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Oxygen reduction reaction (ORR) is becoming increasingly important with the development of fuel cells and metal-air batteries. Manganese oxides have been one of the focuses of recent research for Pt-alternative ORR catalysts. However, the structure-activity relationships of manganese oxides have not been well studied or understood. In the present work, we report a new finding that there is a strong dependence of the ORR activity of Mn 3 O 4 on its morphology. By adopting different solvents in the wet-chemical synthesis, we are able to tailor the morphology of Mn 3 O 4 from nanoparticles (NP-L, 12.5 nm and NP-S, 5.95 nm) to nanorods (NR, exposure of Mn 3 O 4 (101)) and nanoflake (NF, exposure of Mn 3 O 4 (001)). Surprisingly, surface-specific activity of NF toward the ORR was found to be one order of magnitude higher than NP-L. The morphology-activity relationships of Mn 3 O 4 were further studied through a combination of electrochemical experiments and density functional theory (DFT) calculations. It was discovered that the formation of *OOH, concomitant with the first electron transfer, is the potential determining step, which is thermo-dynamically more facile on Mn 3 O 4 (001) than (101) plane. The underlying mechanism could be ascribed to the strong interaction between O 2 and Mn 3 O 4 (001) surface as indicated by the DFT calculations. The study enlarges our understanding of Mn 3 O 4 catalysis and provides clues for rational design of highly efficient transitional metal oxide electrocatalysts for the ORR. [ABSTRACT FROM AUTHOR]

Abstract: Carbon-supported bimetallic PdAg catalysts with Pd/Ag atomic ratios varying from 4/1 to 1/2 were prepared by an impregnation–reduction method. The impregnated black mixture was treated in H2/N2 atmosphere at a temperature varying from 180 to 500°C. The obtained Pd x Ag y /C catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV) and chronoamperometry (CA). XRD results show that the lattice constant of Pd is dilated, suggesting the formation of PdAg alloy. The lattice constant of Pd for the Pd x Ag y /C-500 (reduced at 500°C by H2) increases linearly and the average metal particle size decreases slightly from 6.8 to 5.1nm with increasing Ag fractions from 20% to 67% in the PdAg composition. For Pd x Ag y /C catalysts with a certain specific Pd/Ag atomic ratio, e.g., Pd2Ag1/C, the dilated lattice constant of Pd is independent of the reducing temperature, indicating the alloy degree for the Pd2Ag1/C-t catalysts is comparable. The average metal particle size for the Pd2Ag1/C-t catalysts increases from 3.4 to 5.2nm with H2 reduction temperature increasing from 180 to 500°C. The potentiodynamic measurements on ethanol electrooxidation reaction (EOR) show that the catalytic activities for the Pd x Ag y /C-t catalysts toward the EOR are improved by alloying Pd with Ag. At typical potential of a working fuel cell, e.g., −0.4V vs. Hg/HgO, the EOR current density presents a volcano shape as a function of the Ag fractions in PdAg with the maximum occurs at the Pd/Ag atomic ratios between 2/1 and 3/1. The CA tests show that the Pd x Ag y /C-500 catalysts perform high stability than that of Pd/C-500. The improved EOR activity for the Pd x Ag y /C-t catalysts, compared with whether Pd/C or Ag/C catalyst, may possibly be attributed to the formation of PdAg alloy and the fitted particle size. [Copyright &y& Elsevier]

Abstract: A graphitic mesoporous carbon (denoted as GMC) was synthesized using resorcinol and formaldehyde as carbon precursors and iron nitrate as a graphitization catalyst. The GMC was characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and nitrogen adsorption. The results show that the GMC has a mesoporous structure and a high surface area of 403 m2 g−1, and particularly, a well-defined graphitic framework. Using the GMC as the support, a PtRu/GMC was synthesized to act as an electrocatalyst for the methanol oxidation reaction (MOR). A counterpart with Vulcan® XC-72 (denoted as XC) as the support was prepared for comparison. TEM images show that PtRu nanoparticles are distributed uniformly on the carbon supports for both electrocatalysts. The electrochemical activity of the PtRu/GMC toward the MOR is slightly higher than that of the PtRu/XC in both half cell and single cell measurements. The 1500h stability test of a single cell suggests that the PtRu/GMC is excellent stable. [Copyright &y& Elsevier]

