Catalysts For Ethanol Oxidation Research Articles

Modification of Carbon Black by Thermal Decomposition of Lead Acetylacetonate to Improve Activities for Ethanol Oxidation at Supported Pt Catalysts

Direct ethanol fuel cells (DEFC) are a type of promising energy-conversion device with high efficiency. The investigation of anode catalysts for DEFC is extremely important in improving energy efficiency. Improvement of the catalytic activity and long-term stability of Pt catalysts supported on some metal oxides has been reported for ethanol oxidation in acidic conditions. This synergistic effect mainly arises from the bifunctional effect and charge transfer between metal oxides and Pt catalysts.[1] In our study, thermal decomposition of Pb(acac)2 (acac = acetylecetonate) was used to rapidly prepare lead oxide supports on titanium foil and high surface area carbon electrode materials for electrocatalysis. On titanium electrodes, a thin layer of lead oxide was first prepared, followed by drop coating with a certain amount of a Pt nanoparticle solution. For high surface area carbon electrodes, Pt nanoparticles were adsorbed onto a carbon black-lead oxide composite, followed by painting a catalyst ink onto carbon fibre paper.The catalysts were characterized by X-ray diffraction and energy dispersive X-ray spectrometry. The electrochemical performance of the catalysts for ethanol oxidation was studied through cyclic voltammetry, chronoamperometry and in a proton exchange membrane electrolysis cell. Durability was studied through investigating the composition change before and after performing cyclic voltammetry. The lead oxide support was found to have a significant influence on onset potential, current density and product distribution for ethanol oxidation. Acknowledgments: This work was supported by the Natural Sciences and Engineering, Research Council of Canada and Memorial University.[1] G.M. Alvarenga, H.M. Villullas, Current Opinion in Electrochemistry, 4, 39, (2017).

Tunable long-chains of core@shell PdAg@Pd as high-performance catalysts for ethanol oxidation

High performance nanomaterial catalysts have attracted great attention on the application for the direct alcohol fuel cell. To improve the catalytic behavior, it is a challenge to modulate the surface structure and morphology of catalysts. We integrated properties of advanced networks nanostructure and core@shell structure to form a series of PdAg@Pd worm-like networks catalysts. Importantly, the composition-optimized Pd76Ag24 WNWs exhibited excellent catalytic performance towards ethanol oxidation reaction compared to that of commercial Pd/C catalysts in alkaline media. The mass activity of Pd76Ag24 WNWs is 3.55 times higher than that of commercial Pd/C catalysts for EOR. Moreover, the Pd76Ag24 WNWs also showed superior stability after 250 successive cycles and kept far higher residual activities than that of the other catalysts. The synthesis of PdAg@Pd worm-like networks catalysts provides a reference to well combine the advantages of core@shell and networks structure to form high performance catalysts application for DEFC.

Advanced Catalytic Materials for Ethanol Oxidation in Direct Ethanol Fuel Cells

Direct ethanol fuel cells (DEFCs) have emerged as promising and advanced power systems that can considerably reduce fossil fuel dependence, and thus have attracted worldwide attention. DEFCs have many apparent merits over the analogous devices fed with hydrogen or methanol. As the key constituents, the catalysts for both cathodes and anodes usually face some problems (such as high cost, low conversion efficiency, and inferior durability) that hinder the commercialization of DEFCs. This review mainly focuses on the most recent advances in nanostructured catalysts for anode materials in DEFCS. First, we summarize the effective strategies used to achieve highly active Pt- and Pd-based catalysts for ethanol electro-oxidation, including composition control, microstructure design, and the optimization of support materials. Second, a few non-precious catalysts based on transition metals (such as Fe, Co, and Ni) are introduced. Finally, we outline the concerns and future development of anode catalysts for DEFCs. This review provides a comprehensive understanding of anode catalysts for ethanol oxidation in DEFCs.

