Tb promoted Pd/C catalysts for the electrooxidation of ethanol in alkaline media

Various Pd-Tb/C electrocatalysts with different Pd/Tb ratios were synthesized and tested for ethanol oxidation in alkaline media. The structure and morphology of the nanocatalysts were investigated using X-ray diffraction and transmission electron microscopy. The data showed that face-centered cubic structures were formed for all the Pd-Tb/C catalysts and a well dispersion of nanoparticles on carbon black was observed. The electrocatalytic properties of the catalysts for ethanol oxidation in alkaline solution were tested by cyclic voltammetry, linear sweep voltammetry and chronoamperometry techniques. It was found that Pd-Tb/C catalysts have higher activity and durability for ethanol oxidation than Pd/C. This may be attributed to the promotion effect of Tb on OH⁻ adsorption. The highest performance was observed for 10%Pd-2%Tb/C in terms of the highest activity, stability and lowest activation energy for ethanol oxidation.     

Sawtooth-shaped nickel-based submicrowires and their electrocatalytic activity for methanol oxidation in alkaline media

Sawtooth-shaped nickel and nickel-cobalt submicrowires were fabricated by hydrazine reduction of their salt precursors under magnetic field. The sawtooth-shaped submicrowires exhibited better electrochemical property in electrooxidation of methanol in alkaline media than nickel nanoparticles and smooth submicrowires because the sawtooth-shaped structure benefited more from both geometry of nanowires and nano-size effect. Therefore, the sawtooth-shaped nickel-based submicrowires synthesized in this work have the potential for use as a non-precious electrode catalyst for alkaline fuel cells.     

Tungsten nitride decorated CNTs as efficient hybrid supports for PtRh alloys in electrocatalytic ethanol oxidation

Direct ethanol fuel cells (DEFCs) offer an attractive alternative to fossil fuel-powered devices due to their high energy density and environmental benignity. However, high cost and poor stability of catalysts are still the main obstacles for the commercialization of DEFCs. Herein, a novel catalyst comprising PtRh alloys anchored on carbon nanotubes that decorated with tungsten nitride (Pt₉Rh-WN/CNTs) was synthesized via impregnation-reduction method and followed by thermal annealing in N₂. The X-ray powder diffraction (XRD), scanning electron micrograph (SEM) and transmission electron microscopy (TEM) are employed to characterize the corresponding physico-chemical properties of the as-prepared catalysts. Electrocatalytic performance for ethanol oxidation is evaluated by cyclic voltammetry, linear scan voltammetry, CO-stripping voltammograms, chronoamperometry and chronopotentiometry. The current density on Pt₉Rh-WN/CNTs is 484.8 mA mg_Pt^?1, which is much higher than that of Pt₉Rh/CNTs (305.7 mA mg_Pt^?1) and Pt/CNTs (135.1 mA mg_Pt^?1). Most importantly, the onset potential for CO oxidation on Pt₉Rh-WN/CNTs is 0.27 V, which is more negative than that on Pt₉Rh/CNTs (0.37 V) and Pt/CNTs (0.40 V). Therefore, the Pt₉Rh-WN/CNTs catalyst displays both outstanding catalytic activity and excellent CO-poisoning tolerance for ethanol oxidation. Synergistic effects arising between WN and PtRh alloy along with nitrogen-doping effects of CNTs with ammonia are proposed to contribute to the outstanding performance of this catalyst in ethanol oxidation.     

A perspective on the promoting effect of Ir and Au on Pd toward the ethanol oxidation reaction in alkaline media

There remain great challenges in developing highly efficient electrocatalysts with both high activity and good stability for the ethanol oxidation reaction in alkaline media. Herein, two architectures of tri-metallic PdIrAu/C electrocatalysts are designed and the promoting effect of Au and Ir on Pd toward the ethanol oxidation reaction (EOR) in alkaline media is investigated in detail. On the one hand, the tri-metallic Pd₇Au₇Ir/C electrocatalyst with a solid solution alloy architecture is less active relative to Pd₇Ir/C and Pd/C while the stabilizing effect of Au leads to both a higher activity and a lower degradation percentage after 3000 cycles of the accelerated degradation test (ADT) on Pd₇Au₇Ir/C than those on Pd₇Ir/C. On the other hand, the tri-metallic Pd₇Ir@(1/3Au)/C electrocatalyst with a near surface alloy architecture delivers a much higher activity with an improvement up to 50.4% compared to Pd₇Ir/C. It is speculated that for the tri-metallic Pd₇Ir@(1/3Au)/C electrocatalyst, certain Au atoms are well designed on surfaces to introduce an electronic modification, thus leading to an anti-poisoning effect and improving the EOR activity.     

