Fuel cell and electrochemical studies of the ethanol electro-oxidation in alkaline media using PtAuIr/C as anodes

Ethanol electro-oxidation reaction was investigated considering conventional electrochemical experiments in alkaline media, direct ethanol fuel cell (DEFC), and in situ ATR-FTIR. The working electrode/anodes were composed of monometallic Pt/C, Au/C, Ir/C, and trimetallic PtAuIr/C nanoparticles with atomic Pt/Au/Ir ratios of 40:50:10, 50:40:10, 60:30:10, 70:20:10, and 80:10:10. X-ray diffraction (XRD) suggests PtAuIr/C alloy formation, and according to transmission electron micrographs, the mean particle sizes are from 4 to 6 nm for all catalyst compositions. PtAuIr/C 40:50:10 showed the highest catalytic activity for ethanol electro-oxidation in the electrochemical experiments; using this material, the peak current density from ethanol electro-oxidation on cyclic voltammetry experiment was 50 mA per g of Pt, 3.5 times higher than that observed with Pt/C. The fuel cell performance was superior using all PtAuIr/C compositions than using Pt/C. Au/C and Ir/C presented very poor catalytic activity toward ethanol electro-oxidation. The improved results obtained using PtAuIr/C might be related to the OH_ads species formed at low overpotential on Ir and to the decrease on adsorption energy of poisoning intermediates on Pt sites, promoted by Au.     

An effective electrocatalyst for ethanol oxidation: Pt-modified IrCu alloy nanoparticle

There is a growing interest in ethanol oxidation electrochemistry as it plays an important role in renewable energy technologies. The goal of this work was to develop active multifunctional catalyst materials for ethanol oxidation. Here, a carbon-supported Pt-modified IrCu alloy electrocatalyst (Pt–IrCu/C) was prepared by a two-step method. X-ray diffraction and transmission electron microscope showed that the Pt–IrCu/C has a two-phase structure: Pt nanoparticle-modified IrCu alloy. The Pt–IrCu/C catalyst was found to have not only a large electrochemically active specific area (S _EAS) but also good CO oxidation ability for oxidation of ethanol compared to the commercial Pt/C electrocatalyst using cyclic voltammetry. Furthermore, the Pt current density of Pt–IrCu/C was more than 1.6 times as high as that of Pt/C for ethanol oxidation. The Pt–IrCu/C catalyst also exhibited more efficient usage of Pt and enhanced the stability of ethanol electro-oxidation compared with a Pt/C catalyst.     

Electrochemical characterization of platinum-based anode catalysts for membraneless fuel cells

In the present work, carbon-supported Pt–Sn, Pt–Ru, and Pt–Sn–Ru electrocatalysts with different atomic ratios were prepared by alcohol-reduction method to study the electro-oxidation of ethanol in membraneless fuel cells. The synthesized electrocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses. The prepared catalysts had similar particle morphology, and their particle sizes were 2–5 nm. The electrocatalytic activities were characterized by cyclic voltammetry (CV) and chronoamperometry (CA). The electrochemical results obtained at room temperature showed that the addition of Sn and Ru to the pure Pt electrocatalyst significantly improved its performance in ethanol electro-oxidation. The onset potential for ethanol electro-oxidation was 0.2 V vs. Ag/AgCl, in the case of the ternary Pt–Sn–Ru/C catalysts, which was lower than that obtained for the pure Pt catalyst (0.4 V vs. Ag/AgCl). During the experiments performed on single membraneless fuel cells, Pt ? Sn ? Ru/C (70:10:20) performed better among all the catalysts prepared with power density of 36 mW/cm². The better performance of ternary Pt–Sn–Ru/C catalysts may be due to the formation of a ternary alloy and the smaller particle size.     

