Bromide Anion Exchange Research Articles

Hydrothermal Green Synthesis of LaOx‐Modified Pt/C Catalyst for Glycerol‐to‐Glycerate Electrooxidation in Alkaline Medium

AbstractUsing the bromide anion exchange (BAE) green method to obtain carbon‐supported nanoparticles, Pt(LaOx)/C was successfully prepared under mild conditions. This material, containing LaOx species generated in situ during the synthesis, was efficiently used as an anode to perform glycerol oxidation in alkaline medium in batch mode and at room temperature. In a direct alcohol fuel cell (DAFC), this catalyst was able to boost the glycerol‐to‐glycerate conversion with a 49% selectivity and a 28% power density higher than the same system using a BAE‐synthesized Pt/C anode. The increase in catalytic activity may be due to the interaction of LaOx with the Pt active sites, acting as a bifunctional electrode. Furthermore, when used as an anode in an electrolysis setup, the selectivity of glycerol toward glycerate increased up to 67%. In situ FTIR and HPLC analyses confirmed the formation of the value‐added glycerol oxidation products.

Rare-earth modified Pt-Sn catalysts obtained via bromide anion exchange for enhanced ethanol electrooxidation in alkaline medium

Rare-earth modified Pt-Sn catalysts obtained via bromide anion exchange for enhanced ethanol electrooxidation in alkaline medium

An FTIR Study of the Electrooxidation of C2 and C3 Alcohols on Carbon‐Supported PdxRhy in Alkaline Medium**

AbstractWe have investigated the promoting effect of Rh addition to Pd‐based materials in the electrooxidation of ethanol and glycerol. Physicochemical characterizations (XRD, EDX, TEM, and XPS) of the PdxRhy/C materials, prepared by bromide anion exchange (BAE), showed that the experimental bimetallic compositions were close to the targeted ones. PdxRhy/C particle sizes ranged from 2.2 to 3.8 nm. The ethanol oxidation reaction (EOR) on the PdxRhy/C catalysts yielded four times larger carbonate (CO32−) amount. As for the glycerol oxidation reaction (GOR), the onset potential on the Pd50Rh50/C catalyst occurred at lower potentials. Chromatographic analysis combined with in situ Fourier transform infrared (FTIR) spectroscopy showed that GOR on the Pd50Rh50/C catalyst selectively and quantitatively produced glycerate and tartronate. The outstanding ability of the Pd50Rh50/C catalyst toward EOR and GOR was correlated to the electronic effect expressed by a negative potential shift (200 mV) and the 47 % alloying degree in the Pd50Rh50/C structure.

Insights on the C2 and C3 electroconversion in alkaline medium on Rh/C catalyst: in situ FTIR spectroscopic and chromatographic studies

The present work evaluates ethanol and glycerol electro-oxidation on Rh/C catalysts prepared using the Bromide Anion Exchange (BAE) method. Physicochemical characterizations were performed using Thermogravimetric Analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The SPAIRS investigations revealed that the CO adsorption modes on Rh sites occur on the linearly adsorbed CO (COL) and bridged bonded (COB) modes. In ethanol oxidation reaction (EOR), the Rh effect was evaluated by analyzing the products generated after bulk electrolysis using High-Performance Liquid Chromatography (HPLC) and in situ FTIR spectroscopy. The results confirmed the C-C cleavage Rh ability at low potentials and revealed that EOR follows both reaction pathways on Rh/C. While in glycerol oxidation reaction (GOR), Rh addition increases high added-value products formation such as glycerate ion. The GOR main route follows the glyceraldehyde pathway. The results highlighted that Rh is a good candidate for ethanol and glycerol electrochemical conversion at low potentials.

