Synthesis of (Ni,Mn,Co)O4 nanopowder with single cubic spinel phase via combustion method

(Ni,Mn,Co)O₄ nanopowders with single cubic phase were successfully synthesized using combustion methods. Particle size of the as-burnt nanopowders after combustion was about 20 nm. Crystallization behavior of the NMC was investigated using various techniques such as X-ray diffraction (XRD), thermogravimetric (TG), Fourier transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM). Calcination at different temperature from 400 °C to 700 °C provides the powders with increased crystallinity and grain size. However, further increasing temperature above 800 °C for calcination, cubic spinel phase of NMC partly transformed to tetragonal spinel phase, which implies that cubic spinel phase of NMC nanopowder synthesized by combustion method becomes unstable above 800 °C.     

Preparation of carbon-supported nano-sized LaMnO3 using reverse micelle method for energy-saving oxygen reduction cathode

Two ways of reverse micelle (RM) method were investigated to prepare carbon-supported nano-sized LaMnO₃ with high oxygen reduction activity. Hydrolysis precipitation in reverse micelle (HP-RM) method could give nano-sized particles of LaMnO₃ easily because the particles size decreased with decreasing R_w (=[H₂O]/[surfactant]) value as well as nitrate concentration. The electrode prepared by the resulting particles showed high oxygen reduction activity as compared with that prepared by mechanical mixing-method. Furthermore, it was found that new RM method (ROP-RM) using KMnO₄ as an oxidizer gave higher oxygen reduction activity than the HP-RM method, although particle size of LaMnO₃ obtained by the ROP-RM method was almost same as that by RM-HP method.     

Effect of Co on oxygen reduction reaction catalyzed by Pt catalyst, and its implications for fuel cell contamination

The oxygen reduction reaction (ORR) catalyzed by Pt was studied in the presence of Co²⁺ using cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring-disk electrode (RRDE) techniques in an effort to understand fuel cell cathode contamination caused by Co²⁺. Findings indicated that Co²⁺ could weakly adsorb on the Pt surface, resulting in a slight change in ORR exchange current densities. However, this weak adsorption had no significant effect on the nature of the ORR rate determining steps. The results from both RDE and RRDE indicated that the overall electron transfer number of the ORR in the presence of Co²⁺ was reduced, with ∼9% more H₂O₂ being produced. We speculate that the weakly adsorbed Co²⁺ on Pt could react with the H₂O₂ intermediate and form a Co²⁺-H₂O₂ intermediate, inhibiting the further reduction of H₂O₂ and thus resulting in more H₂O₂ production. The fuel cell performance drop observed in the presence of Co²⁺ could be attributed to the reduction in overall electron transfer number and the increase in H₂O₂ production. Higher production could intensify the attack by H₂O₂ and its radicals on membrane electrode assembly components, including the ionomer, carbon support, Pt particles, and membrane, leading to fuel cell degradation.     

Carbon-supported manganese oxide nanoparticles as electrocatalysts for oxygen reduction reaction (orr) in neutral solution

Manganese oxides (MnO _x ) catalysts were chemically deposited onto various high specific surface area carbons. The MnO _x /C electrocatalysts were characterised using a rotating disk electrode and found to be promising as alternative, non-platinised, catalysts for the oxygen reduction reaction (ORR) in neutral pH solution. As such they were considered suitable as cathode materials for microbial fuel cells (MFCs). Metal [Ni, Mg] ion doped MnO _x /C, exhibited greater activity towards the ORR than the un-doped MnO _x /C. Divalent metals favour oxygen bond splitting and thus orientate the ORR mechanism towards the 4-electron reduction, yielding less peroxide as an intermediate.     