不同温度下乙醇电氧化过程的原位红外光谱研究

直接乙醇燃料电池因其优异的性能备受关注。乙醇的电催化氧化并非简单的燃烧,涉及多种催化反应过程。乙醇的C-C键断裂选择性低,以及乙醇氧化中间产物C1分子由于没有及时氧化离开催化剂表面而造成的催化剂中毒,是制约其应用的瓶颈问题。电化学原位红外光谱是在电化学反应的同时,原位采集反应物种特定官能团的振动信息,可在分子水平揭示反应过程,推测反应机理。不同温度条件下乙醇电氧化过程的研究,有助于合理的设计高性能乙醇燃料电池催化剂。选用高性能的PtRh/RGO催化剂,结合同位素示踪法和电化学原位红外光谱技术,研究了不同温度下乙醇的电氧化过程。循环伏安研究表明,乙醇电氧化性能及其C-C键断裂的程度为PtRh/RGO (45℃)>PtRh/RGO (25℃)>商业Pt/C。电化学原位红外光谱从分子水平跟踪了乙醇的电氧化过程,观察到随着电位的增加, CO2, CO,-CH3,-C-O特征峰的强度逐渐增加。CO2和CH3COOH分别归属于乙醇完全氧化和不完全氧化的终产物,因此红外光谱中两种物质特征峰积分面积的比值[CO2]/[CH3COOH]可做为CO2选择性的量度。用来定量标定CH3COOH的特征峰是位于1 280 cm-1的-C-O振动峰,但对于PtRh/RGO催化剂的红外光谱而言,它的乙酸特征峰振动峰位1 280 cm-1附近出现1 214 cm-1甲醇衍生物的振动峰,通过一种反射红外光谱与标样透射红外光谱差减扣除叠加峰方法,定量计算了叠加峰中1 280 cm-1特征峰的积分强度,从而计算出PtRh/RGO的CO2选择性。结果表明对比25℃时, 45℃下PtRh/RGO具有更高的选择性, 0.3 V时提高48.1%, 0.5和0.6 V时略有提高, 0.4 V时降低,这可能是乙醇中β-C和水中OH竞争吸附所致。在两种反应温度条件下, CO2选择性都在电位高于0.4 V时呈现下降趋势。为了进一步研究CO2来源于α-C或β-C的完全氧化,使用同位素标记的13CH312CH2OH做为探针分子,通过电化学原位红外光谱研究了25和45℃下PtRh/RGO电极上乙醇电氧化过程。结果表明,β-C完全氧化为CO2的起始电位与温度无关,都为0.3 V。通过用13CO2/12CO2积分面积的比值定量分析,发现45℃下,该比值在电位0.3~0.5 V时相比于25℃下分别增加0.11, 0.18和0.22,表明随着温度或电位的增加,β-C完全氧化的选择性增加。     

Electro-oxidation of ethanol using PtRuBi/C electrocatalyst prepared by borohydride reduction

Pt/C, PtRu/C, PtBi/C, and PtRuBi/C electrocatalysts (20 wt.% metal loading) were prepared by borohydride reduction using H₂PtCl₆·6H₂O, RuCl₃·xH₂O, and Bi(NO₃)₃·5H₂O as metal sources and Vulcan XC 72 as support. The electrocatalysts were characterized by energy-dispersive X-ray analysis, X-ray diffraction, and thermogravimetric analysis. The electro-oxidation of ethanol was studied in sulfuric acid solution by cyclic voltammetry and chronoamperometry. The electrochemical studies showed that PtRuBi/C (50:40:10) electrocatalyst has superior performance for ethanol electro-oxidation at room temperature compared to the other electrocatalysts. Preliminary tests at 100 °C on a single direct ethanol fuel cell also confirm the results obtained by electrochemical techniques.     

Electrodeposition of platinum on tourmaline and application as an electrocatalyst for oxidation of methanol

A composite electrode of Pt nanoparticles coupled with tourmaline is prepared on glassy carbon (GC) disk electrode via electrodeposition. The nanocomposite of Pt/tourmaline is characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, and transmission electron microscopy examinations linked with energy dispersive X-ray analysis. The electrocatalytic performance of the composite electrode (Pt/tourmaline/GC) is investigated in electrocatalysis oxidation of methanol at room temperature by cyclic voltammetry and chronoamperometry. It is indicated that Pt nanoparticles with size of ∼5 nm are uniformly assembled along the tourmaline particles and Pt exists in metallic and oxidated states confirmed by XPS. The results of electro-oxidation of methanol show that Pt/tourmaline catalyst is catalytically more active and stable than platinum-modified GC electrode, and the onset potential of Pt/tourmaline shifts 0.15 V to the negative side, and also the current density is significantly enhanced.     