New insights on the selective electroconversion of the cellulosic biomass-derived glucose at PtAu nanocatalysts in an anion exchange membrane fuel cell

Cellulosic biomass, which is basically a polymer of glucose, is the most abundant organic polymer on earth and there is significant interest in the development of advanced materials for its valorization through the waste-to-energy and water-to-chemical scenarios. Hence, a precise investigation of the monomer (glucose) electrooxidation in electrochemical reactors is a key starting point to tackle the whole cellulose and ultimately the entire biomass. To this end, we report herein new insights about the operation of a cogeneration direct alkaline glucose fuel cell (which includes an anion exchange membrane) that simultaneously produces electricity and mainly gluconate as the reaction product. The AuPt nanocatalysts of 3–5 nm particle size finely dispersed onto reduced graphene oxide (rGO) at a 20 wt% metal loading are obtained from an organic surfactant-free method, so-called the bromide anion exchange (BAE). Specifically, the electroanalytical investigation carried out with high-performance liquid ionic chromatography (HPLIC) and liquid chromatography coupled to mass spectrometry (LC-MS) demonstrate no carbon–carbon bond cleavage occurs, which represents an advance towards a CO2-free biomass valorization process. The comparison of the results commonly obtained in a three-electrode half-cell with those in an anion exchange membrane fuel cell shows that the trends in selectivity are the same. The fuel cell operation produces gluconate via a two-electron transfer process at 90% selectivity and 65% Faradaic efficiency. In addition to gluconate, glucuronate is also observed; both compounds are high value-added chemicals. This work contributes towards the engineering of novel electrocatalytic interfaces for the valorization of the surplus biomass into energy and chemicals.

Enhanced catalytic activity of low-Pt content nanocatalysts supported on hollow carbon spheres for the ORR in alkaline media

In this work, low-Pt content nanocatalysts (≈ 5 wt. %) supported on Hollow Carbon Spheres (HCS) were synthesized by two routes: i) colloidal conventional polyol, and ii) surfactant-free Bromide Anion Exchange (BAE). The nanocatalysts were labelled as Pt/HCS-P and Pt/HCS-B for polyol and BAE, respectively. The physicochemical characterization of the nanocatalysts showed that by following both methods, a good control of chemical composition was achieved, obtaining in addition well dispersed nanoparticles of less than 3 nm TEM average particle size (d) on the HCS. Pt/HCS-B contained more Pt0 species than Pt/HCS-P, an effect of the synthesis method. In addition, the structure of the HCS remains more ordered after BAE synthesis, compared to polyol. Regarding the catalytic activity for the Oxygen Reduction Reaction (ORR) in 0.5 M KOH, Pt/HCS-P and Pt/HCS-B showed a similar performance in terms of current density (j) at 0.9 V vs. RHE than the benchmark commercial 20 wt. % Pt/C. However, Pt/HCS-P and Pt/HCS-B demonstrated a 6 and 5-fold increase in mass catalytic activity compared to Pt/C, respectively. A positive effect of the high specific surface area of the HCS and its interactions with metal nanoparticles and electrolyte, which promoted the mass transfer, increased the performance of Pt/HCS-P and Pt/HCS-B. The high catalytic activity showed by Pt/HCS-B and Pt/HCS-P for the ORR, even with a low-Pt content, make them promising cathode nanocatalysts for Anion Exchange Membrane Fuel Cells (AEMFC).