Li3PO4掺杂的Li(Ni0.5Co0.2Mn0.3)O2锂离子电池正极材料的流变相法合成及电化学性能表征

采用氢氧化物共沉淀法制备了锂离子电池正极材料前驱体(Ni_0.5Co_0.2Mn_0.3)(OH)₂,并用流变相反应法合成了Li₃PO₄掺杂的Li(Ni_0.5Co_0.2Mn_0.3)O₂锂离子电池正极材料。运用X射线粉末衍射和恒电流充放电对产物进行了结构和电化学性能的表征,结果表明Li₃PO₄掺杂的Li(Ni_0.5Co_0.2Mn_0.3)O₂具有标准的层状α-NaFeO₂结构,样品为1 μm左右的片状一次颗粒聚集而成的类球形二次颗粒。掺杂1%(质量分数)Li₃PO₄的Li(Ni_0.5Co_0.2Mn_0.3)O₂锂离子电池在0.1C的倍率下首次放电比容量达到188.6 mA·h·g^-1(2.2～4.6 V vs Li⁺/Li),30次循环后容量保持率为 92.9%。循环伏安、交流阻抗测试表明Li₃PO₄的掺杂可减少充放电过程中电解液和电极之间的电荷传递电阻和锂离子扩散电阻,减小极化作用,从而提升了Li(Ni_0.5Co_0.2Mn_0.3)O₂材料的电化学性能。     

高温液相还原法制备超细钴粉末

利用高温液相二醇还原法,在两种表面活性剂存在下制备出磁性钴的超细粉末。利用X射线衍射、X射线光电子能谱、扫描电镜和激光光散射仪等对所制备的超细钴粉末结构、价态、颗粒尺寸分别进行了表征分析,结果表明该种方法制备的超细钴粉末具有hcp,平均粒径大约为0．4μm。     

Durability of carbon-supported manganese oxide nanoparticles for the oxygen reduction reaction (ORR) in alkaline medium

MnO_x/C-based electrocatalysts, prepared by the chemical deposition of manganese oxide nanoparticles on carbon, were tested towards the Oxygen Reduction Reaction (ORR) in their as-synthesized state and after ageing, either in ambient air for a year (mild ageing) or in an O₂-saturated molar KOH solution at 80 °C for three weeks (premature ageing). For each electrocatalyst, the morphology and composition were characterised using TEM, XRD and chemical analysis. ORR kinetic parameters were evaluated using the Rotating Disk Electrode (RDE) and Rotating Ring Disk Electrode (RRDE) setups. Whilst the oxygen reduction activity of the electrocatalysts barely changes after mild ageing, it decreases after premature ageing following dramatic modifications to both the chemical and crystalline structures of the carbon-supported MnO_x nanoparticles. The peroxide yield also sharply increases after premature ageing. Doping MnO_x/C with nickel or magnesium divalent cations is beneficial since it improves both the catalytic activity and selectivity towards the 4-electron ORR pathway, even after ageing.     

Activity-stability relationships of ordered and disordered alloy phases of Pt3Co electrocatalysts for the oxygen reduction reaction (ORR)

We report on synthesis-structure-activity-stability relationships of Pt₃Co nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). We have synthesized Pt₃Co alloy electrocatalysts using liquid impregnation techniques followed by reductive annealing at high and low temperatures. We have performed detailed structural X-ray diffraction (XRD)-based structural characterization (symmetry, lattice parameters and composition) of individual Pt-Co alloy phases before and, importantly, after electrochemical rotating disk electrode (RDE) measurements. This enables us to directly evaluate the corrosion stability of various Pt-Co alloy phases under typical fuel cell cathode conditions.Pt₃Co prepared at low annealing temperatures (600 °C) resulted in multiple phases including (i) a disordered face-centered cubic (fcc) Pt₉₅Co₅ phase and (ii) an ordered face-centered tetragonal (L1₀) Pt₅₀Co₅₀ phase; high temperature annealing (950 C) resulted in a single ordered primitive cubic (L1₂) Pt₃Co phase. The ordered alloy phases in both catalysts were not stable under electrochemical treatment: The ordered face-centered tetragonal (fct) phase showed corrosion and dissolution, while the ordered primitive cubic (L1₂) Pt₃Co phase transformed into a disordered structure. The ordered primitive cubic structure exhibited higher resistance to sintering.Low annealing temperatures resulted in higher Pt surface-area specific activities for ORR. Kinetic Tafel analysis confirmed a general shift in the formation potential of oxygenated surface species, such as Pt-OH, for both alloy catalysts. Reduced OH coverage alone proved insufficient to account for the observed activity trends of the two alloy catalysts.     

