直接甲醇燃料电池纳米结构电催化材料及多孔电极研究

直接甲醇燃料电池(DMFC)因其燃料能量密度高,工作温度低,低污染排放等优点被认为是用作移动设备电源的最佳选择之一,至今已有美国的Oorja Protonics公司和丹麦的IRD公司等新能源相关企业相继发布了多款用于手机、电脑、通信基站、叉式装卸机或房车的商业产品.然而, DMFC内部的复杂情况造成的多种不同的电压损失仍旧使得其实际电压效率远低于理论值.其中从阳极渗透到阴极的甲醇造成的混合电位导致的电压损失尤为明显.目前,众多研究人员都致力于开发高稳定性、高耐久性、高性能且低成本的催化材料体系,以克服传统Pt催化剂存在的各种问题.除了催化剂本身之外, DMFC的问题还与其中膜电极的微结构和电化学特性息息相关.膜电极是化学能通过电催化氧化还原反应转化为电能的反应场所,通常由阳极扩散层、阳极催化层、质子交换膜、阴极催化层和阴极扩散层依序组合而成.通过对MEA中的各层进行优化,如传质管理和甲醇渗透等问题都能得到有效解决.
　　近年来,纳米技术常被用于改进DMFC性能的研究.具备纳米结构的金属-碳/金属氧化物载体类催化材料得到了广泛研究.这些电催化材料在制备方法、结构和组分上都有较大区别.结构方面,许多研究都证明制备纳米级多孔网络结构或者有序阵列结构的催化层有助于提高催化性能和Pt的利用率.组分方面,许多研究人员都开展了引入Pt以外金属成分或金属氧化物来改变Pt催化剂的表面电子状态的研究.引入这些组分导致的配位体效应可以通过弱化Pt与H+, OH-或COads等的相互作用来起到抗催化毒化和提高催化效率的作用.尽管对于DMFC领域的认知逐渐完善,但是仍有许多问题有待解决.因此,本文介绍了目前用于DMFC的纳米结构电催化材料和多孔电极的研究进展.重点介绍了纳米结构催化剂和载体材料的合成及表征.
　　通过对比不同催化材料的特性可以发现,在本文涉及到的催化材料中, In0.1SnO2-Pt和(MoO3)0.2SnO2-Pt/C表现出了最高的催化活性,但是它们高效催化甲醇电氧化所需的碱性环境与现在占绝对主流地位的Nafion质子交换膜所必须的酸性环境相冲突,所以其实际应用价值在碱性阴离子交换膜研究取得突破前都难以有效发挥.而另一类表现较好的采用溶致液晶模板法合成的纳米树枝状和纳米星形Pt催化剂则存在制备工艺难以商业规模化的问题.总的来说,采用溶剂热合成法制备的Pt-NRCeO2/GNs和Pt/Ti0.9Sn0.1O2-C等纳米结构金属氧化物、碳材料复合载体和Pt基贵金属催化剂组成的催化材料体系不仅催化性能相对于商业化Pt纳米颗粒有很大提高,而且制备方法易于商业规模化,值得进一步关注.此外,本文还介绍了如内部传质过程的理论建模计算和膜电极中功能结构的制备等优化DMFC中多孔电极内传质过程的方法.通过计算机模拟得到优化DMFC内部传质过程所需的扩散层、催化层的传质特性相关参数,再通过改进MEA制备工艺,有效控制各层的结构参数向模拟的优化值靠拢,能够实现DMFC性能的有效提升.综合模拟、实验研究及工艺研究结果,根据实际需要,设计和制备包含新功能层的MEA的相关研究也更进一步提高了DMFC的性能和实用性.就目前的研究情况而言,如果在性能提升的基础上,使用寿命再取得突破, DMFC一定会有很好的商业应用前景.     

