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.     

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.     

Porous Carbon as Anode Catalyst Support to Improve Borohydride Utilization in a Direct Borohydride Fuel Cell

Our study explores the use of porous carbon as anode catalyst support to improve borohydride utilization in a direct borohydride fuel cell. Pt catalysts supported by carbon aerogel (CA) and macroporous carbon (MPC) are synthesized by template method. The pores in porous carbon materials catch hydrogen bubbles to regulate the contact of anolyte with catalytic sites, and this leads to the depression of hydrogen evolution during BH₄⁻ electrooxidation. However, the hydrogen bubbles in the pores simultaneously deteriorate charge carrier transport and thus increase anode polarization. The CA‐supported Pt catalyst improves the coulombic efficiency of BH₄⁻ electrooxidation. However, the MPC‐supported Pt catalyst performed better than the CA‐supported Pt catalyst. MPC also has a good pore distribution, which improves the coulombic efficiency of BH₄⁻ electrooxidation without decreasing anode performance.     

常压条件下Pd/C催化邻氯硝基苯加氢反应

用化学还原法制备了活性炭负载Pd、Pt和 Ru共3种贵金属催化剂,在没有添加任何脱氯抑制剂和助剂的前提下,比较研究了3种催化剂在邻氯硝基苯(o-CNB)加氢制邻氯苯胺(o-CAN)反应中的催化性能,发现Pd/C催化剂效果更佳。以Pd/C为催化剂,考察了溶剂种类、反应温度、反应时间和重复使用次数等因素对邻氯硝基苯转化率及邻氯苯胺选择性的影响。实验结果表明:常压条件下,Pd与邻氯硝基苯的质量比为1/2120,反应时间90min,邻氯硝基苯转化率和邻氯苯胺选择性分别可达100%和 87.4%。催化剂在重复使用6次后仍保持较高的活性。该工艺具有反应压力低、催化剂用量少、反应时间短和脱氯少等特点,适合工业化生产。     

Study of Methanol‐tolerant Oxygen Reduction Reaction at Pt–Bi/C Bimetallic Nanostructured Catalysts

The nanostructured platinum–bismuth catalysts supported on carbon (Pt₃Bi/C, PtBi/C and PtBi₃/C) were synthesised by reducing the aqueous metal ions using sodium borohydride (NaBH₄) in presence of a microemulsion. The amount of metal loading on carbon support was found to be 10 wt.‐%. The catalyst materials were characterised by X‐ray diffraction (XRD), X‐ray fluorescence (XRF), transmission electron microscope (TEM) and electroanalytical techniques. The Pt₃Bi/C, PtBi/C and PtBi₃/C catalysts showed higher methanol tolerance, catalytic activity for oxygen reduction reaction (ORR) than Pt/C of same metal loading. The electrochemical stability of these nano‐sized catalyst materials for methanol tolerance was investigated by repetitive cycling in the potential range of –250 to 150 mV_MSE. Bi presents an interesting system to have a control over the activity of the surface for MOR and ORR. All Pt–Bi/C catalysts exhibited higher mass activities for oxygen reduction (1–1.5 times) than Pt/C. It was found that PtBi/C catalyst exhibits better methanol‐tolerance than the other catalysts.     

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.     

Functionalized carbon support with sulfonated polymer for direct methanol fuel cells

Recently electrodes for direct methanol fuel cell (DMFC) have been developed for getting high fuel cell performances by controlling composition of catalysts and sulfonated polymers, developing catalyst particles, modifying carbon supports, etc. The electrodes in DMFCs are porous layers, which are composed of catalyst, which is black or carbon supported, and sulfonated polymers in a blended form. In the present study, carbon support for catalysts was functionalized to play dual roles of a mass transport and a catalyst support. The functionalized carbon support was characterized and compared with pristine one by thermal and spectroscopic analysis, and loading of platinum (Pt) catalysts on modified support was performed by gas reduction. The electrodes with Pt on functionalized carbon support were fabricated, though the conventional electrodes were prepared with sulfonated polymer and Pt catalysts. Membrane electrode assembly with Pt catalyst on functionalized support showed a higher DMFC performance of 30 mW cm⁻² at 50 °C without using additional sulfonated polymer. Integration of electrode components in one body has another advantage of easier and simpler process in preparing electrodes for DMFCs. Improved DMFC performance of the electrode containing functionalized carbon was be attributed to a better mass transport which maximize the catalytic activities.     