Catalytic activity of titanium oxide for oxygen reduction reaction as a non-platinum catalyst for PEFC

A non-platinum cathode electrocatalyst must have the stability and catalytic activity for the oxygen reduction reaction (ORR) in order to be used in polymer electrolyte fuel cells (PEFCs). Titanium oxide catalysts as the non-platinum catalyst were prepared by the heat treatment of titanium sheets in the temperature range from 600 to 1000 °C. The prepared catalysts were chemically and electrochemically stable in 0.1 mol dm⁻³ H₂SO₄. The titanium oxide catalysts showed different catalytic activities for the ORR. The ORR of the catalysts heat-treated at around 900 °C occurred at the potential of about 0.65 V versus RHE. It is considered that the deference in the catalytic activity for the ORR of the heat-treated titanium oxide catalysts was due to the fact that the heat-treatment condition changed the material property of the catalyst surface. In particular, it was found that the catalytic activity for the ORR of the Ti oxide catalysts increased with the increase in the specific crystalline structure, such as the TiO₂ (rutile) (1 1 0) plane and the work function. It is considered that a surface state change, such as the crystalline structure and work function, might affect the catalytic activity for the ORR.     

含锂磷酸盐LiMPO4(M-Mn、Co、Ni)的制备方法

含锂磷酸盐LiMPO4（M=Mn、Co、Ni）是具有有序的橄榄石结构的材料,用于锂离子电池材料具有约170mAh·g^-1的理论容量,制备LiMPO4的方法,有固相合成法,水热法、溶胶一凝胶法,LIMPO4在锂离子电池材料、磁电材料等中得到了不同程度的研究,本文从合成、性能、改性等方面总结了近年来有关LiMPO4的研究进展,并对该材料的研究与应用前景进行了展望。     

The oxygen reduction reaction mechanism on Pt(1 1 1) from density functional theory calculations

We study the oxygen reduction reaction (ORR) mechanism on a Pt(1 1 1) surface using density functional theory calculations. We find that at low overpotentials the surface is covered with a half dissociated water layer. We estimate the barrier for proton transfer to this surface and the barrier for proton transport parallel to the surface within the half dissociated water network. We find both barriers to be small. The only potentially dependent step is the proton transfer from water to the half dissociated water layer. We find that ORR proceeds via four direct e⁻ reductions without significant peroxide formation. We show that the oxygen-oxygen bond breaking is dependent on the local surface environment. The minimum energy pathway is constructed and we confirm that OH removal from the surface determines the overpotential.     

Characterization of oxidized reticulated vitreous carbon electrode for oxygen reduction reaction in acid solutions

The oxidation of reticulated vitreous carbon (RVC) and its impact on the oxygen reduction reaction (ORR) in H₂SO₄ solutions has been studied. The results are compared with that of a planar glassy carbon (GC) electrode. The oxidation process was characterized by using different electrode configurations, GC (planar) and RVC electrodes both with flooded (batch process) and flow-through assembly. Cyclic voltammetry, potentiodynamic and rotating ring-disk electrode voltammetry were used for the characterization of the ORR. Anodically oxidized GC and flooded RVC are similar in that the ORR on both electrodes gave a more defined limiting current plateau. For the flow-through porous electrode, the oxidation process caused a distribution of the oxidation extent within the bed thickness, as evident from the SEM images, and only about half of the porous electrode was utilized in the oxidation process. X-ray photoelectron spectroscopy (XPS) measurements confirmed the above distribution and a gradient of the oxygen-to-carbon ratio was obtained within the porous bed. Oxidation of RVC led to an enhancement of its electrocatalytic properties towards ORR. H₂O₂ production was tested at the oxidized RVC from flowing acid solutions. The oxidation of RVC resulted in higher current efficiencies and higher outlet concentrations of the H₂O₂ acid solutions.     

