Session T34: Materials for Electrochemical Energy Storage I

Vortex Stabilized Compressed Fusion Grade Plasma

Inertial confinement fusion schemes comprise of highly compressed dense plasmas. Some involve short pulses of powerful beams (lasers, particles) applied to solid pellets, while others utilize plasma focus to obtain dense pinch plasmas. Although compression factor \textgreater 1000 has been achieved for starting pressures in the Torr range, the latter is limited by instabilities for initial gas density above 10 Torr. One alternative approach could be shooting electron beams through very dense, atmospheric pressure, vortex stabilized plasma. Large azimuthal magnetic generated by an electron beam can compress and heat the plasma to fusion viable parameters. This configuration is stable against sausage, kink, or beam -- plasma instabilities. Based on experimental evidence beam propagation through the plasma is not be an issue. A second possibility is to tangentially squeeze a quasi-neutral plasma focus flow by a surrounding gas vortex. Based on currently available electron beams, the first scheme viability as an electrical power generating reactor does not seem to be promising. But using a plasma cathode electron beam that was developed a while ago, for which DOE has a patent U.S. Patent 4,942,339, could result in net generation of electricity. Calculations will be presented.   

High Thermal Conducting Boron Arsenide: Crystal Growth and Characterization

Intrigued by recent calculations [Phys. Rev. Lett. 111, 025901(2013)] which predict a remarkably high thermal conductivity of $\sim$ 2,000 $\mathrm{W m^{-1} K^{-1}}$, comparable to that of diamond, in cubic boron arsenide (BAs) crystals, we have succeeded in synthesizing single crystals of BAs with a zinc blende structure and lattice parameters of a = 4.7830(7) $\mathrm{\AA}$ characterized by X-ray single crystal diffraction and transmission electron microscopy (TEM). A relatively high thermal conductivity is obtained but still smaller than the predicted value. We attribute the difference of thermal conductivity value to the defect scattering associated with crystal twinning and As vacancies, verified both from experimental evidence and theoretical calculations. The predicted super-thermal-conductivity may be achieved in BAs single crystals with further improvement of crystal growth by removing the defects.   

Soft Fusion Energy Path: Isotope Production in Energy Subcritical/Economy Hypercritical D$+$D Colliding-Beam Mini Fusion Reactor `Exyder'

Bethe$^{\mathrm{1}}$ and Sakharov$^{\mathrm{2}}$ argued for soft fusion energy path \underline {via} isotope production, substantiated by Manheimer$^{\mathrm{3}}$. - Copious T and $^{\mathrm{3}}$He production$^{\mathrm{4,\thinspace 5}}$ from D(d, p) T and D(d, n) $^{\mathrm{3}}$He reactions in 725 KeV D$+$D colliding beams was measured in weak-focusing Self-Collider$^{\mathrm{6,\thinspace 7}}$ radius 0.15 m, in B $=$ 3.12 T, non-linearly stabilized by electron cloud oscillations$^{8}$ to confinement time $=$ 24 s. Simulations$^{\mathrm{6}}$ predict that by switching to strong focusing$^{\mathrm{9}}$, 10 deuterons 0.75 MeV each, generate 1 $^{\mathrm{3}}$He $+$1T $+$1p $+$ 1n at total input energy cost 10.72 MeV. Economic value of T and $^{\mathrm{3}}$He is 65 and 120 MeV/atom, respectively. We obtain economic gain 205MeV/10.72 MeV $\sim$ 2,000{\%} i.e. $^{\mathrm{3}}$He production funds cost of T. If first wall is made of Thorium n's will breed $^{\mathrm{233}}$U releasing 200 MeV/fission, at neutron cost 5.36 MeV \textit{versus} 160 MeV in beam on target, resulting in no cost $^{\mathrm{3}}$He production, valued {\$}75K/g. 1. Physics Today, May 1979, p.44; 2. Memoirs, Vintage Books, (1992); 3. Phys. Today, May 2012 p. 12; 4. Phys. Rev. Lett. \textbf{54}, 796 (1985); 5. Bull. APS, \textbf{57}, No. 3 (2012); 6. Part. Acc.1, (1970); 7. ANEUTRONIC FUSION NIM \textbf{A 271} 1-167 (1988); 8. Phys. Rev. Lett. \textbf{70}, 1818 (1993); 9. Part. Acc. \textbf{34}, 13 (1990).   

