Effect of pH Value and Temperatures on Performances of Pd/C Catalysts Prepared by Modified Polyol Process for Formic Acid Electrooxidation

The highly active Pd/C catalysts for formic acid electrooxidation have been prepared by a modified polyol process at different pH values of reaction solutions and different reducing temperatures, respectively. Their physical properties have been characterised by energy dispersive analysis of X‐ray, X‐ray diffraction and transmission electron microscopy. Their electrochemical performances for formic acid electrooxidation have been tested by cyclic voltammetry and amperometric i–t curves. The results of physical characterisations show that all the Pd/C catalysts present an excellent face centered cubic crystalline structure. Their particle sizes are decreasing firstly and then increasing with the increasing of the pH values of reaction solutions. The reducing temperatures also markedly affect the Pd particle sizes. And their nanoparticles have narrow size distributions and are highly dispersed on the surface of carbon support, and Pd metal loading in Pd/C catalyst is similar to the theoretical value of 20 wt.%. The results of electrochemical measurements present that the Pd/C catalyst prepared by waterless polyol process at the pH value of 10 and the reducing temperature of 120 °C has the smallest particle size of about 5.6 nm, and exhibits the highest catalytic activity (1172.0 A · g_Pd<?h‐2.85>^–1<?h.8>) and stability for formic acid electrooxidation.     

Effect of pH Value on Performance of PtRu/C Catalyst Prepared by Microwave‐Assisted Polyol Process for Methanol Electrooxidation

PtRu/C catalysts with different mean particle sizes have been synthesised by microwave‐assisted polyol process at various pH values and characterised by transmission electron microscopy (TEM), energy dispersive analysis of X‐ray (EDAX) and X‐ray diffraction (XRD). Their electrochemical performances have been tested by cyclic voltammetry, amperomeric i–t, and CO‐stripping techniques. The effects of pH values on performances of the PtRu/C catalysts have been mainly investigated. It has been found that the particle size, composition and catalytic activity of the PtRu/C catalyst are very sensitive to the pH value of reducing solution, and the PtRu/C catalyst prepared at the pH value of 8 exhibits the better performance for methanol electrooxidation than the other samples. The size of the nanoparticles decreases as the pH value increases from 0.2 to 10 with the largest size of 4.4 nm and the smallest one of 2.1 nm. The two metal elements distribute uniformly in the catalyst and their metal loadings are similar to the theoretical value.     

Highly Active Carbon‐supported PdSn Catalysts for Formic Acid Electrooxidation

PdSn/C catalysts with different atomic ratios of Pd to Sn were synthesised by a NaBH₄ reduction method. Electrochemical tests show that the alloy catalysts exhibit significantly higher catalytic activity and stability for formic acid electrooxidation (FAEO) than the Pd/C catalyst prepared with the same method. XRD and TEM indicate that a particle‐size effect is not the main cause for the high performance. XPS confirms that Pd is modified by Sn through an electronic effect which can decrease the adsorption strength of poisonous intermediates on Pd and thus promote the FAEO greatly.     

Ultrahigh Durable PtPd/C Nanowire Networks Catalyst Synthesized by Modified Phase Transfer Method for Methanol Oxidation

A novel PtPd/C nanowire catalyst with interconnected network and fewer great grain boundaries has been successfully prepared by templateless and modified phase‐transfer method using cetyltrimethylammonium bromide as a capping in ethylene glycol solution by microwave‐assisted process. Its structure, composition, and morphology are characterized by X‐ray diffraction, energy dispersive analysis of X‐ray, and transmission electron microscopy, respectively. The electrochemical measurements demonstrate that the highly dispersed and uniform PtPd/C nanowire networks catalyst has a significantly higher electrocatalytic activity and durability for the methanol oxidation as compared to solid solution PtPd/C. The greatly improved durability of PtPd/C nanowire networks catalyst is mainly a consequence of the unique interconnected network structure with fewer grain boundaries, which provide more facile pathway for the electron transfer, and inhibit the particle growth and agglomeration, as well as prevent the particles embedded in the microporous of carbon support to enhance the Pt utilization.     

