Session Z10: Advances in Energy Storage Materials and Devices for Energy Applications

Electrochemical CO2 reduction reaction in transition metal sputtered thin films

Releasing CO₂ emissions into the atmosphere is one of the main reasons for global warming. CO₂ emissions can be reduced by electrochemical conversion of CO₂ into fuels and chemicals resulting in environment friendly power production. Electrocatalysts capable of efficiently converting CO₂ into fuels and chemicals with high selectivity are extremely important to reduce CO₂ impact on the environment. In this work, we report that electrocatalytic activity of transition metals for electrochemical conversion of CO₂. Molybdenum (Mo), molybdenum nitride (MoN), tungsten (W) and tungsten nitride (WN) samples were synthesized using DC Magnetron sputtering technique. Results indicate that Mo has shown better catalytic response compared to the other electrodes for CO₂ conversion producing current density up to 15 mA.cm^-2 at the applied potential -1.0 V versus RHE. Chronoamperometry (CA) results display stability of electrodes for prolonged period.   

Degradation Mechanisms of GaN HEMTs Terahertz Sources

Abstract: This paper summarizes the main failure modes and the physics behind capturing degradation mechanisms in GaN/AlGaN HEMT transistors. Trapping effect, hot electrons, short channel effects, and processing imperfections  cause device failure during operation conditions. The stability of Terahertz sources need to be proved to guarantee high-quality GaN devices in terahertz spectroscopy systems [1,2]. This review discusses terahertz emission based on Dyakonov-Shur instability to investigate possible device-induced degradation.

1] Yuki Tsuda, Tsuneyoshi Komori, Abdelouahad El Fatimy, Kouhei Horiike, Tetsuya Suemitsu, and Taiichi Otsuji, "Application of plasmon-resonant microchip emitters to broadband terahertz spectroscopic measurement," J. Opt. Soc. Am. B 26, A52-A57 (2009).

[2] Kiarash Ahi, "Review of GaN-based devices for terahertz operation," Opt. Eng. 56(9) 090901 (11 September 2017)

    

Theoretical study of tritium diffusion and formation from bulk and defective surface of γ-LiAlO2 pellets

In tritium-producing burnable absorber rods (TPBAR), γ-LiAlO₂ is used in the form of an annular ceramic pellet enriched with the ⁶Li isotope. When irradiated in a pressurized water reactor (PWR), the ⁶Li pellets absorb neutrons and produce tritium (³H) through ⁶Li + n à ³H + α. The ³H chemically reacts with the metal getter where it is captured and leads to formation of a metal hydride. For TPBARs to enable effective tritium production in PWRs, we investigated the ³H diffusion pathways in the bulk and surface of γ-LiAlO₂ with different concentrations of lithium defects. The calculated results for bulk and low-index surfaces, thermal conductivity, ³H activation energy barriers, and the ³H diffusion coefficients in γ-LiAlO₂ are in good agreement with the available experimental values. In the bulk, our results show that the smallest activation energy barrier is 0.63 eV for substitutional ³H diffusion with a diffusion coefficient of 3.25x10^-12 m²/s. After ³H diffused from bulk to the surface, it could form different species (such as ³H₂, ³H₂O, C³H₄) depending on the surface structure, vacancy types and the impurity carbon. Our results indicate that the ³H₂ is the main product from γ-LiAlO₂ pellets. As the number of V_Li vacancies and ³H atoms increases under irradiation (³H-rich condition), ³H₂O release could increase from the surface of γ-LiAlO₂ pellets.

    

Short-range Order in Group-IV Binary Alloys and Non-universal Deviations from Vegard's Law

Group-IV binary alloys are promising materials for tunable Si-integrated infrared photonics. However, the determination of their structural properties remains elusive. Specifically, for GeSn alloys, previous ab initio calculations based on random alloy model predicted a range of positive deviations of lattice parameters from Vegard’s law, while experiments showed a contradicting range of deviations, from positive to negative to vanishing. The discrepancies between ab initio theory and experiments remain unresolved. Here, we show the short-range order (SRO) that we recently discovered in GeSn¹ and SiSn² alloys plays an important role in their structural properties. For GeSn alloys with SRO, our calculations predict small negative deviations of lattice parameters from Vegard’s law at low Sn content and small positive deviations at higher Sn content, which are in good agreement with the latest experiments. For SiSn alloys, significant negative deviations are observed in the entire composition range. We conjecture that the underlying mechanisms for the non-universal deviations from Vegard’s law are related to local anisotropy and the competition between tetrahedrality breaking and solute-solute repulsion.

