3 research outputs found
Reaction Kinetics of Germanium Nanowire Growth on Inductively Heated Copper Surfaces
This
article describes the chemical kinetics of germanium nanowire
growth on inductively heated copper surfaces using diphenylgermane
as a precursor. Inductive heating of metal surfaces presents a simple,
rapid, and contact-free method to activate the direct growth of nanowires
on metal surfaces. We show the main effects of synthesis temperature,
duration, precursor concentration on the morphology, and loading of
the nanowire film. We describe the complex interplay of precursor
degradation, nucleation, and growth in context of a multistep reaction
mechanism. We studied the temporal evolution of nanowire loading and
morphology to develop a kinetic model, which predicts critical thresholds
that define the onset of sequential axial and radial nanowire growth
modes. These results may be used to commercially scale a nanowire
growth process
Simultaneous Quantification of Electron Transfer by Carbon Matrices and Functional Groups in Pyrogenic Carbon
Pyrogenic
carbon contains redox-active functional groups and polyaromatic
carbon matrices that are both capable of transferring electrons. Several
techniques have been explored to characterize the individual electron
transfer process of either functional groups or carbon matrices individually.
However, simultaneous analysis of both processes remains challenging.
Using an approach that employs a four-electrode configuration and
dual-interface electron transfer detection, we distinguished the electron
transfer by functional groups from the electron transfer by carbon
matrices and simultaneously quantified their relative contribution
to the total electron transfer to and from pyrogenic carbon. Results
show that at low to intermediate pyrolysis temperatures (400ā500
Ā°C), redox cycling of functional groups is the major mechanism
with a contribution of 100ā78% to the total electron transfer;
whereas at high temperatures (650ā800 Ā°C), direct electron
transfer of carbon matrices dominates electron transfer with a contribution
of 87ā100%. Spectroscopic and diffraction analyses of pyrogenic
carbon support the electrochemical measurements by showing a molecular-level
structural transition from an enrichment in functional groups to an
enrichment in nanosized graphene domains with increasing pyrolysis
temperatures. The method described in this study provides a new analytical
approach to separately quantify the relative importance of different
electron transfer pathways in natural pyrogenic carbon and has potential
applications for engineered carbon materials such as graphene oxides
Dynamic Hosts for High-Performance LiāS Batteries Studied by Cryogenic Transmission Electron Microscopy and in Situ Xāray Diffraction
Developing
a high-performance sulfur host is central to the commercialization
and general development of lithiumāsulfur batteries. Here,
for the first time, we propose the concept of dynamic hosts for lithiumāsulfur
batteries and elucidate the mechanism through which TiS<sub>2</sub> acts in such a fashion, using in situ X-ray diffraction and cryogenic
scanning transmission electron microscopy (cryo-STEM). A TiS<sub>2</sub>āS composite electrode delivered a reversible capacity of
1120 mAh g<sup>ā1</sup> at 0.3 C after 200 cycles with a capacity
retention of 97.0% and capacities of 886 and 613 mAh g<sup>ā1</sup> at 1.0 C up to 200 and 1000 cycles, respectively. Our results indicate
that it is Li<sub><i>x</i></sub>TiS<sub>2</sub> (0 < <i>x</i> ā¤ 1), rather than TiS<sub>2</sub>, that effectively
traps polysulfides and catalytically decomposes Li<sub>2</sub>S