Synthesis and characterization of Pd-Ni nanoalloy electrocatalysts for oxygen reduction reaction in fuel cells

Carbon-supported Pd-Ni nanoalloy electrocatalysts with different Pd/Ni atomic ratios have been synthesized by a modified polyol method, followed by heat treatment in a reducing atmosphere at 500-900 °C. The samples have been characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), rotating disk electrode (RDE) measurements, and single-cell proton exchange membrane fuel cell (PEMFC) tests for oxygen reduction reaction (ORR). XRD and TEM data reveal an increase in the degree of alloying and particle size with increasing heat-treatment temperature. XPS data indicate surface segregation with Pd enrichment on the surface of Pd₈₀Ni₂₀ after heat treatment at ≥500 °C, suggesting possible lattice strains in the outermost layers. Electrochemical data based on CV, RDE, and single-cell PEMFC measurement show that Pd₈₀Ni₂₀ heated at 500 °C has the highest mass catalytic activity for ORR among the Pd-Ni samples investigated, with stability and catalytic activity significantly higher than that found with Pd. With a lower cost, the Pd-Ni catalysts exhibit higher tolerance to methanol than Pt, offering an added advantage in direct methanol fuel cells (DMFC).     

Studies on the heterogeneous electron transport and oxygen reduction reaction at metal (Co, Fe) octabutylsulphonylphthalocyanines supported on multi-walled carbon nanotube modified graphite electrode

Heterogeneous electron transfer dynamics and oxygen reduction reaction (ORR) activities using octabutylsulphonylphthalocyanine complexes of iron (FeOBSPc) and cobalt (CoOBSPc) supported on multi-walled carbon nanotube (MWCNT) platforms have been described. The MWCNT-based electrodes (MWCNT-CoOBSPc and MWCNT-FeOBSPc) showed larger Faradaic current responses than the electrodes without the MWCNTs, interpreted as a consequence of the trapped electrolyte species within the porous layers of MWCNTs undergoing a redox process. The EPPGE-MWCNT-FeOBSPc showed onset potential (−0.01 V vs Ag|AgCl) which is comparable and even much lower than recent reports. The MWCNT-FeOBSPc showed the best ORR activity involving a direct 4-electron mechanism, with a Tafel slope of about 124 mV, indicating a 1-electron process in the rate-determining step.     

Nanostructured Pt-M/C (M = Fe and Co) catalysts prepared by a microemulsion method for oxygen reduction in proton exchange membrane fuel cells

Nanostructured Pt-M/C (M = Fe and Co) catalysts have been synthesized by a microemulsion method and a high-temperature route. They have been characterized by cyclic voltammetry in 1 M H₂SO₄ and for oxygen reduction in proton exchange membrane fuel cells (PEMFC). The Pt-M alloy catalysts synthesized by the microemulsion method show higher electrochemical active surface area than those prepared by the high-temperature route, and some of them exhibit improved catalytic activity towards oxygen reduction compared to pure Pt. Among the various alloy catalysts investigated, the Pt-Co/C catalyst prepared by the microemulsion method shows the best performance with the maximum catalytic activity and minimum polarization loss. Mild heat treatment of the catalysts prepared by the microemulsion method at moderate temperatures (200 °C) in reducing atmosphere is found to improve the catalytic activity due to a cleaning of the surface and an increase in the electrochemical surface area.     

