Glycerol Electrooxidation In Alkaline Medium Research Articles

NiFe@Pd/C core–shell nanoparticles with enhanced catalytic activity toward glycerol electrooxidation in alkaline media

We synthesized NixFey@Pdz/C core–shell nanoparticles with different compositions to investigate their activity for glycerol oxidation. EDS and ICP analyses revealed divergences between the nominal and experimental compositions of the catalysts, indicating that the synthesis route was a little inefficient for depositing Ni-Fe. However, the addition of Ni-Fe to Pd increased its activity in glycerol oxidation. The Ni1.5Fe13.5@Pd85/C catalyst presents superior electrocatalytic performance, with a specific activity 1.28 times greater than that of Pd/C. In situ FTIR spectroscopy data revealed favorable formate and CO2 production on NiFe@Pd/C catalysts. Our research highlights the synergistic effect of composition and core–shell morphology on catalytic activity.

Enhanced performance of glycerol electro-oxidation in alkaline media using bimetallic Au-Cu NPs supported by MWCNTs and reducible metal oxides.

Electrochemical technologies for valorizing glycerol, a byproduct of biodiesel production, into electric energy and value-added chemical products continue to be technologically and economically challenging. In this field, an ongoing challenge is developing more active, stable, and low-cost heterogeneous catalysts for the glycerol electro-oxidation reaction (GlyEOR). This paper reports the influence of the preparation procedure, which involves intermatrix synthesis (Cu and Au NPs), followed by galvanic displacement (Cu-Au NPs) in previously functionalized multi-walled carbon nanotubes (MWCNTs). It also discusses the role of the supports, CeO2 NPs, and TiO2 NPs, obtained by a hydrothermal microwave-assisted procedure, on the electroactivity of a hybrid bimetallic Cu-Au/MWCNT/MO2 catalyst in the GlyEOR in alkaline media. The electrocatalytic behavior was studied and discussed in terms of structure, composition, and electroactivity of the synthesized materials, which were determined by Fourier-transform infrared spectroscopy (FTIR), flame atomic absorption spectroscopy (FAAS), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), X-ray photoelectronic spectroscopy (XPS), and cyclic voltammetry (CV). In addition, the role of the oxidation states of Cu and Au in the as-prepared catalysts (Cu/MWCNT, Au/MWCNT, Cu-Au/MWCNT, Cu-Au/MWCNT-CeO2, and Cu-Au/MWCNT-TiO2) was demonstrated. It was concluded that the preparation method of metal NPs for the controlled formation of the most catalytically active oxidation states of Cu and Au, together with the presence of a conductive and oxophilic microenvironment provided by carbon nanotubes and facile reducible oxides in optimized compositions, allows for an increase in the catalytic performance of synthesized catalysts in the GlyEOR.

Platinum nanoparticles deposited on Cu-doped NiO/C hybrid supports as high-performance catalysts for ethanol and glycerol electrooxidation in alkaline medium

In this work, the influence of Cu-doping on the ability of NiO co-catalyst to enhance the electrocatalytic properties of carbon-supported Pt nanoparticles toward ethanol and glycerol oxidation was investigated. The Cu-doped NiO particles were synthesized by a precipitation method, while the noble metal nanoparticles were deposited over the hybrid Cu-doped NiO/C supports via a pulsed microwave-assisted polyol method using ethylene glycol as reductant. Pt-NiO and Pt-NiOCuO(x:y)/C catalysts with Ni:Cu atomic ratios of 9:1 (Pt-NiOCuO(9:1)/C), 7:3 (Pt-NiOCuO(7:3)/C) and 5:5 (Pt-NiOCuO(5:5)/C) were obtained. The physicochemical analysis showed that the as-prepared catalysts are composed of nanoparticles of about 3 nm. The potentiostatic experiments exhibited that the Pt-NiOCuO(7:3)/C catalyst is the most active catalyst for ethanol oxidation, while the Pt-NiOCuO(5:5)/C catalyst exhibited the best performance for glycerol oxidation. These catalysts developed mass current densities of almost 12 and 5 times higher than those of bare Pt/C for ethanol and glycerol oxidation reactions, respectively. Moreover, an accelerated multicycling stability test displayed that the as-prepared catalysts retain almost 98% of their initial mass current density.

