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Halim, Joseph

Publications and source records attributed to Halim, Joseph.

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Ultra-high-rate pseudocapacitive energy storage in two-dimensional transition metal carbides

In this study, the use of fast surface redox storage (pseudocapacitive) mechanisms can enable devices that store much more energy than electrical double-layer capacitors (EDLCs) and, unlike batteries, can do so quite rapidly. Yet, few pseudocapacitive transition metal oxides can provide a high power capability due to their low intrinsic electronic and ionic conductivity. Here we demonstrate that two-dimensional transition metal carbides (MXenes) can operate at rates exceeding those of conventional EDLCs, but still provide higher volumetric and areal capacitance than carbon, electrically conducting polymers or transition metal oxides. We applied two distinct designs for MXene electrode architectures with improved ion accessibility to redox-active sites. A macroporous Ti 3 C 2 T x MXene film delivered up to 210 F g –1 at scan rates of 10 V s –1 , surpassing the best carbon supercapacitors known. In contrast, we show that MXene hydrogels are able to deliver volumetric capacitance of ~1,500 F cm –3 reaching the previously unmatched volumetric performance of RuO 2 .

25 ENERGY STORAGE↗
DOE OSTI2016

Ion-Exchange and Cation Solvation Reactions in Ti 3 C 2 MXene

Ti 3 C 2 and other two-dimensional transition metal carbides known as MXenes are currently being explored for many applications involving intercalated ions, from electrochemical energy storage, to contaminant sorption from water, to selected ion sieving. We report here a systematic investigation of ion exchange in Ti 3 C 2 MXene and its hydration/dehydration behavior. We have investigated the effects of the presence of LiCl during the chemical etching of the MAX phase Ti 3 AlC 2 into MXene Ti 3 C 2 T x (T stands for surface termination) and found that the resulting MXene has Li + cations in the interlayer space. We successfully exchanged the Li + cations with K + , Na + , Rb + , Mg 2+ , and Ca 2+ (supported by X-ray photoelectron and energy-dispersive spectroscopy) and found that the exchanged material expands on the unit-cell level in response to changes in humidity, with the nature of expansion dependent on the intercalated cation, similar to behavior of clay minerals; stepwise expansions of the basal spacing were observed, with changes consistent with the size of the H 2 O molecule. Thermogravimetric analysis of the dehydration behavior of these materials shows that the amounts of H 2 O contained at ambient humidity correlates simply with the hydration enthalpy of the intercalated cation, and that the diffusion of the exiting H 2 O proceeds with kinetics similar to clays. Furthermore, these results have implications for understanding, controlling, and exploiting structural changes and H 2 O sorption in MXene films and powders utilized in applications involving ions, such as electrochemical capacitors, sensors, reverse osmosis membranes, or contaminant sorbents.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesis and characterization of 2D molybdenum carbide (MXene)

Large scale synthesis and delamination of 2D Mo 2 CT x (where T is a surface termination group) has been achieved by selectively etching gallium from the recently discovered nanolaminated, ternary transition metal carbide Mo 2 Ga 2 C. Different synthesis and delamination routes result in different flake morphologies. The resistivity of free-standing Mo 2 CT x films increases by an order of magnitude as the temperature is reduced from 300 to 10 K, suggesting semiconductor-like behavior of this MXene, in contrast to Ti 3 C 2 T x which exhibits metallic behavior. At 10 K, the magnetoresistance is positive. Additionally, changes in electronic transport are observed upon annealing of the films. When 2 μm thick films are tested as electrodes in supercapacitors, capacitances as high as 700 F cm –3 in a 1 m sulfuric acid electrolyte and high capacity retention for at least 10,000 cycles at 10 A g –1 are obtained. Free-standing Mo 2 CT x films, with ≈8 wt% carbon nanotubes, perform well when tested as an electrode material for Li-ions, especially at high rates. In conclusion, at 20 and 131 C cycling rates, stable reversible capacities of 250 and 76 mAh g –1 , respectively, are achieved for over 1000 cycles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

X-ray photoelectron spectroscopy of select multi-layered transition metal carbides (MXenes)

