Methane activation on PdMn/C-ITO electrocatalysts using a reactor-type PEMFC

Various palladium and manganese supported in a mix of carbon and indium thin oxide (PdMn/C-ITO) compositions were synthesized by a sodium borohydride reduction process for methane activation at low temperatures in a proton exchange membrane fuel cell (PEMFC) reactor. These electrocatalysts were characterized by X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy XPS, inductively coupled plasma mass spectrometry ICP-MS, attenuated total reflection-Fourier transform infrared spectroscopy, cyclic voltammetry and a PEMFC reactor. The diffractograms of PdMn/C-ITO electrocatalysts revealed the face-centered cubic structure of palladium and the bixbyite cubic structure of In₂O₃. TEM experiments showed mean nanoparticle sizes between 4.7 and 5.2 nm for all electrocatalysts. XPS results showed the presence of palladium and manganese oxides, as well as Pd⁰ species. Cyclic voltammograms of PdMn/C-ITO electrocatalysts showed an increase in current density values after the methane adsorption, this result is related to formation of methanol or formic acidic. Polarization curves at 80 °C acquired in a PEMFC reactor showed that PdMn(70:30)/C-ITO and PdMn(50:50)/C-ITO have superior performance when compared to Pd/C-ITO indicating the beneficial effect of adding Mn, this behavior can be attributed to the bifunctional mechanism or to the electronic effect of support.

     

Direct oxidation of methane at low temperature using Pt/C,Pd/C,Pt/C-ATO and Pd/C-ATO electrocatalysts prepared by sodium borohydride reduction process

The main objective of this paper was to characterize the voltammetric profiles of the Pt/C,Pt/C-ATO,Pd/C and Pd/CATO electrocatalysts and study their catalytic activities for methane oxidation in an acidic electrolyte at 25 ℃ and in a direct methane proton exchange membrane fuel cell at 80 ℃. The electrocatalysts prepared also were characterized by X-ray diffraction( XRD) and transmission electron microscopy( TEM). The diffractograms of the Pt/C and Pt/C-ATO electrocatalysts show four peaks associated with Pt face-centered cubic( fcc) structure,and the diffractograms of Pd/C and Pd/C-ATO show four peaks associated with Pd face-centered cubic( fcc) structure. For Pt/C-ATO and Pd/C-ATO,characteristic peaks of cassiterite( SnO_2) phase are observed,which are associated with Sb-doped SnO_2( ATO) used as supports for electrocatalysts. Cyclic voltammograms( CV) of all electrocatalysts after adsorption of methane show that there is a current increase during the anodic scan. However,this effect is more pronounced for Pt/C-ATO and Pd/C-ATO. This process is related to the oxidation of the adsorbed species through the bifunctional mechanism,where ATO provides oxygenated species for the oxidation of CO or HCO intermediates adsorbed in Pt or Pd sites. From in situ ATR-FTIR( Attenuated Total Reflectance-Fourier Transform Infrared) experiments for all electrocatalysts prepared the formation of HCO or CO intermediates are observed,which indicates the production of carbon dioxide. Polarization curves at 80 ℃in a direct methane fuel cell( DMEFC) show that Pd/C and Pt/C electroacatalysts have superior performance to Pd/C-ATO and Pt/C-ATO in methane oxidation.     

Pd/C promoted by Au for 2-propanol electrooxidation in alkaline media

Pd/C catalysts promoted by Au are investigated as electrocatalysts for the direct 2-propanol fuel cells in alkaline media. The results show that Pd is a good electrocatalyst for 2-propanol oxidation and the activity for 2-propanol electrooxidation is higher than that for methanol electrooxidation on the Pd/C electrocatalysts in alkaline media. Addition of Au can significantly increase the palladium catalytic activity and stability for the 2-propanol oxidation. PdAu4:1/C has higher electrocatalytic activity and better stability for the electrooxidation of 2-propanol than Pd/C and E-TEK Pt/C electrocatalysts. The present study shows the promising properties of Au promoted Pd/C as effective electrocatalysts for 2-propanol fuel based direct alcohol fuel cells.     

Influence of Pd deposition pH value on the performance of Pd-CuO/SiO2 catalyst for semi-hydrogenation of 2-methyl-3-butyn-2-ol（MBY）

The selective hydrogenation of C≡C to C=C bonds is an important step, yet remains to be a great challenge in chemical industry. In this study, we have revealed the influence of Pd deposition pH value on the catalytic performance of Pd-CuO/SiO₂ catalyst for the semi-hydrogenation of 2-methyl-3-butyn-2-ol（MBY）. Trace amount of Pd（about 500 ppm） was loaded via deposition-reduction method on CuO/SiO₂ support by using H₂PdCl₄ solution as precursor and NaBH<...     