Efficient one-dimensional Pt-based nanostructures for methanol oxidation reaction: An overview

The direct methanol fuel cells (DMFCs) have motivated researchers to conduct multifaceted investigations by the virtues of inexpensive raw material and high energy density. Tuning the morphology and composition of Pt-based catalysts with one-dimensional (1D) nanostructures has been proved to be determinant to design high-performance electrocatalysts towards methanol oxidation reaction (MOR) for DMFCs. Over the past decade, significant progress has been achieved in improving the MOR activity of Pt-based catalysts. Herein, this review briefly presents several typical 1D Pt-based nanostructures, including nanowires, nanorods, nanochains, and nanotubes, for their applications in the MOR process. Some classic instances are listed and detailed to assist readers in better recognizing the superiorities of 1D Pt-based nanostructures. This review firstly focuses on the mechanism of action and evaluation parameters of Pt-based catalysts in MOR, then the strategies employed to synthesize 1D Pt-based nanostructures are briefly summarized. The importance of rationally designing 1D Pt-based catalysts for performance enhancement is emphasized by the MOR application of various 1D nanostructures. Finally, the conclusion and outlook for future research directions in this field were proposed to motivate future challenges.     

Facile synthesis of AuPd nanowires anchored on the hybrid of layered double hydroxide and carbon black for enhancing catalytic performance towards ethanol electro-oxidation

Improving the catalytic performance of ethanol electro-oxidation reaction (EOR) is crucial for accelerating the commercialization of direct ethanol fuel cells (DEFCs). In this work, AuPd nanowires (NWs) anchored on the hybrid of layered double hydroxides and carbon black (CB) was prepared by a facile procedure for anode electrocatalyst of ethanol electro-oxidation reaction (EOR). For comparison, unloaded AuPd NWs and AuPd nanopaticles (NPs) supported on LDH-CB were also prepared. These catalysts were characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The performance of these catalysts was evaluated by the reactions of ethanol in alkaline media by cyclic voltammetry, chronoamperometric measurements and electrochemical impedance spectroscopy. It was found that the as-prepared AuPd NWs/LDH-CB demonstrated higher activity and stability than those of unloaded AuPd NWs, commercial Pd/C and AuPd NPs/LDH-CB attributed to the AuPd nanowires with more active sites, electronic structure of Pd modified by alloyed with Au and interacted with LDH-CB as well as the electron transfer ability facilitated by CB.     

Hybrid palladium-ceria nanorod electrocatalysts applications in oxygen reduction and ethanol oxidation reactions in alkaline media

Fossil fuel alternatives are being increasingly studied, and alkaline direct ethanol fuel cells (ADEFC) have acquired importance, as to ethanol is a renewable fuel. In this context, the aims of the present study were to synthesize, characterize and evaluate electrocatalytic activity in oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR) using hybrid electrocatalysts based on Pd nanoparticles and CeO₂ nanorods supported on carbon black for application in ADEFC. The highest OCV, maximum current and power densities obtained using Pd₁₅(CeO₂ NR)₁₀(Vn)₇₅ as the cathode and Pd₁₀(CeO₂ NR)₂₀(Vn)₇₀ as the anode were 1270 mV, 190 mA cm^?2 and 65 mW cm^?2, respectively. These interesting results are justified by the highest I_D/I_G ratio and ECSA, which suggest a high number of oxygenated species, defects and vacancies in these electrocatalysts and by the synergistic effect between CeO₂ NR and Pd nanoparticles. Therefore, these hybrid electrocatalysts are promising for ADEFC applications.     

