis (EDX). For fuel cell evaluation, electrodes are prepared by the transfer-decal method. Nickel addition to the anode improves DEFC performance. When Pt₇₅Ru₁₅Ni₁₀/C is used as an anode catalyst, the current density obtained in the fuel cell is greater than that of all other investigated catalysts. Tri-metallic catalytic mixtures have a higher performance relative to bi-metallic catalysts. These results are in agreement with CV results that display greater activity for PtRuNi at higher potentials.     

Methanol and ethanol oxidation on carbon supported nanostructured Cu core Pt–Pd shell electrocatalysts synthesized via redox displacement

Six different carbon-supported Cu core Pt–Pd shell (Cu@Pt–Pd) catalysts have been successfully synthesized by the galvanic replacement of Cu atoms by Pt⁴⁺ and Pd²⁺ ions at room temperature and their electrocatalytic activity for methanol and ethanol oxidation have been evaluated in acid media. Cu@Pt–Pd core shell nanoparticles with a narrow size distribution and an average diameter in the range of 3.1–3.5 nm were generated onto the carbon support. The compositional and the structural analysis of the as-prepared materials pointed out that the nanoparticles are formed by a Cu rich core covered by a Pt–Pd rich shell due to the interdiffusion of the metals after the galvanic replacement reaction. The electrocatalytic properties of the Cu@Pt–Pd electrodes in the electro-oxidation of methanol and ethanol was found to be dependent on the electrochemical surface area, lattice strain of the surface, composition and thickness of the Pt–Pd shell surrounding the Cu core. The optimum catalyst composition to obtain the best performance for methanol and ethanol electro-oxidation was determined to be Pt_0.59Pd_0.324Cu_0.167/C (6.2 wt.% Pt, 2.2 wt.% Pd and 0.7 wt.% Cu). This catalyst has a greatly enhanced mass activity, lower onset potential and poisoning rate, and higher turnover number in the MOR and EOR reactions compared to a commercial Pt_0.51Ru_0.49/C (20 wt.% Pt and 10 wt.% Ru). Consequently, this simple preparation method is a viable approach to making a highly active catalyst with low platinum content for application in direct alcohol fuel cells (DAFCs).     

Superhydrophobic Pt–Pd/Al2O3 catalyst coating for hydrogen mitigation system of nuclear power plant

Passive auto-catalytic recombiner (PAR) system is an important hydrogen mitigation method which has been applied in most modern light water nuclear reactors. The two challenges for the highly efficient PAR are the detrimental effect of water and poisoning by fission products. In this study, to address the two challenges, superhydrophobic Pt–Pd/Al₂O₃ catalyst coatings were prepared by wet impregnation method and the grafting of 1H,1H,2H,2H-perfluorooctyltriethoxysilane.The formation of a Pt–Pd intermetallic compound was confirmed by in situ diffuse reflectance infrared Fourier transform infrared spectroscopy for the Pt–Pd/Al₂O₃ catalyst. The Pt–Pd/Al₂O₃ catalyst exhibited a superior resistance of water poisoning to the monometallic catalysts. In addition, compared with the monometallic catalysts, the least influence by the iodine poisoning was observed for the Pt–Pd/Al₂O₃ catalyst, which is attributed to the smallest influence on the bindings of H₂ and O₂ on the Pt–Pd intermetallic compound by the iodine addition. For the reactor with the superhydrophobic Pt–Pd/Al₂O₃ catalyst coating, under the conditions simulating the nuclear accident, the reaction was ignited immediately as soon as the hydrogen was introduced at 298 K and the hydrogen conversion kept 100% when the reaction temperature exceeded 398 K. The superhydrophobic Pt–Pd/Al₂O₃ catalyst coating showed great potential for the mitigation of hydrogen containing various poisons during the nuclear accident.     