Crystal‐Phase‐Engineered PdCu Electrocatalyst for Enhanced Ammonia Synthesis

Crystal phase engineering is a powerful strategy for regulating the performance of electrocatalysts towards many electrocatalytic reactions, while its impact on the nitrogen electroreduction has been largely unexplored. Herein, we demonstrate that structurally ordered body‐centered cubic (BCC) PdCu nanoparticles can be adopted as active, selective, and stable electrocatalysts for ammonia synthesis. Specifically, the BCC PdCu exhibits excellent activity with a high NH₃ yield of 35.7 μg h^?1 mg^?1_cat, Faradaic efficiency of 11.5 %, and high selectivity (no N₂H₄ is detected) at ?0.1 V versus reversible hydrogen electrode, outperforming its counterpart, face‐centered cubic (FCC) PdCu, and most reported nitrogen reduction reaction (NRR) electrocatalysts. It also exhibits durable stability for consecutive electrolysis for five cycles. Density functional theory calculation reveals that strong orbital interactions between Pd and neighboring Cu sites in BCC PdCu obtained by structure engineering induces an evident correlation effect for boosting up the Pd 4d electronic activities for efficient NRR catalysis. Our findings open up a new avenue for designing active and stable electrocatalysts towards NRR.     

A Facile Strategy to PdCu Bimetallic Alloy Nanosponges with Highly Porous Features as a High‐Performance Electrocatalytic Activity for Ethanol Electrooxidation in an Alkaline Medium

Well‐defined three‐dimensional (3D) PdCu bimetallic alloy nanosponges (BANs) with highly porous structure was reported through a rapid and general strategy. Significantly, the as‐prepared PdCu BANs exhibited greatly enhanced activity and stability than commercial Pd/C catalyst towards ethanol electrooxidation in an alkaline medium. Pd₁Cu₁ shows higher active area and better electrocatalytic activity than Pd₁Cu₂ and Pd₂Cu₁. This result demonstrates the potential of applying these PdCu BANs as effective electrocatalysts for direct alcohol fuel cells (DAFCs).     

Facile Synthesis of PdCu Echinus‐Like Nanocrystals as Robust Electrocatalysts for Methanol Oxidation Reaction

Exploiting high‐performance and inexpensive electrocatalysts for methanol electro‐oxidation is conductive to promoting the commercial application of direct methanol fuel cells. Here, we present a facile synthesis of echinus‐like PdCu nanocrystals (NCs) via a one‐step and template‐free method. The echinus‐like PdCu NCs possess numerous straight and long branches which can provide abundant catalytic active sites. Owing to the novel nanoarchitecture and electronic effect of the PdCu alloy, the echinus‐like PdCu NCs display high electrocatalytic performance toward methanol oxidation reaction in an alkaline medium. The mass activity of echinus‐like PdCu NCs is 1202.1 mA mg_Pd^?1, which is 3.7 times that of Pd/C catalysts. In addition, the echinus‐like structure, as a kind of three‐dimensional self‐supported nanoarchitecture, endows PdCu NCs with significantly enhanced stability and durability. Hence, the echinus‐like PdCu NCs hold prospect of being employed as electrocatalysts for direct alcohol fuel cells.     

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.     

Crystal-Phase-Engineered PdCu Electrocatalyst for Enhanced Ammonia Synthesis

Crystal phase engineering is a powerful strategy for regulating the performance of electrocatalysts towards many electrocatalytic reactions, while its impact on the nitrogen electroreduction has been largely unexplored. Herein, we demonstrate that structurally ordered body-centered cubic (BCC) PdCu nanoparticles can be adopted as active, selective, and stable electrocatalysts for ammonia synthesis. Specifically, the BCC PdCu exhibits excellent activity with a high NH₃ yield of 35.7 μg h⁻¹ mg⁻¹_cat, Faradaic efficiency of 11.5 %, and high selectivity (no N₂H₄ is detected) at −0.1 V versus reversible hydrogen electrode, outperforming its counterpart, face-centered cubic (FCC) PdCu, and most reported nitrogen reduction reaction (NRR) electrocatalysts. It also exhibits durable stability for consecutive electrolysis for five cycles. Density functional theory calculation reveals that strong orbital interactions between Pd and neighboring Cu sites in BCC PdCu obtained by structure engineering induces an evident correlation effect for boosting up the Pd 4d electronic activities for efficient NRR catalysis. Our findings open up a new avenue for designing active and stable electrocatalysts towards NRR.     