Synthesis of PtRu alloy nanofireworks as effective catalysts toward glycerol electro-oxidation in alkaline media

Electro-oxidation of glycerol is a key anodic reaction in direct alcohol fuel cell (DAFCs). Exploring the cost-effective nanocatalysts for glycerol oxidation reaction (GOR) is very important for the development of DAFC, but it is still challenging. In this paper, nanofirework-like PtRu alloy catalyst was successfully synthesized and used for GOR in alkaline medium. Thanks to the unique nanofirework-like structure and synergetic effects, the activity and stability of the as-prepared PtRu alloy nanofireworks (NFs) toward GOR were significantly improved relative to Pt NFs. In particular, the peak current density of GOR catalyzed by the optimized Pt1Ru3 NFs catalyst reached 2412.0 mA mg−1, surpassing that of commercial Pt/C catalyst. This work has important guidance for the design of advanced anode electrocatalysts for fuel cells.

Controlled galvanic decoration boosting catalysis: Enhanced glycerol electro-oxidation at Cu/Ni modified macroporous films

We report on glycerol electro-oxidation in alkaline medium at macroporous Ni electrodes decorated with Cu particles. Macroporous Ni film is electrodeposited, using hydrogen bubbles as dynamic templates, atop of a Cu substrate. This film shows good electrocatalytic activity towards glycerol oxidation reaction (GOR). The Ni film is further decorated with Cu via spontaneous deposition from CuSO4 solution. This is done to enhance the catalytic activity of the film towards GOR. The morphology of the Cu-decorated Ni film is controlled using various additives such as KCl and (NH4)2SO4 which are added to the Cu deposition bath. The as-prepared Cu-decorated Ni films are characterized by electrochemical measurements, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that these additives have tremendous effects on the morphology and the electrocatalytic activity of the decorating Cu particles.The decorated Ni foam showed superior electrocatalytic activity towards the GOR, as confirmed by the negative shift in the onset oxidation potential (ca. 100 mV) together with an increase in oxidation current that is up to 1.5-fold during the cyclic voltammetry (CV) measurements, compared to the undecorated Ni foam.

Ag/Co3O4 as an effective catalyst for glycerol electro-oxidation in alkaline medium

Herein, we report two different modes of combustion synthesis to prepare Ag/Co3O4 for glycerol electro-oxidation reaction. The synthesis technique allows us to deposit and disperse cobalt on the surface of silver and understand the effect of silver-cobalt interactions on the electrocatalytic performance. The bimetallic AgCo catalyst was synthesized via conventional solution combustion (AgCo-SCS); in addition, a novel second wave solution combustion synthesis (AgCo-SWC) was also used to synthesize a sample with a higher degree of surface alloying between the elements. XRD results of AgCo-SWC show peak shifts in 2θ to indicate the formation of a solid solution alloy that could improve the structural and electronic characteristic of the material. In AgCo-SCS, smaller Ag particles are found to be more on the surface, while in AgCo-SWC, Ag particles were largely covered with cobalt particles. The electro-oxidation results indicate that AgCo-SWC has improved electrochemical properties in terms of higher oxidation current and lower onset potential, which makes it an ideal candidate for glycerol oxidation reaction.

Electrocatalysis by design: Enhanced electro-oxidation of glycerol at NiOx nanoparticle modified 3D porous carbon felts

This paper addresses the preparation of three-dimensional functionalized carbon felts (CFs), which were coated with nickel (Ni) nanostructures and used as an electrocatalyst for glycerol electrooxidation in alkaline medium. The commercial CFs (3D-carbon fibers) were first functionalized with O- and S- like functionalities via electrochemical pretreatment in NaOH and H2SO4, then the impacts of this pretreatment on the electrodeposited Ni nanoparticles (NiNPs) morphology, distribution, structure and performance for glycerol electrooxidation was investigated. X-ray diffraction (XRD) together with cyclic voltammetry (CV) techniques were used to detect the changes of the electrodeposited Ni oxide phases. Contact angle was used to determine impact of pretreatment on the wettability of CF. X-ray photoelectron spectroscopy (XPS) was used to get information about the added functional groups while scanning electron microscope (SEM) was used to observe the changes of NiNPs morphology, distribution, and particle size. As-synthesized NiNPs modified functionalized CFs exhibited an excellent activity concurrent with good stability for glycerol electrooxidation. The pretreatment of CF in either NaOH or H2SO4 resulted in a significant increase in the Ni surface active sites and improved their electrocatalytic activity for glycerol electrooxidation.