Dispersed platinum and tin polyaniline film electrodes for the anodes of the direct methanol fuel cell

To develop better and cheaper electrocatalysts for the oxidation of methanol in direct methanol fuel cells, several combinations of a conductive polymer polyaniline (PANI) and dispersed metal particles such as Pt and Sn were examined. The anodic current for the methanol oxidation (i _MeOH) showing the electrocatalytic activity of Pt particles was remarkably enhanced when the particles were dispersed on PANI films that should provide higher surface areas for the dispersed particles. The activity strongly depended on the morphology and the electric conductivity of the PANI films electropolymerized in five different acid solutions: H₂SO₄, HNO₃, HClO₄, HBF₄, and HCl. The highest activity was achieved using the dispersed Pt particle on PANI film electropolymerized from H₂SO₄ polymerizing solution. In order to reduce the dispersed amount of the expensive Pt particles, other metal particles were pre-dispersed on the PANI film prepared from the H₂SO₄ polymerizing solution, and then Pt particles were dispersed on the film. Among the pre-dispersed metal particles attempted here (Sn, Cu, Cr, Ni, In, Co, Sb, Bi, Pb, and Mn), the highest activity was obtained with Sn particles. When the ratio of dispersed Pt to Sn particles ranges from 32:68 to 100:0, i _MeOH is higher than that measured with the dispersed Pt particle on PANI films without the Sn particles. This means that the dispersed amount of the Pt particles could be reduced by utilizing dispersed Sn particles.     

Nafion含量对直接甲醇燃料电池阴极催化剂性能表达的影响

燃料电池是一种将燃料反应的化学能转化为电能的装置,可分为氢氧质子交换膜燃料电池(PEMFCs)、直接甲醇燃料电池(DMFCs)和直接甲酸燃料电池等.与 PEMFCs相比, DMFCs以甲醇为燃料,燃料的储存运输和电池操作运行具有较高的安全性,所以近年来受到人们的广泛关注.
　　膜电极组件(MEA)是 DMFCs的核心部分,由气体扩散层(GDL)、催化层(CL)和质子交换膜(PEM)三部分组成. GDL用于提高电池传质能力,并同时作为 MEA的集流体. PEM主要用于隔离燃料和氧气,进行质子传导. CL是 MEA中的主要组成部分,为电化学反应提供场所.
　　催化层由催化剂,质子传输介质和电子传输介质组成.通常,阳极催化剂采用 PtRu/C,阴极采用 Pt/C,质子传输介质为全氟磺酸树脂,如 Nafion. CL的结构对电池性能有直接的影响,因此人们对 CL的结构进行了详细的研究,并通过调节 CL亲水性能、梯度催化层的结构设计等优化其结构.研究表明,当 CL中 Nafion含量为33 wt.%, PEMFCs具有最佳的电池性能. DMFCs与 PEMFCs对 MEA要求不同,其阴极更容易发生水淹现象.本文结合非接触式三维光学轮廓仪、接触角测试系统和电化学测试对阴极不同 Nafion含量的膜电极进行了表面形貌、亲水性、循环伏安和 DMFC性能测试.
　　本文利用喷涂法制备了 GDE,然后与 Nafion115热压形成 MEA.由三维表面形貌图可以看出,随着催化层中 Nafion含量的增加, GDE表面的粗糙度变大,尤其是 N35和 N45.理论上,表面粗糙有利于 Pt的暴露和传质扩散,但是其电池性能并未与粗糙度呈现出正相关的关系,因为 Nafion含量高于35 wt.%, Pt被 Nafion过度包裹,抑制了 O2至催化剂表面的传输,且随着 Nafion含量由15 wt.%增加至45 wt.%,其 GDE表面的接触角由166.8o减至143.1o,说明 CL的亲水性增强,易导致阴极产生的水无法及时排出,从而造成阴极水淹现象.
　　从不同 Nafion含量制备 MEA的 CV图可以看出,随着 Nafion含量的增加, Pt的电化学活性面积(ESA)增加.当 Nafion含量较少时, Nafion无法对全部 Pt纳米粒子(NPs)形成包覆或无法形成连贯的质子传输通道,从而导致大部分的 Pt NPs催化活性较低变为无效 Pt.而有效 Pt NPs要求与连贯的质子传输通道相连接.当 Nafion含量高于35 wt.%时,其 ESA基本保持不变,因为 Pt载量一定,从而限制了 ESA,此时达到该载量条件下的极限 ESA.但是电池极化曲线表明,30 wt.% Nafion含量的 MEA具有最佳的电池性能.因为有效 Pt NPs不一定是高效的,当他们全部被 Nafion包裹后, O2只能依靠溶解在 Nafion中才可以到达催化剂表面,从而阻碍传质.只有 Pt NPs表面包裹和暴露面积达到一定比例时才变得高效.所以当 Nafion含量低于30 wt.%时,主要由质子传输通道导致的有效 Pt NPs较少;当 Nafion含量高于30 wt.%时,出现 Nafion过度包裹 Pt NPs,阻碍 O2传质.因此, Nafion含量30 wt.%时, Pt的包裹面积和裸露面积达到所研究的最佳状态.     