Development and characterization of silica supported cobalt oxides for ethanol oxidation using different preparation methods

Cobalt oxide in spinel structure (Co3O4) is an efficient catalyst for ethanol oxidation due to its potential as an oxygen source. To enhance the catalytic performance, Co3O4 is dispersed on silica (SiO2). The degree of dispersion and form of oxides on the support depend on the preparation method. The objective of this work is to compare physicochemical properties and catalytic performance in ethanol oxidation of silica-supported cobalt catalysts from different preparation methods. The catalysts were prepared by incipient wetness impregnation (IP), precipitation with reverse micelle (RM), and precipitation with NH4OH (PN) methods. The forms and dispersion of cobalt species were investigated by X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and X-ray photoelectron spectroscopy (XPS). The cobalt species from RM and IP methods were mainly Co3O4, but that from PN method was the mixed phases of Co3O4, CoO and Co2SiO4. The RM method provided the best dispersion of Co3O4, surface Co3+ and lattice O2− on SiO2. Consequently, the catalyst from RM method provided the highest ethanol conversion and CO2 yield from all temperature ranges.

Pt/Ru–Sn Oxide/Carbon Catalysts for Ethanol Oxidation

Mixed Ru–Sn oxides have been deposited onto a high surface area carbon support by thermal decomposition of Ru and Sn acetylacetonate (acac) complexes. Adsorption of preformed Pt nanoparticles produced catalysts with enhanced low potential activity for the oxidation of ethanol in aqueous sulfuric acid at ambient temperature and in a proton exchange membrane (PEM) cell at 80 °C. Varying the oxide composition between Ru0.38Sn0.62O2 and Ru0.67Sn0.33O2 did not influence the catalyst’s activity greatly but did increase stability in the sulfuric acid solution. Higher stability was observed in the PEM cell, where a Pt/Ru0.55Sn0.45O2/C anode provided much higher currents than a commercial Pt/C catalyst for ethanol oxidation at low potentials. Anodes for direct ethanol fuel cells can be fabricated by coating a carbon fibre paper backing layer consecutively with carbon black, Ru(acac)3 + Sn(acac)2, and Pt nanoparticles, with appropriate thermal processing.

Comparison of electrocatalytic activity of Pt1-x Pd x /C catalysts for ethanol electro-oxidation in acidic and alkaline media.

In this paper, a comparision of Pt1−xPdx/C catalysts for ethanol-oxidation in acidic and alkaline media has been investigated. We prepared Pt1−xPdx/C catalysts with different ratios of Pt/Pd (x at% = 0, 27, 53, 77 and 100) by the formic acid reduction method. The obtained Pt1−xPdx/C catalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), induced coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Structural and morphological investigations of the as-prepared catalysts revealed that the metallic particle size increases with increasing Pd content in the catalyst. The electrocatalytic performances and stabilities of Pt1−xPdx/C catalysts were tested by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry (CA) measurements for ethanol oxidation in acidic and alkaline media. The electrochemical measurements demonstrate that Pt1−xPdx/C catalysts exhibit much higher electrocatalytic activity for alcohol oxidation in alkaline media than that in acidic media. The composition of Pt/Pd has a significant impact on the ethanol-oxidation in both acidic and alkaline media. The Pt23Pd77/C catalyst shows the highest electrocatalytic performance with a mass specific peak current of 2453.7 mA mgPtPd−1 in alkaline media, which is higher than the Pt77Pd23/C with the maximum of peak current of 339.7 mA mgPtPd−1 in acidic media. Meanwhile, the effect of electrolyte, CH3CH2OH concentrations and scan rates was also studied for ethanol-oxidation in acidic and alkaline media.

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.

Synthesis of free-standing ternary Rh-Pt-SnO2-carbon nanotube nanostructures as a highly active and robust catalyst for ethanol oxidation.