Pt/TiOx Cathode Catalysts for Polymer Electrolyte Fuel Cells

IntroductionDue to carbon materials are easily oxidized at high potential[1], it is necessary to develop carbon-free electro-conductive supports with superior stability for oxygen reduction reaction (ORR) catalyst in polymer electrolyte fuel cells (PEFCs). Lots of conductive or semi-conductive oxides, such as indium tin oxide (ITO)[2], Ti4O7[3], Nb doped SnO2[4] and son on have been reported as catalyst supports or as secondary supports for the improvement of the catalytic activity performance for the ORR. Although these oxide supports showed high stability at high potential region, the low specific surface area, which are significantly lower than carbon materials, limited the actual use in PEFC system. In this study, we focused on Nb doped TiO2 nanoparticles. We found that Nb doped TiO2, which was reduced by NaBH4 and further treated via mixed gas of hydrogen and oxygen, showed high conductivity and high specific surface area compared with pure TiO2. We attempted to evaluate the Nb doped TiO2 as carbon-free electro-conductive supports.Experimental10 atomic% Nb doped TiO2 was prepared by hydrothermal method as a precursor. First, 0.002 mol niobium ethoxide and 0.018 mol titanium butoxide were mixed completely, and then the mixed solution was dropped into 30 mL deionized water. All of product was put into 100 mL Teflon autoclave, and heated at 180 oC for 20 h to proceed the hydrothermal reaction. Reaction products were collected by filtration, and then dried under vacuum at 80 oC for 12 h to obtain a precursor.To improve conductivity, 1g of precursor and NaBH4 were mixed (w/w, 1:8) with 5 mL EtOH, and the mixture was heated under Ar atmosphere for 20 h. Then, the samples washed by 1M HCl 3 times, and dried under vacuum at 80 oC, 12 h. Finally, the samples were treated by mixed gas of pure hydrogen and 0.1% oxygen at given temperature for given time. 20wt%Pt was deposited by a revised bromide anion exchange (BAE) method.Results and DiscussionAfter the heat treatment at 400 oC, 500 oC and 550 oC for 0.25 h under mixed gas of pure hydrogen and 0.1% oxygen, the BET surface areas of the samples reached to 98 m2g-1, 69 m2g-1 and 29 m2g-1, respectively. in addition, the sample heated at 400 oC also had a 143 Ω·cm at 60 MPa, which could be used as a support in PEFCs.Pt/Nb-TiOx was evaluated in 0.1 M HClO4 at 60 oC, the accelerated durability test (ADT) was performed under N2 atmosphere in the potential range from 1.0 to 1.5 V vs. RHE with a scan rate of 500 mVs-1. Figure 1 shows the polarization curves of Pt/Nb-TiOx for the ORR before and after 500 cycles ADT. It could be found that the catalyst showed a good durability after 500 cycles ADT.AcknowledgmentThis research is supported by the Strategic International Joint Research Program (SICORP) of the Japan Science and Technology Agency (JST). In addition, the authors wish to thank the support of JSPS grants-in-aid for scientific research, Suzuki Foundation and Tonen General Sekiyu Research / Development Encouragement & Scholarship Foundation.

The formate electrooxidation on Pt/C and PtSnO2/C nanoparticles in alkaline media: The effect of morphology and SnO2 on the platinum catalytic activity

Pt/C and PtSnO2/C electrocatalysts with and without cubic preferential morphology were used for formate electrooxidation reaction (FER) in alkaline medium. The synthesis of catalysts was carried out by alcohol reduction method using KBr as a shape directing agent (Bromide Anion Exchange method - BAE). The X-ray diffraction (XRD) showed characteristic peaks of the Pt face-centered cubic (FCC) structure, as well as cassiterite SnO2. The Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) micrographs show SnO2 dispersed onto carbon support and adjacent to the Pt nanoparticles (NPs), as well as cubic Pt NPs. The cyclic voltammetry (CV) measurements show that the current density peak for FER on Pt/C (100) is 2.40 times higher than on Pt/C polycrystalline (poly). The current density at end of chronoamperometry (CA) analysis on PtSnO2/C poly was 1.33 and 5.29 times higher than on Pt/C (100) and Pt/C poly, respectively. The presence of SnO2 and the (100) facets of platinum cubic morphology might prevent platinum surface deactivation caused by intermediates formed during the FER process.

