Stability of carbon-supported palladium nanoparticles in alkaline media: A case study of graphitized and more amorphous supports

The stability and degradation mechanism of graphitized (Graphene nanosheets) and more amorphous (Vulcan XC-72R) carbon-supported palladium nanoparticles was investigated. Coupling identical-location transmission electron microscopy (ILTEM) and electrochemistry enabled to correlate the distribution of the Pd nanoparticles under accelerated stress test (up to 1000 cycles between 0.1 and 1.23 V vs. RHE, in a 0.1 M NaOH solution at 25 °C) with changes in electrochemical accessible surface area (ECSA). The carbon-supported Pd nanoparticles undergo similar rates of degradation in terms of electrochemical surface areas on both supports. However, their mechanisms of degradation differ: on amorphous carbon, the primary mode of degradation is Pd nanoparticles detachment (and minor agglomeration), whereas on graphitized supports it is more likely their coalescence and dissolution/redeposition. “Bulk” carbon-corrosion is negligible in both cases, as proven by ex situ Raman spectroscopy. So, using a graphitized carbon support (Graphene nanosheets) versus a more amorphous one (Vulcan XC-72R) does not enable to significantly depreciate the Pd/C catalyst degradation in alkaline media.     

Well-dispersed palladium nanoparticles on three-dimensional hollow N-doped graphene frameworks for enhancement of methanol electro-oxidation

In this work, palladium (Pd) nanoparticles/three-dimensional hollow N-doped graphene frameworks (HNGF) hybrid catalysts were fabricated by using amine-functionalized poly (glycidyl methacrylate) microspheres-templated HNGF as supporting materials for Pd nanoparticles (NPs). The results demonstrate that the Pd NPs with average sizes of ~ 5.5 nm can be well dispersed on the surfaces of HNGF with internal circular holes of ~ 400 nm. The Pd/HNGF catalysts exhibit high electrocatalytic activity and durability toward methanol electro-oxidation in alkaline medium, compared to Pd/graphene and Pd/carbon.     

Synthesis of coin-like hollow carbon and performance as Pd catalyst support for methanol electrooxidation

The coin-like hollow carbon (CHC) has been synthesized by only using ethanol as the carbon source with a novel Mg/NiCl₂ catalytic system via a facile solvothermal method for the first time. The CHC synthesized at optimized conditions shows an average thickness of less than 154 nm and the coin diameter of 1–3 μm. The CHC is characterized by SEM, TEM, XRD and electrochemical techniques. Pd on CHC (denotes as Pd/CHC) electrocatalysts are prepared for methanol oxidation in alkaline media. The Pd/CHC electrocatalyst gives a mass activity of 2930 A g⁻¹ Pd for methanol oxidation against 870 A g⁻¹ Pd on Pd/C electrocatalyst. One main reason for the higher mass activity of the Pd/CHC is the higher electrochemical active surface area (EASA) of the Pd/CHC.     

Facile synthesis of PtRu/C electrocatalyst with high activity and high loading for passive direct methanol fuel cell by synergetic effect of ultrasonic radiation and mechanical stirring

The PtRu/C electrocatalyst with high loading (PtRu of 60 wt%) was prepared by synergetic effect of ultrasonic radiation and mechanical stirring. Physicochemical characterizations show that the size of PtRu particles of as-prepared PtRu/C catalyst is only several nanometers (2–4 nm), and the PtRu nanoparticles were homogeneously dispersed on carbon surface. Electrochemistry and single passive direct methanol fuel cell (DMFC) tests indicate that the as-prepared PtRu/C electrocatalyst possessed larger electrochemical active surface (EAS) area and enhanced electrocatalytic activity for methanol oxidation reaction (MOR). The enhancement could be attributed to the synergetic effect of ultrasound radiation and mechanical stirring, which can avoid excess concentration of partial solution and provide a uniform environment for the nucleation and growth of metal particles simultaneously hindering the agglomeration of PtRu particles on carbon surface.     