Pb- and Bi-Modified Pt Electrodes toward Glycerol Electrooxidation in Alkaline Media. Activity, Selectivity, and the Importance of the Pt Atoms Arrangement

Herein we investigated the effect of the adsorption of Bi and Pb on polycrystalline platinum (Ptp) on the electrooxidation of glycerol (EOG) in alkaline media by combining electrochemical, spectros...

Insights on the unique electro-catalytic behavior of PtBi/C materials

Molecular dynamics simulations have been performed to study the growth and the final structure of PtxBi1-x clusters under conditions close to those encountered in classical low temperature chemical or physical synthesis methods, such as the water-in-oil route or plasma sputtering route, respectively. According to the simulations, PtxBi1-x nanoparticles should consist in well crystallized Pt core surrounded by Bi structures, with strong interaction between Pt and Bi atoms. The simulation results were compared with physicochemical characterizations of PtxBi1-x/C (x = 1.0, 0.9 and 0.8) materials synthesized at room temperature via the water-in-oil microemulsion method. XRD and XPS measurements led to the conclusion that Pt and Bi were not alloyed in PtxBi1-x nanoparticles and that the nanoparticle surface was bismuth-rich, respectively, in perfect agreement with molecular dynamics simulations. XPS and electrochemical measurements allowed also demonstrating a strong electronic interaction between Pt and Bi, still in agreement with molecular dynamics. The electrocatalytic behaviors of the PtxBi1-x/C catalysts have been studied. PtxBi1-x/C displayed the higher activity towards glycerol electrooxidation in alkaline media, with an onset potential of ca. 0.300 V vs RHE and a unique selectivity towards glyceraldehyde/dihydroxyacetone formation for potentials lower than 0.600 V vs RHE. A discussion on the relationship between composition/structure of the PtxBi1-x catalytic materials and activity/selectivity for glycerol electrooxidation allowed proposing a mechanism involving a single-carbon adsorption mode on Pt and an electronic effect for the desorption of low oxidized species from Pt sites driven by the early stage of the Bi0 to BiII transition.

Two-step synthesis of Ir-decorated Pd nanocubes and their impact on the glycerol electrooxidation

Despite intense research to synthesize well-ordered noble-metals nanoparticles to understand catalyzed electrochemical reactions, the synthesis and application of multi-metallic well-ordered nanomaterials is still rare. Here, we report a facile strategy for synthesizing Ir-decorated Pd nanocubes (NCs) in one-batch through two sequential chemical reduction processes. Afterwards, the activity of these materials was investigated for glycerol electrooxidation in alkaline medium by cyclic voltammetry and in situ FTIR. Microscopy images and compositional mapping reveal that Ir deposition barely changes the size of the cubes. The bi-metallic nanocubes shifts the onset potential toward lower values, but decreases the current density. The start potential displacement is rationalized as a consequence of a facilitated CO removal and an anticipated carbonate production; while the decrease in current may be a consequence of a reaction with multiple steps, each one extracting a few electrons. FTIR in situ spectra reveal CO2 production only for Ir-Pd NCs, which is due to a massive production of carbonate, which ultimately acidifies the interfacial pH. The protocol of synthesis showed here may be used to study well-ordered multimetallic nanostructures in several applications, not limited for electrocatalysis.

