Electrocatalysts For Ethanol Oxidation Research Articles

Highly active electrocatalysts for ethanol oxidation based on gold nanodendrites modified with NiFe2O4 nanoparticles decorated multi-walled carbon nanotubes

A nanocomposite consisting of NiFe2O4 spinel and multi-walled carbon nanotubes was produced according to citrate sol–gel method. Then, it is coated on the electrodeposited gold nanodendrites modified electrode (NiFe2O4–MWCNTs/AuNDs/GCE), and was utilized to electrocatalyze ethanol oxidation. NiFe2O4–MWCNTs/AuNDs/GCE provides higher active surface area and stability compared to AuNDs/GCE, so that it induced superior current density toward ethanol oxidation about. In fact, the spaghetti-like NiFe2O4–MWCNTs could create –OHads on the electrode, which decreases significantly the adsorption of poisonous intermediate substrates on the surface of gold nanostructures, and consequently amplifies charge transfer kinetic compared to bare GCE during the ethanol oxidation reaction.

MoS2 nanoflower supported Pt nanoparticle as an efficient electrocatalyst for ethanol oxidation reaction

Developing highly active and stable ethanol oxidation electrocatalysts is crucial for direct ethanol fuel cells. Herein, platinum/molybdenum disulfide nanoflower (Pt/MoS2) nanocomposite is synthesized through a facile method and is first applied as catalyst for ethanol oxidation reaction. In situ electrochemical nuclear magnetic resonance is carried out to investigate the electrocatalytic activity of Pt/MoS2 and the detailed mechanism of ethanol oxidation reaction. Experimental results indicate that in situ electrochemical nuclear magnetic resonance possesses great advantages for real-time investigation of ethanol oxidation reaction, and Pt/MoS2 is found to exhibit better electrocatalytic performances in terms of higher current density, better stability, and stronger anti-poisoning activity compared to commercial Pt/C and pure Pt catalysts in acid electrolyte, suggesting its potential for application in direct ethanol fuel cells. Density functional theory calculations indicate that MoS2-supported Pt atom has a smaller energy barrier for the dissociation of ethanol compared to those of Pt and C-supported Pt atom, leading to the enhancement of catalytic activity. This work reveals the importance of the supporting materials for high performance direct ethanol fuel cells catalysts.

Efficient ethanol oxidation by hemoglobin-capped gold nanoclusters: The critical role of Fe in the heme group as an oxophilic metal active site

Hemoglobin (Hb)-capped gold nanoclusters (Hb/AuNCs) are synthesized, characterized and introduced as durable and high-performance ethanol oxidation electrocatalysts with superior mass and specific activities. The experimental results and computational analysis suggest that the key reasons for the excellent catalytic activity of Hb/AuNCs are: (i) Fe atoms in the heme group of Hb acting as oxophilic metal active centers, via metal–metal bond formation with the AuNCs and (ii) the presence of a protein shell effectively hindering the Ostwald ripening and aggregation of AuNCs.

Platinum-Iridium Modified Gold Nanoparticles Catalysts for Electrooxidation of Ethanol in Alkaline Media

Ethanol is one of the most promising alternative fuels for fuel cells (FC). It is a renewable resource which can be produced on a large scale from biomass originating from agriculture, forestry and urban residues. The energy density of ethanol is as high as 8.01 kWh/kg, which is comparable to that of gasoline. Ethanol is easy to store, transfer and refuel owing to its non-toxicity and high boiling point in comparison with methanol and ammonia. [1] However, the sluggish kinetics and low energy efficiency for ethanol oxidation reaction (EOR) hinder the application of direct ethanol fuel cells (DEFCs). To address this issue, great effort has been made focusing on catalysts discovery as well as reaction mechanism understanding. [2] Here we report a systematic study on Pt-Ir modified Au/C electrocatalysts for efficient ethanol oxidation in alkaline media. In-situ electrochemical Infrared reflection absorption spectra (EC-IRRAS) reveals a high selectivity toward full oxidization to carbonate at low potentials, resulting in a high energy conversion efficiency. EC-IRRAS also indicate that the C-C bond splits upon ethanol interaction with the surface of PtIrAu/C ternary catalyst. More detailed discussion on this topic will be presented at the meeting. Acknowledgements This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. [1] Liang An, Tianshou Zhao, Yinshi Li, Carbon-neutral sustainable energy technology: direct ethanol fuel cells. Renewable and Sustainable Energy Reviews 2015, 50: 1462- 1468 [2] Alexey Serov, Iryna V. Zenyuk, Christopher G Arges, Marian Chatenet. Hot topics in alkaline exchange membrane fuel cells. Journal of Power Sources 2018, 375: 149- 157

