Pd-Sb/C复合纳米催化剂对甲酸电催化氧化的性能研究

以柠檬酸三钠为稳定剂,硼氢化钠为还原剂,制备了碳载型的Pd-Sb复合纳米催化剂（Pd-Sb/C）,通过调制不同Pd:Sb摩尔比研究了其对甲酸电催化性能的影响. TEM结果表明,合成的纳米颗粒粒径较小且均匀分散在碳载体表面. XRD和XPS测试表明,Pd-Sb/C中少量的单质态Sb(0)高度分散在Pd颗粒中或表面,形成合金化程度较低的PdSb合金. 电化学测试表明,当Pd:Sb = 20:1时,合成的催化剂对甲酸的催化效能最佳. 与合成的Pd/C和商业Pd/C相比,Pd-Sb/C(20:1)的电流密度分别是Pd/C的2.6倍、商业Pd/C的4.2倍. Pd-Sb/C的整体催化性能得到改善主要归因于适量的单质态Sb(0)引入到Pd中,诱导产生电子效应和“双功能”效应,一方面减小Pd与CO毒性物种之间的吸附作用,另一方面促使Pd表面吸附的CO快速氧化,提高了Pd-Sb/C催化剂的抗CO中毒能力,使得Pd-Sb/C催化剂的整体催化性能得到改善.     

Structural design and facile synthesis of a highly efficient catalyst for formic acid electrooxidation

The pathway of formic acid electrooxidation strongly depends on the amount of three neighbouring Pt or Pd atoms in the surface of Pd- or Pt-based catalysts. Here, Pt decorated Pd/C nanoparticles (the optimal atomic ratio, Pd?:?Pt = 20?:?1) were designed and then synthesized through a facile galvanic replacement reaction where the amount of three neighbouring Pt or Pd atoms markedly decreased. As a result, discontinuous Pd and Pt atoms suppressed CO formation and exhibited unprecedented catalytic activity and stability toward formic acid electrooxidation while the cost was almost the same as that of Pd/C.     

甲酸在Pt-Sn(111)/C合金表面吸附的量子化学研究

采用周期平板模型, 结合密度泛函理论对HCOOH和CO在Pt-Sn(111)/C表面的top、brigde、hcp和fcc共计8个位点的吸附模型进行构型优化和能量计算, 并对吸附前后的频率、电荷、能带和态密度进行了研究. 计算结果表明fcc-Pt₃是较为有利的吸附位点, Sn掺杂之后费米能级右移, 导带增宽, 价带和导带的位置略微降低, 合金表面电子结构变化利于甲酸的吸附解离催化, 可使甲酸燃料电池阳极催化性能显著提高. 通过催化剂表面的抗中毒分析, 发现CO在Pt-Sn(111)/C表面的吸附能以两种趋势下降, 阳极催化剂掺杂改性后抗CO中毒能力增强.     

In Situ Raman Study of CO Electrooxidation on Pt(hkl) Single-Crystal Surfaces in Acidic Solution

The adsorption and electrooxidation of CO molecules at well-defined Pt(hkl) single-crystal electrode surfaces is a key step towards addressing catalyst poisoning mechanisms in fuel cells. Herein, we employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) coupled with theoretical calculation to investigate CO electrooxidation on Pt(hkl) surfaces in acidic solution. We obtained the Raman signal of top- and bridge-site adsorbed CO* molecules on Pt(111) and Pt(100). In contrast, on Pt(110) surfaces only top-site adsorbed CO* was detected during the entire electrooxidation process. Direct spectroscopic evidence for OH* and COOH* species forming on Pt(100) and Pt(111) surfaces was afforded and confirmed subsequently via isotope substitution experiments and DFT calculations. In summary, the formation and adsorption of OH* and COOH* species plays a vital role in expediting the electrooxidation process, which relates with the pre-oxidation peak of CO electrooxidation. This work deepens knowledge of the CO electrooxidation process and provides new perspectives for the design of anti-poisoning and highly effective catalysts.     

