1313-13-9Relevant academic research and scientific papers
A high performance solid state asymmetric supercapacitor device based upon NiCo2O4 nanosheets//MnO2 microspheres
Khalid, Syed,Cao, Chuanbao,Wang, Lin,Zhu, Youqi,Wu, Yu
, p. 70292 - 70302 (2016)
A high performance solid state asymmetric supercapacitor (SSASCs) device is successfully fabricated by combining NiCo2O4 as positive and MnO2 as negative electrode materials. Herein, we also report a facile strategy to synthesize mesoporous layered NiCo2O4 nanosheets and 3D hierarchical MnO2 microspheres by a simple microwave heating method. Both materials exhibit excellent electrochemical performance due to their unique morphological features along with nanocrystallite size, high specific surface area, narrow pore size distribution and large pore volume. The SSASCs device operates within the potential window of 1.5 V and exhibits high volumetric capacity and energy density of 0.954 mA h cm-3 (2.3 F cm-3) and 0.715 mW h cm-3 at 1 mA cm-2 respectively. The device also demonstrates excellent cyclic stability with capacity retention of 83% by the end of 10000 cycles at a current density of 2 mA cm-2. This work constitutes the first demonstration of using 3D hierarchical MnO2 microspheres as a high energy negative electrode for a SSASCs device. A SSASCs device with high volumetric capacity and energy density has significant potential applications in portable electronics and electrical vehicles.
Mesoporous β-MnO2 air electrode modified with pd for rechargeability in lithium-air battery
Thapa, Arjun Kumar,Hidaka, Yuiko,Hagiwara, Hidehisa,Ida, Shintaro,Ishihara, Tatsumi
, p. A1483-A1489 (2011)
The electrochemical performance and electrode reactions using ordered mesoporous β-MnO2 modified with Pd as a cathode catalyst for rechargeable Li-air batteries was reported. Well-ordered mesoporous β-MnO2 was prepared using mesoporous silica KIT-6 as a template under hydrothermal synthesis of Mn(NO3)2H2O. The obtained mesoporous β-MnO2 shows narrow pore size distribution of 1 nm. With the dispersion of small amounts of Pd to β-MnO2, mesoporous β-MnO2 exhibited a high initial discharge capacity of 817 mAhg-cat. with high reversible capacity. Charging potential is suppressed at 3.6 V vs. LiLi, which is highly effective for preventing the decomposition of organic electrolyte. The mesoporous β-MnO2Pd electrode shows good rate capability and cycle stability. Ex-situ and in-situ XRD results suggested that the observed capacity comes primarily from the oxidation of Li to Li2O 2 followed by Li2O after discharge to 2.0 V vs. LiLi. Electron spin resonance measurements suggest that the formation of superoxide anion radicals contributs to the oxidation of Li and the radicals were recovered during charge. Ex-situ FTIR measurement suggested that no electrolyte decomposition was observed and no Li2CO3 was formed during discharge when ethylene carbonate (EC)-diethyl carbonate (DEC) (3:7), which is highly stable for Li-air battery, was used as the electrolyte.
A new 3D supramolecular manganese(II) complex constructed from benzimidazole-5,6-dicarboxylate and Oxalate: Synthesis, structural, and magnetic properties
Geng, Jin-Peng,Wang, Zhao-Xi,Wu, Qiong-Fang,Li, Ming-Xing,Xiao, Hong-Ping
, p. 301 - 305 (2011)
A new manganese(II) complex [Mn3(bidc)2(C 2O4)(H2O)10]n (1) (bidc = benzimidazole-5,6-dicarboxylate) was synthesized and characterized by X-ray crystallography. X-ray diffraction shows that complex 1 has a neutral, one-dimensional (1D) brick wall chain structure. With the intramolecular and intermolecular hydrogen bonding interactions, the adjacent chains are joined into a 3D suparmolecular architecture. IR spectroscopy and variable temperature magnetic susceptibility measurements were made, which indicated weak antiferromagnetic coupling between the MnII ions in complex 1.