Electrodeposited Pt and Pt-Sn nanoparticles on Ti as anodes for direct methanol fuel cells

Electro-oxidation of methanol was studied on titanium supported nanocrystallite Pt and Pt_x-Sn_y catalysts prepared by electrodeposition techniques. Their electro-catalytic activities were studied in 0.5mol/L H₂SO₄ and compared to those of a smooth Pt, Pt/Pt and Pt-Sn/Pt electrodes. Platinum was deposited on Ti by galvanostatic and potentiostatic techniques. X-ray diffractometer (XRD) and energy dispersive X-ray (EDX) techniques were applied in order to investigate the chemical composition and the phase structure of the modified electrodes. Scanning electron microscopy (SEM) was used to characterize the surface morphology and to correlate the results obtained from the two electrochemical deposition methods. Results show that modified Pt/Ti electrodes prepared by the two methods have comparable performance and enhanced catalytic activity towards methanol electro-oxidation compared to Pt/Pt and smooth Pt electrodes. Steady state Tafel plots experiments show a higher rate of methanol oxidation on a Pt/Ti catalyst than that on a smooth Pt.  Introduction of a small amount of Sn deposited with Pt improves the catalytic activity and the stability of prepared electrode with time as indicated from the cyclic votlammetry and the chronoamperometric experiments. The effect of variations in the composition for binary catalysts of the type Pt_x-Sn_y/Ti towards the methanol oxidation reaction is reported. Consequently, the Pt_x-Sn_y/Ti (x∶y (8∶1), molar ratio) catalyst is a very promising one for methanol oxidation.     

铂纳米棒有序阵列催化电极在被动式直接甲醇燃料电池中的应用

直接甲醇燃料电池(DMFC)具有能量密度高、无需充电、液体燃料添加便捷及环境友好等优点,是新一代便携式移动电源研究热点. DMFC规模应用的主要技术挑战是如何进一步提高电池性能、显著降低成本和可靠延长寿命.催化电极作为 DMFC发电核心和成本的集中体现,其电催化活性和贵金属用量直接影响 DMFC的性能和成本,开发高性能、低成本的催化电极对推进 DMFC实用化进程具有重要意义.特别是在被动式 DMFC中,阴极催化电极不仅需要提高电催化活性和大幅降低贵金属用量,而且还面临内部严重的“水淹”和氧传质受限等问题.近年来,随着纳米技术发展,有序纳米结构已逐渐应用于 DMFC催化电极的构筑中,电池性能得到显著提高.然而,目前的研究主要集中在膜电极纳米有序微孔层、纳米有序改性膜和纳米有序阳极催化电极及其阳极贵金属载量降低等方面,关于阴极催化电极在有序纳米结构以及载量降低等方面的研究相对较少.
　　本文采用模板法直接在微孔层上电沉积定向生长排列有序、直径可控的铂纳米棒阵列,并作为阴极催化电极应用于被动式 DMFC. X射线衍射和透射电镜结果表明,该铂纳米棒结构稳定,表面含有丰富的纳米晶须结构,有利于催化电极比表面积增加和电催化活性提高.不同催化电极上氧还原的极化曲线表明电极性能依下列次序变化：直径为200 nm铂纳米棒阵列电极>100 nm铂纳米棒阵列电极>商业化铂黑催化电极.电池性能表征表明,长度为1–3μm、直径分别为200和100 nm、载量为1.0 mg/cm2的铂纳米棒阵列作为阴极催化电极的 DMFC最大功率密度分别为17.3和12.0 mW/cm2.通过催化电极电化学活性面积和阻抗测试,分析其性能提高的原因可归结于有序排列的铂纳米棒阵列结构提高了电化学活性面积、增强了氧还原电催化活性并促进了阴极氧的传质.     