Synthesis of highly dispersed Pd/C electro-catalyst with high activity for formic acid oxidation

In this study, we present a simple process to obtain highly dispersed palladium nanoparticles on Vulcan XC-72R carbon support without any protective agent. To obtain high metal loading Pd/C catalyst without any surfactant, we modified the polyol process by employing NH₃ species as a mediation to control the reaction pathway to avoid the precipitation of Pd(OH)₂, and hence the agglomeration of Pd nanoparticles. The obtained Pd/C sample was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques. The results show that highly dispersed Pd/C catalyst with an average diameter of 3.0 nm could be obtained in this novel process. The activity of formic acid oxidation on this Pd/C catalyst was examined via cyclic voltammetry technique and it is found that the catalytic activity is greatly enhanced due to the reduced particle size and the improved dispersion of palladium nanoparticles on the carbon surface.     

碳纳米管上原位沉积钯-钴-镍纳米颗粒及其对乙醇氧化的电活性

以水合肼为还原剂,在水和乙醇的混合溶液中制备多壁碳纳米管(MWCNT)负载的纳米镍(Ni/MWCNT)和纳米镍钴(Ni-Co/MWCNT)颗粒,然后将它们分别与氯化钯溶液反应,形成的钯纳米颗粒原位沉积在MWCNT表面,从而得到MWCNT负载的Pd-Ni/MWCNT和Pd-Ni-Co/MWCNT催化剂。SEM和TEM图像显示,MWCNT上的催化剂颗粒是由5~10 nm的小颗粒团聚而成的30~100 nm的大颗粒,三金属催化剂的粒径比双金属的粒径小,在MWCNT上的分散度更高。ICP和EDS分析显示,Pd直接还原并包覆在纳米镍和纳米镍钴表面;采用循环伏安和计时电流技术,研究了催化剂在碱性溶液中对乙醇氧化的电催化活性,结果表明,Pd-Ni-Co/MWCNT催化剂对乙醇氧化具有强的电催化活性,乙醇氧化对应的峰电流密度达101.8 mA·cm^-2,并且催化剂催化活性稳定。     

Pd Nanostructures with High Tolerance to CO Poisoning in the Formic Acid Electrooxidation Reaction

Pd architectures such as nanobars and nanoparticles were synthetized by the polyol method using di-ethylene glycol as reaction media. The morphology, composition and electrocatalytic properties were investigated by transmission electronmicroscopy (TEM), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and electrochemical measurements. The electrocatalytic activity of Pd nanostructures was tested in terms of formic acid electrooxidation reaction (FAOR) in acid media (0.5 M H₂SO₄) and compared with commercial Pd/XC-72 (Pd/C). Results from the electrochemical studies showed that Pdnanobars (PdNB/C) presented higher tolerance to the CO and CO₂ poisoning effect compared with Pd nanoparticles (PdNP/C) and commercial Pd/C. Furthermore, the onset potential toward formic acid electrooxidation at high concentration (1 M) on PdNB/C exhibited a negative shift ca. 100 mV compared with commercial Pd/C. Finally, PdNB/C in the presence of 1 M FA showed a lower poisoning degree compared with commercial Pd/C and PdNP/C.     

碳纳米管上原位沉积钯-钴-镍纳米颗粒及其对乙醇氧化的电活性

以水合肼为还原剂,在水和乙醇的混合溶液中制备多壁碳纳米管(MWCNT)负载的纳米镍(Ni/MWCNT)和纳米镍钴(Ni-Co/MWCNT)颗粒,然后将它们分别与氯化钯溶液反应,形成的钯纳米颗粒原位沉积在MWCNT表面,从而得到MWCNT负载的PdNi/MWCNT和Pd-Ni-Co/MWCNT催化剂。SEM和TEM图像显示,MWCNT上的催化剂颗粒是由5~10 nm的小颗粒团聚而成的30~100 nm的大颗粒,三金属催化剂的粒径比双金属的粒径小,在MWCNT上的分散度更高。ICP和EDS分析显示,Pd直接还原并包覆在纳米镍和纳米镍钴表面;采用循环伏安和计时电流技术,研究了催化剂在碱性溶液中对乙醇氧化的电催化活性,结果表明,Pd-Ni-Co/MWCNT催化剂对乙醇氧化具有强的电催化活性,乙醇氧化对应的峰电流密度达101.8 m A·cm~(-2),并且催化剂催化活性稳定。     