Highly active carbon nanotube supported PdAu alloy catalysts for ethanol electrooxidation in alkaline environment

At present, ethanol electrooxidation study is performed on CNT supported Pd and PdAu catalysts to investigate the effect of Au addition to Pd towards the ethanol electrooxidation activity. NaBH4 reduction method is employed for the synthesis of Pd/CNT, Pd90Au10/CNT, Pd90Au10/CNT, Pd70Au30/CNT, Pd50Au50/CNT, and Pd40Au60/CNT catalysts. These catalysts are characterized via advanced surface analytical techniques namely N2 adsortion-desoprtion measurements,X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM). The characterization results revealed that Pd90Au10/CNT has 205.42 m2/g and 1.18 cm3/g BET surface area (m2/g) and pore volume (cm3/g), respectively. On the other hand, XRD and XPS results revealed that the electronic state of Pd90Au10/CNT catalyst changed by Au addition to Pd. TEM and HRTEM and elemental mapping results reveal that Pd and Au is homogeneously dispersed and alloying of Pd and Au is clearly observed, in agreement with the XRD and XPS results. Ethanol electrooxidation measurements in alkaline environment are performed by Cyclic Voltammetry (CV), Chronoamperometry (CA), Electrochemical impedance spectroscop (EIS) techniques. Pd90Au10/CNT displayed the highest specific and mass activity. The synergistic effect between Pd and Au at optimized metal ratio was utilized to obtain an improvement in specific activity. Furthermore, Pd90Au10/CNT showed the lowest charge transfer resistance (Rct) and a long term stability. As a result, it is clear that PdAu catalyst is a promising catalyst for Alkaline Direct Ethanol Fuel Cells.

Pt/C and Pt/SnOx/C Catalysts for Ethanol Electrooxidation: Rotating Disk Electrode Study

Pt/C and Pt/SnOx/C catalysts were synthesized using the polyol method. Their structure, morphology and chemical composition were studied using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer, transition electron microscope and X-ray photoelectron spectroscope. Electrochemical measurements were based on the results of rotating disk electrode (RDE) experiments applied to ethanol electrooxidation. The quick evaluation of catalyst activity, electrochemical behavior, and an average number of transferred electrons were made using the RDE technique. The usage of SnOx (through the carbon support modification) in a binary system together with Pt causes a significant increase of the catalyst activity in ethanol oxidation reaction and the utilization of ethanol.

Bimetallic Pd/SnO2 Nanoparticles on Metal Organic Framework (MOF)-Derived Carbon as Electrocatalysts for Ethanol Oxidation

Bimetallic Pd/SnO2 nanoparticle electrocatalysts on metal organic framework-derived carbon (MOFDC) were successfully synthesized using microwave-assisted strategies and explored for ethanol oxidation reaction (EOR) in alkaline solution. The materials were thoroughly characterized using XRD, XPS, TEM, and Raman. TEM showed that Pd/SnO2/MOFDC gave the least average particle size of 5.5 nm compared to its counterparts on carbon black (CB). The Pd/SnO2/MOFDC gave the best electrocatalytic performance in terms of high electrochemical active surface area (ECSA) of 962 cm2 mg−1, low onset potential and overpotential for EOR, and high current density (j) of four times more than those of the Pd/CB electrocatalyst. In addition, Pd/SnO2/MOFDC showed superior kinetic parameter (in terms of the Tafel slope (b) = 216.1 ± 8 mV dec−1) and least combined resistance (R = Rs + Rct). These results show that the Pd/SnO2/MOFDPC nanoparticle electrocatalyst is promising for EOR with improved electrocatalytic properties for application in direct ethanol fuel cell (DEFC).