The rational design of durable materials is an important issue for improving the performance of electrocatalysts towards the ethanol oxidation reaction (EOR). In this work, binderless thin nanostructured layers of SnO2, Pt, Rh, bilayers of Pt/SnO2, Rh/Pt and tri-layers of Rh (ca. 10 nm thickness)/PtSnO2 are directly grown by pulsed laser deposition onto carbon nanotubes (CNTs). SEM analysis shows that CNTs are perfectly coated with the catalysts. The onset potentials of the CO stripping and EOR indicate that Rh/Pt/SnO2 is the most active for the CO and the EOR. The incorporation of the CNTs in the catalyst layer is outstandingly beneficial to both the catalytic current activity and the durability. Indeed Rh/Pt/SnO2/CNT delivers mass activity as high as 213.42 mA mg−1Pt. Moreover, Rh/Pt/SnO2/CNT demonstrates not only the lowest poisoning rate (by intermediate species, such as adsorbed CO) but also the highest durability current of 132.17 mA mg−1Pt far superior to CNT-free Rh/Pt/SnO2/CP (58.33 mA mg−1Pt). XPS shows that SnO2, Pt and Rh are all present at the surface of Rh/Pt/SnO2/CNT, the presence of two oxophilic materials like SnO2 and Rh, implies an earlier source of OHads-species, which facilitates the oxidation of CO and assuming a second contribution from Rh is to enhance the cleavage of the C–C bond for the complete oxidation of ethanol. The 3D porous and binderless structure, the low amount of the noble catalyst, the excellent electroactivity and durability of the Rh5/PtSnO2/CNT/CP composite represents an important step in advancing its use as an anode in commercial applications in DEFC.

Tuning the electronic structure of platinum nanocrystals towards high efficient ethanol oxidation

AbstractDirect ethanol fuel cell is a promising low temperature fuel cell, but its development is hindered by sluggish kinetics of anode catalysts for ethanol oxidation. Here a high efficient platinum/tin oxide/Graphene nanocomposite is synthesized through a facile and environmentally benign method. The structure and morphology are carefully characterized by X-ray diffraction and Transmission electron microscopy, showing a clear platinum/tin oxide heterostructure uniformly dispersed on graphene support. This catalyst demonstrates the highest activity among the reported catalysts and much higher durability towards ethanol oxidation compared to conventional platinum nanocatalysts. The ultrahigh activity originates from promoted removal of poisoning carbon monoxide immediate species on platinum due to a strong electronic donating effect from both tin oxide and graphene, which is fully supported by carbon monoxide stripping and X-ray photoelectron spectroscopy analysis. Our platinum/tin oxide/Graphene appears to be a promising candidate for ethanol oxidation electrocatalysts.

High-efficient oxidation removal of ethanol from air over ordered mesoporous Co3O4/KIT-6 catalyst

In this study, cubic Ia3d mesoporous KIT-6 silica was developed as support to prepare Co3O4/KIT-6 catalysts (COKx, x = 10, 15, 20, 25, and 30 wt%) for OVOCs (ethanol as model compound) catalytic oxidation in air. The prepared COKx catalysts were also characterized by XRD (wide-, low-angle), BET, TEM, H2-TPR, and CO2-TPD. The fixed specific surface area and cubic Ia3d mesoporous structure of KIT-6 provided ordered Ia3d mesoporous structure and high specific surface area for COKx catalysts, but the crystal size, dispersion, reducibility, and oxygen storage-mobility properties of Co3O4, which were based on the ordering of Ia3d mesoporous structure with selected proper mass loading of Co3O4 as 25 wt%, decided the higher catalytic performance of COK25 for ethanol complete oxidation than the others. The T50 and T99 of the prepared COKx catalysts for ethanol oxidation in air were in the range of 215–238 °C and 240–270 °C, respectively, and showed positive relationship with the oxygen storage, desorption, and mobility properties (supply efficiency of reactive oxygen species) of COKx catalysts. The ethanol was completely oxidized to CO2 over COKx as the reaction temperature reached T99, otherwise partially oxidized to acetaldehyde at low reaction temperatures. In addition, the COK25 showed desired CO2 selectivity and T50 and T99 were significantly increased after 7 reaction cycles, revealing good catalytic stability, although the T50 and T99 values increase to 230 and 260 °C, respectively. The COK25 catalyst has showed potential application in OVOCs catalytic purification treatment, due to the available industrialized-preparation method and high catalytic performance.

