Co-doped Composites Research Articles

Effect of Bismuth Ferrite Nanometer Filler Element Doping on the Surface Insulation Properties of Epoxy Resin Composites.

In the direct current electric field, the surface of epoxy resin (EP) insulating material is prone to charge accumulation, which leads to electric field distortion and damages the overall insulation of the equipment. Nano-doping is an effective method to improve the surface insulation strength and DC flashover voltage of epoxy resin composites. In this study, pure bismuth ferrite nanoparticles (BFO), as well as BFO nanofillers, which were doped by La element, Cr element as well as co-doped by La + Cr element, were prepared by the sol-gel method. Epoxy composites with various filler concentrations were prepared by blending nano-fillers with epoxy resin. The morphology and crystal structure of the filler were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The effects of different filler types and filler mass fraction on the surface flashover voltage, charge dissipation rate, and trap characteristics of epoxy resin composites were studied. The results showed that element doping with bismuth ferrite nanofillers could further increase the flash voltage of the composites. The flashover voltage of La + Cr elements co-doped composites with the filler mass fraction of 4 wt% was 45.2% higher than that of pure epoxy resin. Through data comparison, it is found that the surface charge dissipation rate is not the only determinant of the flashover voltage. Appropriately reducing the surface charge dissipation rate of epoxy resin composites can increase the flashover voltage. Finally, combining with the distribution characteristics of the traps on the surface of the materials to explain the mechanism, it is found that the doping of La element and Cr element can increase the energy level depth and density of the deep traps of the composite materials, which can effectively improve the flashover voltage along the surface of the epoxy resin.

Simultaneously Enhanced Thermal Conductivity and Breakdown Performance of Micro/Nano-BN Co-Doped Epoxy Composites.

Micro/nano- BN co-doped epoxy composites were prepared and their thermal conductivity, breakdown strength at power frequency and voltage endurance time under high frequency bipolar square wave voltage were investigated. The thermal conductivity and breakdown performance were enhanced simultaneously in the composite with a loading concentration of 20 wt% BN at a micro/nano proportion of 95/5. The breakdown strength of 132 kV/mm at power frequency, the thermal conductivity of 0.81 W·m−1·K−1 and voltage endurance time of 166 s were obtained in the composites, which were approximately 28%, 286% and 349% higher than that of pristine epoxy resin. It is proposed that thermal conductive pathways are mainly constructed by micro-BN, leading to improved thermal conductivity and voltage endurance time. A model was introduced to illustrate the enhancement of the breakdown strength. The epoxy composites with high thermal conductivity and excellent breakdown performance could be feasible for insulating materials in high-frequency devices.

Environmentally Friendly Bark-Derived Co-Doped Porous Carbon Composites for Microwave Absorption

Biomass-derived porous carbon has attracted tremendous attention in many research fields due to its cheap and feasible strategy. In this work, bark-derived porous carbon composites (Co@PC) for microwave absorption applications was successfully prepared through a simple method. The minimum reflection loss (RLmin) of Co@PC (carbonized at 800°C, Co2+ concentration is 0.15 mol/L) is -49.2 dB at 10 GHz and a wide effective absorption bandwidth (EAB) of 6.16 GHz was obtained. Further, by adjusting carbonization temperature of the bark, the microwave absorption performance could be further enhanced. The results show that the RLmin could be -58.4 dB at 8.6 GHz when the bark was carbonized at 900°C. The retained channel structures of the bark played an important role in this excellent microwave absorbing performance. The channel walls with Co nanoparticles form a three-dimensional conductive network, endow conductive loss and magnetic loss of microwave energies. The channel structures provide transmission path for microwaves, which is not only cause multiple reflections and scattering of microwaves, but also benefit to the impedance matching. In addition, radar cross section (RCS) simulation results also demonstrates that Co@PC can be applied in the field of microwave absorption.

In situ and tunable structuring of semiconductor-in-glass transparent composite.