Efficient Ni(OH)2 Supported Ultra-Low Content of Pt Electrocatalyst for Ethanol Oxidation in Alkaline Solution

Background: Direct ethanol fuel cells have gained considerable attention as promising sustainable green power sources for portable electronic devices and automotive propulsion systems. The electrocatalyst is one of the key parameters in DEFCs. However, the current electrocatalyst still suffers from high price due to a relatively large amount of noble metal used, or relatively low activity if non-noble metal was employed. Therefore, the design and fabrication of high-efficient electrocatalyst with low-content of noble metal is still of interest. Methods: Methods: Ni(OH)2 nanoflakes supported ultra-low content of Pt (Pt/Ni(OH)2) electrocatalyst was obtained via microemulsion, impregnation and chemical reduction processes. The Pt/Ni(OH)2 electrocatalyst was characterized by SEM, TEM, XRD and FTIR, and its performance for ethanol electro- oxidation was evaluated by cyclic voltammetry, Tafel and current-time curves. Results: TEM result showed that Pt NPs with sizes of ca. 4-6 nm were highly dispersed on the Ni(OH)2 nanoflakes, indicative of the successful preparation of Pt/Ni(OH)2. No peaks related to Pt NPs were observed in the XRD pattern of Pt/Ni(OH)2, revealing a low content and/or high dispersion of Pt NPs. The electrochemical investigation showed that the Pt/Ni(OH)2 electrode presented a superior catalytic performance and stability for ethanol electro-oxidation in alkaline solution. Conclusion: The Pt/Ni(OH)2 electrode with nominal 0.62 wt.% of Pt was successfully synthesized and showed an excellent catalytic activity and stability toward ethanol electro-oxidation mainly due to its porous structure, high dispersion of Pt and formation of NiOOH facilitating oxidation of ethanol. The acetate species was the major product during ethanol electro-oxidation.

Ternary N, S, and P-Doped Hollow Carbon Spheres Derived from Polyphosphazene as Pd Supports for Ethanol Oxidation Reaction

Ethanol oxidation reaction (EOR) is an important electrode reaction in ethanol fuel cells. However, there are many problems with commercial ethanol oxidation electrocatalysts today, such as poor durability, poor anti-CO poisoning ability, and low selectivity for C–C bond cleavage. Therefore, it is very meaningful to develop a high-performance EOR catalyst. Herein, we designed ternary N, S, and P-doped hollow carbon spheres (C–N,P,S) from polyphosphazene (PCCP) as Pd supports for EOR. Using SiO2 spheres as the templates, the PCCP was first coated on the surfaces of SiO2 spheres by in situ polymerization. Through high-temperature pyrolysis and hydrofluoric acid-etching, the hollow PCCP has a large surface area and porous structure. After loading Pd nanoparticles (NPs), the Pd/C–N, P, S catalysts with Pd NPs decorated on the surfaces of C–N, P, S can achieve a high mass peak current density of 1686 mA mgPd−1, which was 2.8 times greater than that of Pd/C. Meanwhile, the Pd/C–N, P, S catalyst also shows a better stability than that of Pd/C after a durability test of 3600s.

SnO2 patched ultrathin PtRh nanowires as efficient catalysts for ethanol electrooxidation

The delicate combination between amorphous SnO2 patches and PtRh nanowires could enhance EOR activities and stability effectively.

Electrocatalytic Oxidation of Ethanol on Flexible Three‐dimensional Interconnected Nickel/Gold Composite Foams in Alkaline Media

AbstractIn this work, a porous and flexible three‐dimensional (3D) nickel/gold nanoparticle electrode (NiF/AuNPs) is presented as an efficient electrocatalyst for ethanol oxidation in alkaline media. The 3D nanocomposite electrode consists of interconnected porous nickel foam (NiF) with large pores (500±200 μm diameter) surrounded by interconnected struts (∼100 μm) that are decorated with gold nanoparticles (AuNPs, 37±8 nm) through in‐situ electrochemical deposition. The catalytic performance of the 3D electrode was evaluated by different electrochemical methods. An enhancement in the performance (about 253 %) and a remarkable decline in onset potential (about ∼0.63 V) in comparison with pristine NiF for ethanol oxidation are demonstrated. This potential is lower than many reported results except palladium‐ and platinum‐based catalysts, which are expensive. It is shown that both hydroxyl anions and cations affect the ethanol oxidation on the 3D electrode. The interconnected porous structure provides efficient mass diffusivity, which along with its high specific surface area combined with the catalytic nature of AuNPs, may open new opportunities for in‐inexpensive and highly efficient electro‐oxidation of ethanol for energy applications.