Evidence for Critical Energy for Ion Confinement in Magnetic Fusion Reactors

It is shown here that fusion test reactors could not ignite for half-a-century because trials were conducted at thermonuclear ion energies 10-30 KeV, an order of magnitude lower than \textit{critical energy} [1-2], E$_{\mathrm{c}}$ $\sim$ 200 KeV. At subcritical energies, plasma is destroyed by neutralization of ions \underline {via} overlooked atomic (non-nuclear) charge transfer collisions with giant cross-section, 10$^{\mathrm{9}}$ barns,~100 times greater than that for \textit{ionization} collisions that counters neutralization. Neutral injection sets limit on ion magnetic confinement time \textless 10$^{-6}$ s \underline {vs.} \textgreater 1 s required for ignition. In contrast, at~energies \textit{above} E$_{\mathrm{c}}$, ionization prevails; near $\sim$ 1 MeV, stable confinement of 20 s was routinely observed [3] with \textit{charged} injection.~- To render ITER viable,~ion energy must be increased to \textgreater /$=$ 1 MeV; neutral radioactive DT fuel replaced with~charged, nonradioactive~deuterium, giving rise to compact~\textit{aneutronic }reactor with direct conversion into RF power [4]. \\[4pt] [1] Physics Scripta, \textbf{23}, 143 (1981);\\[0pt] [2] Bull. APS DPP96 Meet, Denver, 1996, http://flux.aps.org/meetings/YR9596/BAPSDPP96/abs/G280014.html available on http://www.aneutronicfusion.org/;\\[0pt] [3] Phys. Rev. Lett. \textbf{54}, 769 (1985);\\[0pt] [4] ANEUTRONIC ENERGY, NIM A \textbf{271}, 209 (1988); Inst. Advanced Study Princeton, Symposium Coll. Beam Fusion.   

High Performance and Economic Supercapacitors for Energy Storage Based on Carbon Nanomaterials

We designed and manufactured very inexpensive prototypes of supercapacitors for energy storage based on carbon nanomaterials comprised of: reduced graphene oxide (RGOs) and carbon nanotubes (CNTs) as electrodes filled with polymer gel electrolytes. The electrochemical properties of supercapacitors made using these materials were compared and analyzed. A significant tradeoff between the energy density and the power density was determined; RGO electrodes demonstrated the highest energy density, while composite RGO/CNT electrodes showed the highest power density. The thickness of the RGO electrode was varied to determine its effect on the power density of the supercapacitor and results showed that with decreasing electrode thickness power density would increase. The specific capacitances of over 600 F/g were observed.   

Nanoporous Hydrogen-Reduced BiVO$_{4}$: better charge separation with Ni-B$_{\mathrm{i}}$ Electrocatalysts for Photoelectrochemical Water Oxidation

BiVO$_{4}$ as a photoanode material has attracted broad attention recently as an inexpensive and robust semiconductor for potential application for solar water oxidation. However its photochemical activity is limited by poor charge carrier separation. Here we show that this problem can be solved by constructing a nanoporous morphology as well as controlled introduction of oxygen vacancies via hydrogenation. In comparison to pristine BiVO$_{4}$, the hydrogen-treated BiVO$_{4}$ (H-BiVO$_{4})$ show superior photocurrent and electron-hole separation yield of 0.95 at 1.23 V vs. reversible hydrogen electrode (RHE) due to enhanced carrier density and conductivity. Significantly, we adopt a layer of nickel-borate (Ni-B$_{\mathrm{i}})$ complex on the BiVO$_{4}$ surface as an oxygen evolution catalyst. Modification of H-BiVO$_{4}$ photoanode with Ni-Bi has yielded a large ($\sim $300 mV) cathodic shift in the onset potential at pH 7. It shows an outstanding performance in the low bias region and the maximum power point for solar water oxidation was achieved at potential as low as 0.75 V vs. RHE with a photocurrent density of 2.25 mA/cm$^{2}$. We attribute these improved PEC performances to the enhanced charge separation, carrier density and conductivity in these photoanodes.   