Influence of Pyridine‐Polybenzimidazole Film Thickness of Carbon Nanotube Supported Platinum on Fuel Cell Applications

Pyridine‐polybenzimidazole (PyPBI) films of different thickness (∼1.0–2.4 nm) are wrapped on the surfaces of multi‐walled carbon nanotubes (CNTs). To prepare Pt on PyPBI/CNT (Pt‐PyPBI/CNT) catalysts, Pt⁴⁺ ions are immobilized on these PyPBI wrapped CNTs (PyPBI/CNTs) via Lewis acid‐base coordination between Pt⁴⁺ and :N‐ of imidazole groups, followed by reducing Pt⁴⁺ to Pt nanoparticles. The influence of PyPBI film thickness on the Pt particle size, loading and electrochemical surface area, respectively, of Pt‐PyPBI/CNTs is investigated. Fuel cell performances of the PBI/H₃PO₄ based membrane electrode assemblies (MEAs) prepared from these Pt‐PyPBI/CNT catalysts are also evaluated at 160 °C with unhumidified H₂/O₂ gases. Among the catalysts, the Pt‐PyPBI/CNT catalyst with a PyPBI film thickness of ∼1.6 nm (which is around half of the Pt particle size), a Pt loading of ∼44 wt.%, and a Pt particle size of ∼3.3 nm exhibits the best fuel cell performance.     

铂炭催化脱除超级电容器用多孔炭含氧官能团

开发可耐受高于2.7 V电压的多孔炭电极材料是双电层超级电容器（EDLCs）实现高能量密度的重要途径之一。以粒径小于10 nm的超细铂炭催化剂（Pt/C）引发了氢溢流,强化了高活性氢原子的解离,进而更加有效地脱除了多孔炭表面的含氧基团。利用5% Pt/C （质量分数,下同）可将多孔碳表面的含氧量降低至2%（摩尔分数,下同）。研究发现,重复使用多次后的Pt/C催化剂仍保持优于热还原法的脱氧效率。Pt/C催化剂作用下氢溢流脱氧后所得多孔炭（PC-Pt5/C-600-1st）的石墨微晶结构的有序度提高且孔结构得到较好保持,其作为EDLCs的电极材料可在3.3 V的高电压窗口下展现出良好的循环稳定性,在1 A·g^-1的电流密度下循环8 000圈后,容量保持率为88.4%。可重复使用的特点有利于降低相关工艺过程的成本负担。     

Effect of Porosity in Catalyst Layers on Direct Methanol Fuel Cell Performances

Effects of porosity of catalyst layers (CLs) on direct methanol fuel cell (DMFC) performances are investigated using silicon dioxide (SiO₂) particles as a pore former. The pore size and volume of CLs are controlled by changing the size and content of SiO₂. As the size of pore formed by removal of SiO₂ increases, DMFC performances are enhanced. The augmentation in performances can be explained by facilitation of fuel transport to catalyst particles, increase of utilization efficiency of catalysts, diminishment in methanol crossover, reduction in activation loss and facilitation of water discharging out of CLs of cathode due to the controlled porosity in CLs. The enhanced fuel transport, accessibility of fuels to Pt catalyst surface, is proved by the active areas of Pt catalyst. In addition to the active area of Pt catalyst, porous CLs exhibit a decline in methanol crossover, leading to increase of open circuit voltage (OCV). The porous CLs also show improvements in activation loss due to high porosity, causing enhancement in DMFC performances. In aspect of pore volume contribution to cathode performance, the SiO₂ content is optimized. Based on the DMFC performances, it can be suggested that the optimum conditions of SiO₂ are 500 nm in size and 20 wt.% in content. The porosity effect on both electrodes appears as follows: the pores in cathode are more effective on DMFC performances (55.5%) than those of anodes (44.5%) based on the maximum power of DMFC, indicating that the pores in CLs facilitate removal of water from electrodes.     