In situ formation of porous trimetallic PtRhFe nanospheres decorated on ultrathin MXene nanosheets as highly efficient catalysts for ethanol oxidation

MXene as a new family of two-dimensional (2D) materials, has attracted more and more attention for its flexibility, superior structural stability, high electrical conductivity, and hydrophilic surfaces. Herein, we successfully report the porous ternary PtRhFe nanospheres supported on the surface of Ti3C2Tx MXene nanosheets (denoted as PtRhFe-PNS@MXene) as the enhanced catalyst for ethanol oxidation reaction (EOR), which is constructed via a one-pot solvothermal synthesis. Impressively, the composition optimized Pt69Rh8Fe23-PNS@MXene catalyst exhibits the highest specific and mass activity and excellent stability for EOR, which could be due to the porous structure and the “metal–support” effect between trimetallic PtRhFe nanospheres and MXene nanosheets. The porous structure provides abundant active sites and channels, which significantly promote charge and mass transfer. Moerover, the participation of MXene can significantly improve the catalytic performance due to the rich termination groups (–O, –OH and –F) on the surfaces and the frequent electron exchange with the teimetallic alloys. This work helps to open up a new pathway for designing the highly efficient EOR catalysts.

Small-sized Pt nanoparticles supported on hybrid structures of MoS2 nanoflowers/graphene nanosheets: Highly active composite catalyst toward efficient ethanol oxidation reaction studied by in situ electrochemical NMR spectroscopy

In this work, highly active MoS2 nanoflowers/graphene nanosheets (GNS) composites are successfully prepared through a simple hydrothermal method and are employed as Pt supports to prepare Pt/MoS2/GNS for ethanol oxidation. The catalyst is characterized both physically and electrochemically to investigate the effect of MoS2/GNS on Pt. Moreover, in situ electrochemistry - nuclear magnetic resonance, with the strength in structural characterization, quantitative analysis, and real-time measurement, is carried out to monitor molecular changes of reaction products and elucidate reaction mechanism of ethanol oxidation reaction, providing sampling resolution of 4s. Significantly, a small size of 5.4 nm Pt decorated Pt/MoS2/GNS is achieved. Pt/MoS2/GNS exhibits 2.1-fold increase in electrochemical active surface area, 2.2-fold increase in catalytic activity, and 2.0-fold increase in durability compared to commercial Pt/C during ethanol oxidation, which can be attributed to the synergistic effect of the interconnected nanoflower-on-nanosheet structure of MoS2/GNS, the better dispersion of Pt nanoparticles, and the interactions between substrate materials and Pt. The results suggest that Pt/MoS2/GNS could be an alternative electrocatalyst for efficient ethanol oxidation reaction. This work provides a promising strategy in the synthesis and monitoring of composite materials as high-performance ethanol oxidation catalysts.

NiS2 Nanoparticles with Tunable Surface Area As Catalyst for Ethanol Oxidation

NiS2 is rationally and readily prepared via a simple and general hydrothermal synthetic route. The particle sizes of NiS2 species are tunable by adjusting the pH value of the hybrid solution. The optimized sample (NiS2-4) contains NiS2 nanoparticles of about 32.6 nm, and large surface area of 368.5 m2 g–1. The high surface area renders NiS2-4 an excellent electrocatalytic performance for ethanol oxidation. NiS2-4 electrode also exhibits a good long-term cycling stability. 93.3% of the initial current density is recovered by moving the NiS2-4 electrode into fresh 0.1 M NaOH solution with 0.5 M ethanol after 500 cycles. The excellent electrocatalytic properties of NiS2-4 for ethanol oxidation stems from the high surface areas.