Oxygen reduction reaction on carbon-supported palladium nanocubes in alkaline media

Carbon-supported Pd nanocubes with the size of 30, 10 and 7 nm were prepared and their electrocatalytic activity towards the oxygen reduction reaction (ORR) in alkaline solution was studied. For comparison carbon-supported spherical Pd nanoparticles and commercial Pd/C catalyst were used. The catalysts were characterised by transmission electron microscopy, electro-oxidation of carbon monoxide and cyclic voltammetry and the ORR activity was evaluated using the rotating disk electrode method. The ORR on all studied Pd/C catalysts proceeded via four-electron pathway where the rate-limiting step was the transfer of the first electron to O₂ molecule. The specific activity of Pd nanocubes was more than two times higher than that of spherical Pd nanoparticles and increased with increasing the particle size.     

Preparation of Pd/C catalyst for formic acid oxidation using a novel colloid method

A novel colloid method using (WO₃)_n·xH₂O as colloidal source was developed to prepare Pd/C catalyst for formic acid oxidation. Transmission electron microscopy image shows that the Pd/C nanoparticles have an average size of 3.3 nm and a narrow size distribution. Electrochemical measurements indicate that the Pd/C catalyst exhibits significantly high electrochemical active surface area and high catalytic activity with good stability for formic acid oxidation compared with that prepared by common method. The colloid method is very simple and has great potentials for mass-producing Pd/C and others noble metal catalysts.     

Fe-N/C catalysts for oxygen reduction based on silicon carbide derived carbon

Two different Fe-N/C(SiC) catalysts (Fe + Bipyr/C(SiC) and Fe + Phen/C(SiC)) for oxygen reduction based on silicon carbide derived carbon were synthesized and investigated in 0.1 M KOH aqueous solution by rotating disc electrode method. It was found that the electrocatalytic activity and stability are significantly influenced by the change of the nitrogen ligand in the catalyst. Comparable current density values obtained for 20%Pt-Vulcan electrode could be achieved for Fe + Bipyr/C(SiC) and Fe + Phen/C(SiC) catalysts in alkaline media. The durability tests (~ 150 h) showed that the decrease of the activity for Fe + Bipyr/C(SiC) and Fe + Phen/C(SiC) is only 0.5 mV h^− 1 and 0.17 mV h^− 1, respectively. The Fe + Bipyr/C(SiC) catalyst demonstrated higher activity in the RDE measurements, but during the long-term test the Fe + Phen/C(SiC) catalyst prove to be more stable than Fe + Bipyr/C(SiC).     

Highly active PtRuFe/C catalyst for methanol electro-oxidation

High methanol electro-oxidation activity was obtained on novel PtRuFe/C (2:1:1 at.%) catalyst. Mass and specific activities were 5.67 A  g⁻¹ catal. and 177 mA m⁻² for the PtRuFe/C catalyst while those of the commercial PtRu/C catalyst were 2.28 A g⁻¹ catal. and 87.7 mA m⁻², respectively. CO stripping results showed that on-set voltage for CO electro-oxidation was lowered by incorporation of Fe. XRD and XPS results revealed that Fe₂O₃ was formed instead of Fe(0), which resulted in large electron deficiency in Pt and easy CO electro-oxidation. The electron deficiency of Pt was proved by XPS results of Pt4f peaks, which moved to higher binding energies in PtRuFe/C than PtRu/C.     

Electrodeposited fabrication of highly ordered Pd nanowire arrays for alcohol electrooxidation

Highly ordered Pd nanowire arrays (NWAs) are prepared using a porous aluminum oxide template by pulse electrodeposition. The obtained Pd nanowire arrays with the diameter of 50 nm and length of 850 nm have been characterized by scanning electron microscopy, energy dispersive X-ray analysis, and high resolution transmission electron microscope. Meanwhile, the electrocatalytic activity of Pd NWAs electrodes for methanol and isopropanol oxidation in alkaline media is studied. It is found that the obtained nanostructures exhibit excellent catalytic activity for alcohol electrooxidation. The isopropanol oxidation shows the higher activity on Pd NWAs electrode than methanol in alkaline medium.     