SummarySemiconductor-in-glass composites are an exciting class of photonic materials for various fundamental applications. The significant challenge is the scalable elaboration of composite with the desirable combination of tunable structure, high semiconductor loading ratio, and excellent transparency. Here we report that the topological engineering strategy via hybridization of the glass network former enables to surmount the aforementioned challenge. It not only facilitates the in situ precipitation of (Ga2-xAlx)O3 domains with continuously tunable composition but also allows to simultaneously refine the grain size and enhance the crystallinity. In addition, the composites exhibit excellent transparency and can host various active dopants. We demonstrate the attractive broadband optical response of the composite and achieve the pulse laser operation in mid-infrared waveband. The findings are expected to provide a fundamental principle of in situ modification in hybrid system for generation of high-performance semiconductor-in-glass composites.

The reduction of thermal conductivity in Cd and Sn co-doped Cu3SbSe4-based composites with a secondary-phase CdSe

In this paper, we reported the enhanced thermoelectric properties of Cd and Sn dual-doped Cu3SbSe4-based material prepared by the vacuum melting combined with spark plasma sintering process. X-ray photoelectron spectroscopy studies revealed the presence of Cu+, Cd2+, Sb5+, Sn4+ and Se2− states of Cu, Cd, Sb, Sn and Se, respectively. All samples exhibited p-type conduction with carrier concentrations varying from 0.54 × 1018 to 46.42 × 1018 cm−3, while carrier mobility changes from 18.2 to 46.6 cm2 V−1 s−1 at room temperature. Cd doping at Cu sites in the Cu3SbSe4 can reduce the lattice thermal conductivity, while Sn doping at Sb sites is effective to adjust the carrier concentration. The further reduction in thermal conductivity is observed in Cd-Sn co-doped samples resulting from an accumulated effect combining point defects and the secondary-phase CdSe. Consequently, the maximum dimensionless figure of merit (ZT) value reaches 0.66 at 623 K for the Cu2.75Cd0.25Sb0.94Sn0.06Se4 sample, which is 190% larger than that of the intrinsic sample (ZT of 0.35). The findings provide an alternative strategy of boosting the carrier and phonon transports of the Cu3SbSe4, which is also a meaningful guidance to achieve high performance in other copper-based chalcogenides.

Insights into the enhanced sodium storage property and kinetics based on the Zr/Si codoped Na3V2(PO4)3/C cathode with superior rate capability and long lifespan

Na3V2(PO4)3(NVP) is a promising cathode material. However, the poor intrinsic conductivity and sever volumetric shrinkage constrain the applications of NVP. Herein, we propose a remarkable Si/Zr co-doped Na3V2-xZrx(PO4)3-x(SiO4)x/C composite. The optimized co-doped sample exhibits superior rate and cycling performance resulting from the improved ionic conductivity. The synergetic effects of Si/Zr co-doping on the crystal structural stability and Na+ migration capability are significant, leading to superior electrochemical performance for the co-doped composites. Moreover, the Na3V2-xZrx(PO4)3-x(SiO4)x/C possess an extra high voltage plateau at 3.7 V, corresponding to the V4+/V5+ reaction. The optimized Na3V1.97Zr0.03(PO4)2.97(SiO4)0.03/C reveals an initial capacity of 109.6 mA h g−1 at 0.1 C. It performs a capacity retention of 87.7% at 6 C after 500 cycles. At a higher density of 12 C, the initial capacity is 95.7 mA h g−1, and it retains a value of 68.3 mA h g−1 after 2000 cycles, corresponding to a low decay of 0.014% per cycle. Due to the high potential platform and superior capacity value, it delivers an energy density of 403.5 Wh kg−1, surpassing the theoretical one (397.8 Wh kg−1). The kinetic behavior is explored by GITT, and the lowest diffusion coefficients appeared at 3.4 V and 3.7 V conforms to the electrochemical tests.