Real-time electrochemical ATR-SEIRAS investigation of CO adsorption and oxidation on Rh electrode in 0.1 M NaOH and 0.1 M H2SO4

Rh gets close attention recently since it might improve C1 pathway efficiency toward ethanol oxidation reaction. Considering COad species are the vital intermediates for the C1 pathway, thus we fundamentally investigate the CO adsorption and oxidation on Rh surface. The results show that the formation of COad layer on Rh is more sluggish in alkaline media, may be due to the high OH− concentration induced bigger electronegativity of Rh electrode. This local environment change also leads to the onset potential of COML oxidation in 0.1M NaOH negatively shift about 200mV (at ca. 0.43V) with respect to that in 0.1M H2SO4. The oxidation of COML on Rh in alkaline media might be divided into two potential sections. One may follow the Eley-Rideal mechanism at 0.45–0.55V with OH− ions directly attracting the surface weakly adsorbed COL species; the other is the oxidation of COML species through the Langmuir-Hinshelwood mechanism. This work may provide some fundamental supporting for fabricating highly efficient ethanol oxidation catalysts.

Nanocatalysts for Electrocatalytic Oxidation of Ethanol.

The use of ethanol as a fuel in direct alcohol fuel cells depends not only on its ease of production from renewable sources, but also on overcoming the challenges of storage and transportation. In an ethanol-based fuel cell, highly active electrocatalysts are required to break the C-C bond in ethanol for its complete oxidation at lower overpotentials, with the aim of increasing the cell performance, ethanol conversion rates, and fuel efficiency. In recent decades, the development of wet-chemistry methods has stimulated research into catalyst design, reactivity tailoring, and mechanistic investigations, and thus, created great opportunities to achieve efficient oxidation of ethanol. In this Minireview, the nanomaterials tested as electrocatalysts for the ethanol oxidation reaction in acid or alkaline environments are summarized. The focus is mainly on nanomaterials synthesized by using wet-chemistry methods, with particular attention on the relationship between the chemical and physical characteristics of the catalysts, for example, catalyst composition, morphology, structure, degree of alloying, presence of oxides or supports, and their activity for ethanol electro-oxidation. As potential alternatives to noble metals, non-noble-metal catalysts for ethanol oxidation are also briefly reviewed. Insights into further enhancing the catalytic performance through the design of efficient electrocatalysts are also provided.

Evaluation of silver as an active direct ethanol fuel cell electrode catalyst prepared by pulsed current electrodeposition technique

Pulsed current electrodeposition of silver on graphite from non-cyanide bath has been employed. The influence of pulse parameters on electrocatalytic activity of Ag catalyst for ethanol oxidation in alkaline media have been evaluated by field emission scanning electron microscopy (FESEM), X- ray diffraction (XRD) and cyclic voltammetry (CV). The results reveal that the optimum condition can be obtained at 60 % duty cycle, 50 mAcm-2 average current density, 10 min. deposition time, and 10 Hz pulse frequency. The electrocatalytic activity and stability of Ag/C electrode prepared, at corresponding optimum condition, by pulse current (PC) and direct current (DC) electrodeposition for ethanol oxidation in alkaline media have been compared. The results illustrate that PC silver catalyst exhibits higher oxidation peak current density, higher surface coverage, higher poisoning tolerance as well as smaller charge transfer resistance, in alkaline ethanol solution, than that prepared by DC technique and thus can be used as an active anode material for direct ethanol fuel cell at a reduced cost.

Insights into the electrode reaction process of nickel nanoparticles @reduced graphene oxide catalyst for ethanol oxidation in alkaline solution

Nickel nanoparticles uniformly anchored on reduced graphene oxide (Ni/RGO) nanosheets is successfully prepared by a facile wet-chemical method. It is found that many small Ni nanoparticles with the particle size of 4–8 nm are anchored on RGO, showing uniform dispersion. The Ni/RGO nanocomposite-modified glassy carbon electrode (GCE) (i.e., Ni/RGO/GCE) is investigated as an electrocatalyst for the ethanol oxidation reaction. Especially, the as-prepared Ni/RGO/GCE delivers excellent electrocatalytic performance in terms of the low peak potential value, the low reduction of its overvoltage, and satisfactory peak current density. The excellent electrocatalytic properties could be ascribed to the synergistic effect of Ni spherical nanoparticles and RGO nanosheets, which can lead to the high use ratio of Ni. It is proposed that the anodic peak that emerged in the potential negative-going sweep may be attributed to the oxidation of ethanol, which results from the high concentration of ethanol and an autocatalytic process at Ni/RGO/GCE.