Abstract: To investigate the effect of carbon support adding sequence on Pt particle sizes and Pt utilizations during the polyol process of the electrocatalyst preparation, a series of Pt/C electrocatalysts (different Pt loadings, two kinds of carbon supports−Vulcan XC and Black Pearls 2000) were prepared, namely, Pt/C-a (first reduced Pt ions to form Pt nanoparticles, which subsequently deposited on carbon supports) and Pt/C-b (Pt precursors were first impregnated with carbon supports, then reduced to Pt nanoparticles). The physical properties of the electrocatalysts were characterized by X-ray diffraction, transmission electron microscopy and nitrogen adsorption. The catalytic activities of the electrocatalysts toward the oxygen reduction reaction and the methanol oxidation reaction were characterized by potentiodynamic measurements. The results show that the carbon support adding sequence has significant effects on the Pt particle sizes, especially for the carbon supports with large amount of micropores, as a result, leading to different catalytic activities. [Copyright &y& Elsevier]

Abstract: Carbon-supported bimetallic Pt m Pb1 (m =1, 2, 3) electrocatalysts with different Pt/Pb atomic ratios were synthesized by a polyol method. The X-ray diffraction results reveal that a PtPb alloy formed in the Pt m Pb1/C electrocatalysts. TEM images show that the PtPb nanoparticles distribute uniformly on the carbon support, and are about 4–5nm in size. The Pt m Pb1/C bimetallic catalysts show superior activities toward methanol electrooxidation reaction (MOR) than the Pt/C in alkaline media. Both CO stripping measurements and density functional theory studies reveal that CO adsorption decreased significantly on the Pt m Pb1/C bimetallic catalysts compared with on pure Pt, which may offer an explanation for the enhanced MOR activity of the Pt m Pb1/C bimetallic catalysts. [Copyright &y& Elsevier]

Abstract: A carbon supported PtNi/C electrocatalyst synthesized via a polyol process was characterized by XRD, TEM and voltammetry techniques. The XRD analysis showed a decreased lattice constant of Pt for the PtNi/C catalyst compared with the Pt/C, indicating partial PtNi alloy formed. The PtNi/C exhibited enhanced mass activity towards methanol oxidation reaction as well as decreased CO stripping currents in alkaline media compared with the Pt/C. Density functional theory studies revealed the electronic structure modification of Pt by Ni atoms and weakened CO adsorption energy on the Pt3Ni than on the Pt4 clusters, which may account for the increased MOR activity. [ABSTRACT FROM AUTHOR]

Abstract: We synthesized and characterized a highly active electrocatalyst for oxygen reduction reactions (ORRs) in alkaline media by coating carbon-supported silver nanoparticles with Pd (Pd@Ag/C) via a galvanic displacement method. The electrochemical measurements were carried out using an ultrathin film rotating disk electrode. Compared to the Pt/C electrocatalyst, the specific and mass activities of the Pd@Ag/C were enhanced by a factor of 3 and 2.5, respectively. The potentiostatic measurements showed that the Pd@Ag/C is less stable than the Pt/C at the potential of −0.1V vs. Hg/HgO/OH− in alkaline media. The Pd@Ag/C is insensitive to alcohol, and, as a cathode electrocatalyst of a direct alcohol fuel cell, can resist poisoning by the possible alcohol crossover from the anode. [Copyright &y& Elsevier]

Abstract: Carbon supported PtSn alloy and PtSnO x particles with nominal Pt:Sn ratios of 3:1 were prepared by a modified polyol method. High resolution transmission electron microscopy (HRTEM) and X-ray microchemical analysis were used to characterize the composition, size, distribution, and morphology of PtSn particles. The particles are predominantly single nanocrystals with diameters in the order of 2.0–3.0nm. According to the XRD results, the lattice constant of Pt in the PtSn alloy is dilated due to Sn atoms penetrating into the Pt crystalline lattice. While for PtSnO x nanoparticles, the lattice constant of Pt only changed a little. HRTEM micrograph of PtSnO x clearly shows that the change of the spacing of Pt (111) plane is neglectable, meanwhile, SnO2 nanoparticles, characterized with the nominal 0.264nm spacing of SnO2 (101) plane, were found in the vicinity of Pt particles. In contrast, the HRTEM micrograph of PtSn alloy shows that the spacing of Pt (111) plane extends to 0.234nm from the original 0.226nm. High resolution energy dispersive X-ray spectroscopy (HR-EDS) analyses show that all investigated particles in the two PtSn catalysts represent uniform Pt/Sn compositions very close to the nominal one. Cyclic voltammograms (CV) in sulfuric acid show that the hydrogen ad/desorption was inhibited on the surface of PtSn alloy compared to that on the surface of the PtSnO x catalyst. PtSnO x catalyst showed higher catalytic activity for ethanol electro-oxidation than PtSn alloy from the results of chronoamperometry (CA) analysis and the performance of direct ethanol fuel cells (DEFCs). It is deduced that the unchanged lattice parameter of Pt in the PtSnO x catalyst is favorable to ethanol adsorption and meanwhile, tin oxide in the vicinity of Pt nanoparticles could offer oxygen species conveniently to remove the CO-like species of ethanolic residues to free Pt active sites. [Copyright &y& Elsevier]