The enhanced activity of AuAg/C nanonetwork catalysts for glycerol electrooxidation by small amounts of Pd

The catalytic properties of the Au/C catalyst toward glycerol electrooxidation in alkaline medium have been tremendously improved by an incorporation of Au with Ag. In this work, the catalytic performance of the AuAg/C was further improved by introducing small amount of a third metal, Pd. The catalysts were synthesized by a facile synthesis using the co-reduction of metal precursors in the presence of polyvinyl alcohol. Two series of catalysts with Au:Ag atomic ratios of 1:4 and 1:8 were prepared. Each series consisted of 4 catalysts with various ratios of Au:Pd ranging from 1:0.1 to 1:0.2 and a catalyst without Pd. The resulting metal nanoparticles were formed as nanonetworks with Ag-rich shell. The catalytic activity of the Pd-promoted AuAg-based catalysts was superior over the unpromoted one except for the AuAgxPd0.2/C in which containing too high Pd amount. The most active catalyst was AuAg4Pd0.1/C yielding 2.5 times higher current density than did the AuAg4/C catalyst. Hence, the proposed catalyst model makes use of the surface modifications of the segregated surface, which may influence further catalyst designs for other applications.

Effect of Bi modification on Pt single crystals towards the glycerol electrooxidation in alkaline media

The high demand for the biodiesel has increased the glycerol (GlOH) generation, since it is a co-product of biodiesel production, surpassing the industrial demand. In this context, the glycerol electrooxidation reaction (GER) is an interesting option for its chemical valorization, generating high value-added products. In the present work, we studied the GER on different surfaces of Pt single crystals modified with bismuth to understand the effect of the catalyst structure on the activity and reaction pathways.

Glycerol electrooxidation in alkaline media on platinum surfaces modified by bismuth

We studied the glycerol electrooxidation reaction (GEOR) on Pt surfaces modified by Bi adatoms to understand the effect of catalyst strucutre on the activity and selectivity. This investigation was performed using a combination of electrochemical (cyclic voltammetry), chromatographic (HPLC) and spectroscopic (FTIR) techniques. Our results show that the presence of Bi blocks the reaction pathways that lead to CO formation, a poisoning intermediate, and increase the production rate of glyceric acid.

Au/NiCo2O4/3D HPG (Three-Dimensional Hierarchical Porous Graphene) Composite as Electrocatalyst for Glycerol Electrooxidation in Alkaline Medium

Au/NiCo2O4/3D HPG (Three-Dimensional Hierarchical Porous Graphene) Composite as Electrocatalyst for Glycerol Electrooxidation in Alkaline Medium

Nanostructured Ni and Ni-Pd Catalysts for Glycerol Electro-Oxidation in Alkaline Media

The great interest of shifting towards biodiesel from vegetable oils or waste fats results in a tremendous increase of glycerol production as an inevitable by-product. This waste sparked the need for glycerol valorization to justify biodiesel as alternative for diesel from petroleum. Our research efforts are to partially electro-oxidize glycerol into value-added chemicals in order to make biodiesel production more environmentally benign with added financial benefits. The primary objective of this project is the identification of an active and stable electro-catalyst that can affect the selective electrooxidation of glycerol to value-added products without C-C-C bond cleavage leads to the formation of a large number of high value-added chemicals [1]. The control of catalyst selectivity and activity could be achieved through formulation of novel, nanostructured electrocatalysts [2]. Nickel is an attractive material for glycerol electrooxidation in alkaline media [3, 4], due to its natural abundance and good stability in alkaline media. Designing nanostructured 3D Ni electrodes could enhance the catalytic activity of Ni, whereas its selectivity could be altered by addition of small amounts of the second metal [5]. Monometallic Ni nanoparticles were synthesized using modified polyol method. Change of NaOH concentration resulted in the variation of Ni nanoparticles (NPs) shape: triangular NiNPs were synthesized at lower concentrations while Ni NPs of urchin-like structure were fabricated at higher NaOH concentration. Bi-metallic NixPdx-1 (x=95,90 and 80 at.%) were also synthesized by hydrazine reduction in the presence of ethylene glycol. The synthesised nanoparticles were characterized by XRD, SEM, TEM, EDS mapping and HAADF imaging. In this work, electro-oxidation of glycerol reaction (GEOR) is investigated in detail on mono- and bimetallic Ni nanoparticles in alkaline medium. In order to better understand the role of the nickel surface on GEOR, electrochemical measurements have been carried out on synthesized unsupported nickel nanoparticles using different electrochemical tests such as cyclic voltammetry (CV), chronoamperometry (CA) and linear sweep voltammetry (LSV). Results indicated that the Ni was able to catalyze the GEOR at the NiOOH surface, well known as the active species. Ni80Pd20 displays the highest activity toward glycerol electro-oxidation. Chronoamperommetry coupled with in-situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) for the simultaneous analysis of products on the Ni surface and in the bulk solution showed that the main reaction products on Ni surface are glyceraldehyde, carbonyl, carboxylate ions and some carbon dioxide. The correlation of electrocatalytic activity and selectivity with nanoparticle shape, size, surface and bulk composition, as well as structure of Ni-based nanoparticles will be discussed in terms of mass activities and product distribution during GEOR. References Behr, J. Eilting, K. Irawadi, J. Leschinski, F. Lindner, Green Chemistry 10 (2008) 13.M. Simoes, S. Baranton, C. Coutanceau, Applied Catalysis B: Environmental110 (2011) 40.M.S.E. Houache, E. Cossar, S. Ntais, E.A. Baranova, J. Power Sources 375 (2018) 310.V.L. Oliveira, C. Morais, K. Servat, T.W. Napporn, G. Tremiliosi-Filho, K.B. Kokoh, Electrochim.Acta. 117 (2014) 255.M. Simoes, S. Baranton, C. Coutanceau, ChemSusChem 5 (2012) 2106.