碳载PtSn催化剂上乙醇电氧化的原位时间分辨红外光谱研究

采用调变的多元醇法制备了高分散碳载PtSn催化剂(PtSn/C),XRD测试结果表明金属粒子的平均粒径为2.2 nm,略小于Pt/C催化剂,而晶格参数相对增大。通过电化学原位时间分辨红外光谱研究了乙醇在PtSn/C催化剂上的吸附和氧化过程,表明线性吸附态CO(CO_L)是主要的乙醇解离吸附物种,导致催化剂中毒,阻止反应继续进行;当电位增大到0.3 V时,出现了乙醛和乙酸的红外吸收峰,作为乙醇解离吸附的竞争反应,乙醛和乙酸的生成有效抑制了催化剂中毒,随着电位的增大和时间的延长,生成乙酸的选择性增大;电位进一步增大至0.4 V时有微弱CO₂吸收峰出现,是乙醇电氧化的最终产物,主要来自于CO_L的氧化消耗。根据实验结果讨论了PtSn/C催化剂上乙醇的电催化氧化机理。     

Investigation of a Pt–Fe/C catalyst for oxygen reduction reaction in direct ethanol fuel cells

Three cathode catalysts (60% Pt/C, 30% Pt/C and 60% Pt–Fe/C), with a particle size of about 2–3 nm, were prepared to investigate the effect of ethanol cross-over on cathode surfaces. All samples were studied in terms of structure and morphology by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Their electrocatalytic behavior in terms of oxygen reduction reaction (ORR) was investigated and compared using a rotating disk electrode (RDE). The tolerance of cathode catalysts in the presence of ethanol was evaluated. The Pt–Fe/C catalyst showed both higher ORR activity and tolerance to ethanol cross-over than Pt/C catalysts. Moreover, the more promising catalysts were tested in 5 cm² DEFC single cells at 60 and 80 °C. An improvement in single cell performance was observed in the presence of the Pt–Fe catalyst, due to an enhancement in the oxygen reduction kinetics. The maximum power density was 53 mW cm⁻² at 2 bar rel. cathode pressure and 80 °C.     

High catalytic performance of Pt nanoparticles on plasma treated carbon nanotubes for electrooxidation of ethanol in a basic solution

Nanosized Pt particles deposited on plasma treated multi-walled carbon nanotubes have been used in electrocatalytic oxidation of ethanol in a basic solution. These Pt nanoparticles have very narrow size distribution and exhibit significant higher catalytic activities, higher Pt utilization efficiency (93.77%) and improved durability in comparison to the commercial available Johnson Matthey Pt/C catalyst.     

Preparation of cholesterol oxidase nanoparticles and their application in amperometric determination of cholesterol

Highly dispersed platinum nanoparticles were deposited on gram quantities of non-functionalized multiwalled carbon nanotubes (MWCNTs) by atomic layer deposition (ALD) in a fluidized bed reactor at 300 °C. (Methylcyclopentadienyl) trimethylplatinum and oxygen were used as precursors. The results of TEM analysis showed that ~1.3 nm Pt nanoparticles were highly dispersed on non-functionalized MWCNTs. The porous structures of MWCNTs did not change with the deposition of Pt nanoparticles. For comparison, the commercial 3 wt% Pt/C catalyst was also characterized. The ALD-prepared Pt/MWCNT was used for the hydrogenation of xylose to xylitol. The ALD-prepared Pt/MWCNT showed the best catalytic performance with 100 % conversion of xylose and 99.3 % selectivity to xylitol, compared to commercially available Pt/C, Ru/C, and Raney Ni catalysts. The stability of ALD produced Pt/MWCNT catalyst was higher than that of the commercial Pt/C, due to the presence of surface defects on the MWCNTs and the strong metal–support interaction for the ALD-prepared Pt/MWCNT catalyst.     

Palladium nanoparticles supported on phosphorus-doped carbon for ethanol electro-oxidation in alkaline media

Palladium nanoparticles supported on carbon Vulcan XC72 (Pd/C) and on phosphorus-doped carbon (Pd/P-C) were prepared by an alcohol reduction process. X-ray diffractograms of Pd/C and Pd/P-C showed the typical face-centered cubic (fcc) structure of Pd. The crystallite sizes of Pd fcc phase were around 8 nm for both samples. X-ray photoelectron spectroscopy revealed to Pd/C and Pd/P-C that Pd was found predominantly in the metallic state and to Pd/P-C, the presence of P increases the amount of oxygen on the electrocatalyst surface. The activity and stability of the electrocatalyts for ethanol electro-oxidation in alkaline medium was investigated by cyclic voltammetry and chronoamperometry experiments. The peak current density on Pd/P-C was 50% higher than on Pd/C, while the current density measured after 30 min at ? 0.35 V vs. Hg/HgO was 65% higher on Pd/P-C than on Pd/C. The enhancement of the catalytic activity of Pd/P-C electrocatalyst might be related to the presence of higher amounts of oxygen species on the surface, which could contribute to the oxidation of intermediates formed during ethanol electro-oxidation process.     