Novel nanocrystalline PdNi alloy catalyst for methanol and ethanol electro-oxidation in alkaline media

Nanocrystalline Pd₄₀Ni₆₀ alloy catalyst has been fabricated by dealloying a ternary Al₇₅Pd₁₀Ni₁₅ alloy in a 20 wt.% NaOH aqueous solution under free corrosion conditions. The microstructure and catalytic performance of the catalyst have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and cyclic voltammetry. The Pd₄₀Ni₆₀ alloy consists of nanocrystals with sizes of 5-10 nm, and Pd/Ni elements exist in a solid solution form. Moreover, nanocrystalline zones, amorphous zones and lattice distortion can be observed in the Pd₄₀Ni₆₀ alloy. Electrochemical measurements demonstrate that, for equivalent mass Pd, Pd₄₀Ni₆₀ has an enhanced electrocatalytic performance towards methanol and ethanol oxidation in alkaline media than nanoporous Pd. The nanocrystalline Pd₄₀Ni₆₀ alloy is a promising catalyst towards alcohol oxidation in alkaline media for fuel cell applications.     

Design the PdCu/Ni2P electrocatalyst with high efficiency for ethanol oxidation reaction in alkaline media

To facilitate the electrocatalytic behavior of Direct Ethanol Fuel Cells (DEFCs), a sequence of bimetallic Pd_xCu_y/Ni₂P-C catalysts are synthesized via the microwave-assisted ethylene glycol reduction method. The results indicate that our designed Pd₂Cu/Ni₂P-C(1:1) catalyst owns high activity (3974.08 mA mg^?1_Pd), 8.3 times higher than the commercial Pd/C. The durability and the CO tolerance of the corresponding catalysts are also investigated by chronoamperometry (CA) and CO stripping measurements, implying Pd₂Cu/Ni₂P-C(1:1) shows good durability and the anti-CO poisoning ability for EOR in alkaline media. The electrochemical impedance spectra (EIS) analysis reveals lower charge transfer resistance for Pd₂Cu/Ni₂P-C(1:1). Combined with the results of XRD, HRTEM, XPS and electrochemical measurements, we found that the good electrocatalytic activity, CO tolerance and long-term durability of Pd₂Cu/Ni₂P-C(1:1) may be provided by the electronic and strain effect among Pd, Cu and Ni₂P, which will bring the downshift in the d-band center of catalysts and the weakened adsorption of intermediates.     

Microwave assisted synthesis of nitrogen doped and oxygen functionalized carbon nano onions supported palladium nanoparticles as hybrid anodic electrocatalysts for direct alkaline ethanol fuel cells

In this study, we present the synthesis of pristine carbon (p-CNO), nitrogen doped (N–CNO) and oxygen functionalized (ox-CNO) nano onions, using flame pyrolysis, chemical vapour deposition, and reflux methods, respectively. Pd/p-CNO, Pd/N–CNO and Pd/ox-CNO electrocatalysts are prepared using a simple and quick microwave-assisted synthesis method. The various CNO and Pd/CNO electrocatalysts are fully characterized and the FTIR and XPS results reveal that the synthesized CNOs contain oxygen and nitrogen functional groups that facilitates the attachment and dispersion of the Pd nanoparticles. Electrochemical tests show that the N–CNO and Pd/N–CNO electrocatalysts exhibit high current density (4.2 mA cm ^?2 and 17.4 mA cm ^?2), long-term stability (1.2 mA cm ^?2 and 6.9 mA cm ^?2), and fast electron transfer when compared to the equivalent pristine and oxidized catalysts (and their Pd counterparts), and a commercial Pd/C electrocatalyst, towards ethanol oxidation reactions in alkaline medium.     