Quantified mass transfer and superior antiflooding performance of ordered macro‐mesoporous electrocatalysts

For oxygen reduction reaction (ORR), constructing porous catalysts are highly important for mass transfer inside. However, the various porous structures usually possess significantly different water buffer efficiency, that is, the antiflooding capability, for which one is still difficult to give a quantitative evaluation. In this work, we designed a special “rattle‐drum” like working electrode, by which an exactly quantitative assessment on the mass transfer efficiencies can be conducted. Particularly, ordered macro‐mesoporous Pt/C shows quantified mass transfer and antiflooding efficiency to be four times high as that of the commercial one. This observation should be attributed to their different pore characteristics, as the dual‐porosity Pt/C has 3.4 times the pore volume of the commercial one, together with regular pore arrangement. Simultaneously, it also demonstrated excellent durability, indicating that the macro‐mesoporous Pt/C indeed owns high stability in both antiflooding and durability. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2881–2889, 2018     

Hydrogen generation from hydrolysis of alkaline sodium borohydride solution using Pt/C catalyst

Hydrogen generation from catalytic hydrolysis of aqueous NaOH-stabilized sodium borohydride solutions was investigated using platinum catalysts dispersed on active carbon, carbon black, and alumina supports. The Pt/C catalyst shows high catalytic activity due to the large BET surface area of active carbon support. The investigations on the effects of Pt loading and calcination temperature on the performance of Pt/C catalyst were also performed. After filtration from the reaction medium and rinsing with water, the used catalyst was re-evaluated and almost the same catalytic activities as fresh catalyst were obtained during several cycles.     

Electroreduction of dioxygen (ORR) in alkaline medium on Ag/C and Pt/C nanostructured catalysts—effect of the presence of methanol

Ag/C catalysts with different loading were prepared using a colloidal route to obtain well dispersed catalysts on carbon, with a particle size close to 15 nm. An amount of 20 wt.% Ag on carbon was found to be the best loading in terms of current density and mass activity. The 20 wt.% Ag/C catalyst was then studied and the kinetics towards ORR was determined and compared with that of a 20 wt.% Pt/C catalyst. The number of exchanged electrons for the ORR was found to be close to four with the rotating disk electrode (RDE) as well as with the rotating ring disc electrode (RRDE) techniques. From the RDE results, the Tafel slopes b, the diffusion limiting current density inside the catalytic film (j_l^film) and the exchange current density (j₀) were evaluated. The Tafel slopes b and diffusion limiting current densities inside the catalytic film (j_l^film) were found to be in the same order for both catalysts, whereas the exchange current density (j₀), which is a suitable estimation of the activity of the catalyst, was at least 10 times higher at the Pt/C catalyst than at the Ag/C catalyst. The behavior of both catalysts in methanol containing electrolyte was investigated and it was found that at a low methanol concentration, the Pt/C catalyst was quasi-tolerant to methanol. But, at a high methanol concentration, the ORR at a Pt/C was affected. However, the Pt/C catalyst showed in each case better activity towards ORR than the Ag/C catalyst, even if the latter one was less affected by the presence of methanol than the former one.     