Mechanically activated Pt–Ni and Pt–Co alloys as electrocatalysts in the oxygen reduction reaction

Mixtures of powders of platinum with nickel or cobalt to obtain Ni_0.75Pt_0.25 or Co_0.75Pt_0.25 were mechanical alloyed by high energy ball milling. The results of crystal structure, morphology and electrocatalytic performance are presented for mechanically activated powders after 3 and 9 h of ball milling. Total solid solutions of Ni and Co with platinum were analyzed by X-ray diffraction after 3 h of ball milling. After 9 h of ball milling, in both cases, the total solid solution was accompanied by the appearance of NiO or CoO and ZrO associated with a redox reaction with the milling media. The presence of zirconium monoxide was confirmed by energy dispersive spectroscopy analysis. In both cases, an amorphization was detected. X ray absorption spectroscopy measurements showed changes in atomic and electronic environment of platinum, a reduction of the distance to the first coordination sphere and increased d-band vacancy vs pure Pt and Pt nanoparticles were observed for both studied systems. The electrocatalytic activity was determined using cyclic and linear voltammetry. The Co_0.75Pt_0.25 alloy milled for 9 h showed a higher electrochemical activity for the oxygen reduction reaction (ORR) compared with the other samples, including Pt-Etek. The degree of the ORR electrochemical activity was correlated with the presence of ZrO, which could affect the oxygen adsorption and improve the catalytic activity for the oxygen reduction reaction.     

Electrodeposition of Pt–Ru and Pt–Ru–Ni nanoclusters on multi-walled carbon nanotubes for direct methanol fuel cell

A full-electrochemical method is developed to deposit three dimension structure (3D) flowerlike platinum-ruthenium (PtRu) and platinum-ruthenium-nickel (PtRuNi) alloy nanoparticle clusters on multi-walled carbon nanotubes (MWCNTs) through a three-step process. The structure and elemental composition of the PtRu/MWCNTs and PtRuNi/MWCNTs catalysts are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray polycrystalline diffraction (XRD), IRIS advantage inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The presence of Pt(0), Ru(0), Ni(0), Ni(OH)₂, NiOOH, RuO₂ and NiO is deduced from XPS data. Electrocatalytic properties of the resulting PtRu/MWCNTs and PtRuNi/MWCNTs nanocomposites for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) are investigated. Compared with the Pt/MWCNTs, PtNi/MWCNTs and PtRu/MWCNTs electrodes, an enhanced electrocatalytic activity and an appreciably improved resistance to CO poisoning are observed for the PtRuNi/MWCNTs electrode, which are attributed to the synergetic effect of bifunctional catalysis, three dimension structure, and oxygen functional groups which generated after electrochemical activation treatment on MWCNTs surface. The effect of electrodeposition conditions for the metal complexes on the composition and performance of the alloy nanoparticle clusters is also investigated. The optimized ratios for PtRu and PtRuNi alloy nanoparticle clusters are 8:2 and 8:1:1, respectively, in this experiment condition. The PtRuNi catalyst thus prepared exhibits excellent performance in the direct methanol fuel cells (DMFCs). The enhanced activity of the catalyst is surely throwing some light on the research and development of effective DMFCs catalysts.     

Crystallographic and electrochemical characteristics of Ti–Zr–Ni–Pd quasicrystalline alloys

Ti₄₅Zr₃₅Ni_20−xPd_x (x = 0, 1, 3, 5 and 7, at%) alloys were prepared by melt-spinning. The phase structure and electrochemical hydrogen storage performances of melt-spun alloys were investigated. The melt-spun alloys were icosahedral quasicrystalline phase, and the quasi-lattice constant increased with increasing x value. The maximum discharge capacity of alloy electrodes increased from 79 mAh/g (x = 0) to 148 mAh/g (x = 7). High-rate dischargeability and cycling stability were also enhanced with the increase of Pd content. The improvement in the electrochemical hydrogen storage characteristics may be ascribed to better electrochemical activity and oxidation resistance of Pd than that of Ni.     

Effect of Pt–Pd/C coupled catalyst loading and polybenzimidazole ionomer binder on oxygen reduction reaction in high-temperature PEMFC

Polybenzimidazole (PBI) was studied as an ionomer binder at varying ratios (1–7) in a 20–40 wt% Pt–Pd/C cathode-coupled catalyst layer for the oxygen reduction reaction (ORR) in a high-temperature proton exchange membrane fuel cell (HT-PEMFC). Catalytic activity was examined by CV and LSV, while the properties of the catalysts were characterized by FESEM-EDX, N₂ adsorption–desorption, XRD and FTIR. The results showed that the distribution of metals on the carbon surface, carbon wall thickness and the interaction between ionomer and coupled catalysts affected the ORR performance. The fabricated membrane electrode assembly with 5:95 PBI: 30 wt% Pt–Pd/C catalyst ratio exhibited the best performance and highest durability for HT-PEMFC at 170 °C, yielding a power density of 1.30 Wcm⁻² with 0.02 mg_Pt/cm Pt loading. This performance of ultra-low metal loading of coupled Pt–Pd/C electrocatalyst with PBI binder was comparable to those reported by other studies, highlighting a promising catalyst for fuel cell application.     