Decorating Pt/C Nanoparticles with Ru by Wall‐Jet Configuration: The Role of Coverage Degree on the Catalyst Activity for Glycerol Electrooxidation

Here, we built Ru‐decorated Pt/C nanoparticles with different coverage degrees (θ_Ru) by wall‐jet configuration for the first time, and we investigated their catalytic properties towards glycerol electrooxidation in acidic medium. Moreover, we used the most active catalysts as the anode in electrolysis to produce carbonyl compounds. The use of an electrochemical cell in wall‐jet configuration allows for the controlling of electrodeposition through easily handling parameters; namely, the θ_Ru is controlled by changing the concentration of the metallic precursor, speed, and volume of injection onto a Pt/C‐modified glassy carbon electrode under applied potential. Excess of Ru on a Pt surface inhibits glycerol dissociative adsorption, which limits further electrooxidation; whereas low θ_Ru do not provide surface oxygen species to the anodic reaction. Hence, intermediates θ_Ru reveal active catalysts – namely, θ_Ru=0.42 shifts the onset potential 170 mV towards lower values and increases 1.65‐fold the current density at 0.5 V. The stability of this catalyst is also enhanced by maintaining a more constant current density during successive potential cycles in the presence of glycerol and by avoiding Ru leaching from the surface. The electrolysis on Ru‐decorated Pt/C is shown to lead the reaction towards formic acid (‘high oxidation state’), decreasing the amounts of glyceradehyde, glycolic acid, and dihydroxyacetone, as a result of the improved catalytic properties.     

Electrocatalytic activity of platinum—polyaniline and palladium—polyaniline systems obtained by cycling the electrode potential

Steady-state current densities of electrooxidation of CH₃OH, HCOOH, and CO at the Pt-PAN-GC electrodes (where PAN and GC stand for polyaniline and glassy carbon, respectively) and those of electrooxidation of HCOOH at the Pd-PAN-GC electrodes are measured (per cm₂ of the true metal-catalyst surface area). The found higher activity of Pt and Pd particles incorporated in PAN, as compared with Pt/Pt and Pd/Pt, is attributed to interaction between metal-catalyst particles and the polymeric matrix. The activation effect is the most pronounced for the HCOOH electrooxidation at Pd-PAN-GC. The data concerning hydrogen evolution testify in favor of a decrease in exchange currents of this reaction upon going from Pt to Pt-PAN-GC electrodes     

In situ FTIRS studies of kinetics of HCOOH oxidation on Pt(110) electrode modified with antimony adatoms

The electrochemical behavior of irreversibly adsorbed antimony on a Pt(110) electrode (Pt(110)/Sb) with various coverages was studied using cyclic voltammetry. The kinetics of HCOOH oxidation via reactive intermediates on Pt(110)/Sb were investigated quantitatively by employing the potential step technique and in situ FTIR spectroscopy. The results demonstrated that Sb adatoms were stable on Pt(110) when the electrode potential was below 0.45 V (SCE). It has been revealed that the dissociative adsorption of formic acid can be inhibited by the presence of Sb_ad on the Pt(110) surface. The electrocatalytic effects of Sb_ad towards HCOOH oxidation consist in a negative shift of the oxidation potential (about 350 mV) and the enhancement of the oxidation current. Based on the data processing method of integration transform developed in our previous papers, the kinetics of HCOOH oxidation on Pt(110)/Sb electrodes of different θ_Sb have been investigated quantitatively, and both the rate constant k_f and the transfer coefficient β were determined and reported.     