Synthesis and characterization the multifunctional nanostructures TixW1-xO2 (x = 0.5; 0.6; 0.7; 0.8) supports as robust non-carbon support for Pt nanoparticles for direct ethanol fuel cells

In the present study, various mesoporous Ti_xW_1-xO₂ (x = 0.5; 0.6; 0.7; 0.8) supports were fabricated via a facile solvothermal approach and explored the effect of doping tungsten concentration on electrochemical properties of Ti_xW_1-xO₂-supported Pt electrocatalysts toward ethanol electrochemical reaction. Interestingly, the incorporation of tungsten into TiO₂ lattices with the doping tungsten amounts (20 and 30 at %) resulted in boosting both the surface area and electrical conductivity, however, a reverse trend was observed when increasing the doped tungsten content more than 40 at %. Additionally, the relatively well-distributed Pt nanoparticles with the small particle size (ca. 3 nm) anchored on supports were achieved using a microwave-assisted polyol route. Electrochemical results indicated that various Ti_xW_1-xO₂-supported Pt catalysts exhibited the catalytic performance greater than that of the commercial carbon-supported Pt (E-TEK) catalyst for ethanol electro-oxidation reaction (EOR). For as-obtained electrocatalysts, the Ti_0.7W_0.3O₂-supported Pt catalyst showed the highest mass activity (~260.23 mA/mg_Pt) and greatest I_f/I_b ratio (~1.34), which ~2.0-fold and ~1.57-time higher than that of carbon-supported Pt (E-TEK) catalyst (~130.62 mA/mg_Pt for mass activity and ~0.85 for I_f/I_b ratio, respectively). After 5000 cycling tests, the mass activity loss of Ti_xW_1-xO₂-supported Pt catalysts was around twice lower than that of the commercial Pt/C (E-TEK) catalysts, suggesting that the Ti_xW_1-xO₂-supported Pt catalysts exhibited the superior stability toward ethanol electrochemical oxidation. The outstanding electrochemical activity and stability of Ti_xW_1-xO₂-supported Pt electrocatalysts were owing to the synergetic effect between Pt nanocatalyst and non-carbon Ti_xW_1-xO₂ supports as well as superior natural durability of TiO₂-based materials.     

Pt supported on mesoporous material for methanol and ethanol oxidation in alkaline medium

Pt nanoparticles supported on a mesoporous material of zeolite Faujasite-C composite is a highly active catalyst for methanol and ethanol oxidation in alkaline media. Pt was synthesized by a simple methodology of chemical reduction using ultrasound method. Faujasite-C composite was prepared by sol-gel method using fly ash as economic precursor. Pt/Faujasite-C was characterized by X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopy to investigate its structure, morphology, composition and size. The electrochemical activity of catalyst towards methanol and ethanol oxidation reaction in alkaline media was evaluated by cyclic voltammetry and chronoamperometry techniques. The results obtained were compared with Pt/C synthesized and tested at the same conditions. According to TEM results Pt/Faujasite-C electrocatalyst exhibits a higher Pt agglomeration compared to Pt/C. Pt/Faujasite-C is more active for alcohol oxidation reactions compared to Pt/C. Pt electrocatalysts are more active for ethanol oxidation than methanol oxidation. Chronoamperometric results indicated that Pt deactivation by intermediate poisoning is more severe for ethanol than methanol. Pt/Faujasite-C can be used as anodic electrocatalyst in direct liquid fuel cells.     

Pd/Hemin-rGO as a bifunctional electrocatalyst for enhanced ethanol oxidation reaction in alkaline media and hydrogen evolution reaction in acidic media

H₂ generation needs a cost-effective, robust, stable, long-durable, and super-active electrocatalyst. This study reveals a rapid and facile method for fabricating Pd NPs on Hemin-rGO as novel support. The obtained electrocatalyst was characterized by UV–Vis, XPS, FESEM, EDS, HRTEM, and AFM. The electrochemical measurements reveal the superb effect of Hemin-rGO for enhancing the catalytic activity of Pd as bifunctional electrocatalysts for hybrid water electrolysis (hydrogen evolution reaction (HER) and ethanol electrooxidation reaction (EOR)). Pd/Hemin-rGO displays a low peak potential (−210 V) with remarkable current density (1.95 A mg⁻¹ Pd) in 0.1 M EtOH and 0.1 M NaOH. The ratio of j_f/j_b of Pd/Hemin-rGO compared with Pd electrocatalyst reveals this novel support's ani-poisoning effect. Besides, it shows the Tafel slope of 26 mV dec⁻¹ and overpotentials of 47 and 131 mV were obtained at 10 and 100 mA cm⁻² in acidic media toward HER. Exploring and designing new electrocatalysts may be enhanced by this research, which can use Hemin as a novel support for noble metals such as Pt, Pd, Rh, Au, and Ru for diverse energy-related applications.     