Structural analysis of PdRh/C and PdSn/C and its use as electrocatalysts for ethanol oxidation in alkaline medium

The Pd/C, PdRh(50:50)/C and PdSn(50:50)/C nanomaterials were used as electrocatalysts for ethanol (EtOH) oxidation in Direct Ethanol Fuel Cell (DEFC) in an alkaline medium. This work aims to provide a complete physical characterization of the nanomaterials, elucidate the bifunctional mechanism concerning ethanol oxidation reaction and understand the influence of carbon – metal bonding in the electrochemical activity. These nanomaterials were investigated by X-ray photoelectron spectroscopy (XPS) and revealed that the atomic percentage of the surface is different of those obtained by Energy Dispersive X-ray spectroscopy (EDS). Raman spectroscopy showed a bonding between palladium and carbon atoms which can play a decisive role in the performance of the materials. Attenuated Total Reflectance technique coupled to the Fourier Transform Infrared spectroscopy (ATR-FTIR) made possible to investigate the oxidation products originated by the ethanol oxidation, and all the electrocatalysts showed the presence of acetaldehyde, carbonate ions, acetate and carbon dioxide, suggesting that the mechanism of oxidation is incomplete. Among all the nanomaterials studied, PdSn(50:50)/C showed the best electrochemical and Fuel Cell's results. It is about 33% better than Pd/C. The micrographs obtained by Transmission Electron Microscopy (TEM) revealed some agglomerate regions, but they are consistent with the literature data.

Graphene-supported palladium phosphide PdP2 nanocrystals for ethanol electrooxidation

We present a procedure to produce single-phase PdP2 nanocrystals (NCs). The approach involves the reaction of palladium(II) acetylacetonate and hexamethylphosphoroustriamide to nucleate defective Pd5P2 nanoparticles that subsequently, with further phosphorous incorporation, crystallize into PdP2. The synthesized PdP2 NCs were supported on reduced graphene oxide (rGO) and applied as electrocatalysts for ethanol oxidation. The activity of PdP2 toward the ethanol oxidation reaction (EOR) was over a threefold higher than that of Pd NCs prepared under similar conditions. Even better performance was obtained from PdP2 NCs supported on rGO, which showed current densities up to 51.4 mA cm−2 and mass activities of 1.60 A mg-1Pd, that is 4.8 and 15 times higher than Pd NCs. Besides, PdP2 NCs and PdP2/rGO catalysts showed improved stability during EOR than Pd NCs and Pd/rGO.

High selectivity PtRh/RGO catalysts for ethanol electro-oxidation at low potentials: Enhancing the efficiency of CO2 from alcoholic groups

Conversion the ethanol into CO2 at low potential through CC bond cleavage is vital to further improve the utilization of ethanol in direct ethanol fuel cells. The addition of Rh into Pt lattice is considered as an efficient route to improve the CO2 selectivity during ethanol electro-oxidation. In this work, PtRh alloy nanoparticles with different element ratios supported on reduced graphene oxide (RGO) were synthesized. Among them, Pt1Rh1/RGO shows an ultrahigh mass activity of 0.285 A mgpt−1 at 0.4 V (vs.SCE), 2.48 times as high as that of commercial Pt/C. Results of high-resolution transmission electron microscopy (HRTEM) reveal that the supported Pt1Rh1 alloy nanoparticles are in cubic shape with preferential (100) orientation and high-density of step sites. Results of in-situ FTIR spectra indicate that the addition of Rh greatly alleviates the COad poisoning on Pt surface. CO2 was generated at a low potential of −0.10 V, and the CO2 selectivity is 16.2 times as high as that of commercial Pt/C at 0.40 V. In-situ FTIR spectra using isotopically-labeled ethanol further confirm the superior CO2 selectivity on Pt1Rh1/RGO under low potentials is derived from the addition of Rh and high-density of step sites, which facilitates the CC bond cleavage and the oxidation of alcoholic groups.

