Preparation of hard carbon carbon nitride nanocomposites by chemical vapor deposition to reveal the impact of open and closed porosity on sodium storage

The sodium ion battery is a promising successor for the lithium ion battery. Its energy density is limited by the anode, where sodium ideally is stored at low potentials vs. Na Na . The understanding of the fundamental relationships between material properties and sodium storage is often lagging behind materials development. There is a discord regarding the involvement of so called closed pores in carbons in sodium storage. To investigate their influence, a chemical vapor deposition CVD process to deposit polymeric carbon nitride p C3N4 on hard carbon fibres of both, open and closed microporosity, is developed. High storage capacity at a low potential is only possible, when suitable, sealed pores are present. In fibers without notable gas accessible surface, p C3N4 is deposited on the external area, whereas in open microporous samples the p C3N4 phase grows in micropores. Consequently, except for the untreated fibres with closed pores, the composite with a pore gradient along the fibers is the only one in the study that is able to accommodate sodium at low potentials. Neither the remaining graphitic domains, nor the introduced p C3N4 are able to accommodate sodium in a quasimetallic state. Finally, not only the sodium storage but also the solid electrolyte interphase SEI build up is influenced by the additional p C3N4 laye

Morphological evolution of a single crystal silicon battery electrode during lithiation and delithiation An operando phase contrast imaging study

Operando phase contrast radiography combined with impedance spectroscopy and electron microscopy is applied to study the morphological changes in a lithium silicon cell over several cycles. The single crystal silicon 100 surface is employed as a working electrode. A checkerboard like cracking pattern aligned with the crystallographic axis is formed in the 4th cycle during the second step of the delithiation. With the crack position kept fixed, this crack pattern vanishes during lithiation and gets more pronounced in the subsequent cycles. This pattern forms just after the first delithiation peak that corresponds to the decomposition of the highly lithiated phase. It vanishes during lithiation in the potentiostatic step. Therefore, capacity limited cycling, which partly maintains the highly lithiated phase, may avoid the formation of fractures. The surface area of the crack cells remains almost constant with increasing cycle numbers, and no electrochemically inactive sites were observe

Synthesis and Characterization of Cobalt and Nitrogen Co Doped Peat Derived Carbon Catalysts for Oxygen Reduction in Acidic Media

In this study, several peat derived carbons PDC were synthesized using various carbonization protocols. It was found that depending on the carbonization method, carbons with very different surface morphologies, elemental compositions, porosities, and oxygen reduction reaction ORR activities were obtained. Five carbons were used as carbon supports to synthesize Co N PDC catalysts, and five different ORR catalysts were acquired. The surface analysis revealed that a higher nitrogen content, number of surface oxide defects, and higher specific surface area lead to higher ORR activity of the Co N PDC catalysts in acidic solution. The catalyst Co N C 2 ZnCl2 , which was synthesized from ZnCl2 activated and pyrolyzed peat, showed the highest ORR activity in both rotating disk electrode and polymer electrolyte membrane fuel cell tests. A maximum power density value of 210 mW cm2 has been obtained. The results of this study indicate that PDCs are promising candidates for the synthesis of active non platinum group metal type catalyst

Poly ionic liquid Nanovesicle Templated Carbon Nanocapsules Functionalized with Uniform Iron Nitride Nanoparticles as Catalytic Sulfur Host for Li S Batteries

Poly ionic liquid s PIL are common precursors for heteroatom doped carbon materials. Despite a relatively higher carbonization yield, the PIL to carbon conversion process faces challenges in preserving morphological and structural motifs on the nanoscale. Assisted by a thin polydopamine coating route and ion exchange, imidazolium based PIL nanovesicles were successfully applied in morphology maintaining carbonization to prepare carbon composite nanocapsules. Extending this strategy further to their composites, we demonstrate the synthesis of carbon composite nanocapsules functionalized with iron nitride nanoparticles of an ultrafine, uniform size of 3 5 nm termed FexN C . Due to its unique nanostructure, the sulfur loaded FexN C electrode was tested to efficiently mitigate the notorious shuttle effect of lithium polysulfides LiPSs in Li S batteries. The cavity of the carbon nanocapsules was spotted to better the loading content of sulfur. The well dispersed iron nitride nanoparticles effectively catalyze the conversion of LiPSs to Li2S, owing to their high electronic conductivity and strong binding power to LiPSs. Benefiting from this well crafted composite nanostructure, the constructed FexN C S cathode demonstrated a fairly high discharge capacity of 1085 mAh g 1 at 0.5 C initially, and a remaining value of 930 mAh g 1 after 200 cycles. In addition, it exhibits an excellent rate capability with a high initial discharge capacity of 889.8 mAh g 1 at 2 C. This facile PIL to nanocarbon synthetic approach is applicable for the exquisite design of complex hybrid carbon nanostructures with potential use in electrochemical energy storage and conversio