The Influence of Pt Loading,Support and Nafion Content on the Performance of Direct Methanol Fuel Cells: Examined on the Example of the Cathode

Nano‐sized Pt colloids were prepared using the polyol method and supported on Ketjen black EC 600J (KB), Vulcan XC‐72 (VC) and high surface area graphite 300 (HG). The effects of the Nafion ionomer content, and the Pt loading of the cathode catalyst layer as well as the Pt loading on the support on the performance of direct methanol fuel cells (DMFCs), were studied. The membrane electrode assemblies (MEAs) were analysed using current–voltage curves, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and adsorbed CO stripping voltammetry. Optimum Nafion to carbon (N/C) ratios (N/C being defined as the weight ratio of the Nafion ionomer to the carbon) were determined. The optimum N/C ratios were found to depend on the support as follows, 1.4, 0.7 and 0.5 for Pt/KB, Pt/VC and Pt/HG, respectively and to be independent of the Pt/C loading range of 20–80 wt% tested in this work. The highest DMFC performances, as well as the highest electrochemical active surface areas, and improved gas diffusivities, were achieved using these ratios. For the catalysts prepared in this work, the average Pt crystallite size was found to decrease with increasing surface area of the support for a particular Pt loading. MEAs made using KB as support and the optimal N/C ratio of 1.4 showed the best performances, i.e. higher than the VC and HG supports for any N/C ratio. The highest DMFC performance was observed using 60 wt% Pt on KB cathode electrodes of 1 mg Pt cm^–2 loading and an N/C value of 1.4. For all three supports studied, the 60 wt% Pt on carbon loading resulted in the best DMFC performance. This may be linked to the Pt particle size and catalyst preparation method used in this work. In comparison to literature results, high DMFC performances were achieved using relatively ‘low' Pt and Ru loadings. For example, a maximum power density of >100 mW cm^–2 at 60 °C was observed using a 1 mg Pt cm^–2 cathode loading and a 2 mg PtRu cm^–2 anode loading.     

Pt/Pt-Ce/γ-Al2O3催化氧化甲苯研究

通过等体积浸渍法制备单贵金属Pt/γ-Al₂O₃和双金属Pt-Ce/γ-Al₂O₃催化剂,考察Ce对催化剂活性的影响,确定催化剂最优配比。结果表明,当Pt的负载量为质量分数0.5%时,Pt/γ-Al₂O₃催化活性最高;当Pt的负载量为质量分数0.2%,Ce的负载量为质量分数1.0%时,Pt-Ce/γ-Al₂O₃催化剂的催化活性最高。Pt-Ce/γ-Al₂O₃催化剂的甲苯转化率高于Pt/γ-Al₂O₃催化剂。随着Pt负载量增大,催化剂孔容、孔径减小。粉体式催化剂性能优于整体式催化剂,但差别不大;Ce的添加有助于催化剂活性的提升。     

Effect of Nickel Addition on Ceria‐Supported Platinum Catalysts for Medium‐Temperature Shift Reaction in Fuel Processors

Medium‐temperature shift reaction (MTS, 280–340 °C) has received much attention for use in fuel processors. In this study, bifunctional Pt‐Ni/CeO₂ catalysts were prepared by different Pt (0.1–0.5 %) and Ni (5–20 %) loadings, and investigated for MTS reaction. X‐ray diffraction, N₂ adsorption and temperature‐programmed reduction tests were used to characterize the prepared samples. The results showed that Pt‐Ni bimetallic catalysts have higher CO conversion in comparison to Pt/CeO₂ monometallic catalyst. Furthermore, the sequential synthesis method of Pt and Ni impregnation was preferred to the simultaneous one, which is due to the better Pt dispersion on catalytic surface. Steam to carbon ratio variations study showed the maximum CO conversion to be in the range of 4.5.     

Preparation of High Performance Pt/CNT Catalysts Stabilized by Ethylenediaminetetraacetic Acid Disodium Salt

A novel method with ethylenediaminetetraacetic acid disodium salt (EDTA‐2Na) as a stabilizing agent was developed to prepare highly dispersed Pt nanoparticles on carbon nanotubes (CNTs) to use as proton exchange membrane (PEM) fuel cell catalysts. These nanocatalysts were obtained by altering the molar ratio of ethylenediaminetetraacetic acid disodium salt to chloroplatinic acid (EDTA‐2Na/Pt) from 1:2, 1:1, 2:1 to 3:1. The well‐dispersed Pt nanoparticles of around 1.5 nm in size on CNTs were obtained when the EDTA‐2Na/Pt ratio was maintained at 1:1. And the Pt/CNT catalyst exhibited large electrochemical active surface areas, very high electrocatalytic activity and excellent stability in the oxidation of methanol at room temperature. The Pt/XC‐72R catalyst with narrow size distribution was also prepared by this method for comparison purposes. Comparison of the catalytic properties of these catalysts revealed that the activity of the Pt/CNT catalyst was a factor of ∼3 times higher than that of the Johnson Matthey catalyst and ∼2 times higher than that of our Pt/XC‐72R catalyst, which can be assigned to the high level of dispersion of Pt nanoparticles and the particular properties of the CNT supports.     