Methanol oxidation on carbon-supported Pt–Ru–Ni ternary nanoparticle electrocatalysts

Methanol oxidation on carbon-supported Pt–Ru–Ni ternary alloy nanoparticles was investigated based on the porous thin-film electrode technique and compared with that on Johnson–Matthey Pt–Ru alloy catalyst. Emphasis is placed on the effect of alloying degree on the electrocatalytic activity and stability of the ternary catalysts. The as-prepared Pt–Ru–Ni nanoparticles exhibited a single phase fcc disordered structure, and a typical TEM image indicates that the mean diameter is ca. 2.2 nm, with a narrow particle size distribution. Also, the as prepared Pt–Ru–Ni catalysts exhibited significantly enhanced electrocatalytic activity and good stability for methanol oxidation in comparison to commercial Pt–Ru catalyst available from Johnson–Matthey. The highest activity of methanol oxidation on Pt–Ru–Ni catalysts was found with a Pt–Ru–Ni atomic ratio of 60:30:10 and at a heat-treatment temperature of ca. 175 °C. The significantly enhanced catalytic activity for methanol oxidation is attributed to the high dispersion of the ternary catalyst, to the role of Ni as a promotion agent, and especially to the presence of hydroxyl Ru oxide. Moreover, the stability of the ternary nanocatalytic system was found to be greatly improved at heat-treatment temperatures higher than ca. 250 °C, likely due to a higher alloying degree at such temperatures for the ternary catalysts.     

Reverse hydride transformations in the Pd–H system

In the present review, the development of notions about hydride transformations is described. It is shown that hydride transformations were classified as a special type of phase transition in a number of classic phase transformations. Then, the available information about reverse hydride transformations in the Pd–H system is summarized and it is shown that reverse hydride transformations in this system proceed by the mechanism of generation and growth. The C-shaped kinetic isothermal diagrams describe kinetics of direct α→β$\alpha \to \beta$ HT. Another type of kinetic diagram is typical for reverse β→α$\beta \to \alpha$ hydride transformations, and the rate of these hydride transformations just accelerates with temperature increase or hydrogen pressure decrease. Morphological peculiarities of reverse hydride transformations are described in detail. In the conclusion, a discussion of the unique role of hydrogen concentrational and hydrogen phase stresses in processes of hydride transformations is given. It has been found that these stresses are the most important thermodynamic and kinetic factors in the hydride transformation development.     

Methanol electrooxidation at Pt–Ru–W sputter deposited on Au substrate

This work reports an improved electrocatalytic activity for methanol oxidation at Pt–Ru–W electrode sputter deposited on Au substrate. The performance of Pt–Ru–W was compared with that of Pt–W and of Pt–Ru alloy electrodes. All the alloys tested exhibited catalytic activity higher than Pt. Among the alloys tested, the Pt–Ru–W demonstrated a significant cathodic shift in the onset potential and a remarkable enhancement in the current density for methanol oxidation reaction (MOR). The onset potentials for the MOR matched well the anodic peak potentials recoded in the base electrolyte (H₂SO₄), i.e., 0.15 V versus Ag/AgCl for Pt–Ru–W and 0.35 V versus Ag/AgCl for Pt–W and Pt–Ru electrodes. From these findings, it was postulated that the background peak current generates oxide species necessary to complete the methanol oxidation to CO₂. Next, it was observed that the current density at Pt–Ru–W electrode decreased when the Au substrate was changed to Pt, C, or Si, although, the onset potential for MOR remained almost unaffected by the nature of the substrate. Afterwards, the effect of Au substrate on methanol oxidation at Au-based alloy electrodes was investigated.