Enhanced electrocatalytic activity and stability of Pd nanoparticles supported on TiO2-modified nitrogen-doped carbon for ethanol oxidation in alkaline media

TiO₂-modified nitrogen-doped carbon (TiO₂-NC), prepared by a polymerization-pyrolysis process, is used to support the Pd catalyst for ethanol oxidation reaction (EOR) in alkaline media. X-ray photoelectron spectroscopy characterization indicates that the incorporation of TiO₂ and nitrogen into the carbon matrix could improve the percentage of Pd⁰ in Pd/TiO₂-NC catalyst. Electrochemical characterization shows that the Pd/TiO₂-NC catalyst presents higher electrocatalytic activity and stability for EOR than the nitrogen-doped carbon-supported Pd (Pd/NC) catalyst and the carbon black-supported Pd (Pd/CB) catalyst, which can be mainly attributed to the high percentage of Pd⁰ in Pd/TiO₂-NC catalyst (65%) than those in Pd/NC (48%) and Pd/CB (31%) catalysts. The results indicate that the Pd/TiO₂-NC catalyst holds great potential as high-performance anode catalyst for direct ethanol fuel cells.     

PtxSn/C electrocatalysts synthesized by improved microemulsion method and their catalytic activity for ethanol oxidation

The Pt_xSn/C (x = 1, 2, 2.5, 3, 4) anodic catalysts for direct ethanol fuel cell (DEFC) have been prepared by an improved microemulsion method. Ethylene glycol is used as cosurfactant, and metal precursors are dissolved in it beforehand to prevent the hydrolysis of metal precursors. The composition, particle size and structure of these catalysts are characterized by energy dispersive X-ray spectrum (EDX), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results show that the synthesized Pt₃Sn/C catalyst has part of Pt and Sn alloying. The average diameter is about 2.9 nm, and has a narrow size distribution and a good dispersivity. The electrochemical experiments indicate that the Pt₃Sn/C catalyst prepared in the neutral microemulsion has superior catalytic activity for ethanol oxidation. The Pt_xSn/C nanoparticle formation in the improved microemulsion is also discussed.     

Preparation and characterization of nano-sized Pt–Pd/C catalysts and comparison of their electro-activity toward methanol and ethanol oxidation

In the present work nano-sized Pt–Pd alloys have been prepared by polyol process on Vulcan XC72. The information on structural characteristics and surface chemistry of the nano-material was obtained using TEM, XRD and XPS.     

Preparation and electrocatalytic characteristics of the Pt-based anode catalysts for ethanol oxidation in acid and alkaline media

The current study reports the preparation and investigation of several Pt-based anode catalysts loaded on reduced graphene oxide (rGO) as electrocatalysts in both acid and alkaline media for ethanol electrooxidation. The synthesized catalysts are evaluated by the method of XRD, Raman spectroscopy, XPS and TEM. Electrocatalytic properties of these catalysts for ethanol oxidation were investigated by cyclic voltammetry and chronoamperometry. It was found that the as-prepared nanocatalysts doped by metals and oxide metals showed the improvement of catalytic performance compared to Pt-only supported on graphene catalyst. The results indicated that the presence of Al favoured Pt nanoparticles dispersing on the surface of rGO sheets. Indeed, the PAG catalyst exhibits the highest mass activity for the ethanol oxidation of 1194 mA mg^?1_Pt in acid medium and 3691 mA mg^?1_Pt in alkaline medium. In addition, the PAG catalyst also shows good antipoisoning ability for ethanol electrooxidation in both media. This catalyst could be a potential catalyst for direct ethanol fuel cell (DEFC).     