Uncovering the intrinsic delithiation mechanism in Li-excess Li$_{2}$MnO$_{3}$ through defect calculations

Layered Li-excess Li$_{2}$MnO$_{3}$ has been of great interest for lithium-ion battery cathodes because of its high theoretical capacity. The compound is also an important component in $x$Li$_{2}$MnO$_{3}$$\cdot$(1$-$$x$)LiMO$_{2}$ and other high-capacity cathode materials. It has been reported that Li$_{2}$MnO$_{3}$ can be made electrochemically active by acid leaching or charging to high voltages. Several different mechanisms have been proposed to explain its unconventional lithium extraction behavior, including one that involves oxidation at the oxygen site. In this talk, we will present a comprehensive computational approach based on first-principles hybrid density functional defect calculations, and illustrate how it helps uncover the defect physics and chemistry and the intrinsic mechanisms for delithiation and electronic and ionic conduction in layered Li$_{2}$MnO$_{3}$. In light of our results, we discuss the relevance of the proposed mechanisms and suggest solutions for improving the electronic conduction and hence the electrochemical performance of Li$_{2}$MnO$_{3}$ and related materials.   

Bias-dependent local structure of water molecules at an electrochemical interface

Following the need for new - and renewable - sources of energy worldwide, fuel cells using electrocatalysts can be thought of as a viable option. Understanding the local structure of water molecules at the interfaces of the metallic electrodes is a key problem. Notably the system is under an external potential bias, which makes the task of simulating this setup difficult. A first principle description of all components of the system is the most appropriate methodology in order to advance understanding of electrochemical processes. There, the metal is usually charged. To correctly compute the effect of an external bias potential applied to electrodes, we combine density functional theory (DFT) and non-equilibrium Green's functions methods (NEGF), with and without van der Waals interactions. In this work, we apply this methodology to study the electronic properties and forces of one water molecule and water monolayer at the interface of gold electrodes. We find that the water molecule has a different torque direction depending on the sign of the bias applied. We also show that it changes the position of the most stable configuration indicating that the external bias plays an important role in the structural properties of the interface.   

Effect of Transition Metal Ordering on the Electronic Properties of LiNi$_{1-y-x}$Co$_{y}$Mn$_{x}$O$_{2}$ Cathode Materials for Li-ion Batteries

Current Li-ion batteries use layered oxides as cathode materials, specially LiCoO$_{2}$ or LiNi$_{1-y-x}$Co$_{y}$Mn$_{x}$O$_{2\, }$(NCM), and graphite as anode. Co layered oxides suffer from the high cost and toxicity of cobalt, together with certain instability at high operational temperatures. To overcome these difficulties, the synthesis of novel materials composed of layered oxides with different sets of Transition Metals (TM) has become the most successful way to solve the particular drawbacks of every single-oxide family.$^{\, }$ Although layered materials can deliver larger capacity than other families of cathode materials, the energy density has yet to be increased in order to match the expectations deposited on the NCM oxides. To acquire a high capacity, they need to be cycled at high operational voltages, resulting in voltage and capacity fading over a large number of cycles. In this work, we examine the phase diagram of the Li-Ni-Co-Mn-O system and the effect of TM ordering on the electronic properties of NCM cathode materials, using density-functional theory. Our findings will provide conceptual guidance in the experimental search for the mechanisms driving the voltage and capacity fading of the NCM family of cathode materials, in an attempt to solve such structural instability problems and, thus, improving the performance of the NCM cathode materials.   