Abstract: In the present paper, a 60h life-time test of a direct ethanol fuel cell (DEFC) at a current density of 20mAcm−2 (the beginning 38h) and 40mAcm−2 (the last 22h) was carried out. After the life-time test, the MEA could not achieve the former performance. X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) were employed to characterize the anode and cathode catalyst before and after the life-time test. The XRD and TEM results showed that the particle size of the anode catalyst increased from 2.3 to 3.3nm and the cathode from 3.0 to 4.6nm. The EDX results of PtSn/C anode catalysts before and after the life-time test indicated that the content of the oxygen and tin, especially the content of the platinum, decreased prominently after the life-time test. The results suggest that the agglomeration of electrocatalysts, the destruction of the anode catalyst together with the fuel/water crossover from anode to cathode concurrently contribute to the performance degradation of the DEFC. [Copyright &y& Elsevier]

Abstract: In this work, high-surface supported PtRu/C were prepared with Ru(NO)(NO3)3 and [Pt(H2NCH2CH2NH2)2]Cl2 as the precursors and hydrogen as a reducing agent. XRD and TEM analyses showed that the PtRu/C catalysts with different loadings possessed small and homogeneous metal particles. Even at high metal loading (40wt.% Pt, 20wt.% Ru) the mean metal particle size is less than 4nm. Meanwhile, the calculated Pt crystalline lattice parameter and Pt (220) peak position indicated that the geometric structure of Pt was modified by Ru atoms. Among the prepared catalysts, the lattice parameter of 40–20wt.% PtRu/C contract most. Cyclic voltammetry (CV), chronoamperometry (CA), CO stripping and single direct methanol fuel cell tests jointly suggested that the 40–20wt.% PtRu/C catalyst has the highest electrochemical activity for methanol oxidation. [Copyright &y& Elsevier]

Highly active PtSn/C catalyst was prepared by a polyol method. The catalyst was reduced in H2/Ar atmosphere at 600 °C for 2 h in order to obtain different metallic phase. TEM images show uniform dispersion of spherical metal nanoparticles with average diameters of 1.8 and 3.9 nm for the as-prepared and treated catalysts, respectively. UV–vis spectrophotometry is employed to monitor the preparation process and the results indicate that Pt–Sn complex formed once the precursors of Pt and Sn were mixed together. The structure properties of the samples were characterized using X-ray diffraction. The results show that after reduction, the catalyst tends to form PtSn alloy. TPR experiment results show that Sn exists in multivalent state in the as-prepared sample while only zero-valence Sn was detected in the treated sample, while it could not be excluded that the multivalent tin existed in the treated sample. Cyclic voltammetry (CV) technique and single direct ethanol fuel cell (DEFC) tests indicate that the as-prepared catalyst possesses superior catalytic activity for ethanol oxidation to the treated sample. The results suggest that Pt and multivalent Sn are the active species for ethanol oxidation. [Copyright &y& Elsevier]

The proper construction of high efficiency, low-cost, earth-abundant oxygen evolution reaction (OER) catalyst is essential for hydrogen formation by water splitting. A novel electrocatalyst with highly active OER performance was manufactured by a simple electroless deposition method of Ni-Fe-P-WO 3 on nickel foam (NF). Benefiting from outstanding mass transfer capability of Ni-Fe-P-WO 3 /NF heterogeneous structure, abundance of active sites in the amorphous architecture and etc., the Ni-Fe-P-WO 3 /NF shows extremely superb electrocatalytic properties compare to noble metal catalyst IrO 2 /NF for OER, which needs an overpotential of only 218 mV in 1.0 M KOH solution to achieve the current density of 10 mA cm−2. It also has remarkable OER activity at high current density that only needs 298 mV to attain 100 mA cm−2 current density. Moreover, the Ni-Fe-P-WO 3 /NF has low Tafel slope of 42 mV dec−1. This study offers a novel approach to the production of OER multiphase electrocatalysts from oxides and alloys. [Display omitted] • The Ni-Fe-P-WO 3 /NF electrode is synthesized by a facile electroless deposition method. • The Ni-Fe-P-WO 3 /NF exhibits excellent performances for OER: 218 mV at 10 mA cm−2 in 1 M KOH. • Interfacial effect of heterogeneous structures and synergistic effect between metals. [ABSTRACT FROM AUTHOR]

