Penerapan Metode Pembelajaran Numbered Heads Together (Nht) Untuk Meningkatkan Motivasi Dan Hasil Belajar Kelarutan Dan Hasil Kali Kelarutan Kelas XI IPA 4 Sman 8 Surakarta Tahun Pelajaran 2012/2013

Tujuan penelitian ini adalah untuk meningkatkan (1) motivasi belajar kelarutan dan hasil kali kelarutan dan (2) hasil belajar kelarutan dan hasil kali kelarutan melalui penerapan metode pembelajaran Numbered Heads Together (NHT). Penelitian ini merupakan penelitian tindakan kelas (Classroom Action Research) yang dilaksanakan dalam dua siklus dimana setiap siklusnya terdiri atas empat tahapan, yaitu perencanaan, pelaksanaan, pengamatan, dan refleksi. Subjek penelitian adalah siswa kelas XI IPA 4 SMAN 8 Surakarta Tahun Pelajaran 2012/2013. Pengumpulan data dilakukan melalui pengamatan, wawancara, kajian dokumen, angket, dan tes. Data yang diperoleh divalidasi menggunakan teknik triangulasi sumber dan dianalisis menggunakan analisis deskriptif kualitatif yang mengacu pada Miles dan Huberman. Hasil penelitian menunjukkan capaian motivasi belajar pada siklus I dan siklus II masing-masing mencapai 58,33% dan 79,17%. Hasil belajar yang diukur pada aspek kognitif dan afektif menunjukkan pada siklus I mencapai 29,17% dan 62,5% serta pada siklus II mencapai 70,83% dan 83,33%. Simpulan penelitian ini adalah penerapan metode pembelajaran Numbered Heads Together (NHT) mampu meningkatkan (1) motivasi belajar kelarutan dan hasil kali kelarutan dan (2) hasil belajar kelarutan dan hasil kali kelarutan kelas XI IPA 4 SMAN 8 Surakarta

IrPdRu/C as H₂ Oxidation Catalysts for Alkaline Fuel Cells

H₂ oxidation kinetics on Pt in alkaline media are very sluggish, being over 100 times slower than in acidic media, and thus, new and more active H₂ oxidation electrocatalysts must be developed in order to enable alkaline exchange membrane fuel cells (AEMFCs). In this Communication, we present a new type of catalystscarbon-supported IrPdRu nanoparticlesas H₂ oxidation catalysts in alkaline media. These catalysts exhibit higher activity than Pt/C and Ir/C catalysts and are also quite stable. In particular, Ir₃Ru₇/C and Ir₃Pd₁Ru₆/C catalysts are significantly more active and less expensive than Pt/C and Ir/C, and are thus promising new anode catalysts for alkaline fuel cell applications

Key Parameters Governing the Energy Density of Rechargeable Li/S Batteries

Rechargeable lithium–sulfur batteries have high theoretical capacity and energy density. However, their volumetric energy density has been believed to be lower than that of conventional lithium ion batteries employing metal oxide cathodes like LiCoO₂. Here, we study the effects of sulfur loading percentage, develop a simple model and calculate the gravimetric and volumetric energy densities based on the total composition of electrodes in a lithium–sulfur cell, and compare those results with a typical graphite/LiCoO₂ cell. From the model output, we have identified and established key parameters governing the energy density of rechargeable Li/S batteries. We find that the sulfur loading percentage has a much higher impact on the volumetric energy density than on the gravimetric energy density. A lithium–sulfur cell can exceed a lithium ion cell’s volumetric energy density but only at high sulfur loading percentages (ca. 70%). We believe that these findings may attract more attention of lithium–sulfur system studies to high sulfur loading levels

Origin of Multiple Peaks in the Potentiodynamic Oxidation of CO Adlayers on Pt and Ru-Modified Pt Electrodes

The study of the electrooxidation mechanism of CO_ad on Pt based catalysts is very important for designing more effective CO-tolerant electrocatalysts for fuel cells. We have studied the origin of multiple peaks in the cyclic voltammograms of CO stripping from polycrystalline Pt and Ru modified polycrystalline Pt (Pt/Ru) surfaces in both acidic and alkaline media by differential electrochemical mass spectrometry (DEMS), DFT calculations, and kinetic Monte Carlo (KMC) simulations. A new CO_ad electrooxidation kinetic model on heterogeneous Pt and Pt/Ru catalysts is proposed to account for the multiple peaks experimentally observed. In this model, OH species prefer to adsorb at low-coordination sites or Ru sites and, thus, suppress CO repopulation from high-coordination sites onto these sites. Therefore, CO_ad oxidation occurs on different facets or regions, leading to multiplicity of CO stripping peaks. This work provides a new insight into the CO electrooxidation mechanism and kinetics on heterogeneous catalysts