Au/C catalysts promoted with Ni for glycerol electrooxidation in alkaline media

Au/C catalysts promoted by Ni at different Au:Ni atomic ratios (3:1, 2:1, and 1:1) were prepared for glycerol electrooxidation in alkaline media by a polyvinyl alcohol protection method. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, and inductively coupled plasma atomic emission spectroscopy. According to the cyclic voltammogram, Ni enhanced the catalytic activity of gold for glycerol electrooxidation in the alkaline media, although the average particle size of the AuxNiy/C catalysts was slightly larger than that of the Au/C with small cluster formation. The optimum atomic ratio of Au:Ni was found to be 2:1, since the Au2Ni1/C provided the maximum mass current density at approximately 18% higher than did the Au/C. The stability of the Au2Ni1/C also improved, as evidenced by chronoamperometry. These improvements are attributed to the ability of Ni to enhance the OH-adsorbed species on the Au surface, thereby inducing a lower onset potential and helping to remove intermediates from the active site. To reduce cluster formation, the effects of metal sol preparation and metal loading sequence on the catalysts’ performance were further studied at this atomic ratio (2:1). Catalysts with preloading of Ni (Au2/Ni1/C) were found to provide the highest maximum mass current density with comparable decay rates among all the catalysts tested.

Improvement of catalytic performance of AuAg/C catalysts prepared by galvanic displacement technique for glycerol electrooxidation in alkaline medium

The activity and stability of AuAg/C electrocatalysts prepared by a galvanic displacement between Au3+ and Ag on carbon were investigated. First, Ag/C was prepared by citrate reduction in alkaline and used as the displaced material. The addition of Au3+ into the Ag/C resulted in smaller fragments of AuAg nanoparticles. These AuAg/C catalysts were prepared at four Au loadings ranging from 5 to 30%wt Au. Upon interaction with glycerol, the catalyst surface became an Au-rich surface, thereby activating the catalysts. The promotion effects of Ag, such as negative shifts of both an onset potential and a potential at maximum current density, were observed on the catalysts with low Au content but not on those with high Au content. The AuAg/C catalysts with low Au content were more active than the Au/C one despite the very much larger size of the metal particles on the AuAg/C catalysts. The most active catalysts were 5%AuAg/C and 10%AuAg/C, providing much higher mass normalized current densities in electrolytes containing 0.1 and 1 M glycerol, respectively. The final current density of 10%AuAg/C after 60 min in 1 M glycerol electrolyte was 445 mA mgAu−1, which was about 9 times higher than that of Au/C. A synergistic effect between Au and Ag improved the stability of the AuAg/C catalysts.