Highly active and robust biomimetic ceramic catalyst for oxygen reduction reaction: Inspired by plant leaves

Structural instability under working conditions is critical issue that restricts applications of perovskite O₂ catalysts in the field of solid oxide fuel cells. Inspired by plant leaves, a biomimetic ceramic catalyst with PrBaCo₂O_5+δ ‘mesophyll’ and Gd_0.1Ce_0.9O_1.95 ‘epidermis’ and ‘vein’ was successfully engineered in this work. The ‘epidermis’ reduces the polarization resistance of O₂ reduction reaction on catalyst surface by ∼24%, and the ‘vein’ reduces resistance of O²⁻ transport through cathode layer by ∼65%. Moreover, this biomimetic catalyst increases output power density of the cell by 79% and reverses rapid decay trend of the cell with a 23% increase in power density during first 20 h followed by stabilization at 0.91 W cm⁻² (at 750 °C and 0.7 V). This discovery provides new avenue for the development of high-performance O₂ catalysts with practical applications and enriches the scientific understanding of catalysis.     

Band gap modulation and improved magnetism of double perovskite Sr2KMoO6 (K = Fe,Co, Ni,Mn) doped BaTiO3 ceramics

BaTiO₃ ceramics doped with double perovskite Sr₂KMoO₆ (BT-SKM) are fabricated via solid-state reaction technology. The effects of SKM dopants on the structure, band gap and electrical/magnetic properties of BT are systematically studied. XRD and Raman spectra analysis show polycrystalline perovskite structure of the samples, which confirms the structural changes. With the addition of SKM dopants, the grain size of the samples decreases significantly. The band gaps of doped BT samples reduce, and the minimum band gap of BT-SCM is 1.77 eV, which is apparently reduced compared with the band gap of pure BT of 3.22 eV. However, the ferroelectric properties are weakened in samples doped with SKM. This ascribes to the introduction of more oxygen vacancies by dopants, which impedes the switching of domains, resulting in deterioration of ferroelectric properties. Furthermore, ferromagnetism of BT-SNM is observed, which may be attributed to the long-range exchange interaction between Ni²⁺ ions and oxygen vacancies. These results reveal the potential applications of these perovskite oxides in photovoltaic and memory devices.     

Preparation of novel Pt-based nanoparticles by double potential step electrolysis and their electrocatalytic activity for oxygen reduction reaction

We have developed a novel preparation method for Pt-based nanoparticles by means of double potential step electrolysis (DPSE), in which Pt-Ni alloy deposited at the first step and Ni dissolved at the following step. A cycle of the DPSE in a nickel plating bath containing PtCl₆²⁻ led to the formation of the Pt-Ni nanoparticles with size of about 5.4 ± 1.5 nm, which gradually grew up with repeating the DPSE process, and surface Ni content of the particles by XPS was controllable by changing some parameters of the DPSE. The Pt-Ni nanoparticles deposited by the DPSE were covered with a Pt skin layer, which influence the improvement of both catalytic activity for oxygen reduction reaction (ORR) and corrosion resistance. The Pt-Ni nanoparticles by the DPSE exhibit ca. two times higher electrocatalytic activity for ORR than Pt nanoparticles, and further, of which catalytic activity was maintained high even with more than 1000 cycles of potential cycling test in H₂SO₄ solution, showing good corrosion resistance.     

纳米LaMO3(M＝Cr,Mn,Fe,Co)化合物的光催化氧化活性分析

采用柠檬酸络合法制备了纳米钙钛矿型LaMO3(M =Cr,Mn ,Fe ,Co)化合物 ,并对其进行XRD和TEM分析 ,发现所制样品具有单一晶相结构 ,粒径在 1～ 10 0nm之间。在纳米LaMO3(M =Cr,Mn ,Fe ,Co)悬浮体系中进行了水溶性染料酸性红 3B光催化降解实验 ,其光催化氧化活性变化趋势为LaCrO3相似文献   

La0.9Ce0.1MnO3的固相法制备及光催化性能研究

本文采用固相法制备出钙钛矿型La0.9 Ce0.1 MnO3催化剂,研究了钙钛矿型La0.9 Ce0.1 MnO3催化剂对废水中间苯二酚的降解效果,通过实验确定间苯二酚降解的优化反应条件,采用UV法处理浓度为10mg/L的间苯二酚废水。