Sonochemical preparation of stable porous MnO2 and its application as an efficient electrocatalyst for oxygen reduction reaction
Zuo, Ling-Xia,Jiang, Li-Ping,Abdel-Halim,Zhu, Jun-Jie
, p. 219 - 225 (2017)
Porous MnO2 as a non-noble metal oxygen reduction reaction (ORR) electrocatalyst was prepared by a simple sonochemical route. The as-prepared porous MnO2 exhibited higher electrocatalytic activity, superior stability and better methanol tolerance than commercial Pt/C catalyst in alkaline media. Furthermore, the ORR proceeded via a nearly four-electron pathway. Cyclic voltammetry (CV) and rotating-disk electrode (RDE) measurements verified that the ORR enhancement was attributed to the porous structure and good dispersity, which facilitated sufficient transport of ions, electrons, O2 and other reactants in the process of ORR. The results indicated that a facile and feasible sonochemical route could be used to prepare highly active porous MnO2 electrocatalyst for ORR, which might be promising for direct methanol fuel cells.
Controllable explosion: fine-tuning the sensitivity of high-energy complexes
Wang, Kun,Zeng, Dihao,Zhang, Jian-Guo,Cui, Yan,Zhang, Tong-Lai,Li, Zhi-Min,Jin, Xin
, p. 12497 - 12501 (2015)
Tuning the sensitivity of energetic materials has always been a research topic of interest. A lot of attention has been paid on changing the ligands previously used in traditional high energy density materials (HEDMs). Recently, we have stepped further along this path by thinking from another angle, i.e., changing the metal centre. Herein, we report 4 transition metal complexes bearing the 1,5-diaminotetrazole ligand, which have similar structures but drastically different sensitivities. These differences are apparently due to the different metal centres used.
Local atomic arrangement and electronic structure of nanocrystalline transition metal oxides determined by X-ray absorption spectroscopy
Hwang, Seong-Ju,Choy, Jin-Ho
, p. 5791 - 5796 (2003)
The local crystal structure and electronic configuration of transition metal in X-ray amorphous MnO2 and CrO2 nanocrystals have been examined by using X-ray absorption (XAS) spectroscopy at Mn K and Cr K-edges. The Mn K-edge XAS study reveals that tetravalent manganese ions are stabilized in ?±-MnO2-type local atomic arrangement consisting of the intergrowth of edge- and corner-shared MnO6 octahedra. On the other hand, it is found from Cr K-edge XAS results that nanocrystalline CrO2 possesses two different kinds of local structures around chromium, that is, Cr2O3-type with octahedral site and CrO3-type with tetrahedral site. The presence of Cr+VI species on the surface would be helpful for Li grafting process, giving rise to excellent electrochemical performances. This work can be regarded as a strong evidence for the usefulness of XAS to study nanocrystalline electrode materials.
Kinetics of lab prepared manganese oxide catalyzed oxidation of benzyl alcohol in the liquid phase
Saeed, Muhammad,Ilyas, Mohammad,Siddique, Mohsin
, p. 447 - 460 (2015)
The oxidation of benzyl alcohol in the liquid phase was studied over manganese oxide catalyst using molecular oxygen as an oxidant. Manganese oxide was prepared by a mechanochemical process in solid state and was characterized by chemical and physical techniques. The catalytic performance of manganese oxide was explored by carrying out the oxidation of benzyl alcohol at 323-373 K temperature and 34-101 kPa partial pressure of oxygen. Benzaldehyde and benzoic acid were identified as the reaction products. Typical batch reactor kinetic data were obtained and fitted to the Langmuir-Hinshelwood, Eley-Rideal, and Mars-van Krevelene models of heterogeneously catalyzed reactions. The Langmuir-Hinshelwood model was found to give a better fit. Adsorption of benzyl alcohol at the surface of the catalyst followed the Langmuir adsorption isotherm. The heat of adsorption for benzyl alcohol was determined as -18.14 kJ mol-1. The adsorption of oxygen followed the Temkin adsorption isotherm. The maximum heat of adsorption for oxygen was -31.12 kJ mol-1. The value of activation energy was 71.18 kJ mol-1, which was apparently free from the influence of the heat of adsorption of both benzyl alcohol and oxygen.