A General Protocol for the Synthesis of Pt–Sn/C Catalysts for the Ethanol Electrooxidation Reaction

A general protocol for the synthesis of Pt–Sn/C catalysts for ethanol electrooxidation by the polyol method is developed after a systematic variation of the preparation variables. This protocol enables the complete transfer of all catalytic elements in the preparation solution to the catalyst support; thereby providing a convenient means of catalyst composition control. Water is a necessary co‐solvent for ethylene glycol in the polyol synthesis of Pt–Sn/C catalysts. The best preparation medium for controlling the particle size to small sizes is 0.1 M NaOH solution in a mixture of equal volumes of water and ethylene glycol. With this medium composition Pt–Sn/C catalysts with the optimized target Pt:Sn atomic ratio of 3:1 could be expeditiously prepared for ethanol electrooxidation.     

ZrC–C and ZrO2–C as Novel Supports of Pd Catalysts for Formic Acid Electrooxidation

The Pd/ZrC–C and Pd/ZrO₂–C catalysts with zirconium compounds ZrC or ZrO₂ and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO₂–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO₂ may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO₂–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO₂, and metal–support interaction between Pd nanoparticles and ZrC, ZrO₂. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.     

Electrooxidation of formic acid on carbon supported PtxPd1−x (x = 0-1) nanocatalysts

In this work, carbon supported Pt_xPd_1−x (x = 0-1) nanocatalysts were investigated for formic acid oxidation. These catalysts were synthesized by a surfactant-stabilized method with 3-(N,N-dimethyldodecylammonio) propanesulfonate (SB12) as the stabilizer. They show better Pt/Pd dispersion and higher catalytic performance than the corresponding commercial catalysts. Furthermore, the electrocatalytic properties of Pt_xPd_1−x/C were found to depend strongly on the Pt/Pd deposition sequence and on the Pt/Pd atomic ratio. At a lower potential, formic acid oxidation current on co-deposited Pt_xPd_1−x/C catalysts increase with increasing Pd surface concentration. Nanoscale Pd/C is a promising formic acid oxidation catalyst candidate for the direct formic acid fuel cell.     

Formic acid oxidation by carbon-supported palladium catalysts in direct formic acid fuel cell

The oxidation of formic acid by the palladium catalysts supported on carbon with high surface area was investigated. Pd/C catalysts were prepared by using the impregnation method. 30 wt% and 50 wt% Pd/C catalysts had a high BET surface area of 123.7 m²/g and 89.9 m²/g, respectively. The fuel cell performance was investigated by changing various parameters such as anode catalyst types, oxidation gases and operating temperature. Pd/C anode catalysts had a significant effect on the direct formic acid fuel cell (DFAFC) performance. DFAFC with Pd/C anode catalyst showed high open circuit potential (OCP) of about 0.84 V and high power density at room temperature. The fuel cell with 50 wt% Pd/C anode catalyst using air as an oxidant showed the maximum power density of 99 mW/cm². On the other hand, a fuel cell with 50 wt% Pd/C anode catalyst using oxygen as an oxidant showed a maximum power density of 163 mW/cm² and the maximum current density of 590 mA/cm² at 60 °C.     

Co改性的Pd/C催化剂在转移加氢中的应用研究

通过调整Co和Pd的浸渍顺序制备了不同的钴改性的Pd/C催化剂,考察了催化剂在3,5-二羟基苯甲酸转移加氢制备3,5-二氧代环己烷羧酸反应中的活性。确认先浸渍钴后浸渍钯、并在300℃以氢气还原得到的Co-Pd/C催化剂具有最佳活性,反应转化率和选择性分别达到94.6%和99.5%。对该催化剂以BET、TPR、XRD、SEM、TEM、XPS等手段进行了表征。结果表明,先浸渍的钴占据了活性炭的微孔使最可几孔径由2.72nm增大为3.32nm,并且与一些对反应不利的官能团作用,使后浸渍的钯主要分布在催化剂的大孔中,避免了过多深度加氢副产物的生成。催化剂活性组分为零价的钯,其平均粒径约10nm,以有利于转移加氢的聚集态存在,使催化剂获得了较高的活性和选择性。     

Investigations of Compositions and Performance of PtRuMo/C Ternary Catalysts for Methanol Electrooxidation