Electrochemical DNA biosensors based on platinum nanoparticles combined carbon nanotubes

Platinum nanoparticles were used in combination with multi-walled carbon nanotubes (MWCNTs) for fabricating sensitivity-enhanced electrochemical DNA biosensor. Multi-walled carbon nanotubes and platinum nanoparticles were dispersed in Nafion, which were used to fabricate the modification of the glassy carbon electrode (GCE) surface. Oligonucleotides with amino groups at the 5′ end were covalently linked onto carboxylic groups of MWCNTs on the electrode. The hybridization events were monitored by differential pulse voltammetry (DPV) measurement of the intercalated daunomycin. Due to the ability of carbon nanotubes to promote electron-transfer reactions, the high catalytic activities of platinum nanoparticles for chemical reactions, the sensitivity of presented electrochemical DNA biosensors was remarkably improved. The detection limit of the method for target DNA was 1.0 × 10⁻¹¹ mol l⁻¹.     

In situ formation of platinum nanoparticles in Nafion recast film for catalyst-incorporated ion-exchange membrane in fuel cell applications

Platinum (Pt) nanoparticles were synthesized inside a Nafion polyelectrolyte membrane for use as a catalyst membrane integrated layer in fuel cells. The integrated membrane was prepared by making use of the cation exchange between the tetraammineplatinum (II) cations ([Pt(NH₃)₄]²⁺) and sulfonic groups in the Nafion molecules, followed by film casting and chemical reduction. The synthesized Pt nanoparticles, which had a cubic shape with diameters of 11.5–14.5 nm, dispersed in the recast Nafion film, increased its proton conductivity and open circuit voltage compared with the pristine Nafion membrane. The Pt-incorporated membrane provided a 29% increment of the maximum power density, seemingly by oxidizing the crossover methanol passing through the proton-exchange membrane. At a high loading of Pt (over 3 wt.% in this study), the Nafion clusters were likely squeezed by the synthesized Pt nanoparticles so as to decrease the water uptake and proton conductivity. This hypothesis was also supported by the increased Ohmic resistance in the I–V polarization curve.     

WO3 decorated carbon nanotube supported PtSn nanoparticles with enhanced activity towards electrochemical oxidation of ethylene glycol in direct alcohol fuel cells

This paper describes the concept of the utilization of metal oxide (WO₃) modified multi-walled carbon nanotubes (MWCNT) for supporting and activating PtSn nanoparticles (PtSn/WO₃-MWCNT and PtSn/MWCNT) for ethylene glycol oxidation. The resulting nanocomposite was developed and characterized using electrochemical and microscopic (TEM, SEM−EDS) techniques, as well as XRD analysis. The electrocatalytic currents measured under voltammetric and chronoamperometric conditions were greater than those found with the commercially available Vulcan-supported Pt₃Sn nanoparticles, which were used as reference catalysts. In situ FTIR spectroscopy was used to detect the formation of oxidation intermediates or products during the ethylene glycol oxidation. Combining the transition metal oxide species with Pt-based nanoparticles can generate OH groups at low potentials. These groups participate in the oxidation of passivating CO adsorbates on the Pt surface, and can also potentially break CH bonds. Further, the effectiveness of synthesized catalyst has been assessed through testing both catalysts in the single fuel cell. A single fuel cell with a PtSn/WO₃-MWCNT anode gave a better performance than one with a pristine PtSn/Vulcan anode, with a current density of around 79.8 mA cm⁻² and an output power density of 20.5 mW cm⁻².     