High Performance Sn@Pt/C and Sn@Pt/NG (C= Vulcan, NG= N-doped graphene) Core-Shell Nanostructures for the Hydrogen Evolution and Oxidation Reactions in Acid Media

In this work, the catalytic activity of nanostructured core-shell electrocatalysts synthesized by the polyol and bromide anion exchange (BAE) methods was evaluated for the Hydrogen Oxidation Reactions (HOR), and the Hydrogen Evolution Reaction (HER). The electrocatalysts were supported on Vulcan (C) and nitrogen-doped graphene (NG), and labeled as Sn@Pt/C-P, Sn@Pt/NG-P, Sn@Pt/C-B and Sn@Pt/NG-B. For comparison purposes, the monometallic electrocatalysts Pt/C-P, Pt/NG-P, Pt/C-B and Pt/NG-B were synthesized. The nominal metal:support ratio in all cases was 20:80 (wt. %), while the theoretical Pt:Sn atomic relationship at the core-shell nanostructures was 1:1. EDS analysis showed a C content of approximately 80 wt. %, although in general, the experimental metals concentration was not closed to the nominal one. XRD analysis indicated the crystalline structure of the electrocatalysts, with a crystallite size of less than 7 nm. TEM characterization confirmed the formation of core-shell nanostructures, with an average particle size of ~ 2.3 nm. The highest mass activity for the HOR was shown by the Sn@Pt/C-B electrocatalyst, while in terms of specific activity its performance similar to that of Sn@Pt/C-P. On the other hand, the evaluation of the HER indicated that the best electrocatalyst considering specific activity was Sn@Pt/NG-B, which also showed the highest mass activity (like that of Sn@Pt/NG-B at low overpotentials). The results of the evaluation of catalytic activity showed that the core-shell nanostructures have an enhanced performance for the two reactions, compared with the monometallic electrocatalysts. This indicated that they are good candidates to be applied in Polymer Electrolyte Membrane Fuel Cells (PEMFC) cells, as well as in PEM electrolyzers.

Rhodium effects on Pt anode materials in a direct alkaline ethanol fuel cell.

The development of efficient catalysts for ethanol oxidation in alkaline medium requires a synthetic approach that may prevent the surfactant molecules from being adsorbed at the catalytic sites and decreasing the electrochemical performance of the final direct ethanol fuel cell. Toward this goal, the recently reported surfactant-less Bromide Anion Exchange (BAE) method, appears as a promising route to conveniently aim at preparing PtRh alloys dispersed on carbon substrates. The catalysts prepared herein by the BAE method were characterized physicochemically to obtain structural information on the PtRh/C nanomaterials, their morphology (size and shape), and their chemical and surface composition. Electrochemical behavior and properties of these electrodes were then investigated in a half-cell before the implementation of a direct ethanol fuel cell (DEFC) in a home-made anion exchange membrane Teflon cell. The analysis of the electrolytic solution in the anodic compartment by chromatography revealed that acetate was the major reaction product and the carbonate amount increased with the Rh content in the bimetallic composition. With 2.8–3.6 nm particle sizes, the Pt50Rh50/C catalyst exhibited the highest activity towards the ethanol electrooxidation.

Fe3O4@Pt Core-Shell Nanocatalyst Supported on N-Doped Functionalized Graphene As Novel Cathode Catalysts for Microbial Fuel Cells