Organic-inorganic hybrid lead iodide perovskite with zero-dipole-moment guanidinium (GA$=$[C(NH$_{2}$)$_{3}$]$^{+}$) cations: a Density Functional based analysis

Mixed organic-inorganic halide perovskites have been reported to have superior performances [1] and unique features [2, 3] when used as light harvesters in photovoltaics. Interestingly, they can undergo several assembling procedures like sensitization and thin-film architecture. The latter one has been anyway recently reported to be affected by a noticeable hysteresis in the $J-V$ curves at slow scan rate [4]. No conclusive reasons for such behaviour have been provided so far. By means of an \textit{ab-initio} campaign of calculations [5], we predict possible chemical solutions based on the replacement of the widely employed methylammonium (MA$=$CH$_{3}$NH$_{3}^{+})$ cation with cations with reduced dipole moment, thus less sensitive to any applied external bias. \\[4pt] [1] Researchers at KRICT certified PCE of 17.9{\%}.\\[0pt] [2] Xing et al., Science 342, 344 (2013); Stranks et al., Science 342, 341 (2013).\\[0pt] [3] Giorgi et al. J. Phys. Chem. Lett. 2013, 4 (24), pp 4213; J. Phys. Chem. C, 2014, 118 (23), 12176; J. Mater. Chem. A, (2014), DOI: 10.1039/c4ta05046k.\\[0pt] [4] Snaith et al., J. Phys. Chem. Lett., 2014, 5, 1511.\\[0pt] [5] www.vasp.at   

Properties of adsorbed hydrogen films in nanospaces

Various high surface area materials were evaluated for their gas storage properties. From supercritical hydrogen isotherms at 77 Kelvin, we estimated the adsorbed film densities, film thicknesses and intrapore gas densities. Intrapore gas density is a measurement of the average hydrogen density within a pore. Furthermore, we investigated the correlation between the isosteric heat of adsorption, surface chemistry, and pore size distribution with an adsorbed film. In most of the samples both saturated film densities and intrapore gas densites exceed the liquid hydrogen density at 1 bar and 20 Kelvin. The saturated film density surpassed it even by 40{\%}. The adsorbed film seems to be independent of the isosteric heat of adsorption or the samples pore size distribution. They behave like a universal constant for all carbon-based surfaces.   

Pickering Emulsification to Mass Produce Nanoencapsulated Phase-change-material

Phase changing materials (PCM) have useful applications in thermal management. However, mass production of micro and nano encapsulated PCM has been a challenge. Here, we present a simple and scalable method via a two-step Pickering emulsification method. We have developed interface active nanoplates by asymmetric modification of nanoplates of layered crystal materials. Nanoencapsulated PCM is realized with exfoliated monolayer nanoplates surfactants using very little energy input for emulsification. Further chemical reactions are performed to convert the emulsions into core-shell structures. The resulted capsules are submicron in size with remarkable uniformity in size distribution. DSC characterization showed that the capsulation efficiency of NEPCM was 58.58{\%} and were thermal stable which was characterized by the DSC data for the sample after 200 thermal cycling.   

Application of Henry's Law for Binding Energies of Adsorbed Hydrogen

The method of isosteres is the simplest method used to calculate the differential enthalpy of adsorption. However, it is incredibly sensitive to the choice of model and respective fitting parameters. For a set of isotherms measured on a specific sample, most models converge upon a similar value at high coverage, but are inconsistent in the low pressure regime. In this talk, we investigate the application of various models for localized and mobile adsorption at low pressures in order to obtain binding energy of hydrogen to the adsorbent surface. Henry's Law analysis of the Langmuir Model of adsorption yield binding energies in excellent agreement with those obtained from the Clausius Clapeyron relation.   

Measurements of Current Densities and Skin Effects in Current Carrying Conductors Using Electro-optic and Magneto-optic Sensors

In this presentation, we will describe experiments involving all-dielectric electromagnetic field sensors based on electro-optic (EO) and magneto-optic (MO) crystals. EO sensors measure electric fields through the Pockels Effect, while MO sensors measure magnetic fields through the Faraday Effect. These sensors have been attached to optical fibers and calibrated in a variety of radio frequency, pulsed power and microwaves sources ranging in frequencies from dc to 20 GHz and ranging in power from 10$^{-4}$ to 10$^{6}$ Watts. In this talk, we will focus on recent experimental measurements of electric and magnetic fields generated by current carrying conductors. Our EO and MO sensor data, when combined, allows us to determine current densities and current distributions within a conductor cross section. Additionally, skin effects, which are a major source of Joule heating and resistive wear, can be characterized in detail.