PdCu nanoalloys deposited on porous carbon as a highly efficient catalyst for ethanol oxidation

Ultrafine and highly dispersed PdCu nanoalloys anchored on porous carbon were synthesized by a facile NaBH4 reduction method in a ionic liquid (IL)/water solution system. During the synthesis, the IL solvent can act not only as a stabilizer to slow down the particle growth and prevent the agglomeration, but also as a functional agent to improve the hydrophilicity and sorption property of carbon support due to the functional groups. The resulting PdCu/porous carbon (PdCu/PC) exhibits a remarkable activity for ethanol oxidation in alkaline solution (ethanol oxidation specific activity of 6.54 mA cm−2, only 2.14 mA cm−2 for commercial Pd/C), high poison tolerance (if/ib = 1.09), and excellent catalytic stability (only a loss of 4.3% of the initial ethanol oxidation reaction activity after 100 cycles). The superior performance of PdCu/PC can be ascribed to the abundant active reaction sites of porous carbon, uniform and good dispersion of PdCu nanoaolloys, as well as the strong metal-support interaction. This work is anticipated to be useful for the development of low-cost and highly active catalysts for fuel cells.

A simple and clean method for the synthesis of Pd/G catalyst for ethanol oxidation

In this research work, a clean method, in which no reducing agents, surfactants and high temperature are required, is reported for the decoration of palladium nanoparticles on graphene. In this attractive method, Pd/G catalyst is prepared by auto-reduction of palladium (II) formate solution at 60 ̊C. Palladium (II) formate is reduced to metallic Pd at a mild temperature and yields Pd nanoparticles (NPs) that are decorated on graphene. The resultant catalyst was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Energy dispersive X-ray spectroscopy (EDS) and electrochemical measurements. Electrochemical techniques including cyclic voltammetry (CV) and chronoamperometry (CA) results reveal that compared to commercial Pd/C catalyst, as-prepared Pd/G catalyst shows outstanding activity for ethanol oxidation in alkaline media.

1D-2D integrated hybrid carbon nanostructure supported bimetallic alloy catalyst for ethanol oxidation and oxygen reduction reactions

Herein, 1-D carbon nanotubes and 2-D graphene hybrid carbon hetero-structure is employed as the catalyst support material for low temperature fuel cell. Partial unraveling of carbon nanotubes results in 1D-2D hybrid hetero-structure with enhanced surface area, while the intact inner tubes result in good electrical conductivity. Platinum-tin alloy decorated on partially exfoliated carbon nanotubes (Pt–Sn/PCNT) were prepared by ethylene glycol reduction method and investigated its electrocatalytic activity towards ethanol oxidation reaction (EOR) for direct ethanol fuel cell (DEFC) and oxygen reduction reaction (ORR) for hydrogen fuelled polymer electrolyte membrane fuel cell (PEMFC). Along with the intrinsic properties of carbon nanotubes, PCNT provides more anchoring sites, thereby facilitates complete utilization of catalysts. The electrochemical EOR studies reveal that Pt–Sn/PCNT has better tolerance to the accumulation of intermediate species than Pt–Sn/CNT. Besides, as-synthesized electrocatalysts exhibit good ORR activity with four-electron pathway. The enhanced EOR and ORR activity of as prepared electrocatalysts is attributed to the high dispersion of catalyst nanoparticles on PCNT along with the inhibition of production of intermediate species on the Pt surface by alloying. Further, the practical suitability of PCNT supported Pt–Sn nanocatalysts as EOR and ORR electrocatalysts has been examined by performing the full fuel cell measurements.