Microbial Fuel Cells (MFCs) are bio-electrochemical systems that use bacteria to generate bioelectricity via the oxidation of organic matter contained in a substrate (such as wastewater). However, this new method of renewable energy recovery has several technical challenges. At the cathode, for example, the Oxygen Reduction Reaction (ORR) takes place. This reaction is kinetically slow, remaining one of the main drawbacks of MFCs. Even though Pt/C nanocatalysts are widely used to promote the ORR, their performance in MFC is low due to the complex operating conditions. Therefore, alternative cathode nanocatalysts must be developed. Regarding to this issue, core-shell nanocatalysts are a promising alternative for MFCs cathodes. In this study, Fe3O4@Pt core-shell nanoparticles have been supported on N-doped and functionalized graphene (N-Gf) to obtain the Fe3O4@Pt/N-Gf nanocatalyst. First, nitrogen-doped graphene (N-G) has been synthesized by a one-step ball milling process using graphite as carbon source and melamine as both exfoliating agent and nitrogen source. Then, N-G has been functionalized by a mild acid treatment and labeled as N-Gf. Separately, the Fe3O4 core has been obtained by co-precipitation reaction of Fe2+/Fe3+, using citric acid as surfactant. The Pt shell has been deposited on the core by the Bromide Anion Exchange (BAE) method, resulting in a Fe3O4@Pt nanostructure having a 1:1 Fe3O4:Pt molar ratio. The 20 wt.% Fe3O4@Pt/N-Gf core-shell nanocatalyst has been obtained also by the BAE method. Regarding N-Gf, its X-ray diffraction (XRD) pattern shows well-defined peaks at 2θ=26.5°, 44.39 and 54.4°, characteristic of graphitic structures. Moreover, its ID/IG intensity ratio calculated from Raman spectra is 1.40, which indicates a high degree of disorder in the carbon lattice, most likely due to the incorporation of N species into the structure. Additionally, an N content of 1.40 at. % has been determined by energy-dispersive X-ray spectroscopy (EDS). The XRD pattern of the magnetite phase shows reflections at 2θ= 30.44, 35.53, 43.46, 54.01, 57.79, 63.06 and 74.75°, attributed to the (220), (311), (400), (422), (511) (440) and (531) planes. The crystallite size of Fe3O4 has been calculated as 9.2 nm. In addition, its Raman spectrum shows signals corresponding to the A1g, Eg and T2g vibrational modes, characteristic of magnetite. Meanwhile, the catalytic activity of the Fe3O4@Pt/N-Gf nanocatalyst for the ORR has been evaluated by the Rotating Ring-Disk Electrode (RRDE) technique in 0.5 M H2SO4 and in H2SO4 having a pH=6.1. The latter is because of the pH of the pharmaceutical residual water used as substrate in the MFC. Electrochemical parameters such as hydrogen peroxide percentage, number of electrons transferred, and onset and half wave potentials has been determined. The results show that Fe3O4@Pt/N-Gf has a catalytic activity for the ORR in low and almost neutral pH comparable to that of a commercial Pt/C nanocatalyst. Therefore, these results suggest that Fe3O4@Pt/N-Gf is a promising cathode nanocatalyst for MFC applications. To the best of the authors knowledge, this is the first time that such nanostructures have been evaluated in MFCs.

Surfactant-Induced Anion Exchange and Morphological Evolution for Composition-Controlled Caesium Lead Halide Perovskites with Tunable Optical Properties.

Environmentally stable lead halide perovskite nanostructures with engineered composition and morphology are attractive because of their exotic optical properties. Here, we report the synthesis of monodispersed (∼20 nm) CsPbI3 cubic perovskite nanocrystals (NCs) using edible olive oil as a solvent as well as a chelating reagent. Thereafter, bromide anion exchange reaction using the cetyl trimethyl ammonium bromide surfactant in hexane is carried out at relatively lower temperatures to synthesize caesium lead halide perovskites with variable halide compositions and tunable band gaps. Interestingly, because of the formation of micelles, continuous morphology evolution varying from NCs of different sizes to nanowires (NWs) and nanosheets is observed. The anion exchange temperature has a distinct effect on the morphology of the CsPbBr3 nanostructure and the anion exchange reaction rate. Finally, an easy solution-processed photoconductive device is demonstrated using as-grown CsPbBr3 NWs, indicating its potential for optoelectronic applications.