高分散Fe-N-C氧还原反应电催化剂及其在直接甲醇燃料电池中的应用

氧还原反应(ORR)是燃料电池和金属空气电池等洁净发电装置中阴极的主要反应,该反应动力学过程慢,电化学极化严重. Pt基电催化剂具有较好的ORR活性,然而Pt资源有限、价格昂贵,研制高活性、低成本的代Pt电催化剂意义重大.经过几十年的探索,研究者发现将含有C, N和Fe等元素的前体进行高温热处理得到的Fe-N-C电催化剂对ORR具有良好的活性,然而在高温热解过程中Fe容易发生聚集而形成大块颗粒,导致Fe的利用率不高,影响了电催化剂的ORR活性.
　　本文分别以聚吡咯和乙二胺四乙酸二钠(EDTA-2Na)为C和N的前驱体,利用高温热解形成的富含微孔的碳材料对铁前体的吸附及锚定作用,获得了一种Fe高度分散的Fe-N-C电催化剂.采用物理吸脱附技术、高分辨透射电镜(HRTEM)和扫描电镜对Fe-N-C及其制备过程中相关电催化剂的孔结构及表面形貌进行了表征.结果表明,在第一步热解过程中, EDTA-2Na的Na对碳材料起到了活化作用,形成富含微孔的N掺杂碳材料(N-C-1),其BET比表面积达到1227 m2/g,孔径约1.1 nm.在第二步热解过程中, N-C-1有效地抑制了Fe的聚集,产物Fe-N-C中的Fe元素均匀地分布在碳材料中,其比表面积高达1501 m2/g.
　　电化学测试结果表明,在碱性介质(0.1 mol/L NaOH)中, Fe-N-C电催化剂对ORR具有良好的催化活性, ORR起始电位(Eo)为1.08 V (vs. RHE),半波电位(E1/2)0.88 V,电子转移数n接近4, H2O2产率<3%,与商品20%Pt/C(Johnson Matthey)接近.电化学加速老化测试结果表明, Fe-N-C的E1/2未发生明显变化,而Pt的负移45 mV,表明Fe-N-C具有很好的稳定性;在酸性介质(0.1 mol/L HClO4)中, Fe-N-C的Eo为0.85 V, E1/2为0.75 V,其E1/2比Pt/C负移约0.15 V,表明在酸性介质中Fe-N-C对ORR的催化活性还有待提高.采用TEM、X射线衍射、X射线光电子能谱以及穆斯堡尔谱等方法研究了电催化剂构效关系.结果表明, Fe-N-C较好的ORR活性主要来自于高分散的Fe-N4结构,此外, N(吡啶N和石墨N)掺杂的C也对反应具有一定的催化活性.
　　与Pt/C相比, Fe-N-C电催化剂具有很好的耐甲醇性能.本文对比了Fe-N-C和Pt/C作为阴极催化剂的直接醇类燃料电池(DMFC)性能,采用质子交换膜的DMFC最大功率密度分别为47(Fe-N-C)和79 mW/cm2(Pt/C),而采用碱性电解质膜的则分别为33(Fe-N-C)和8 mW/cm2(Pt/C).结合半电池结果表明, Fe-N-C电催化剂在碱性介质中具有比Pt更为优秀的催化活性和稳定性,有望用作DMFC阴极代Pt催化剂.     

Supercritical carbon dioxide treated Nafion 212 commercial membranes for direct methanol fuel cells

Supercritical carbon dioxide (Sc-CO₂) thermal treatment to enhance performance of Nafion 212 (NR212) commercial membranes for direct methanol fuel cells (DMFCs) is described. It is shown that the microstructure of NR212 membranes is re-organized after the Sc-CO₂ treatment, and then the performance of NR212 membranes is improved. Specifically the thinner NR212 membranes after the Sc-CO₂ treatments have higher proton conductivity and better capacity of barrier to methanol crossover compared with the thicker Nafion 117 membranes. It is demonstrated that the DMFC performance of the Sc-CO₂ treated NR212 membranes is better than that of Nafion 117 membranes.     

铂银合金的制备及其对甲醇电氧化反应的催化性能

采用一种无需使用任何有机表面活性剂或溶剂的方法，在熔融盐体系中制备了铂银纳米合金颗粒，考察了合金中元素银对碱性电解质中甲醇电氧化反应（MOR）的催化作用。透射电子显微镜表征结果显示，当前躯体铂银物质的量比为1时，可以得到组成为Pt₅₂Ag₄₈的合金纳米管。甲醇电氧化反应测试结果表明，具有干净表面的Pt₅₂Ag₄₈纳米管比常规的Pt黑具有更好的催化性能。Pt₅₂Ag₄₈合金纳米管的催化活性与其最大正扫电位密切相关，正扫电位从-1.0到0.5 V（vs.SCE），MOR峰值电流达到1.61 mA/μg_Pt，是从-1.0到0.1 V（vs.SCE）正扫电位的1.92倍。铂银合金表面层中的Ag元素主要通过在电化学循环中发生氧化还原反应来促进合金的MOR活性。研究结果可以为铂银合金在直接甲醇燃料电池（DMFC）中的应用提供理论支持。     