PtRuMo/C catalyst was prepared by impregnation reduction method and characterised. Comparison is made between a home‐made PtRu/C prepared by similar method and Pt/C (E‐Tek Co., Pt/C‐ET) catalysts. One glassy carbon disc electrode for ternary alloy catalyst was used to evaluate the catalytic performances by cyclic voltammetric, chronoamperometric, amperometric i–t curves, and electrochemical impedance spectra (EIS). The electrochemical measurement results indicated that the performance of PtRuMo/C with a molar ratio of 6:3:1 was the highest among 15 Pt_xRu_yMo_10–x–y/C catalysts with different molar ratios. The composition, particle size, lattice parameter and morphology of the PtRuMo(6:3:1)/C catalyst were determined by means of X‐ray energy dispersive analysis, X‐ray diffraction (XRD) and transmission electron micrographs (TEM). The result of XRD analysis exhibits that PtRuMo(6:3:1)/C has the fcc structure with the smaller lattice parameter than the home‐made PtRu/C and Pt/C‐ET. Its typical particle sizes is only about 5 nm. With respect to the catalytic activity and stability, the PtRuMo(6:3:1)/C catalyst is superior to PtRu/C despite their comparable active areas. Though the electrochemically active surface area of Pt/C‐ET is the biggest, its performance is the lowest. EIS results also indicate that the reaction resistances for methanol electrooxidation on the PtRuMo(6:3:1)/C catalyst are smaller than those of PtRu/C at different polarisation potentials.     

Study on the Oxidation Enhancement of Formic Acid and Formate Blended Fuel Solution on Pt Catalyst

The effect of [HCOOH]/[HCOONa] ratio on the oxidation activity of HOOH and HCOONa blended fuel solution on Pt nanocatalyst is studied using cyclic voltammetry, chronoamperometry, and Tafel analysis. Five electrolyte solutions with the same total concentrations of HCOOH and HCOONa but different [HCOOH]/[HCOONa] ratios are tested. Blended solutions containing both higher HCOOH and HCOONa concentrations are found to be more active than single HCOOH or HCOONa solution, with the solution containing 0.8 mol dm^–3 HCOONa and 0.2 mol dm^–3 HCOOH exhibiting the best activity. The reasons behind the better performance of the HCOOH and HCOONa blended solutions – such as electric conductivity, pH, concentrations of HCOOH, and HCOONa, ionic strength of the solution, and oxidation mechanism of HCOOH – are investigated. Enhanced oxidation activity of the HCOOH and HCOONa blended solution is observed to be the mutual effect of various reasons, with pH and [HCOO^–] assuming the key roles.     

Direct Formic Acid Fuel Cells with 600 mA cm–2 at 0.4 V and 22 °C

A demonstration of direct formic acid fuel cells (DFAFCs) generating very high power density at ambient temperature is reported. In particular, the performance of the Pd black as an anode catalyst for DFAFCs with different formic acid feed concentrations at different operating temperatures has been evaluated. The Pd black based DFAFCs with dry air and zero backpressure can generate a maximum power density of 248 and 271 mW cm^–2 at 22 °C and 30 °C respectively. The open cell potential is 0.90 V. These results show that DFAFCs are potentially excellent alternative power sources for small portable electronic devices.     

苯丙酮酸在Pd/C催化剂上还原胺化合成DL-苯丙氨酸

以苯丙酮酸 (PPA)在Pd/C催化剂上还原胺化合成DL 苯丙氨酸 (Phe)。实验表明 :在 5 5℃、1 0MPa,苯丙酮酸初始质量浓度 ρ(PPA) =6 0g/L ,n(NH3)∶n(PPA) =3 0∶1 0 ,还原胺化 3h ,苯丙氨酸收率在 95 %以上 ,产品纯度w(DL Phe) >96 % ,并通过红外光谱、核磁共振对产物结构进行了确证     

Simultaneous Determination of the Permeability of a Nafion Membrane to Formic Acid and Water

The simultaneous diffusion of formic acid and water through Nafion was measured for four formic acid concentration differentials (1–17.5 M) and for two counter‐ions in the membrane (H⁺ and Ba²⁺). An iterative method based on Fick's law is presented to calculate the volumes and concentrations of the solutions as a function of time. Besides the initial conditions, the input parameters are two diffusion coefficients, one of formic acid and one of water, which were adjusted to fit the experimental data. Once the difference in liquid fraction between the two types of membranes is taken into account, the diffusion coefficient of formic acid through Nafion appears independent of the nature of the counter‐ion and the conductivity of the formic acid solution. The diffusion coefficient of water is 10 times higher than the formic acid diffusion coefficient and is systematically lower in membranes in the Ba²⁺ form than in H⁺ form.     