Rhenium Complexes of 2,3-Di(2-pyridyl)-5,6-diphenylpyrazine: Synthesis, Characterization, and Reactivity

The reaction of 2,3-di­(2-pyridyl)-5,6-diphenylpyrazine (dpdpz) with Re­(CO)₅Cl in acetonitrile or toluene afforded mono-Re and bis-Re complexes [Re­(CO)₃Cl-dpdpz] and [Re­(CO)₃Cl-dpdpz-Re­(CO)₃Cl], respectively. A heterodinuclear complex [Ru­(bpy)₂-dpdpz-Re­(CO)₃Cl]­(PF₆)₂ could be prepared by the reaction of [Re­(CO)₃Cl-dpdpz] with Ru­(bpy)₂Cl₂ or the reaction of Re­(CO)₅Cl with a previously reported mono-Ru complex [Ru­(bpy)₂-dpdpz]­(PF₆)₂ in moderate yields. Surprisingly, the reaction of [Re­(CO)₃Cl-dpdpz] or [Re­(CO)₃Cl-dpdpz-Re­(CO)₃Cl] with Ru­(tpy)­Cl₃ in the presence of AgOTf both afforded an asymmetric bis-Ru complex [Ru­(tpy)-dpdpz-RuCl­(tpy)]­(PF₆)₂. The solid-state structures of [Re­(CO)₃Cl-dpdpz-Re­(CO)₃Cl] and [Ru­(tpy)-dpdpz-RuCl­(tpy)]­(PF₆)₂ were determined by single-crystal X-ray analysis. The electrochemical, absorption, and emission properties of these compounds were studied by cyclic voltammetric and spectroscopic analyses. In addition, DFT calculations were carried out to aid in the interpretation of these experimental findings

Rhenium Complexes of 2,3-Di(2-pyridyl)-5,6-diphenylpyrazine: Synthesis, Characterization, and Reactivity

The reaction of 2,3-di­(2-pyridyl)-5,6-diphenylpyrazine (dpdpz) with Re­(CO)₅Cl in acetonitrile or toluene afforded mono-Re and bis-Re complexes [Re­(CO)₃Cl-dpdpz] and [Re­(CO)₃Cl-dpdpz-Re­(CO)₃Cl], respectively. A heterodinuclear complex [Ru­(bpy)₂-dpdpz-Re­(CO)₃Cl]­(PF₆)₂ could be prepared by the reaction of [Re­(CO)₃Cl-dpdpz] with Ru­(bpy)₂Cl₂ or the reaction of Re­(CO)₅Cl with a previously reported mono-Ru complex [Ru­(bpy)₂-dpdpz]­(PF₆)₂ in moderate yields. Surprisingly, the reaction of [Re­(CO)₃Cl-dpdpz] or [Re­(CO)₃Cl-dpdpz-Re­(CO)₃Cl] with Ru­(tpy)­Cl₃ in the presence of AgOTf both afforded an asymmetric bis-Ru complex [Ru­(tpy)-dpdpz-RuCl­(tpy)]­(PF₆)₂. The solid-state structures of [Re­(CO)₃Cl-dpdpz-Re­(CO)₃Cl] and [Ru­(tpy)-dpdpz-RuCl­(tpy)]­(PF₆)₂ were determined by single-crystal X-ray analysis. The electrochemical, absorption, and emission properties of these compounds were studied by cyclic voltammetric and spectroscopic analyses. In addition, DFT calculations were carried out to aid in the interpretation of these experimental findings

Rhenium Complexes of 2,3-Di(2-pyridyl)-5,6-diphenylpyrazine: Synthesis, Characterization, and Reactivity