A new type of superior activity and highly cost-effective amorphous electrocatalyst Co–Mo–Fe on nickel foam (NF) supports is prepared by facile one-step rapid electrodeposition. The amorphous electrocatalyst Co–Mo–Fe/NF shows excellent oxygen evolution reaction (OER) performance, with a small overpotential of 218 mV at 10 mA cm−2 current density in 1 M KOH. It only needs overpotential of 252 mV at 50 mA cm−2 current density in 1 M KOH, and the Tafel slope is 45 mV dec−1. The results show that the doping of Fe significantly improves the oxygen evolution capacity of the Co–Mo–Fe system. The synergistic effect of the three metals and the doping of the third metal iron make the oxygen evolution active sites of the whole system increase significantly. This provides a feasible direction for the oxygen evolution reaction of cobalt transition metal. • The amorphous Co–Mo–Fe is synthesized by a facile electrodeposition method. • The Co–Mo–Fe has excellent electrocatalytic performance for oxygen evolution reaction. • The excellent oxygen evolution performance of Co–Mo–Fe promotes the process of hydrogen production from water splitting. • The addition of Fe to Co–Mo–Fe adjusts the structure and improves the synergistic effect of the three metals. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel dilute gold-in-nickel host nanoalloy is reported. • Electrochemical reconstruction of Ni-Au nanodimer is discovered. • NiAu nanoalloys exhibits both a remarkable activity and stability. • The driven force for NiAu nanoalloys formation is disclosed. • NiAu nanoalloys has a lower d band center than Ni. Ni-based nanomaterials are currently the most promising electrocatalysts for the alkaline hydrogen oxidation reaction (HOR), yet limited by their poor electrochemical stability. Herein, we report a nickel-gold nanodimer (Ni 100 Au 1 /C-P) synthesized via a galvanic replacement reaction, which via an electrochemical activation mostly transforms into highly dilute gold-in-nickel host nanoalloys (Ni 100 Au 1 /C-EA). The Ni 100 Au 1 /C-EA exhibits both a remarkable specific HOR activity of 47.3 µA cm-2 Ni , 20% higher than Ni 100 Au 1 /C-P and 34% higher than Ni/C, as well as exceptional stability for 6000 cycles and CO-tolerance. Membrane electrode assembly tests further identify the practical application of Ni 100 Au 1 /C-EA, which delivers a power density of 192 mW cm−2 and good durability. Theoretical studies suggest that the formation of NiAu alloys is thermodynamically favored with the help of adsorbed hydrogen intermediates. The in situ-formed NiAu nanoalloy, with a lower d band center than Ni, is endowed with improved anti-oxidation ability and appropriate intermediate binding energy, leading to a robust and excellent HOR performance. This electrochemical activation route provides a straightforward and novel strategy for regulating the microstructure of materials and therefore the catalytic activity and endurance of catalysts. [ABSTRACT FROM AUTHOR]

• Few-layered nitrogen-doped graphene wrapped 3D flower-like TiO 2 is synthesized. • The anti-corrosion support has a high surface area and electronic conductivity. • Pt-TiO 2 @N-Gr-800 exhibits superior ORR activity, stability, and CO tolerance. • Pt-TiO 2 @N-Gr-800 shows a strong metal and support interaction. Carbon materials are commonly used as electrocatalyst supports in fuel cells. Nevertheless, carbon corrosion is a severe concern under strong acidic and oxidizing environments. Hence, developing a robust catalyst support is critical to ensuring fuel cells stability. Herein, we report a unique support of few-layered nitrogen-doped graphene wrapped three-dimensional (3D) flower-like anatase TiO 2 (TiO 2 @N-Gr) via in-situ polymerizing dopamine on the surface of a 3D-TiO 2 flower precursor, followed by pyrolysis. After loading Pt nanoparticles, Pt-TiO 2 @N-Gr-800 exhibits comparable ORR activity to the commercial Pt/C catalyst (E 1/2 = 0.91 V RHE), superior stability in a 30 K cycling stability test and strong CO resistance capability. The outstanding performance of the Pt-TiO 2 @N-Gr-800 catalyst is attributed to the strong anti-corrosion property and high electronic conductivity of the nanocomposite support, as well as a strong metal and support interaction. The unique flower-like scaffold is also of great advantage for mass transfer. This work provides a facile strategy to synthesize robust nanocomposite supports for fuel cells. [ABSTRACT FROM AUTHOR]