Ferromagnetic, electric, and ferroelectric properties of samarium and cobalt co-doped bismuth ferrite nanoparticles

Pure and co-doped multiferroic bismuth ferrite (BFO) nanoparticles were synthesized by the sol-gel method. Samarium and cobalt were used as co-dopants in BFO. The co-doped composites had the formula Bi1-xSmxFe1-yCoyO3, where x = 0.1 and y = 0.05, 0.1, or 0.15. Rietveld refinement of X-ray diffraction patterns showed a well-arranged crystalline rhombohedral structure with space group R3c. The rhombohedral structure transformed to an orthorhombic structure with space group Pbam in co-doped BFO nanoparticles. The ferromagnetic properties of synthesized nanoparticles were investigated in detail. Bi0.9Sm0.1Fe0.85Co0.15O3 showed a large increase in saturation magnetization and remanent magnetization to 3.2 and 1.5 emu/g, respectively. The large increase in magnetization with a reasonable squareness ratio and coercive field of co-doped BFO nanoparticles means they have potential uses in memory and spintronic devices. Electric properties such as resistance, reactance, AC resistivity, and AC conductivity were analyzed as a function of frequency. The AC resistivity decreased and the AC conductivity increased greatly with increasing co-dopant concentration. The ferroelectric behavior of pure and co-doped samples was also investigated. The maximum polarization and remanent polarization greatly increased to 12.5 and 7.5 μC/cm2, respectively, in Bi0.9Sm0.1Fe0.85Co0.15O3. The increased conductivity and reduced resistivity of co-doped samples may also be useful in efficient photovoltaic solar cells.

Nonlinear conductivity and breakdown strength characteristics of silicon carbide and hexagonal boron nitride co-doped epoxy resin composites

In this study, the method of co-doping semi-conductor silicon carbide (SiC) and insulating inorganic phase hexagonal boron nitride (h-BN) in epoxy resin (EP) composites has been proposed for considering both the nonlinear conductivity and the breakdown strength. First, the epoxy-based composites were fabricated and prepared by hot press vulcanization. Then, the phase structure and the microstructure of the composites were characterized by XRD and SEM. Finally, the nonlinear conductivity and the breakdown strength of the composites were tested. The results indicate that the breakdown strength of the 1 wt. % h-BN/3 wt. % SiC/EP composite reaches 115.6 kV/mm, which is 4 times higher than that of the single-doped 3 wt. % SiC/EP composite. More importantly, the appropriate h-BN and SiC contents of the co-doped EP composites still exhibit excellent nonlinear electrical conductive properties. The results indicate that both the nonlinear conductivity and the breakdown strength have been obtained by the semi-conductor and insulator co-doping strategy.

High‐performance N, P‐CNL nanocomposites as catalyst for oxygen reduction reaction in fuel cell

Transition metal and heteroatom codoped carbon materials have become the most promising materials to replace commercial platinum carbon (Pt / C) catalysts due to their low cost, high stability, and methanol resistance. In this work, iron-nitrogen and phosphorus codoped carbon nanorod-layer composites (N, P-CNL) derived from phosphorus-doped polyaniline (P-PANI) by phytic acid (PA) and iron salt were successfully obtained after high-temperature pyrolysis. As a result, the N, P-CNL materials exhibited good electrocatalytic performance due to abundant active sites. The N, P-CNL with 50% mass filling ratio of iron salt (named as N, P-CNL-1:1) displayed an enhanced limiting current density of −5.97 mA cm−2 at 1600 rpm and outstanding onset potential (−0.004 V) and oxygen reduction peak potential (−0.144 V). In general, this work can give insights into understanding the mechanism of codoped catalysts and synthesis the catalyst with excellent long-term stability and resistance to methanol crossover and poisoning better than commercial Pt/C.

Nitrogen, sulfur Co-doped porous graphene boosting Li4Ti5O12 anode performance for high-rate and long-life lithium ion batteries

Enhancing the electron/ion transfer ability of Li4Ti5O12 materials is very important to achieve advanced high-rate and long-life anode in lithium ion batteries (LIBs). Here, for the first time, we report Li4Ti5O12/nitrogen, sulfur co-doped porous graphene composites (LTO/N, S-PG) via one-step facile calcination and activation process by using LiOH as Li source and activating agent. Mechanisms underlying the beneficial effects of N, S co-doped graphene for LTO anode were substantiated by the Density Functional Theory (DFT) calculations, revealing that co-doped N and S atoms not only significantly facilitate Li+ adsorption, but also ameliorate Li+ diffusion in graphene. Furthermore, the synergistic effects of nanosized LTO and porous graphene endow the composites with efficient Li+ diffusion channels and electron-conductive networks. Therefore, the LTO/N, S-PG can deliver extraordinarily high rate capability (e.g. 130 ​mA ​h ​g−1 at 80 ​C and 123 ​mA ​h ​g−1 at 100 ​C), and excellent cycling stability (83.1% capacity retention after 4000 cycles at 20 ​C). In addition, their superior electrochemical performance was also demonstrated in the full cells with LiNi0.5Mn1.5O4 cathode, which displayed 89.5% capacity retention after 500 cycles at 5 ​C. These results suggest the great promise of using the LTO/N, S-PG as a novel anode material for high-rate and long-life LIBs.