Paper-structured catalyst with porous fiber-network microstructure for autothermal hydrogen production

Copper–zinc oxide catalyst powders were supported on a microstructured matrix composed of ceramic fiber-network by a papermaking technique. As-prepared catalyst materials, called paper-structured catalyst, were applied to the autothermal reforming (ATR) of methanol to produce hydrogen for fuel cell applications. The paper-structured catalyst demonstrated higher methanol conversion and lower undesirable carbon monoxide concentration, as compared with commercial catalysts. Besides, excellent catalyst durability was exhibited by the suppression of Cu sintering during the ATR reaction. The paper-structured catalyst showed remarkable superiority in methanol conversion even in the case of using sintered catalysts. Such features were possibly induced by the unique fiber-network microstructure (average pore size: ca. 20 μm and porosity: ca. 50%) of the paper composites, which may allow the effective transfer of heat and reactants to the catalyst surfaces. The porous paper-structured catalyst is expected as a promising catalytic material for improving the practical performances in the catalytic gas-reforming process.     

A Crystalline Catalyst Based on a Porous Metal‐Organic Framework and 12‐Tungstosilicic Acid: Particle Size Control by Hydrothermal Synthesis for the Formation of Dimethyl Ether

The strategy for obtaining a crystalline catalyst based on a porous copper‐based metal‐organic framework and 12‐tungstosilicic acid with different particle sizes is reported. Through the control of hydrothermal synthesis and some simple treatments, catalyst samples with average particle diameters of 23, 105, and 450 μm, respectively, were prepared. This crystal catalyst has both the Brønsted acidity of 12‐tungstosilicic acid and the Lewis acidity of the copper‐based metal‐organic framework, and has high density of accessible acid sites. Its catalytic activity was fully assessed in the dehydration of methanol to dimethyl ether. The effect of particle size on the catalytic activity of catalyst was studied, in order to select the particle size appropriate for avoiding the diffusion limitation in heterogeneous gas‐phase catalysis. In the selective dehydration of methanol to dimethyl ether, this catalyst exhibited higher catalytic activity than the copper‐based metal‐organic framework, γ‐alumina, and γ‐alumina‐supported 12‐tungstosilicic acid catalysts. It showed high catalytic performances, even at higher space velocity or in the presence of excess water. In addition, the catalyst was also preliminarily assessed in the formation of ethyl acetate from acetic acid and ethylene. It also exhibited a high activity which was comparable with that of silica‐supported 12‐tungstosilicic acid catalyst.     

Effects of Carbonization Temperature and Time during Carbon Riveting Process on the Stability of Pt/C Catalyst

Effects of carbonization temperature and time during carbon riveting process on the stability of Pt/C catalysts have been investigated systematically. X‐ray diffraction, transmission electron microscopy, cyclic voltammograms, and accelerated potential cycling tests have been performed to characterize the catalysts. The experimental results show that the activity of the riveted Pt/C catalyst decreases with the increasing of the heat‐treated temperature and the extension of heat‐treated time due to sintering of Pt nanoparticles. The stability of the carbon riveted Pt/C catalysts exhibits the increasing trend with the increase of the carbonization time and temperature. Considering both of the activity and stability of the riveted Pt/C catalysts, the optimized carbonization temperature and time are 400 °C and 60 min for a Pt/VulcanXC‐72 catalyst with starting particle size before carbonization of 2.2 nm and 20 wt% platinum loading, respectively.