Self-assembly of mixed Pt and Au nanoparticles on PDDA-functionalized graphene as effective electrocatalysts for formic acid oxidation of fuel cells

Pt and Au nanoparticles with controlled Pt?:?Au molar ratios and PtAu nanoparticle loadings were successfully self-assembled onto poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene (PDDA-G) as highly effective electrocatalysts for formic acid oxidation in direct formic acid fuel cells (DFAFCs). The simultaneously assembled Pt and Au nanoparticles on PDDA-G showed superb electrocatalytic activity for HCOOH oxidation, and the current density associated with the preferred dehydrogenation pathway for the direct formation of CO(2) through HCOOH oxidation on a Pt(1)Au(8)/PDDA-G (i.e., a Pt?:?Au ratio of 1?:?8) is 32 times higher than on monometallic Pt/PDDA-G. The main function of the Au in the mixed Pt and Au nanoparticles on PDDA-G is to facilitate the first electron transfer from HCOOH to HCOO(ads) and the effective spillover of HCOO(ads) from Au to Pt nanoparticles, where HCOO(ads) is further oxidized to CO(2). The Pt?:?Au molar ratio and PtAu nanoparticle loading on PDDA-G supports are the two critical factors to achieve excellent electrocatalytic activity of PtAu/PDDA-G catalysts for the HCOOH oxidation reactions.     

二十四面体Pt纳米晶电极上甲酸解离吸附反应动力学研究

研究了甲酸在二十四面体Pt纳米晶（THHPtNCs）电极表面解离吸附反应过程.电化学原位红外反射光谱结果显示,甲酸在低电位（-0.20V（SCE））即可在THHPtNCs电极上氧化到CO2,同时发生分子内化学键断裂生成吸附态CO物种.运用程序电位阶跃暂态方法定量研究甲酸解离吸附反应动力学,测得5×10^-3mol·L^-1 HCOOH＋0.1mol·L^-1 H2SO4溶液中甲酸在THHPtNCs电极上解离吸附的最大平均速率υamax为13.19×10^-10mol·cm^-2·s^-1,是商品Pt/C催化剂电极上υamax的1.5倍.研究结果揭示了THHPtNCs的反应活性显著高于Pt/C催化剂.     

Fast and Controlled Decorating of Metallic Nanoparticles Using Wall‐jet Configuration

A new method to decorate metallic nanoparticles (NPs) based on the wall‐jet configuration was developed. A homemade wall‐jet amperometric cell coupled to an electronic micropipette was used to decorate Pt NPs with Sb and Sn hydrodynamically through the injection of metallic precursor solutions onto an electrode modified with NPs under applied potential. The method allows the control of the coverage degree (θ) by changing easy handling parameters such as injection flow rate, injected volume and concentration of precursors. The decoration procedure is fast, reproducible, simple and economic, since it only uses a few microlitres of precursors to prepare each electrode composition. It is possible to prepare an average of 1000 electrodes using the same amount of precursors for each one prepared by a conventional method using a typical three‐electrode cell. Sb‐ and Sn‐decorated Pt/C NPs were first evaluated towards diluted glucose electrooxidation in buffer solution. These first insights reveal that the output current density increases with θ_Sb and θ_Sn; Sb‐decorated Pt/C shows the greatest improvement.     

炭载Pd-Ni合金纳米粒子对甲酸的电催化氧化

通过液相还原法制备了具有不同原子比例的Pd-Ni/C催化剂,并且使用X射线衍射（XRD）、透射电子显微镜(TEM)和X射线光电子能谱(XPS) 等表征手段对制备的催化剂进行了表征,总结了Ni的掺杂对Pd-Ni合金纳米粒子的尺寸及晶体结构的影响。电化学测试结果表明：适量的Ni的掺杂不但能够增强催化剂对甲酸催化氧化的活性,而且还能够提高催化剂的稳定性。因此,Pd-Ni/C催化剂是一类具有潜在应用前景的直接甲酸燃料电池阳极催化剂     

The mechanism of formic acid electrooxidation on iron tetrasulfophthalocyanine-modified platinum electrode

The mechanism of formic acid electrooxidation on iron tetrasulfophthalocyanine (FeTSPc) modified Pt electrode was investigated with electrochemical methods. It was found that a “third-body” effect of FeTSPc on Pt electrode predominates during the electrooxidation process based on unusual electrochemical results. The modification leads formic acid electrooxidation to take place through a desired direct pathway, in which the mechanism is proposed to be the gradual dehydrogenation of formic acid and the reaction of formate with hydroxyl species.     

FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell

Fe_xC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell was investigated for the first time. The resultant Pt/Fe_xC–C catalysts were prepared by using a simple reduction reaction to load Pt on Fe_xC–C hybrid material, which was synthesized through the carbonization of sucrose and Fe(NO₃)₃. It was found that the Pt/Fe_xC–C catalysts exhibited excellent catalytic activity for formic acid electrooxidation. The great improvement in the catalytic performance is attributed to the fact that Fe_xC–C hybrid material ameliorated the tolerance to CO adsorption of Pt and facilitated the uniform dispersion of Pt.     

Size effects on the electrochemical oxidation of oxalic acid on nanocrystalline platinum

The electrocatalytic activity of platinised platinum (Pt Pt) electrodes in the electrooxidation of oxalic acid was found to be dependent on the degree of ageing. Pt Pt electrodes prepared by electrodeposition were aged by cycling the potential with an upper positive potential limit corresponding to Pt surface oxidation. This procedure results in surface reconstruction with an increase of mean particle size. The changes of surface area and roughness of Pt Pt during ageing have been discussed in terms of sintering processes for supported catalysts or ceramic materials. An increase of mean particle size is accompanied by a decrease in oxygen adsorption, e.g. through changes in the surface concentration of defects on the particle surface. Two possible mechanisms for the electrooxidation of oxalic acid involving either an oxygen adsorbate species (CE mechanism) or direct electrode transfer can be distinguished. Changes of oxidation rate are related to changes of oxygen coverage with ageing.     

Structure dependent electrooxidation of small organic molecules on Pt-decorated nanoporous gold membrane catalysts

We describe the electrocatalytic properties of self-supported Pt-decorated nanoporous gold (Pt-NPG) membranes towards the electrooxidation of formic acid and some other small organic molecules. By effectively enhancing the Pt utilization and providing a unique surface structure, the electrooxidation of formic acid on Pt-NPG was found to be highly sensitive to its surface structure. An unparalleled increase by nearly two orders of magnitude in catalytic activity was achieved on NPG electrodes decorated with sub-monolayer Pt atoms, as compared to the commercial Pt/C catalyst under the same testing conditions.     

不同介质对Pt/GC电极制备及其性能的影响

应用循环伏安法(CV),扫描电子显微镜(SEM)和电化学原位红外反射光谱(in situFTIRS)研究了不同介质对碳载铂纳米薄膜电极(Pt/GC)的表面结构以及该薄膜电极对甲酸电催化氧化性能的影响.结果表明,使用不同介质的镀铂溶液,均可电沉积出分布较为均匀的Pt粒子,但其尺寸与形貌却相差很大.当以H2SO4作介质,由循环伏安法于玻碳电极上电沉积Pt得到的(Pt/GC1)电极,其Pt粒子粒径约100~200 nm;而在HClO4介质得到的(Pt/GC2)电极,则含有两种Pt微晶:其一是立方体形,粒径约200 nm,其二为菜花状,粒径约400 nm.电化学循环伏安和原位红外反射光谱测试指明,不同介质制备的Pt/GC电极对甲酸的电催化氧化均表现出与本体铂电极(Pt)相类似的特性,即可通过活性中间体或毒性中间体将甲酸氧化至CO2,但不同结构的Pt/GC电极具有不同的电催化活性.进一步以Sb或Pb修饰Pt/GC电极,不仅可以有效地抑制毒性中间体CO的生成,而且还能显著提高其电催化活性.比较本文研究的7种电极,其电催化活性顺序依次为:Sb-Pt/GC2>Pb-Pt/GC2>Pb-Pt/GC1>Sb-Pt/GC1>Pt/GC2>Pt/GC1>Pt.     