Confined sulfidation strategy toward cobalt sulfide@nitrogen, sulfur co-doped carbon core-shell nanocomposites for lithium-ion battery anodes

Abstract A confined sulfidation strategy is developed for the preparation of cobalt sulfide@nitrogen, sulfur co-doped carbon composites (CoS@NSC) with a unique core-shell structure. The as-fabricated CoS@NSC composites are beneficial for efficient lithium ion diffusion, fast electron transfer and improved structural integrity. As a demonstration, the CoS@NSC, as an anode material for lithium-ion battery, exhibits a high initial stable discharge capacity of 754 mA h g−1 and high capacity retention by maintaining 635 mA h g−1 at 1 A g−1 after 100 charge/discharge cycles. This confined sulfidation strategy can be readily extended to a large-scale and cost-effective production of other transition metal sulfide@carbon core-shell nanocomposites.

Synthesis of Co2P nanoparticles decorated nitrogen, phosphorus Co-doped Carbon-CeO2 composites for highly efficient oxygen reduction

The oxygen reduction reaction is an important cathode reaction, thus seeking for low cost and high activity catalysts is highly demanded. Herein, a ternary catalyst composed of Co2P nanoparticles, N and P co-doped carbon (NPC) and CeO2 nanosheets (Co2P-NPC-CeO2) is reported for efficient oxygen reduction. In such composite, CeO2 nanosheets are coated with a carbon layer derived from dopamine, and then decorated with Co2P nanoparticles by using phytic acid as the phosphorus source. High ORR catalytic activity was achieved in the optimized sample with a high onset potential of 880 mV (vs RHE), a positive half-wave potential of 827 mV (vs RHE), a diffusion limited current density of 5.24 mA cm−2, and a good durability (the half-wave potential exhibited almost 0 mV after 1000 cycles). Together with the good durability and methanol tolerance, the composite catalyst demonstrated here can be potentially applied in energy conversion devices.

Study of the hydrogenation and re-heating of Co-doped ZnO and In2O3 Nano composites

Nanocomposite samples of zinc oxide (ZnO) and indium oxide (In2O3) doped with Co (at 1.5% molar concentration) are synthesized through conventional solid-state reaction technique. These samples are taken in a quartz tube and placed in reduction furnace for post-annealing in the presence of hydrogen for ~ 10 h at around 550 °C. The X-ray diffraction (XRD) study confirms the formation of hexagonal wurtzite structure for ZnO, Zn0.985CO0.015O and Zn0.985CO0.015O:H samples whereas cubic bixbyite structure for In2O3, (In0.985CO0.015)2O3 and (In0.985CO0.015)2O3:H samples. The magnetization data investigations depict that both undoped ZnO and In2O3 have small negative susceptibilities and exhibit diamagnetic behavior at room temperature. The doping of Co ions induces paramagnetic property in both the samples. Interestingly, the hydrogenated samples Zn0.985CO0.015O:H and (In0.985CO0.015)2O3:H exhibited a perceptible ferromagnetic behavior at 300 K whereas it overturns significantly after long air sintering. An effort has been made to fit the experiential M-H data of hydrogenated samples to the Bound Magnetic Polaron (BMP) model. MATLAB-based simulations have been performed to validate the homogeneity in particle distribution of the samples evinced through SEM micrographs. A multivariate assessment viz. hierarchical cluster analysis is also executed to corroborate and strengthen the experimental findings of magnetic properties.