Palladium nanoparticles supported on mesoporous biocarbon from coconut shell for ethanol electro-oxidation in alkaline media

Palladium nanoparticles supported on carbon Vulcan XC72 (Pd/C) and biocarbon (Pd/BC) synthesized by sodium borohydride process were used as catalysts for ethanol electro-oxidation in alkaline media. The biocarbon (BC) from coconut shell with mesoporous and high surface area (792 m2 g−1) was obtained by carbonization at 900 °C and the hydrothermal treatment in a microwave oven. The D-band and G-band intensity ratio (ID/IG) from Raman analysis showed high disorder of the biocarbon, while X-ray photoelectron spectroscopy (XPS) suggests higher percentage of oxygen groups on the surface of biocarbon than of Vulcan XC72. From X-ray diffraction (XRD), it was observed peaks in 2θ degree related to the face centered cubic (fcc) structure of palladium and the mean crystallite sizes calculated based on the diffraction peak of Pd (220) were 5.6 nm for Pd/C and 5.3 nm for Pd/BC. Using Transmission Electron Microscope (TEM), it was observed particles well dispersed on both carbons support materials. The electrocatalytic activity of the materials was investigated by cyclic voltammetry (CV) and chronoamperometry (CA) experiments. The peak current density (on CV experiments) from ethanol electro-oxidation on Pd/BC was 50% higher than on Pd/C, while the current density measured at 15 min of CA experiments was 80% higher on Pd/BC than on Pd/C. The higher catalytic activity of Pd/BC might be related to the large surface area of the biocarbon (792 m2 g−1) vs (239 m2 g−1) of Vulcan carbon, the defects of the biocarbon structure and higher amount of oxygen on the surface than Carbon Vulcan XC 72.

Cyclic Penta-Twinned Rhodium Nanobranches as Superior Catalysts for Ethanol Electro-oxidation

Developing active and durable electro-catalysts toward ethanol oxidation reaction (EOR) with high selectivity toward the C-C bond cleavage is an important issue for the commercialization of direct ethanol fuel cell. Unfortunately, current ethanol oxidation electro-catalysts (e.g., Pt, Pd) still suffer from poor selectivity for direct oxidation of ethanol to CO2, and rapid activity degradation. Here we report a facile route to the synthesis of a new kind of cyclic penta-twinned (CPT) Rh nanostructures that are self-supported nanobranches (NBs) built with 1-dimension CPT nanorods as subunits. Structurally, the as-prepared Rh NBs possess high percentage of open {100} facets with significant CPT-induced lattice strains. With these unique structural characteristics, the as-prepared CPT Rh NBs exhibit outstanding electrocatalytic performance toward EOR in alkaline solution. Most strikingly, the selectivity of complete conversion ethanol to CO2 on the CPT Rh NBs is measured to be as high as 14.5 ± 1.1% at -0.15 V, far exceeding that for single-crystal tetrahedral nanocrystals, icosahedral nanocrystals, and commercial Rh black, as well as majority of reported values for Pt or Pd-based electro-catalysts. By combining with density functional theory calculation, the effects of different structural features of Rh on EOR are definitively elucidated. It was found that the large amount of open Rh (100) facets dominantly contribute to the outstanding activity and exceptionally high selectivity, while the additional tensile strain on (100) planes can further boost the catalytic activity by enhancing the adsorption strength and lowering the reaction barrier of dehydrogenation process of ethanol. As a proof of concept, the present work shows that rationally optimizing surface and electronic structure of electro-catalysts by simultaneously engineering their surface and bulk structures is a promising strategy to promote the performance of electro-catalysts.