Oxygen reduction reaction on carbon supported Palladium–Nickel alloys in alkaline media

Carbon supported Palladium–Nickel alloys with various compositions (Pd–Ni/C) were synthesized by chemical reduction of the co-precipitated Pd and Ni hydroxides on carbon. The structure of these alloys was characterized using X-ray diffraction (XRD) analysis. The catalytic activity of Pd–Ni/C for oxygen reduction reaction (ORR) in alkaline media was studied using a glassy carbon rotating disk electrode (RDE). Pd/C showed ORR activity close to that of Pt/C. The activities of Pd–Ni (3:1)/C and Pd–Ni (1:1)/C were found unchanged compared with that of Pd/C. Ni/C showed about 175 mV lower onset potential than Pt/C, and the activity of Pd–Ni (1:3)/C was observed to be between that of Pd/C and Ni/C.     

Highly efficient Fe/N/C catalyst using adenosine as C/N-source for APEFC

An environmentally friendly precursor, adenosine, has been used as a dual source of C and N to synthesize nitrogen-doped carbon catalyst with/without Fe. A hydrothermal carbonization method has been used and water is the carbonization media. The morphology of samples with/without Fe component has been compared by HRTEM, and the result shows that Fe can promote the graphitization of carbon. Further electro-chemical test shows that the oxygen reduction reaction(ORR) catalytic activity of Fe-containing sample(C–Fe N) is much higher than that of the Fe-free sample(C–N). Additionally, the intermediates of C–Fe N formed during each synthetic procedure have been thoroughly characterized by multiple methods,and the function of each procedure has been discussed. The C–Fe N sample exhibits high electro-catalytic stability and superior electro-catalytic activity toward ORR in alkaline media, with its half-wave potential 20 mV lower than that of commercial Pt/C(40 wt%). It is further incorporated into alkaline polymer electrolyte fuel cell(APEFC) as the cathode material and led to a power density of 100 m W/cm~2.     

Synthesis of Pd-Cu Bimetallic Electrocatalyst for Ethylene Glycol and Glycerol Oxidations in Alkaline Media

PdCu/C (XC-72) electrocatalyst was synthesized by a chemical reduction method using ethylene glycol as reaction media, polyvinylpyrrolidone as surfactant and sodium borohydride as reducing agent. Vulcan carbon XC-72 was employed as support and added through the PdCu synthesis procedure; further, Pd commercial (Pd/C, 20% ETEK) was used for comparison purposes. Physicochemical characterization consisted in XRD, XRF, EDS and TEM analyses. TEM micrographs showed the presence of semi-spherical nanoparticles with a particle distribution around 6 nm. X-ray diffraction patterns showed the typical face-centered cubic structure of Pd materials for commercial Pd and revealed a low crystallinity for PdCu/C. The XRF analysis showed a mass metal composition of 81% Pd and 19% Cu. EDS analysis was made to single particles exhibiting an average elemental composition of 92% Pd and 8% Cu. The electrocatalytic activity of PdCu/C and Pd/C was evaluated by cyclic voltammetry experiments toward ethylene glycol and glycerol oxidations using three concentrations (0.1, 1 and 3 M) and 0.3 M KOH as electrolyte. These experiments exhibited the superior performance of PdCu compared with commercial Pd by means of current densities associated to the electro-oxidation reactions where values at least 3-fold higher than Pd/C were found.     