PtCeOx/C as a novel methanol-tolerant electrocatalyst of oxygen reduction for direct methanol fuel cells

A prominent methanol-tolerant characteristic of the PtCeO_x/C electrocatalyst was found during oxygen reduction reaction process. The carbon-supported platinum modified with cerium oxide (PtCeO_x/C) as cathode electrocatalyst for direct methanol fuel cells was prepared via a simple and effective route. The synthesized electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. It was found that the cerium oxide within PtCeO_x/C present in an amorphous form on the carbon support surface and the PtCeO_x/C possesses almost similar disordered morphological structure and slightly smaller particle size compared with the unmodified Pt/C catalyst.     

Activity evaluation of carbon paste electrodes loaded with pt nanoparticles prepared in different radiolytic conditions

Three Pt-based catalysts prepared in different radiolytic conditions and supported on graphite powder were packed into a carbon paste electrode configuration. They were compared to each other, to the commercial (Pt) deposited on activated carbon powder (Johnson Matthey) and to pure Vulcan XC-72 for their respective abilities toward the hydrogen evolution reaction (HER). The Tafel parameters were determined for all these electrodes. From the I–V curves and their quantitative treatment, the following order of activity emerged unambiguously and reads: (PtCO)₂ (fcc structure) > (PtCO)₁ (Chini cluster) > (Pt)_neat > (Pt)_JM (Johnson Matthey) ≫ (Vulcan XC-72). As expected, all the Pt-loaded electrodes were more efficient than Vulcan XC-72. The classification appears to be linked with the mean nanoparticle size, and for comparable sizes, with the surface morphology of the materials. The results and the stability of the electrodes suggest that the small particle sizes and the good dispersity on the carbon support were maintained during the HER.     

Sulfonated polysulfone with 1,3-1H-dibenzimidazole-benzene additive as a membrane for direct methanol fuel cells

1,3-1H-Dibenzimidazole-benzene (DBImBenzene) has been synthesized using phosphorus pentoxide-methanesulfonic acid (PPMA) as a solvent and dehydration agent and investigated as an additive (up to 2.0 wt.%) in sulfonated polysulfone (SPSf) membranes to promote proton conduction via acid–base interactions. The SPSf/DBImBenzene blend membranes with various DBImBenzene contents (0–2.0 wt.%) have been prepared and characterized by proton conductivity measurement and electrochemical polarization and methanol crossover measurements in direct methanol fuel cells (DMFCs). The blend membranes with DBImBenzene content of 0.5 and 1.0 wt.% show higher proton conductivities (3.4 and 2.9 × 10⁻⁴ S/cm, respectively) than plain SPSf (2.4 × 10⁻⁴ S/cm) even though the blend membranes have lower ion exchange capacity (0.81 and 0.75 mequiv./g, respectively) than plain SPSf (0.86 mequiv./g). The blend membranes exhibit better electrochemical performance in DMFC than plain SPSf membrane due to an enhancement in proton conductivity through acid–base interactions and lower methanol crossover.     

Poly(arylene ether sulfone)s containing pendant sulfonic acid groups as membrane materials for direct methanol fuel cells

A series of poly(arylene ether sulfone)s containing pendant sulfonic acid groups have been prepared by an aromatic substitution polymerization reaction using 4,4-difluorodiphenylsulfone, 6,7-dihydroxy-2-naphthalenesulfonate, and various hydroxyl terminated monomers in the presence of potassium carbonate. The synthesized sulfonated polymers have been characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, ion exchange capacity, thermogravimetric analysis, and proton conductivity measurements. With a molecular weight of 50,000–59,000 g/mol and an ion exchange capacity of 1.17 meq./g, these polymers are thermally stable up to 250 °C. They are found to exhibit better performance at 65 and 80 °C in direct methanol fuel cells than Nafion 115 membrane despite lower proton conductivity due to a significantly lower methanol crossover.     