Pd/C催化剂催化分解甲酸反应动力学研究

采用湿空气氧化法研究了常压下Pd/C催化剂催化分解甲酸的反应动力学。建立了甲酸催化分解反应速率经验方程,Pd/C催化分解甲酸在323～363K范围内表观活化能为22.1kJ·mol-1。     

Evaluation of the Performance of Carbon Supported Pt–Ru–Ni–P as Anode Catalyst for Methanol Electrooxidation

This research is aimed to improve the activity and stability of ternary alloy Pt–Ru–Ni/C catalyst. A novel anodic catalyst for direct methanol fuel cell (DMFC), carbon supported Pt–Ru–Ni–P nanoparticles, has been prepared by chemical reduction method by using NaH₂PO₂ as a reducing agent. One glassy carbon disc working electrode is used to test the catalytic performances of the homemade catalysts by cyclic voltammetric (CV), chronoamperometric (CA) and amperometric i–t measurements in a solution of 0.5 mol L^–1 H₂SO₄ and 0.5 mol L^–1 CH₃OH. The compositions, particle sizes and morphology of home‐made catalysts are evaluated by means of energy dispersive analysis of X‐ray (EDAX), X‐ray diffraction (XRD) and transmission electron micrographs (TEM), respectively. TEM images show that Pt–Ru–Ni–P nanoparticles have an even size distribution with an average diameter of less than 2 nm. The results of CV, CA and i–t curves indicate that the Pt–Ru–Ni–P/C catalyst shows significantly higher activity and stability for methanol electrooxidation due to the presence of non‐metal phosphorus in comparison to Pt–Ru–Ni/C one. All experimental results indicate that the addition of non‐metallic phosphorus into the Pt–Ru–Ni/C catalyst has definite value of research and practical application for enhancing the performance of DMFC.     

络合还原法制备Pd/C催化剂及甲酸电催化氧化性能

分别以硼氢化钠和乙二醇为还原剂,经络合还原法制备了炭载钯(Pd/C)催化剂。透射电镜(TEM)和X射线粉末衍射谱(XRD)结果表明,以乙二醇为还原剂制备的Pd/C催化剂中Pd粒子具有较小的粒径、均匀的粒径分布和较大的相对结晶度,Pd粒子的平均粒径和相对结晶度分别为(4.2±2)nm和1.88。电化学测试结果显示,Pd/C催化剂具有较大的电化学活性面积,对甲酸氧化表现出较高的电催化活性和稳定性。     

Pd/C催化剂失活原因分析与改进措施

在精对苯二甲酸（PTA）的生产中，有多种原因会导致Pd/C催化剂失活，影响其使用寿命。根据多年生产经验及有关测试数据，分析了催化剂失活的机理与原因，并提出了预防与改进的具体措施。     

Investigation on Electrocatalytic Activity and Stability of Pt/C Catalyst Prepared by Facile Solvothermal Synthesis for Direct Methanol Fuel Cell

Pt nanoparticles supported on Vulcan XC‐72 carbon black have been synthesized by a facile solvothermal method. The obtained Pt/C catalysts are characterized by X‐ray diffraction (XRD), energy dispersive X‐ray analysis (EDAX), and transmission electron microscopy (TEM) analysis to identify Pt mean size and Pt content. The results of electrochemical measurements demonstrate that the Pt/C catalyst prepared at the reaction temperature of 140 °C and the reaction time of 2 h shows the biggest initial electrochemical area with an initial electrochemically active specific surface area (ESA) of 70.6 m²g_Pt⁻¹, the highest electrocatalytic stability with an ESA loss of 48.7% after 1,000 CV cycles, and the best electrocatalytic activity and stability toward methanol oxidation reaction (MOR) with a specific activity of 0.6 mA cm⁻² and a retention rate (the ratio of the final current density to the maximum current density) after 3,600 s of 42.8%. Moreover, the electrochemical performance of homemade Pt/C catalyst is superior to that of commercial Pt/C catalyst, suggesting that the solvothermal synthesis is a promising method for preparing Pt based catalyst.     

Nd修饰的PtSn/C催化剂对乙醇的电催化氧化性能

利用浸渍还原法,以甲酸为还原剂制备了PtSnNd/C和PtSn/C纳米催化剂。XRD测量了催化剂的粒径和晶格参数,循环伏安法和计时电流法测试了催化剂对乙醇的催化氧化性能。结果表明,添加Nd可以明显提高PtSn/C催化剂对乙醇的电催化氧化活性,峰电流密度增大了86%。