Rrde Studies of Glycerol Electro-Oxidation: Local pH Variation and Oscillatory Dynamics

Using Ptdisk-Ptring electrodes we investigated glycerol electro-oxidation in alkaline media under both conventional and oscillatory conditions. The estimation of pH variation was done by polarizing the ring electrode at 100mV vs. RHE. The local depletion of OH- (variation in hydronium concentration) during oxidative steps at the disk is seen by the cathodic currents at the ring associated with hydrogen evolution, whose equilibrium potential (Nernstian potential) is shifted due to its well-known pH dependence. Typical voltammetric experiments at 20mV.s-1 in hydrodynamic conditions reveal ΔpH of around 1 unit. Higher rotation rates yielded lower peak currents. Under oscillatory conditions the situation is rather complicated as rotation of the electrode impacts on the critical population of intermediates required to sustain oscillations. It was only possible to obtain reproducible oscillatory dynamics under stationary conditions and pH variations seem not detectable by this technique.

Rrde Studies of Glycerol Electro-Oxidation: Local pH Variation and Oscillatory Dynamics

Based on the fast consumption and depletion of OH- that generate considerable local pH variations from reference bulk values during anodic processes on platinum, rotating ring-disk electrode (RRDE) studies are expected to contribute in elucidating mechanisms and pH implications on kinetics. As more recently demonstrated by Feliu and co-workers[1] , significant pH variations of up to 1.5 pH units during the voltammetric electro-oxidation of ethanol in alkaline media over platinum, even under hydrodynamic conditions, were detected. Using Ptdisk-Ptring electrodes we investigated glycerol electro-oxidation in alkaline media under both conventional (Figure 1) and oscillatory conditions. All ring currents were corrected by the collection efficiency of the electrode, N, of 25.6%. Importantly, the intrinsic ohmic drop of the system might bring about distortions on the ring currents that must be taken into account in order to rule out the cross-talk of the disk and ring electrodes. Parameters such as ionic strength, distance between working and reference electrodes, and, current magnitudes in the disk require special attention in order to avoid misleading conclusions. The detection of pH variation under voltammetric conditions was done by polarizing the ring electrode at 100mV vs. RHE. The local generation of H+ is seen by the cathodic currents registered at the ring (Fig.1,bottom) whose potential is shifted to lower values due to the well-known pH dependence on the equilibrium potential (Nernstian potential). In oscillatory conditions[2] the situation is rather complicated as many soluble intermediate species are produced at the disk, introducing relevant mass-transport limitations to the oscillatory dynamics being recorded. For example, galvanostatic oxidation of glycerol is only observable in stationary conditions: rotation of the electrode modifies importantly the population of intermediates necessary to sustain oscillations. A systematic study of the effects of rotation speed and of different ring polarizations was conducted. Additionally, the interaction of platinum oxides and glycerol in alkaline media, at open circuit potential, was also followed by collection experiments with the ring polarized at different potentials. The results so far demonstrate particular features for the glycerol system unseen for other model systems, yet to be understood. Acknowledgments: A.A.Z., P.B.P. E.G.M. and H.V. acknowledge São Paulo Research Foundation (FAPESP) and Sao Paulo University Research Office for the scholarships (grants #2013-06205-3 and #2012/07313-1) and financial support (grants #2009/07629-6, #2012/21204-0, and #2013/16930-7).

Water-Based Synthesis of Palladium Trigonal Bipyramidal/Tetrahedral Nanocrystals with Enhanced Electrocatalytic Oxidation Activity.

Well-defined palladium trigonal bipyramidal/tetrahedral nanocrystals were synthesized by an aqueous-phase hydrothermal method. The final products were a mixture of trigonal bipyramidal and tetrahedral nanocrystals. Statistics indicated that there were more trigonal bipyramids than tetrahedra in the products. Ethylenediamine tetraacetic acid disodium salt (EDTA-2Na) was proven to be essential in controlling the final shapes of palladium nanocrystals. Some control experiments were also conducted to investigate the shape evolution and formation mechanisms. The synthesized palladium nanocrystals showed enhanced catalytic properties for ethanol and glycerol electrooxidation in alkaline medium. This work provides a new method in preparing Pd nanomaterials with well-defined shapes.