Direct Glucose Fuel Cell: Carbon Support Effect on the Anode Nanocatalysts Efficiency

Glucose is a promising fuel for new implantable electrochemical power sources due to its abundance in the human body. The selective oxidation of this sugar to gluconic acid requires an active and efficient catalyst surface. Platinum is the reference catalyst, but displays a fast deactivation due to the poisoning effect of strongly chemisorbed intermediates during glucose electro-oxidation1. On the other hand, gold is well known for its exceptional electrochemical activity and selectivity on aldehydes and hemiacetals conversion in a large pH window2. Combining these two metals as unique electrocatalyst for glucose oxidation, becomes a way to overcome poisoning issue. Furthermore, the nature of the support also plays an important role in the enhancement of the catalyst activity and stability. Recently, researches on graphene-like materials have shown the benefit of their utilization as support for electrocatalysts3. In the present work, gold and platinum monometallic and bimetallic nanoparticles have been synthesized on different carbon supports: amorphous carbon Vulcan XC 72R and reduced graphene oxide (rGO). Physicochemical and electrochemical characterizations show that i) Bromide Anion Exchange (BAE) synthesis method provides good anchorage and dispersion of the nanoparticles (particle mean size < 10 nm) on supports, ii) glucose electro-oxidation on gold monometallic catalysts starts at 0.3 V/RHE in alkaline media and before 0.1 V/RHE for platinum monometallic and bimetallic catalysts, iii) rGO supported platinum, and gold-platinum alloys (Au70Pt30 and Au50Pt50 ) exhibit higher power density than the corresponding nanocatalysts supported on Vulcan when used as anode in an alkaline glucose/oxygen fuel cell (Figure 1). The electrochemical study in near-biological conditions confirms and even accentuates the differences between the supports in terms of efficiency, stability and compatibility. The chromatographic and mass spectrometry analyses of the reactions products from the operation of this direct glucose fuel cell in alkaline medium demonstrate the presence of gluconate as a major product. Moreover, glucuronate considered as a high value added compound, has been clearly identified. References Kerzenmacher, S.; Ducree, J.; Zengerle, R.; von Stetten, F., An abiotically catalyzed glucose fuel cell for powering medical implants: Reconstructed manufacturing protocol and analysis of performance. Journal of Power Sources 2008, 182 (1), 66-75. Pasta, M.; La Mantia, F.; Cui, Y., Mechanism of glucose electrochemical oxidation on gold surface. Electrochim. Acta 2010, 55 (20), 5561-5568. Yadav, R.; Subhash, A.; Chemmenchery, N.; Kandasubramanian, B., Graphene and Graphene Oxide for Fuel Cell Technology. Ind. Eng. Chem. Res. 2018. Figure 1: Polarization and power density curves of different nanocatalysts used as anode in a glucose/oxygen fuel cell recorded in 0.1 mol L-1 KOH + 50 mmol L-1 glucose. All catalysts have a metal loading of 20 wt. % on carbon substrates. Pt/Vulcan is used as cathode catalyst. Figure 1

Preparation and characterization of active and cost-effective nickel/platinum electrocatalysts for hydrogen evolution electrocatalysis

Designing active and cost-effective electrocatalysts is important in the field of energy economics, particularly for hydrogen production, which is at the core of many energy conversion technologies. This investigation reports on the preparation of nickel-based materials targeting electrocatalytic hydrogen evolution in either alkali or physiological solutions. Nickel-based metallic nanoparticles were synthesized via the bromide anion exchange method, and their performance was compared with the performances of a homemade nickel mesh and a high-purity nickel foil. The Ni99Pt01/C electrocatalyst performed the best in terms of overpotential and generated current density, notably in physiological conditions. In addition, the homemade electroformed nickel mesh behaved as well as a commercial high-purity nickel foil in alkaline medium and even better in buffered solution at pH 7. Both materials are environmentally friendly and economically viable candidates for technologies that require large cathode materials, especially when hydrogen production in neutral electrolytes is sought.