Bimetallic alloy Pt/Ag nanoparticles with enhanced catalytic activity for formic acid oxidation

Here, we report the synthesis of Pt/Ag bimetallic alloy catalyst through combining the ion implantation and electrodeposition method. Ag nanoparticles are employed as the seeds for the growth of Pt nanoparticles. Pt/Ag alloy catalyst demonstrates much higher catalytic activity than pure Pt catalyst, which is about three times more active on the basis of equivalent Pt electrochemically active surface area than that of the pure Pt catalyst. The ion implantation of Ag efficiently enhances the catalytic activity of Pt catalyst for formic acid oxidation.     

Performance characteristics of dye-sensitized solar cells with counter electrode based on NiP-plated glass and titanium plate

The counter electrodes based on NiP-plated glass and titanium plate were prepared. The performance characteristics of the dye-sensitized solar cells with platinized NiP-plated glass electrode (Pt/NiP electrode) and platinized titanium plate electrode (Pt/TP electrode) were discussed. Pt/NiP electrode and Pt/TP electrode showed the same catalytic activity for triiodide reduction compared with platinized fluorine-doped tin oxide conducting glass electrode (Pt/FTO electrode). However, Pt/NiP electrode and Pt/TP electrode have the advantage over Pt/FTO electrode in reducing the sheet resistance and increasing light reflectivity, which resulted in improving the photovoltaic performance of dye-sensitized solar cells effectively. Compared with the cell using Pt/FTO electrode, the incident photon conversion efficiency of dye-sensitized solar cells with Pt/NiP electrode and Pt/TP electrode was increased by 20% and 5%, respectively, the overall energy efficiency of dye-sensitized solar cells with Pt/NiP electrode and Pt/TP electrode was increased by 32% and 27%, respectively.     

Effect of the degree of alloying of PtRu/C (1:1) catalysts on ethanol oxidation

The effect of alloying degree on the ethanol oxidation activity of a PtRu/C catalyst with a Pt/Ru atomic ratio of 1:1 was investigated by measurements in a half-cell and in a single direct ethanol fuel cell. The increase of the amount of Ru alloyed from one third to two thirds of the total Ru content in the catalyst clearly resulted in a decrease of the ethanol oxidation activity. As the amount of the highly active hydrous ruthenium oxide was near the same, the lower activity of the PtRu/C catalyst with higher alloying degree was mainly ascribed to the presence of an excessive number of Ru atoms around Pt active sites, hindering ethanol adsorption on Pt sites. The reduced ethanol adsorption could be also related to the decreased Pt–Pt bond distance and to the electronic effects by alloying.     

Template preparation of Pt nanowire array electrode on Ti/Si substrate for methanol electro-oxidation

Platinum (Pt) nanowire array electrode is obtained by dc electrodeposition of Pt into the pores of anodic aluminum oxide (AAO) template on Ti/Si substrate. Transmission electron microscope (TEM) examination shows all the nanowires have uniform diameter of about 30 nm. The brush shapes Pt nanowire array electrode can be seen clearly by field emission scanning electron microscope (FESEM). Pt nanowire array electrode gives the X-ray diffraction (XRD) pattern of face-centered cubic (fcc) crystal structure. The electro-oxidation of methanol on this electrode is investigated at room temperature by cyclic voltammetry. The results demonstrated that the Pt nanowire array electrode will have good potential applications in portable power sources.     

A comparative study for the electrocatalytic oxidation of alcohol on Pt-Au nanoparticle-supported copolymer-grafted graphene oxide composite for fuel cell application

The platinum-gold bimetallic nanoparticles supported poly(cyclotriphosphazene-co-benzidine)-grafted graphene oxide (poly(CP-co-BZ)-g-GO) composite has been prepared for electrochemical performance studies. Cyclic voltammetry and chronoamperometric studies were carried out to check the electrochemical properties of Pt-Au/poly(CP-co-BZ)-g-GO and Pt/poly(CP-co-BZ)-g-GO catalysts for methanol, ethylene glycol and glycerol in alkaline medium. The morphology and crystalline structure of the prepared Pt-Au/poly(CP-co-BZ)-g-GO and Pt/poly(CP-co-BZ)-g-GO and catalysts have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FT-IR). From the electrochemical results, it was concluded that Pt-Au/poly(CP-co-BZ)-g-GO catalyst shows higher catalytic activity and stability compared to Pt/poly(CP-co-BZ)-g-GO catalyst. The catalytic activity of Pt/poly(CP-co-BZ)-g-GO catalyst has been compared with Pt/poly(CP-co-BZ), Pt/GO and Pt/C catalysts. In addition, oxidation current of ethylene glycol is higher than the methanol and glycerol in alkaline medium on the prepared catalyst.     