Synthesis and electrochemical sodium-storage of few-layered MoS2/nitrogen, phosphorus-codoped graphene

Few-layered molybdenum disulfide/nitrogen, phosphorus co-doped graphene composites are synthesized by a quaternary phosphonium salt-assisted hydrothermal and annealing procedure. The prepared composites are analyzed by x-ray powder diffraction, x-ray photoelectron spectra, scanning electronic microscopy, transmission electronic microscopy, Raman spectra and nitrogen adsorption and desorption. Experimental results indicate that the MoS2 nanosheets are of few-layered and defective structures and are well anchored on flexible conductive nitrogen, phosphorus co-doped graphene to constitute mesoporous composites with increased surface areas. Benefiting from the structural merits as well as surface-dominated pseudocapacitive contribution, the composite electrode presents a high electrochemical sodium storage capacity that arrives at 542 mAh g−1 at a current density of 100 mA g−1 with an excellent cyclability. Moreover, a superior high-rate capability can also be achieved.

Metal−Organic Framework−Derived Iron and Nitrogen Co-Doped Composites as Non-Precious Catalysts for Oxygen Reduction Reaction

Fuel cells can employ hydrogen and oxygen to produce water and electrical energy, which act as the alternative power sources for zero-emission electric vehicles and portable electronic devices. Several types of fuel cells have been developed during the past few years, such as the anion exchange membrane fuel cell (AEMFC). The AEMFC is attractive owing to low-cost non-precious metal catalysts (NPMCs) can be utilized in the electrodes, showing high oxygen reduction reaction (ORR) activity and enhanced durability of NPMCs in alkaline solution [1-6]. Metal–organic frameworks (MOFs) can be considered as a novel structure of porous material, which they are usually consisted of the different metal ions or second-building unit (SBU) of metal clusters combining with the organic ligands to form three-dimensional structure [7-15]. MOFs possess the different structures because of various metal ions combine with various organic ligands, and some of them have the characteristics of uniform porous and high surface area. From many studies, MOFs have acted as catalysts via different processing methods that expect to improve the activity of ORR. This work synthesizes the porous ZIF-67 (zeolitic imidazolate framework) -800-AL and FeN-67 (iron and nitrogen-doped ZIF-67) -800-AL through the microwave hydrothermal, pyrolysis and acid leaching. FeN-67-800-AL shows high oxygen reduction reaction capability, with an almost-ideal electron transfer number of 3.99. The half-wave potential of FeN-67-800-AL only decays 6 mV after potential cycling for 30,000 cycles. From XRD pattern, ZIF-67-800-AL and FeN-67-800-AL both show strong peaks of metallic cobalt and weak peaks of carbon. N2 adsorption–desorption isotherms indicate ZIF-67-800-AL and FeN-67-800-AL