Pd/Cu bimetallic nanoparticles supported on graphene nanosheets: Facile synthesis and application as novel electrocatalyst for ethanol oxidation in alkaline media

Well distributed Pd/Cu bimetallic nanoparticles supported on graphene nanosheets as novel electrocatalyst has been prepared via a facile synthetic method: started with an electroless deposition route to anchor Cu nanoseeds on graphene nanosheets, followed by a latter displacement reaction to achieve Pd/Cu overlaying nanostructure. The loading density and morphology of bimetallic nanoparticles on graphene are varied by adjusting the initial amount of Cu precursor and reducing agent proportionally. Scanning transmission electron microscopy (STEM) images combining energy dispersive X-ray spectroscopy (EDX) mapping results confirm the existance and distribution of Pd and Cu in the bimetallic nanoparticles, while transmission electron microscopy (TEM) reveals the nanoparticle size and overlaying nanostructure. Cyclic voltammograms tests for the hybrid electrocatalysts in 1.0 M KOH solution show a gradual increase of electrochemically active surface area (EASA) against the increment of nanoparticle loading. Meanwhile, a significantly enhanced tolerance to poisoning of electrocatalyst is observed by cyclic voltammograms curves for ethanol electrooxidation in alkaline media with high I_f/I_b ratios compared to previous research. The large enhancement on I_f/I_b ratios of the hybrid electrocatalysts can be ascribed to the well distributed overlaying bimetallic nanostructure supported on graphene nanosheets. The facilely prepared Pd/Cu/graphene hybrid materials demonstrate vastly superior electrocatalytic properties compared to the commercial Pd/C catalyst, indicating a great potential in fuel cells application.     

Evaluation of the catalytic activity of Pd-Ag alloys on ethanol oxidation and oxygen reduction reactions in alkaline medium

Pd-Ag alloys containing different amounts of Ag (8, 21 and 34 at.%) were prepared in order to evaluate their catalytic activity towards the ethanol oxidation (EOR) and oxygen reduction (ORR) reactions. A sequential electroless deposition of Ag and Pd on a stainless steel disc, followed by annealing at 650 °C under Ar stream, was used as the alloy electrode deposition process.From half-cell measurements in a 1.0 M NaOH electrolyte at ≅20 °C, it was found that alloying Pd with Ag leads to an increases of the ORR and EOR kinetics, relative to Pd. Among the alloys under study, the 21 at.% Ag content alloy presents the highest catalytic activity for the EOR and the lowest Ag content alloy (8 at.% Ag) shows the highest ORR activity. Moreover, it was found that the selectivity of Pd-Ag alloys towards ORR is sustained when ethanol is present in the electrolyte.     

Preparation, characterization and application of Pt-Ru-Sn/C trimetallic electrocatalysts for ethanol oxidation in direct fuel cell

This work aimed to develop a method for the preparation of carbon-supported platinum nanocatalysts modified with Ruthenium and Tin, which were then evaluated for ethanol eletrooxidation in direct fuel cells. The Pechini method was employed to obtain these catalysts. This method consists in the decomposition of a polymeric precursor of metal salts. Nanocatalysts containing different Pt/Ru/Sn molar ratios were prepared by keeping the carbon/metal ratio at a constant value of 60/40%. The obtained nanoparticles were physico-chemically characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and Energy Dispersive X-ray Spectroscopy (EDX). Crystallite size of around 7.0 nm and 5.8 nm were achieved for the bimetallic and trimetallic nanocatalysts, respectively. The experimental composition was close to the nominal one, but the metal particles were not evenly distributed on the carbon surface. Electrochemical characterization of the nanoparticles was accomplished by cyclic voltammetry (CV) and chronoamperometry. High Performance Liquid Chromatography (HPLC) was carried out after ethanol electrolysis for determining the products generated. Acetaldehyde was the main electrolysis product and traces of CO₂ and acetic acid were also detected. Addition of Ru and Sn to the pure Pt nanoelectrocatalyst significantly improved its performance in ethanol oxidation. The onset potential for ethanol electrooxidation was 0.2 V vs. RHE, in the case of the trimetallic nanocatalyst Pt_0.8Ru_0.1Sn_0.1/C, which was lower than that obtained for the pure Pt catalyst (0.45 V vs. RHE).