New Routes for the Synthesis of Pt-Sn-Rare Earth/C Catalysts for Ethanol Oxidation Reaction

In the last years, direct ethanol fuel cells (DEFC) have emerged as a promising energy conversion system for portable applications. Efforts for improving the Pt electrode activity have been focused on the addition of co-catalysts able to provide external oxygen-like species at low potentials. Up to now, Pt–Sn materials seem to be the most effective catalysts for ethanol oxidation but improvements are essential for the commercialization of this technology, especially in alkaline medium [1, 2]. The rare earth oxides have a number of features that make them interesting for catalysis and also for ethanol oxidation reaction (EOR) [3-5]. The development of effective and durable electrocatalysts for alcohol electrooxidation becomes one of the goal to achieve the commercialization of DEFC. In this work, PtSn/C and PtSnEu/C were synthesized by two different routes: bromide anion exchange (BAE) method and microwave-assisted heating polyol (MWP). The trimetallic PtSnRE/C (RE: La, Ce and Pr) nanomaterials were obtained by BAE route [6]. The nanomaterials were physically characterized by inductively coupled plasma-optical emission spectrometry (ICP-OES), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results from ICP measurements revealed the presence of platinum, rare earth metal and tin in the materials obtained from both synthesis methods. No-alloy of Pt-Sn or Pt-Rare earth was observed from XRD data of materials obtained by BAE method. Probably the second added metal could be in oxides and amorphous oxy-hydroxides states. The XPS investigations permitted to confirm that tin and the rare earths were mostly in oxide form. The active area of each electrocatalyst was estimated from CO-stripping in a three-electrode cell and the current densities resulted in the EOR are higher for catalysts prepared from BAE. The in situ Fourier Transform Infrared Spectroscopy (FTIRS) technique was helpful to confirm that catalysts obtained by MWP method were less effective towards a complete ethanol oxidation. The addition of tin and rare earth in the material compositions obtained by BAE method did not change the EOR mechanism, but promoted a shift of the onset potential towards lower values. The effects of tin and rare earth were over their ability of providing oxygen species, which leads to a bifunctional mechanism. The difference in activity can probably be explained by electronic and structure changes that enhance the ethanol oxidation reaction. Acknowledgments: São Paulo Research Foundation (FAPESP, grant#2012/12189-8; grant#2015/13218-0) and Brazilian National Nanotechnology Laboratory (LNNano, Project XPS-20257).

Reversible Electrocatalytic Activity of Carbon-Supported Ptx Ni1-x in Hydrogen Reactions.

Hydrogen oxidation and evolution reactions (HOR and HER) are studied on Ptx Ni1-x /C materials synthesized by the bromide anion exchange method. Physicochemical characterization shows that this surfactant-free method enables the preparation of well-dispersed and effective catalysts for the processes involved in the anode of H2 /O2 fuel cells (HOR) and the cathode of water electrolyzers (HER). The Pt-based materials are modified with different Ni contents to decrease the amount of costly precious metal in the electrode materials. These modified Pt-based materials are found to be electroactive for both reactions without additional overpotential. Kinetic parameters such as the Tafel slope, exchange (j0 ) and kinetic current densities, and the rate-determining steps of the reaction mechanisms are determined for each Pt-Ni catalyst and compared to those obtained at the Pt/C surface in alkaline medium. The high j0 values that are obtained indicate a probable contribution of the surface structure of the catalysts due to their roughness and the presence of oxygenated Ni species even at low potentials.

Recent Advances in Carbon Supported Metal Nanoparticles Preparation for Oxygen Reduction Reaction in Low Temperature Fuel Cells

The oxygen reduction reaction (ORR) is the oldest studied and most challenging of the electrochemical reactions. Due to its sluggish kinetics, ORR became the major contemporary technological hurdle for electrochemists, as it hampers the commercialization of fuel cell (FC) technologies. Downsizing the metal particles to nanoscale introduces unexpected fundamental modifications compared to the corresponding bulk state. To address these fundamental issues, various synthetic routes have been developed in order to provide more versatile carbon-supported low platinum catalysts. Consequently, the approach of using nanocatalysts may overcome the drawbacks encountered in massive materials for energy conversion. This review paper aims at summarizing the recent important advances in carbon-supported metal nanoparticles preparation from colloidal methods (microemulsion, polyol, impregnation, Bromide Anion Exchange…) as cathode material in low temperature FCs. Special attention is devoted to the correlation of the structure of the nanoparticles and their catalytic properties. The influence of the synthesis method on the electrochemical properties of the resulting catalysts is also discussed. Emphasis on analyzing data from theoretical models to address the intrinsic and specific electrocatalytic properties, depending on the synthetic method, is incorporated throughout. The synthesis process-nanomaterials structure-catalytic activity relationships highlighted herein, provide ample new rational, convenient and straightforward strategies and guidelines toward more effective nanomaterials design for energy conversion.