Binary-surfactant (Brij 35 + Tween 20) assisted preparation of highly dispersed Pt nanoparticles on carbon

Pt nanoparticles supported on Vulcan XC-72R, synthesized by a surfactant-stabilized colloidal method, exhibited excellent properties as anode catalyst for low-temperature fuel cell. The Pt/C catalyst prepared with binary-surfactant (Brij 35 + Tween 20) at 10 times CMC had an average particle size of 2.8 nm with quite a narrow distribution between 2 and 4 nm. Our preparation method resulted in complete reduction of Pt and full loading of Pt nanoparticles on the carbon. The home-made Pt/C catalyst showed higher EAS and better catalytic activity than a commercial Pt/C catalyst. The method used in this study provided an easy and reproducible procedure for the preparation of Pt nanoparticles supported on carbon.     

Synthesis of Pt-Ni-Fe/CNT/CP nanocomposite as an electrocatalytic electrode for PEM fuel cell cathode

In order to use carbon nanotube (CNT)-supported catalyst as fuel cell electrodes, Pt-Ni-Fe/CNT/carbon paper (CP) electrode was prepared using an ethylene glycol reduction method. CNTs were directly synthesized on Ni-impregnated carbon paper, plain carbon cloth, and Teflonized carbon cloth using chemical vapor deposition. FESEM and TEM images and thermogravimetric analysis indicated that in situ CNT on carbon paper (ICNT/CP) possesses more appropriate structural quality and stronger adhesion to the substrate than other substrates. The contact angle analysis demonstrated that the degree of ICNT/CP surface hydrophobicity encountered a 24% increase in comparison to CP and promoted to superhydrophobicity from hydrophobicity. The polarization curves and electrochemical impedance spectroscopy results of the loaded Pt-Ni-Fe on in situ and ex situ CNT/CP illustrated that the power density increased and charge transfer resistance reduced compared to commercial Pt/C loaded on CP. The results can be attributed to the outstanding properties of CNTs and high catalytic activity of triple catalysts causing alloying of Pt with Ni and Fe, which makes them a proper candidate to be used as cathode electrodes in proton exchange membrane fuel cells.     

Successive electrodeposition of polydopamine and PtPd metal on a graphene oxide support for use as anode fuel cell catalysts

Successive electropolymerization of dopamine and electrodeposition of Pd and/or Pt on a graphene oxide (GO) support were used to prepare anode catalysts for low-temperature fuel cells. Transmission electron microscopy images were used to investigate the morphologies and distribution of the prepared catalysts, which showed the metal formed as nanoparticles on the catalysts. The GO surface was favorable for the modification with electropolymerized polydopamine (PDA) and the electrodeposition of metal catalyst nanoparticles using a simple preparation process. The PDA-loaded GO composite was used as a matrix for the dispersion of Pt and Pd nanoparticles. GO could be simultaneously modified by PDA and reduced without using reducing agents. The electrocatalytic performance of the catalysts for the oxidation of selected small molecule fuels (e.g., methanol, ethanol and formic acid) was examined. An outstanding catalytic activity and stability was found for the prepared Pt/Pd/PDA/GO composite, which was attributed to the high active surface area.     

Surface analysis for catalyst layer (PT/PTFE/C) and diffusion layer (PTFE/C) for proton exchange membrane fuel cells systems (PEMFCs)

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) studies have been used to analyze the surface of diffusion layer (PTFE/C) and catalyst layer (Pt/C/PTFE) of electrode. Detail analysis of carbon C_1s peak showed that the carbon was of the form of C, C-O, CO, CF, CF₂ and CF₃ with CF₂ is more dominated on the surface compared to CF and CF₃. The oxygen O_1s photoelectron peak showed that the oxygen was of the form of CO and C-O. The platinum was of the form of Pt⁰ with some Pt oxidized to PtO. The scanning electron microscopy was used to observe the dispersion of Teflon in the diffusion layer, the distribution of platinum in the catalyst layer loaded with 0.38 mg Pt/cm² and also the cross section of the membrane electrode assembly. The prepared electrode delivers a superior performance compared with the commercial electrode (E-TEK). The difference in performance between the two electrodes is due to the good localization of the platinum particles.