A detailed high resolution X-ray photoelectron spectroscopy (XPS) analysis is presented in this work for select MXenes—a recently discovered family of two-dimensional (2D) carbides and carbonitrides. Given their 2D nature, understanding their surface chemistry is paramount. Thus we identify and quantify the surface groups present before, and after, sputter-cleaning as well as freshly prepared vs. aged multi-layered cold pressed discs. The nominal compositions of the MXenes studied here are Ti 3 C 2 T x , Ti 2 CT x , Ti 3 CNTx, Nb 2 CT x and Nb 4 C 3 T x , where T represents surface groups that this work attempts to quantify. In all the cases, the presence of three surface terminations, single bondO, single bondOH and single bondF, in addition to OH-terminations relatively strongly bonded to H 2 O molecules, was confirmed. Moreover, from XPS peak fits, it was possible to establish the average sum of the negative charges of the terminations for the aforementioned MXenes. Based on this work, it is now possible to quantify the nature of the surface terminations. This information can, in turn, be used to better design and tailor these novel 2D materials for various applications.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Two-Dimensional Nb-Based M 4 C 3 Solid Solutions (MXenes)

Two new two-dimensional Nb 4 C 3 -based solid solutions (MXenes), (Nb 0.8 ,Ti 0.2 ) 4 C 3 T x and (Nb 0.8 ,Zr 0.2 ) 4 C 3 T x (where T is a surface termination) were synthesizedas confirmed by X-ray diffractionfrom their corresponding MAX phase precursors (Nb 0.8 ,Ti 0.2 ) 4 AlC 3 and (Nb 0.8 ,Zr 0.2 ) 4 AlC 3 . In our report we discuss Zr-containing MXene. We also studied intercalation of Li ions into these two compositions, and Nb 4 C 3 T x in order to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb 4 C 3 T x , but were not present in Nb 2 CT x . After 20 cycles at a rate of C/4, the specific capacities of (Nb 0.8 ,Ti 0.2 ) 4 C 3 T x and (Nb 0.8 ,Ti 0.2 ) 4 C 3 T x were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb 4 C 3 T x .

36 MATERIALS SCIENCE↗
DOE OSTI2015

Experimental and theoretical characterization of ordered MAX phases Mo{sub 2}TiAlC{sub 2} and Mo{sub 2}Ti{sub 2}AlC{sub 3}

Herein, we report on the phase stabilities and crystal structures of two newly discovered ordered, quaternary MAX phases—Mo{sub 2}TiAlC{sub 2} and Mo{sub 2}Ti{sub 2}AlC{sub 3}—synthesized by mixing and heating different elemental powder mixtures of mMo:(3-m)Ti:1.1Al:2C with 1.5 ≤ m ≤ 2.2 and 2Mo: 2Ti:1.1Al:2.7C to 1600 °C for 4 h under Ar flow. In general, for m ≥ 2 an ordered 312 phase, (Mo{sub 2}Ti)AlC{sub 2}, was the majority phase; for m < 2, an ordered 413 phase (Mo{sub 2}Ti{sub 2})AlC{sub 3}, was the major product. The actual chemistries determined from X-ray photoelectron spectroscopy (XPS) are Mo{sub 2}TiAlC{sub 1.7} and Mo{sub 2}Ti{sub 1.9}Al{sub 0.9}C{sub 2.5}, respectively. High resolution scanning transmission microscopy, XPS and Rietveld analysis of powder X-ray diffraction confirmed the general ordered stacking sequence to be Mo-Ti-Mo-Al-Mo-Ti-Mo for Mo{sub 2}TiAlC{sub 2} and Mo-Ti-Ti-Mo-Al-Mo-Ti-Ti-Mo for Mo{sub 2}Ti{sub 2}AlC{sub 3}, with the carbon atoms occupying the octahedral sites between the transition metal layers. Consistent with the experimental results, the theoretical calculations clearly show that M layer ordering is mostly driven by the high penalty paid in energy by having the Mo atoms surrounded by C in a face-centered configuration, i.e., in the center of the M{sub n+1}X{sub n} blocks. At 331 GPa and 367 GPa, respectively, the Young's moduli of the ordered Mo{sub 2}TiAlC{sub 2} and Mo{sub 2}Ti{sub 2}AlC{sub 3} are predicted to be higher than those calculated for their ternary end members. Like most other MAX phases, because of the high density of states at the Fermi level, the resistivity measurement over 300 to 10 K for both phases showed metallic behavior.

36 MATERIALS SCIENCE↗