Fabrication and catalytic properties of Pt and Ru decorated TiO2⧹CNTs catalyst for methanol electrooxidation

Highly ordered anodic titania nanotube arrays provide a large surface area for electrodepositing nickel nanoparticles which are used as the catalyst for carbon nanotube growth. Pt and Ru nanoparticles, approximately 3 nm in diameter, are uniformly electrodeposited on the as synthesized titania-supported carbon nanotubes (CNTs), constructing a novel catalyst for electrocatalytic oxidation of methanol. An enhanced and stable catalytic activity is obtained due to the uniformly dispersed Pt and Ru nanoparticles, and the large CNT network facilitating the electron transfer between the adsorbed methanol molecules and the catalyst substrate. An oxidation peak current density of 55 mA/cm² is achieved at a low Pt load of 0.126 mg/cm² with a Pt/Ru mole ratio of 1:1.     

Pd/Fe3O4-C催化剂对甲醇、乙醇和丙醇氧化的电催化活性

制备对醇氧化反应具有优异电活性的钯催化剂是醇燃料电池研究的重要内容。本文用硼氢化钠还原法制备了钯纳米颗粒, 然后沉积在Fe3O4/C复合物表面, 得到了不同Fe₃O₄负载量的Pd/Fe₃O₄-C催化剂. 透射电镜（TEM）图显示钯纳米颗粒均匀地分散在Fe₃O₄/C表面. 对制备好的Pd/Fe₃O₄-C催化剂进行了循环伏安法（CV）、计时电流（CA）和电化学阻抗谱（EIS）的测试, 研究了其在碱性介质中对C1-C3醇类（甲醇、乙醇和丙醇）氧化的电催化活性. 结果表明, 所制备的不同Fe₃O₄负载量的Pd/Fe₃O₄(2%)-C,Pd/Fe₃O₄(5%)-C, Pd/Fe₃O₄(10%)-C和Pd/C催化剂中, Pd/Fe₃O₄(5%)-C催化剂表现出最高的醇氧化电流密度. 依据循环伏安（CV）数据,Pd/Fe₃O₄(5%)-C催化剂对甲醇、乙醇、正丙醇和异丙醇氧化的阳极峰电流密度分别是Pd/C催化剂的1.7、1.4、1.7和1.3倍. Pd/Fe₃O₄(5%)-C催化剂对乙醇氧化的电荷传递电阻也远低于Pd/C催化剂. 制备的所有催化剂对C1-C3醇类电氧化的电流密度大小排序如下: 正丙醇﹥乙醇﹥甲醇﹥异丙醇. 此外, 碳粉中Fe₃O₄纳米颗粒的存在提高了钯纳米颗粒的电化学稳定性.     

Bismuth modified Pd/C as catalysts for hydrogen related reactions

The electrocatalytic activity of bimetallic BiPd catalysts supported on Sibunit carbon towards hydrogen oxidation/evolution reactions (HOR/HER) was studied in a gas diffusion electrode (GDE) setup. Catalysts were synthesized by deposition of Pd on the carbon support, followed by impregnation of Pd/C precursor with Bi(NO₃)₃ solution and reduction in hydrogen. Transmission electron microscopy and local EDX elemental analysis revealed that BiPd/C catalysts contain bimetallic particles with narrow size distribution with maxima at 3.2–4.1 nm. X-ray diffraction evidenced that bimetallic particles are constituted by Pd–Bi solid solution. It was shown that modification of Pd/C by bismuth increases the specific activity of palladium towards HOR/HER by a factor of 3.     

Pd/TiO2/C复合催化剂的制备及其在碱性溶液中对乙醇氧化的电催化性能

钛酸四丁酯前驱体水热合成制备纳米TiO₂颗粒,在TiO₂和Vulcan XC-72活性炭复合载体上液相还原负载Pd纳米颗粒,制得Pd/TiO₂/C复合催化剂. 通过透射电镜（TEM）和X射线衍射（XRD）测试表明其具有面心立方结构,Pd金属粒子（粒径约3 ~ 4 nm）均匀分散在锐钛矿型的纳米TiO₂和活性炭的复合载体上. 循环伏安和计时电流曲线测试表明,与相同Pd载量的Pd/C相比,20% Pd载量的Pd/TiO₂/C颗粒在常温常压下对乙醇的电催化氧化有很高活性和稳定性. 这主要归功于纳米TiO₂改变了Pd表面的电子特性,且增大了其比表面积.