The reaction of 2,3-di­(2-pyridyl)-5,6-diphenylpyrazine (dpdpz) with Re­(CO)₅Cl in acetonitrile or toluene afforded mono-Re and bis-Re complexes [Re­(CO)₃Cl-dpdpz] and [Re­(CO)₃Cl-dpdpz-Re­(CO)₃Cl], respectively. A heterodinuclear complex [Ru­(bpy)₂-dpdpz-Re­(CO)₃Cl]­(PF₆)₂ could be prepared by the reaction of [Re­(CO)₃Cl-dpdpz] with Ru­(bpy)₂Cl₂ or the reaction of Re­(CO)₅Cl with a previously reported mono-Ru complex [Ru­(bpy)₂-dpdpz]­(PF₆)₂ in moderate yields. Surprisingly, the reaction of [Re­(CO)₃Cl-dpdpz] or [Re­(CO)₃Cl-dpdpz-Re­(CO)₃Cl] with Ru­(tpy)­Cl₃ in the presence of AgOTf both afforded an asymmetric bis-Ru complex [Ru­(tpy)-dpdpz-RuCl­(tpy)]­(PF₆)₂. The solid-state structures of [Re­(CO)₃Cl-dpdpz-Re­(CO)₃Cl] and [Ru­(tpy)-dpdpz-RuCl­(tpy)]­(PF₆)₂ were determined by single-crystal X-ray analysis. The electrochemical, absorption, and emission properties of these compounds were studied by cyclic voltammetric and spectroscopic analyses. In addition, DFT calculations were carried out to aid in the interpretation of these experimental findings

Operando Investigation of Solid Electrolyte Interphase Formation, Dynamic Evolution, and Degradation During Lithium Plating/Stripping

The solid electrolyte interphase (SEI) dictates the stability and cycling performance of highly reactive battery electrodes. Characterization of the thin, dynamic, and environmentally sensitive nature of the SEI presents a formidable challenge, which calls for the use of microscopic, time-resolved operando methods. Herein, we employ scanning electrochemical microscopy (SECM) to directly probe the heterogeneous surface electronic conductivity during SEI formation and degradation. Complementary operando electrochemical quartz crystal microbalance (EQCM) and ex situ X-ray photoelectron spectroscopy (XPS) provide comprehensive analysis of the dynamic size and compositional evolution of the complex interfacial microstructure. We have found that stable anode passivation occurs at potentials of 0.5 V vs Li/Li+, even in cases where anion decomposition and interphase formation occur above 1.0 V. We investigated the bidirectional relationship between the SEI and lithium plating-stripping, finding that plating-stripping ruptures the SEI. The current efficiency of this reaction is correlated to the anodic stability of the SEI, highlighting the interdependent relationship between the two. We anticipate this work will provide critical insights on the rational design of stable and effective SEI layers for safe, fast-charging, and long-lifetime lithium metal batteries

Thermodynamic, Kinetic, Surface p<i>K</i>_a, and Structural Aspects of Self-Assembled Monolayers of Thio Compounds on Gold

The thermodynamic and kinetic aspects of the formation of self-assembled monolayers (SAMs) of thio compounds on gold have been studied via electrochemical and quartz crystal microbalance (QCM) techniques. The data indicate that the adsorption process involves a significant free energy of adsorption (Δ<i>G</i>° = −36.43 kJ/mol) and that there are slight repulsive interactions between adjacent molecules on the surface. A method for the calculation of surface p<i>K</i>_a values of molecules containing more than one protonation site is proposed and used for the determination of the p<i>K</i>_a values of SAMs derived from thioisonicotinamide, thionicotinamide, 5-(4-pyridyl)-1,2,4-oxadiazole-2-thiol, and 4-mercaptopyridine (pyS) on gold. Structural aspects of the SAMs were studied by using impedance with [Fe­(CN)₆]^4–/3– as redox probe. Evidence of faster kinetics for an oxidative decomposition of pyS SAM in the presence of [Fe­(CN)₆]^3– is discussed based on electrochemical and impedance data

New Insights into the Mechanism and Kinetics of Adsorbed CO Electrooxidation on Platinum: Online Mass Spectrometry and Kinetic Monte Carlo Simulation Studies

The electrooxidation of saturated CO adlayers on Pt/Vulcan and polycrystalline Pt has been studied by potential step techniques combined with differential electrochemical mass spectrometry (DEMS) and kinetic Monte Carlo (KMC) simulations. DEMS was used to selectively monitor the CO_ad electrooxidation, via the CO₂ formation rate, without interference from the pseudocapacitive double-layer charging and electrode surface oxidation, while the KMC simulations were employed to understand the mechanism and kinetics of CO_ad electrooxidation at the molecular level. Our DEMS data show that the current transients of CO_ad electrooxidation on polycrystalline Pt and Pt/Vulcan exhibit an initial spike immediately after the potential step, followed by a slow current decay and finally a broad main peak. The temporal evolution of the transients depends strongly on the oxidation potential applied, resulting in the overlap of the initial spike and the main peak for high potentials. A model is proposed to account for the observed phenomena. On the basis of this model, we developed a kinetic Monte Carlo simulation code specific to the electrooxidation of adsorbed CO on Pt. The simulations reproduce the experimental data very well, confirming the robustness of our model