A novel self-assembly approach for synthesizing nanofiber aerogel supported platinum single atoms
Jiang, Zheng,Kato, Kenichi,Li, Xiaopeng,Lin, Chao,Sun, Yu,Xu, Qing,Yamauchi, Miho,Yang, Ruoou,Zhang, Hao,Zhang, Haojie,Zhao, Yonghui
, p. 15094 - 15102 (2020)
A great challenge in catalyst engineering is precisely assembling and positioning nanoscale active metals at desired locations while constructing robust functional architectures. This article presents a novel approach for constructing macroscopic Ag-doped manganese oxide aerogels (up to 2 L) while homogeneously incorporating active Pt single atoms (Pt/Ag-MnO2) based on a solution-solid-solid (SSS) mechanism. AgOx seeds were identified as key species for triggering the octopus-like growth of MnO2 nanofibers and inserting Ag and Pt into the MnO2 crystalline framework. The interconnection and entanglement among nanofibers allowed the formation of mechanically strengthened hierarchical structures, leading to one of the most robust manganese-based aerogels to date. Impressively, the Pt/Ag-MnO2 aerogel also possessed promising selectivity and stability toward the electrocatalytic oxygen reduction reaction, with Pt showing a high mass activity of 1.6 A/(mgPt) at 0.9 V vs. RHE. Experimental characterization and theoretical calculation confirmed Pt single atoms to be located at substitutional lattice sites, which reduced the overall oxygen reduction barriers. Our approach suggests that SSS or other analogous nanofiber or nanowire growth strategies are powerful in controlling structural formation over the entire range of length scales while being applicable to fabricating single-atom catalysts.
Synthesis of NaxMnO2+δ by a reduction of aqueous sodium permanganate with sodium iodide
Jeong,Manthiram
, p. 331 - 338 (2001)
Reduction of sodium permanganate with sodium iodide in aqueous solutions has been investigated systematically. The products formed have been characterized by X-ray diffraction, wet-chemical analysis, and surface area and magnetic susceptibility measurements after firing at various temperatures. The results reveal that the sodium content x in the reduction products NaxMnO2+δ depends strongly on the reaction pH and mildly on the relative concentrations of the reactants. Na0.7MnO2+δ obtained at pH>11 followed by firing at T>500°C adopts the P2 layer structure (hexagonal) with cation vacancies arising from a δ≈0.3. Na0.7 MnO2+δ crystallizing in a distorted P2 structure (orthorhombic) without cation vacancies (δ≈0) could be obtained by annealing the hexagonal Na0.7MnO2+δ (δ≈0.3) in N2 atmosphere around 600°C. While the orthorhombic Na0.7MnO2+δ (δ0.7MnO2+δ (δ≈0.3) transforms to spinel-like phases due to the presence of cation vacancies. Na0.5MnO2+δ obtained at a controlled pH of 9.3 adopts a metastable layer structure on firing at 500°C and a tunnel structure isostructural with Na4Mn4Ti5O18 on firing at T≥600°C. The tunnel structure is stable to ion-exchange reactions without transforming to spinel-like phases. In addition, washing the reduction products with various organic solvents before firing at higher temperatures is found to influence the reaction kinetics, composition, and crystal chemistry.
Synthesis of boron/nitrogen substituted carbons for aqueous asymmetric capacitors
Tomko, Timothy,Rajagopalan, Ramakrishnan,Aksoy, Parvana,Foley, Henry C.
, p. 5369 - 5375 (2011)
Boron/nitrogen substituted carbons were synthesized by co-pyrolysis of polyborazylene/coal tar pitch blends to yield a carbon with a boron and nitrogen content of 14 at% and 10 at%, respectively. The presence of heteroatoms in these carbons shifted the hydrogen evolution overpotential to -1.4 V vs Ag/AgCl in aqueous electrolytes, providing a large electrochemical potential window (～2.4 V) as well as a specific capacitance of 0.6 F/m2. An asymmetric capacitor was fabricated using the as-prepared low surface area carbon as the negative electrode along with a redox active manganese dioxide as the positive electrode. The energy density of the capacitor exceeded 10 Wh/kg at a power density of 1 kW/kg and had a cycle life greater than 1000 cycles.