Pd nanonetwork decorated on rGO as a high-performance electrocatalyst for ethanol oxidation

A three-dimensional palladium nanonetwork decorated on reduced graphene oxide (rGO) is synthesized by a simple and rapid method. In this method, graphene oxide (GO) is reduced on a glassy carbon electrode by Zn/HCl system. After reduction of GO to rGO, three dimensional Pd nanonetwork is fabricated on rGO by reduction of deposited PdCl2 using Zn/HCl system. The morphology and chemical composition of as-prepared 3-D Pd/rGO catalyst are characterized by scanning electron microscopy and energy dispersive spectroscopy, respectively. We revealed that the as-synthesized 3-D Pd nanonetwork shows excellent electrocatalytic activity and durability toward ethanol oxidation due to the formation of the 3-D nanonetwork and porous structure. The specific activity of 3-D Pd/rGO toward ethanol oxidation is 12.3 times higher than commercial Pd/C. Durability and tolerance to carbonaceous intermediates accumulation of the as-prepared catalyst are also greatly improved.

Nickel-Modified Co-Mo Electrocatalysts for Ethanol Oxidation in Alkaline Medium

As-deposited Co-Ni-Mo electrocatlyst on carbon support was investigated for the ethanol oxidation, and its activity was compared to that of Ni, Co, and bimetallic Co-Mo electrocatalysts. All electrocatalysts were prepared by electroless deposition method on carbon substrate support (CCS) made active for electroless deposition with Pd-ink. For ternary eletrocatalysts, the effects of electroless deposition time, reaction temperature (30-60°C) were studied. The result showed that CoNiMo/CCS was highly active in alkaline ethanol solution (0.5M NaOH+1 M EtOH) for ethanol oxidation. Furthermore, the reaction performances for all electrodes were investigated using cyclic voltammetry (CV). The result shows that Ni and Co electrodes showed not only oxidation peaks but also reduction peaks, which were typical behaviors for ethanol oxidation. For Co-Mo and Co-Ni-Mo electrodes provided the similar CV patterns. However, the current densities for tri-metallic electrode were higher than those from Co-Mo electrode. This suggests that the nickel has helped increase the reaction activity. Furthermore, the oxidation kinetics parameters, activation energy (Ea) and rate constant (k) were determined form CV, which were tested at different temperature and ethanol concentrations. Overall, this study provides a promising novel and effective non-noble Co-Ni-Mo electrocatalyst with an onset potential of -0.7 V (vs. Ag/AgCl).

Three-dimensional Pd-Cd nanonetwork decorated on reduced graphene oxide by a galvanic method as a novel electrocatalyst for ethanol oxidation in alkaline media

Two galvanic reduction steps and one galvanic displacement reaction are developed as a new and simple method for modification of glassy carbon electrode (GCE). The GCE was modified by a three-dimensional Pd-Cd nanostructure that decorated on reduced graphene oxide. For the preparation of the modified electrode, firstly deposited graphene oxide layer and cadmium (II) chloride on the GCE are reduced to graphene (rGO) and metallic cadmium, respectively by new strategy using Zn/HCl system. Then, three-dimensional palladium nanonetwork is created on the electrode by the galvanic displacement reaction. As-prepared catalyst has been characterized by the field emission scanning electron microscopy (FESEM), the energy-dispersive X-ray spectra (EDX), and the electrochemical measurements. The obtained peak current density of ethanol oxidation on the Pd-Cd/rGO is 179 mAcm−2, which is 4.47 times higher than that commercial Pd/C catalyst (40 mAcm−2).

Palladium Nanoparticles Anchored on Three-Dimensional Nitrogen-Doped Carbon Nanotubes as a Robust Electrocatalyst for Ethanol Oxidation

Palladium nanoparticles were uniformly anchored on nitrogen-doped carbon nanotubes with a three-dimensional network structure (denoted as Pd/3DNCNTs) through a facile, surfactant-free, and green approach with ethanol as the reducing agent. As a robust catalyst for the ethanol electrocatalytic oxidation reaction (EOR), Pd/3DNCNTs exhibit superior improved electrocatalytic activity, accelerated kinetics, and robust stability, mainly attributed to the unique architecture features of the 3DNCNTs. The results of this part of the work reveal that the Pd/3DNCNTs with an infusive electrochemical property for EOR are promising for direct ethanol fuel cells (DEFCs) and various other applications in electrochemistry. Additionally, the green approach probably provides some new ideas for the design of other new catalysts for fuel cells.