both type IV curve, which suggesting the existence of both micropores and mesopores. Moreover, Fe-N67-800-AL obtains the highest BET surface areas. TEM images of FeN-67-800-AL prove the porous structure. On the other hand, TEM mapping images of FeN-67-800-AL prove the existent of Co, Fe and C. TEM results are consistent with XRD and BET analysis. X-ray photoelectron spectroscopy (XPS) results show that the catalyst has high contents of graphitic N and CoNx, which can improve the ORR performance. X-ray absorption spectroscopy (XAS) data show that the oxidation state of cobalt and/or iron as well as the interatomic distance of the heteroatoms in ZIF-67-800-AL and FeN-67-800-AL. The extended X-ray absorption fine structure spectrum (EXAFS) of ZIF-67-800-AL and FeN-67-800-AL show the bonding of Co-Co (2.36Å) and Co-N/Co-C (1.84Å). On the other hand, the bonding of Fe-Fe (2.39Å) and Fe-N/Fe-C (1.78Å) appear on the EXAFS spectrum of FeN-67-800-AL. Due to FeN-67-800-AL has additional Fe-N/Fe-C that can enhance the ORR performance. These data indicate that the presence of the porous structure, the high surface area, and the functional nitrogen can be favored for ORR. Reference [1] J. Xu, P. Gao, T.S. Zhao, Energy and Environmental Science, 5 (2012) 5333-5339. [2] M. Wang, W. Zhang, J. Wang, D. Wexler, S.D. Poynton, R.C.T. Slade, H. Liu, B. Winther-Jensen, R. Kerr, D. Shi, J. Chen, ACS Applied Materials and Interfaces, 5 (2013) 12708-12715. [3] A. Arunchander, M. Vivekanantha, S.G. Peera, A.K. Sahu, RSC Advances, 6 (2016) 95590-95600. [4] G.A. Ferrero, K. Preuss, A. Marinovic, A.B. Jorge, N. Mansor, D.J.L. Brett, A.B. Fuertes, M. Sevilla, M.-M. Titirici, ACS Nano, 10 (2016) 5922-5932. [5] Y.J. Sa, D.-J. Seo, J. Woo, J.T. Lim, J.Y. Cheon, S.Y. Yang, J.M. Lee, D. Kang, T.J. Shin, H.S. Shin, H.Y. Jeong, C.S. Kim, M.G. Kim, T.-Y. Kim, S.H. Joo, J. Am. Chem. Soc., 138 (2016) 15046-15056. [6] H.C. Huang, Y.-C. Lin, S.-T. Chang, C.-C. Liu, K.-C. Wang, H.-P. Jhong, J.-F. Lee, C.-H. Wang, J. Mater. Chem. A, (2017). [7] S. Ma, G.A. Goenaga, A.V. Call, D.-J. Liu, Chemistry - A European Journal, 17 (2011) 2063-2067. [8] T. Palaniselvam, B.P. Biswal, R. Banerjee, S. Kurungot, Chemistry - A European Journal, 19 (2013) 9335-9342. [9] F. Afsahi, S. Kaliaguine, J. Mater. Chem. A, 2 (2014) 12270-12279. [10] W. Chaikittisilp, N.L. Torad, C. Li, M. Imura, N. Suzuki, S. Ishihara, K. Ariga, Y. Yamauchi, Chemistry - A European Journal, 20 (2014) 4217-4221. [11] P. Miao, G. Li, G. Zhang, H. Lu, Journal of Energy Chemistry, 23 (2014) 507-512. [12] G. Song, Z. Wang, L. Wang, G. Li, M. Huang, F. Yin, Chinese Journal of Catalysis, 35 (2014) 185-195. [13] X. Wang, J. Zhou, H. Fu, W. Li, X. Fan, G. Xin, J. Zheng, X. Li, J. Mater. Chem. A, 2 (2014) 14064-14070. [14] W. Xia, J. Zhu, W. Guo, L. An, D. Xia, R. Zou, J. Mater. Chem. A, 2 (2014) 11606-11613. [15] W. Zhang, Z.-Y. Wu, H.-L. Jiang, S.-H. Yu, J. Am. Chem. Soc., 136 (2014) 14385-14388.