A spin-coated TiOx/Pt nanolayered anodic catalyst for the direct formic acid fuel cells

The CO poisoning of the platinum anodic catalyst which typically functions the catalytic deterioration of the direct formic acid fuel cells could be minimized with a simple modification for Pt with titanium oxide. The fabrication scheme involved the spin-coating of a Ti precursor onto a Pt thin layer that was physically sputtered onto a Si substrate. The whole assembly was subjected to a post-annealing processing to produce the TiOx layer (60 nm) in a porous structure (mostly Anatase) atop of the Pt surface. The porous nature of the TiOx layer permitted the participation of Pt in the electrocatalysis of the formic acid electro–oxidation (FAO). The annealing temperature was critical in identifying the catalytic efficiency and durability of the catalyst toward the FAO. Interestingly, if compared to bare-Pt substrates, the TiOx-modified catalysts could successfully steer the FAO toward the direct dehydrogenation (favorable and less energetic) pathway with more than an order of magnitude increase in the catalytic activity. It also provided a great opportunity for the mitigation of poisoning CO; concurrently with a lowering (~0.3 V) in the onset potential of the FAO. The scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction spectroscopy (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were all combined to evaluate, respectively, the catalyst’s morphology, composition, crystal structure and activity and further to understand the role of the TiOx in the catalytic enhancement.     

Electrocatalytic activities of binary and ternary composite electrodes of Pd, nanocarbon and Ni for electro-oxidation of methanol in alkaline medium

Films of binary and ternary composites of Pd, nanocarbon (C), and Ni are obtained on glassy carbon electrodes and investigated as electrocatalysts for methanol oxidation (MOR) in alkaline medium. Results show that among the electrocatalysts investigated, the apparent electrocatalytic activity of the Pd-0.5%C electrode is the greatest and that it decreases with increasing percentage of C in the composite. The Pd-0.5%C composite electrode has approximately two times higher activity than that of Pd electrode for MOR under similar experimental conditions. Introduction of Ni (1–2%) into the active Pd-0.5%C catalyst somewhat declines the apparent electrocatalytic activity of the electrode. The onset potential for MOR is observed to be the greatest negative at the Pd-0.5%C composite electrode, which gets shifted towards noble side by 80–100 mV with addition of Ni (1–2%).     

促进型PtMoSi/C催化剂的制备、表征及电催化活性

采用甲醛还原、H2还原、肼还原三种方法制备了添加硅钼酸的PtMoSi/C阳极催化剂, 并用XRD、XPS和TEM技术对催化剂进行了表征. XRD表明Pt粒子呈立方面心晶态结构, TEM显示PtMoSi/C催化剂粒径小(3−4 nm), 分布窄, 分散性好. XPS分析可知Pt主要以0价, Mo主要以6价, Si主要以4价形态存在于催化剂中. 同时通过循环伏安法和线性扫描法考察了制备方法和添加硅钼酸对催化剂电化学活性的影响. 结果表明, 甲醛还原法制备的PtMoSi/C催化剂(Pt、Mo的原子比为3:1)对甲醇氧化的电化学性能和抗中毒性能优于自制的PtRu/C和E-TEK PtRu/C催化剂, 可能是因为添加硅钼酸可以使活性组分的分散度提高, 从而提高了催化剂的活性和抗毒性能.     

三维结构氧化石墨烯载铂催化剂对甲醇电催化性能

喷雾干燥法制备具有三维结构的氧化石墨烯(PGO),在其表面进一步负载活性成分Pt,得到纳米Pt/PGO复合催化剂。采用X射线粉末衍射(XRD)、透视电镜(TEM)和扫描电镜(SEM)等对催化剂的形貌和结构进行表征。结果表明,PGO具有类似于长4-6μm和宽2.0-3.0μm的三维纸团结构,平均粒径为4.2 nm的Pt纳米粒子均匀分布在其表面。采用循环伏安和计时电流法研究了在酸性溶液中催化剂对甲醇的电催化氧化性能。结果表明,Pt/PGO催化剂对甲醇呈现出更高的电催化氧化活性和稳定性。PGO所具有的三维结构和双功能作用机理有利于甲醇在铂表面的电催化氧化过程的发生。