Pd-based PdPt(19:1)/C electrocatalyst as an electrode in PEM fuel cell

A carbon supported Pd-based PdPt catalyst with a Pd:Pt atomic ratio of 19:1 was synthesized and applied to a polymer electrolyte membrane fuel cell (PEMFC). Three different types of single cells with the electrodes containing (PdPt/C:Pt/C), (Pt/C:PdPt/C) and (PdPt/C:PdPt/C) as their anode and cathode electrocatalysts were fabricated and the performance of them was compared. The single cell using PdPt/C as the anode electrocatalyst showed a high performance comparable to the cell with a commercial Pt/C electrocatalyst. This indicates that Pd-based electrocatalysts can be used as an anode electrocatalyst in PEMFC with very small amount of Pt (just about 5 at.%).     

Methanol oxidation in acidic and alkaline electrolytes using PtRuIn/C electrocatalysts prepared by borohydride reduction process

PtRuIn/C electrocatalysts( 20% metal loading by weight) were prepared by sodium borohydride reduction process using H_2PtCl6·6H_2O,RuCl_3·xH_2O and InCl_3·xH_2O as metal sources,borohydride as reducing agent and Carbon Vulcan XC72 as support. The synthetized PtRuIn/C electrocatalysts were characterized by X-ray diffraction( XRD),energy dispersive analysis( EDX),transmission electron microscopy( TEM),cyclic voltammetry( CV),chronoamperommetry( CA) and polarization curves in alkaline and acidic electrolytes( single cell experiments). The XRD patterns showPtpeaks are attributed to the face-centered cubic( fcc) structure,and a shift of Pt( fcc) peaks indicates that Ru or In is incorporated into Ptlattice. TEMmicrographs showmetal nanoparticles with an average nanoparticle size between 2.7 and 3.5 nm. Methanol oxidation in acidic and alkaline electrolytes was investigated at room temperature,by CV and CA. PtRu/C( 50 ∶ 50) shows the highest activity among all electrocatalysts in study considering methanol oxidation for acidic and alkaline electrolyte. Polarization curves at 80 ℃ showPtRuIn/C( 50 ∶ 25 ∶ 25)with superior performance for methanol oxidation,when compared to Pt/C,PtIn/C and PtRu/C for both electrolytes. The best performance obtained by PtRuIn/C( 50 ∶ 25 ∶ 25) in real conditions could be associated with the increased kinetics reaction and/or with the occurrence simultaneously of the bifunctional mechanism and electronic effect resulting from the presence of Ptalloy.     

Electrocatalytic oxidation of formic acid on functional MWCNTs supported nanostructured Pd–Au catalyst

In this work, PdAu nanocatalysts with different weight ratio of Pd and Au supported on functional multi-walled carbon nanotubes (f-MWCNTs) were prepared, and their electrocatalytic activity for the oxidation of formic acid was also studied. The electrocatalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical results showed that the 4Pd1Au/f-MWCNTs (by weight) catalyst, exhibited distinctly higher activity and better stability in formic acid electrooxidation than the Pd/f-MWCNTs catalyst. The Nano-Au improves potentially the performance of Pd-based electrocatalysts for the direct formic acid fuel cells (DFAFCs).     

Performance of Pd Electrocatalyst Supported on a Physical Mixture Indium Tin Oxide–carbon for Glycerol Electro–oxidation in Alkaline Media

Palladium electrocatalysts, supported on Vulcan XC 72 carbon and indium tin oxide (ITO) with different ratios, were prepared by borohydride reduction method and analysed for glycerol electro‐oxidation application in the presence of KOH solution. Transmission electron microscopy (TEM) and X‐ray diffraction (XRD) techniques were used to characterize the particle size and crystal electrocatalyst structures, whereas their catalytic activities regarding the glycerol electro‐oxidation were evaluated by cyclic voltammetry (CV), chronoamperometry and tested in a direct alkaline glycerol fuel cell (DGFC) by electrochemical techniques. Micrographs results showed that the ITO presence promotes a large agglomeration of particles. Pd/C–ITO electrocatalysts showed peaks associated with the face‐centered cubic (fcc) structure of palladium and several others peaks associated with ITO used as support. Similar performance was found on all Pd/C–ITO electrocatalysts where measurements in CV were compared to Pd/C and Pd/ITO with Pd/C–ITO 50:50 chronoamperometry, presenting a better performance for glycerol electro‐oxidation. When using Pd/C–ITO 85:15 electrocatalyst and 1.0 mol L⁻¹ glycerol at 90 °C, the maximum power density found was 2,1 times higher than that obtained using Pd/C and Pd/CITO electrocatalysts. Therefore, the physical mixture of ITO and carbon, to be used as a support improves the electrocatalytic activity for glycerol oxidation reaction.     