Poly ionic liquid nanovesicles via polymerization induced self assembly and their stabilization of Cu nanoparticles for tailored CO2 electroreduction

Herein, we report a straightforward, scalable synthetic route towards poly ionic liquid PIL homopolymer nanovesicles NVs with a tunable particle size of 50 to 120 nm and a shell thickness of 15 to 60 nm via one step free radical polymerization induced self assembly. By increasing monomer concentration for polymerization, their nanoscopic morphology can evolve from hollow NVs to dense spheres, and finally to directional worms, in which a multilamellar packing of PIL chains occurred in all samples. The transformation mechanism of NVs internal morphology is studied in detail by coarse grained simulations, revealing a correlation between the PIL chain length and the shell thickness of NVs. To explore their potential applications, PIL NVs with varied shell thickness are in situ functionalized with ultra small 1 amp; 8764; 3 nm in size copper nanoparticles CuNPs and employed as electrocatalysts for CO2 electroreduction. The composite electrocatalysts exhibit a 2.5 fold enhancement in selectivity towards C1 products e.g., CH4 , compared to the pristine CuNPs. This enhancement is attributed to the strong electronic interactions between the CuNPs and the surface functionalities of PIL NVs. This study casts new aspects on using nanostructured PILs as new electrocatalyst supports in CO2 conversion to C1 product

Carbonaceous Materials Investigated by Small Angle X ray and Neutron Scattering

Carbonaceous nanomaterials have become important materials with widespread applications in battery systems and supercapacitors. The application of these materials requires precise knowledge of their nanostructure. In particular, the porosity of the materials together with the shape of the pores and the total internal surface must be known accurately. Small angle X ray scattering SAXS and small angle neutron scattering SANS present the methods of choice for this purpose. Here we review our recent investigations using SAXS and SANS. We first describe the theoretical basis of the analysis of carbonaceous material by small angle scattering. The evaluation of the small angle data relies on the powerful concept of the chord length distribution CLD which we explain in detail. As an example of such an evaluation, we use recent analysis by SAXS of carbide derived carbons. Moreover, we present our SAXS analysis on commercially produced activated carbons ACN, RP 20 and provide a comparison with small angle neutron scattering data. This comparison demonstrates the wealth of additional information that would not be obtained by the application of either method alone. SANS allows us to change the contrast, and we summarize the main results using di erent contrast matching agents. The pores of the carbon nanomaterials can be filled gradually by deuterated p xylene, which leads to a precise analysis of the pore size distribution. The X ray scattering length density of carbon can be matched by the scattering length density of sulfur, which allows us to see the gradual filling of the nanopores by sulfur in a melt impregnation procedure. This process is important for the application of carbonaceous materials as cathodes in lithium sulfur batteries. All studies summarized in this review underscore the great power and precision with which carbon nanomaterials can be analyzed by SAXS and SAN

Oxygen reduction reaction in alkaline solution Influence of catalyst loading and carbon support characteristics

Oxygen electroreduction reaction in 0.1 M KOH aqueous solution has been investigated varying the catalyst loading deposited onto glassy carbon electrode. It was found that with increasing the catalyst loading the electrocatalytic activity increased. Comparable current density values obtained for 1.0 mg cm-2 Pt-Vulcan electrode could be achieved for Pt-C(Mo2C) electrode with approximate loading of 0.3 mg cm-2, indicating that Pt-C(Mo2C) catalyst has noticably higher activity towards ORR than Pt-Vulcan catalyst

Influence of Temperature on the Oxygen Electroreduction Activity at Micro Mesoporous Carbon Support

Influence of temperature on the oxygen reduction kinetics of various catalysts has been analyzed in O2 saturated 0.1M KOH solution using rotating disc electrode method. Several important reaction parameters, such as the number of electrons transferred per one oxygen molecule, the slope values of Tafel-like plots at different temperatures, and the apparent activation energies for the oxygen reduction reaction were obtained. The calculated absolute kinetic current density value (62.6 A m-2) at the half-wave potential (-0.05V vs. HgêHgOê0.1M KOH) of platinum nanoparticles modified catalyst was maximum at 60oC. Calculated apparent activation energies were within a range from 19 to 27 kJ mol-1 at Pt nanoparticles modified molybdenum carbide derived carbon catalyst within potential range from 0.05 to -0.07V vs. HgêHgOê0.1M KOH.</jats:p