Competitive adsorption of gases dissolved in transformer oil on Co-doped ZnO (0 0 0 1) surface

The use of gas sensors to monitor gases dissolved in transformer oil is of great value to prevent safety issues of power grid. As a part of developing high performance gas sensor, the deeply sensing mechanism in material aspect study has great guiding significance. In this paper, a new surface adsorption model is proposed which provides an approach to achieve the improvement of the gas-sensing performance of Co-doped ZnO sensor theoretically. Utilizing first-principle density functional theory, the adsorption properties of six main characteristic fault gases (C2H2, CO2, CH4, C2H4, CO, and H2) on Co-doped ZnO (0001) surface were systemically investigated which indicated that H2 and CH4 molecules were physically adsorbed, whereas CO, CO2, C2H2, and C2H4 were chemisorbed. In addition, using the as-prepared Co-doped ZnO material, the gas-sensing response for these fault gases were experimentally measured, which matches well with the theoretical analysis. This work reveals the gas-sensing performance of Co-doped ZnO composites in microscopic. It lays the foundation for the preparation of gas sensors to serve for monitoring the condition of power transformers.

Dehydrogenation properties and mechanisms of MgH2-NiCl2 and MgH2-NiCl2-graphene hydrogen storage composites

The four hydrogen storage systems including pure MgH2, MgH2-5 wt%NiCl2, MgH2-10 wt%NiCl2 and MgH2-10 wt%NiCl2-10 wt%graphene were prepared by ball-milling in this work. Using experimental X-ray diffraction, scanning electron microscopy and differential scanning calorimetry testing methods in combination with first-principle calculations, the dehydrogenation properties and mechanisms of NiCl2 single-doped and NiCl2-graphene co-doped MgH2 composites were systematically investigated. Experimental results show that the NiCl2 single-doping is conductive to decreasing the size of MgH2 grains and particles. The co-doping of NiCl2 and graphene not only reduces the size of MgH2 grains and particles, but also contributes to the uniformity of MgH2 particles. As compared with milled pure MgH2, the dehydrogenation peak temperatures are decreased by 24 °C and 47 °C for the 10 wt%NiCl2 single-doped and 10 wt%NiCl2-10 wt%graphene co-doped MgH2 systems, respectively. It is demonstrated that the co-doping of NiCl2 and graphene exhibits the synergistic effects of confinement and catalysis on improving the dehydrogenation properties of MgH2. The first-principle calculations indicate that the co-doping of NiCl2 and graphene leads to the distortion of MgH2 atomic-configuration and results in the charge transfer between the dopants and MgH2, which induce the weakened structural stability and decreased dehydrogenation enthalpy of MgH2.

Recent progress in active sites for non-noble metal carbon-based oxygen reduction catalysts

Platinum-based materials are widely applied to catalyze cathodic oxygen reduction reaction in H2/O2 fuel cell. Due the high price and scarcity of Pt, developing novel non-noble metal catalysts is of great importance for wide application of H2/O2 fuel cell due to their low price and abundance compared to platinum-based materials. Non-noble metal carbon-based oxygen reduction reaction catalysts, including transition-metals-nitrogen co-doped carbon composites and heteroatom-doped carbon composites, are intensively studied. Recognizing the active sites for such catalysts is of great importance for further improving the catalytic performance and scaled up synthesis, thus it has attracted tremendous research efforts. For the M–N–C type catalysts, M-N x /C ( x =1,2,3,4), N x -C, as well as active graphene layers in iron encapsulated within carbon nanotubes or graphene layers have been regarded as active sites in varied research, respectively. For the heteroatoms-doped carbon catalysts, carbon atoms adjacent to pyridinic nitrogen are accepted as active sites. However, it is difficult to eliminate trace amount of metal that introduced from precursors and during the synthesis course, thus synthetizing absolute non-metal heteroatoms-doped carbon and identifying the active sites are almost impossible. Therefore, distinguishing active sites from several components and improving catalysts active sites density are issues that we must resolve. This short review focuses on our recent results acquired regarding the activity and active sites for ORR, and we expect that this effort will promote further research on this challenging and important topic.

Microwave-hydrothermal synthesis of Co-doped FeS2 as a visible-light photocatalyst

Co-doped FeS2 composites were successfully synthesized through a facile microwave-hydrothermal process. The products were characterized by X-ray diffraction, X-ray Photoelectron Spectroscopy, field emission scanning electron microscope, UV–Vis diffuse reflectance spectra, and Raman spectroscopy. Cobalt doping didn’t change the basic structure of pyrite FeS2. But the spherical FeS2 product changed into some aggregated laminar particles. The Co-doped FeS2 product exhibited higher absorption in visible-light region and the photocatalytic performance was greatly enhanced. The Co0.333Fe0.667S2 product could decompose 48.9 % methylene blue within 210 min, which was 36.5 % higher than that of the pristine FeS2.

Room temperature ferromagnetism in Co-doped amorphous carbon composites from the spin polarized semiconductor band

This study provides conclusive evidence of room temperature ferromagnetism in Co-doped amorphous carbon (a-C) composites from the spin polarized semiconductor band. These composites are constructed from discontinuous [Co(3 nm)/a-C(dc nm)]5 multilayers with dc = 3 nm and dc = 6 nm. Only remnant circular dichroism (CD) was observed from the dc = 3 nm sample but not when dc = 6 nm. In addition, the remnant CD peaks at 5.5 eV, which is comparable with the absorption peak associated with the C σ-σ* gap transition. We suggest that the possible mechanism for this coupling can be considered as a magnetic proximity effect in which a ferromagnetic moment in the C medium is induced by Co/C interfaces.