Atom-Ratio-Conducted Tailoring of PdAu Bimetallic Nanocrystals with Distinctive Shapes and Dimensions for Boosting the ORR Performance

Systematically manipulating the shape, dimension, and surface structure of PdAu nanocrystals is an active subject because it offers a powerful means to regulate and investigate their structure–activity relationship. Meanwhile, it is still urgent to reduce the use of two-dimensional precious-metal-based nanomaterials. This work demonstrates that PdAu nanocrystals with a variety of shapes/dimensions, including 1D anisotropic nanowires, 2D porous nanosheets, and 3D penetrative nanoflowers, can be systematically synthesized by simply adjusting the atomic ratio or the reaction time in the same protocol. The resultant PdAu nanocrystals with distinctive shapes, but the same building blocks triumphantly avoid the effects of facet and surface properties; this represents an ideal platform for directly comparing the oxygen reduction reaction (ORR) activity. 2D porous PdAu nanosheets demonstrate superior ORR performance (E_onset = 1.040 V, E_1/2 = 0.932 V) compared with other-dimension-based samples and commercial Pd black; this is attributed to the abundant surface atoms and omni-directional mass-transfer channels. This work not only paves the way for systematically measuring a series of distinctive PdAu nanocrystals as non-Pt electrocatalysts, but also sheds light on the study of structures/dimensions in tuning the catalytic properties of bimetallic nanocrystals.     

Pt@Pd(x)Cu(y)/C core-shell electrocatalysts for oxygen reduction reaction in fuel cells

A series of carbon-supported core-shell nanoparticles with Pd(x)Cu(y)-rich cores and Pt-rich shells (Pt@Pd(x)Cu(y)/C) has been synthesized by a polyol reduction of the precursors followed by heat treatment to obtain the Pd(x)Cu(y)/C (1 ≤ x ≤ 3 and 0 ≤ y ≤ 5) cores and the galvanic displacement of Pd(x)Cu(y) with [PtCl(4)](2-) to form the Pt shell. The nanoparticles have also been investigated with respect to the oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells (PEMFCs). X-ray diffraction (XRD) analysis suggests that the cores are highly alloyed and that the galvanic displacement results in a certain amount of alloying between Pt and the underlying Pd(x)Cu(y) alloy core. Transmission electron microscopy (TEM) images show that the Pt@Pd(x)Cu(y)/C catalysts (where y > 0) have mean particle sizes of <8 nm. Compositional analysis by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) clearly shows Pt enrichment in the near-surface region of the nanoparticles. Cyclic voltammograms show a positive shift of as much as 40 mV for the onset of Pt-OH formation in the Pt@Pd(x)Cu(y)/C electrocatalysts compared to that in Pt/C. Rotating disk electrode (RDE) measurements of Pt@PdCu(5)/C show an increase in the Pt mass activity by 3.5-fold and noble metal activity by 2.5-fold compared to that of Pt/C. The activity enhancements in RDE and PEMFC measurements are believed to be a result of the delay in the onset of Pt-OH formation.     

Oxidation of ethanol on carbon-supported oxide-rich Pd–W bimetallic nanoparticles in alkaline media

Carbon-supported oxide-rich Pd–W bimetallic nanoparticles were prepared by chemical reduction methods. The existence of oxides in the electrocatalysts is confirmed by X-ray photoelectron spectrum (XPS) and high resolution transmission electron microscopy. XPS analysis indicates that the oxygen atoms account for about 50% of all the atoms in Pd–W bimetallic nanoparticles. Compared to Pd/C catalyst, the carbon-supported oxide-rich Pd–W bimetallic nanoparticles exhibit a better catalytic activity for the anode oxidation of ethanol in alkaline media. The onset potential of the as prepared oxide-rich Pd_0.8W_0.2/C catalyst (Pd: W = 8: 2, metal atom ratio) for ethanol oxidation is negative shifted about 90 mV comparing to Pd/C catalyst. The oxide-rich Pd–W/C electrocatalysts provide a new model of noble-metal/promoter system as an extreme case of making the promoter (WO₃) closely adjacent to the noble metal (Pd) by fabricating nanoparticles containing both atom-clusters of oxides and the noble metal atoms.