Electrochemical and Physicochemical Characterizations of Gold-Based Nanomaterials: Correlation between Surface Composition and Electrocatalytic Activity

Seminal papers have highlighted the promoting effect of gold when associated with other metals. There is still a lack of information about the origin of the exceptional electrochemical performances of gold-based nanostructures, known so far as one of the most active electrocatalysts for glucose-based energy conversion devices. In this report, we examined the correlation between the electrocatalytic properties and the surface composition on a line-up of Au-based nanostructures: gold-palladium, gold-platinum binaries, and gold-palladium-platinum ternaries from the so-called Bromide Anion Exchange (BAE) method. BAE enables to obtain carbon supported nanocrystals having high Miller indices. These truncated octahedron nanocrystals present twins as well as (110) facets. Both X-ray photoelectron spectroscopy (XPS) and electrochemical characterizations have shown that the surface of the multimetallic nanomaterials contains less atoms of gold. The most exposed platinum and palladium enable improving glucose electrooxidation reaction kinetics at low electrode potentials. Additionally, XPS measurements have shown that the binding energy (BE) of either Pd or Pt shifts towards low values when associated with Au, indicating strong electronic interactions between the different elements in the multimetallic nanomaterials. These properties have led to improved catalytic performances when tested for CO stripping experiments and glucose (potential fuel) electrooxidation reaction in alkaline medium.

Electrocatalytic properties of nanomaterials synthesized from “Bromide Anion Exchange” method - Investigations of glucose and glycerol oxidation

In this work, different experimental parameters influencing the straightforward nanoparticles synthesis method, so-called Bromide Anion Exchange (BAE) were scrutinized. It was found that a bromide ion to metal(s) molar ratio of 1.5 gave the best electrochemical activity of the obtained catalysts toward the organics oxidation. The revisited BAE synthesis approach allows the preparation of highly active AuPt/C and AuPd/C nanomaterials. It has been highlighted that this method changes drastically the structure of AuPd nanostructures leading to alloyed system when Au atomic content is higher than 50%. These gold-based materials can be considered as advanced surfactant-free nanoparticles for anode electrodes design in abiotic or hybrid glucose biofuel cell. Furthermore, qualitative and quantitative analyses of glycerol conversion indicate that glycolate and glycerate are the main final products with selectivity higher than 40 and 30%, respectively.

Electrochemical Behavior of Organics Oxidation on Palladium-Based Nanocatalysts Synthesized from Bromide Anion Exchange

Palladium-based and gold nanomaterials were synthesized by the so-called “Bromide Anion Exchange” method. This soft and clean synthetic route leads to well dispersed small nanoparticles on carbon support. Accordingly, these nanoscale structures have a high active surface area like 81 m2 g-1 for the 20 wt.% Pd/C electrocatalyst. The CO stripping experiments performed in alkaline medium have highlighted the dependence of the CO adsorption mode on palladium. When used as anode for glycerol or glucose electrooxidation in alkaline medium, they exhibit good activities. Moreover, the bimetallic catalysts showed an important improvement of the kinetics at lower potentials when compared to Pd/C. Some added value products like glycerate or glycolate have been detected by chromatographic analysis. These nanomaterials are promising electrodes in fuel or hybrid biofuel cell devices in a cogeneration of high value chemicals and energy process