Adsorption and oxidation of ethanol on colloid-based Pt/C, PtRu/C and Pt3Sn/C catalysts: in situ FTIR spectroscopy and on-line DEMS studies

The interaction of colloid-based, carbon supported Pt/C (40 wt%), PtRu/C (45 wt%) and Pt3Sn/C (24 wt%) catalysts with ethanol and their performance for ethanol electrooxidation were investigated in model studies by electrochemical, in situ infrared spectroscopy and on-line differential electrochemical mass spectrometry measurements. The combined application of in situ spectroscopic techniques on realistic catalysts and under realistic reaction (DEMS, IR) and transport conditions (DEMS) yields new insight on mechanistic details of the reaction on these catalysts under the above reaction and transport conditions. Based on these results, the addition of Sn or Ru, though beneficial for the overall activity for ethanol oxidation, does not enhance the activity for C-C bond breaking. Dissociative adsorption of ethanol to form CO2 is more facile on the Pt/C catalyst than on PtRu/C and Pt3Sn/C catalysts within the potential range of technical interests (<0.6 V), but Pt/C is rapidly blocked by an inhibiting CO adlayer. In all cases acetaldehyde and acetic acid are dominant products, CO2 formation contributes less than 2% to the total current. The higher ethanol oxidation current density on the Pt3Sn/C catalyst at these potentials results from higher yields of C2 products, not from an improved complete ethanol oxidation to CO2.     

Facile electrochemical synthesis of a conducting copolymer from 5-aminoindole and EDOT and its use as Pt catalyst support for formic acid electrooxidation

5-Aminoindole and 3,4-ethylenedioxythiophene (EDOT) were copolymerized electrochemically on a carbon cloth (CC) electrode in an aqueous sulfuric acid solution. The as-prepared copolymer was characterized by cyclic voltammogram, SEM, and UV-vis and FT-IR spectra through which the electrochemical properties, structure, and composition of the as-obtained copolymer were determined. The electrochemical activity and stability of the as-formed copolymer are significantly improved in comparison with poly(5-aminoindole) due to the incorporation of EDOT units into the conjugated chain. The copolymer film-modified CC electrode was used as substrate for Pt particle deposition (denoted as Pt/copolymer/CC), and then, its catalytic activity towards formic acid electrooxidation was studied. Experimental results indicate that the catalytic activity of Pt/copolymer/CC towards formic acid electrooxidation is enhanced in comparison with that of Pt/homopolymer/CC, which can be attributed to the homogeneous distribution of Pt nanoparticles on the copolymer/CC substrate and the improved electrochemical activity of the copolymer film.     

碳载Pt和PtRu催化剂的甲醇电氧化比较

利用电化学方法对商用Pt/C和PtRu/C催化剂在酸性介质中的甲醇电氧化进行了比较研究.动电位和恒电位氧化实验结果皆表明PtRu/C比Pt/C对甲醇电催化活性高.PtRu合金的形成不仅改变了催化剂表面对氢的吸附性质,而且使氧化物还原峰电位向阴极方向移动.Ru与甲醇的相互作用为温度活化过程,需要较高的温度.     

A Nanoporous PdCo Alloy as a Highly Active Electrocatalyst for the Oxygen‐Reduction Reaction and Formic Acid Electrooxidation

A nanoporous (NP) PdCo alloy with uniform structure size and controllable bimetallic ratio was fabricated simply by one‐step mild dealloying of a PdCoAl precursor alloy. The as‐made alloy consists of a nanoscaled bicontinuous network skeleton with interconnected hollow channels that extend in all three dimensions. With a narrow ligament size distribution around 5 nm, the NP PdCo alloy exhibits much higher electrocatalytic activity towards the oxygen‐reduction reaction (ORR) with enhanced specific and mass activities relative to NP Pd and commercial Pt/C catalysts. A long‐term stability test demonstrated that NP PdCo has comparable catalytic durability with less loss of ORR activity and electrochemical surface area than Pt/C. The NP PdCo alloy also shows dramatically enhanced catalytic activity towards formic acid electrooxidation relative to NP Pd and Pd/C catalysts. The as‐made NP PdCo holds great application potential as a promising cathode as well as an anode electrocatalyst in fuel cells with the advantages of superior catalytic performance and easy preparation.