     

热处理碳载Fe-三聚氰胺及Fe-g-C3N4催化剂的氧还原催化性能

分别以三聚氰胺和三聚氰胺的聚合物为配体, 采用浸渍法合成了两种氧还原反应(ORR)催化剂Fe-N/C(1)和Fe-N/C(2). 通过X射线衍射光谱(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和电化学测试对催化剂的成分、形貌和电催化性能进行了表征. 结果表明, 以三聚氰胺聚合物为配体制备的Fe-N/C具有更高的ORR催化活性. 在高温热处理过程中, 催化剂表面能形成更多的石墨N活性点, 是其ORR性能提高的重要原因.     

具有优异甲醇耐受性的Rh掺杂PdCu有序金属间化合物纳米粒子增强氧还原电催化

Direct methanol fuel cells (DMFCs), as one of the important energy conversion devices, are of great interest in the fields of energy, catalysis and materials. However, the application of DMFCs is presently challenged because of the limited activity and durability of cathode catalysts as well as the poisoning issues caused by methanol permeation to the cathode during operation. Herein, we report a new class of Rh-doped PdCu nanoparticles (NPs) with ordered intermetallic structure for enhancing the activity and durability of the cathode for oxygen reduction reaction (ORR) and achieving superior methanol tolerance. The disordered Rh-doped PdCu NPs can be prepared via a simple wet-chemical method, followed by annealing to convert it to ordered phases. The results of transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), power X-ray diffraction (PXRD) analysis and high resolution TEM (HRTEM) successfully demonstrate the formation of near-spherical NPs with an average size of 6.5 ± 0.5 nm and the conversion of the phase structure. The complete phase transition temperatures of Rh-doped PdCu NPs and PdCu are 500 and 400 ℃, respectively. The molar ratio of Rh/Pd/Cu in the as-synthesized Rh-doped PdCu NPs is 5/48/47. Benefitting from Rh doping and the presence of the ordered intermetallic structure, the Rh-doped PdCu intermetallic electrocatalyst achieves the maximum ORR mass activity of 0.96 A·mg^-1 at 0.9 V versus reversible hydrogen electrode (RHE) under alkaline conditions—a 7.4-fold enhancement compared to the commercial Pt/C catalyst. For different electrocatalysts, the ORR activities follow the sequence, ordered Rh-doped PdCu intermetallics > ordered PdCu intermetallics > disordered Rh-doped PdCu NPs > disordered PdCu NPs > commercial Pt/C catalyst. In addition, the distinct structure endows the Rh-doped PdCu intermetallics with highly stable ORR durability with unaltered half-wave potential (E_1/2) and mass activity after continuous 20000 cycles, which are higher than those of other electrocatalysts. Furthermore, the E_1/2 of the Rh-doped PdCu intermetallics decreases by only 5 mV after adding 0.5 mol·L^-1 methanol to the electrolyte, while the commercial Pt/C catalyst negatively shifts by 235 mV and a distinct oxidation peak can be observed. The results indicate that the ORR activity of the Rh-doped PdCu intermetallic electrocatalyst can be well maintained even in the presence of poisoning environment. Our results have demonstrated that Rh-doped PdCu NPs with ordered intermetallic structures is a potential electrocatalyst toward the next-generation high-performance DMFCs.     

Nanostructured PdRu/C catalysts for formic acid oxidation

Pd and bimetallic PdRu nanoparticles supported on Vulcan XC-72 carbon prepared by the microwave-assisted polyol process are examined as electrocatalysts for the electrooxidation of formic acid. The catalysts are characterized by transmission electron microscopy and X-ray diffraction. The Pd and PdRu nanoparticles with sizes of <10 nm display the characteristic diffraction peaks of a Pd face-centered cubic (fcc) crystal structure. It is found that the addition of Ru to Pd/C can decrease the lattice parameter of Pd (fcc) crystal. The electrocatalytic activities of the catalysts are evaluated in sulfuric acid solution containing 1 M formic acid using linear sweeping voltammetry and chronoamperometry. The results show that Pd₅Ru₁/C displays the best electrocatalytic performance among all catalysts for formic acid electrooxidation.