1. ACS Appl Mater Interfaces 12, 57245 (2020)

2. Phys Rev Mater 5, 104606 (2021)   

Oxygen states in highly oxidized oxides: battery cathodes at high voltages

The high-voltage operation of a battery is highly desirable due to the high capacity and energy nature of performance. However, the electrochemical operation at high voltages of Alkali-ion batteries often drives the active cathode materials, which are transition metal oxide based, into an unusually high oxidation state. This triggers unconventional electronic configurations that are yet to be understood. In this presentation, we will discuss the importance of understanding and controlling the oxygen states in such highly oxidized oxide cathodes. We discuss the nature of the so-called oxygen redox (reduction and oxidation) state that strongly depends on transition metals, however, should be distinguished from the metal-oxygen hybridization itself. We try to specify a unified picture of the fundamental driving force, and provide guidelines for practical optimizations will be discussed.     

Spatially Resolved Potential and Li-Ion Distributions Reveal Performance-Limiting Regions in Solid-State Batteries

The performance of solid-state electrochemical systems is intimately tied to the potential and lithium distributions across electrolyte-electrode junctions that give rise to interface impedance. Here, we combine two operando methods, Kelvin probe force microscopy (KPFM) and neutron depth profiling (NDP), to identify the rate-limiting interface in operating Si-LiPON-LiCoO₂ solid-state batteries by mapping the contact potential difference (CPD) and the corresponding Li distributions. The contributions from ions, electrons, and interfaces are deconvolved by correlating the CPD profiles with Li-concentration profiles and by comparisons with first-principles-informed modeling. We find that the largest potential drop and variation in the Li concentration occur at the anode-electrolyte interface, with a smaller drop at the cathode-electrolyte interface and a shallow gradient within the bulk electrolyte. Correlating these results with electrochemical impedance spectroscopy following battery cycling at low and high rates confirms a long-standing conjecture linking large potential drops with a rate-limiting interfacial process.   

Expanded Graphite/Paraffin composite phase change materials: Effect of solvent and ultrasonication on thermal properties.

The broad application of phase change materials (PCMs) is restricted due to their low thermal conductivity. Numerous techniques have been applied to enhance the thermal conductivity of PCMs, one of which is the use of Expanded-graphite (EG) as a thermal enhancer. High thermal conductivity, low density, and chemical inertness make EG a great candidate for enhancing the thermal conductivity of PCMs. The present work focuses on enhancing the thermal conductivity of Paraffin based PCMs with the use of EG via various preparation techniques. Two different mesh sizes of EG were used to make EG/Paraffin composite PCM (CPCM). The results demonstrated that the smaller mesh size EG leads to a better enhancement in the thermal conductivity of CPCM. The CPCM was prepared via the vacuum impregnation method followed by hot pressing the prepared mixture in the mold. Acetone and Dimethylformamide (DMF) were used as solvents during the mixing of paraffin and EG. When solvents were used better homogeneous dispersion of EG in the CPCM. An ultrasonic tip-sonication time study showed sonicating EG in acetone for 30sec at 20% amplitude gave the best enhancement in thermal conductivity of CPCM.   

Recycling of Ceramics–Salt Electrolytes using Cold-Sintering

The increasing demand for high energy storage technology in consumer electronics and electric vehicles leads to large-scale production of lithium-ion batteries. This raises concerns regarding disposal issues on end-of-life battery wastes. A major challenge in recycling spent batteries is in that components in batteries show dramatic differences in thermal and chemical stabilities, making it difficult to engineer recycling approaches without breaking each component down into precursor forms. Herein, we developed a sustainable recycling strategy that enables direct regeneration of ceramics–salt solid-state electrolytes, Li_1+x+yAl_xTi_2−xSi_yP_3−yO₁₂ (LATP) with bis(trifluoromethanesulfonyl)imide (LiTFSI) salts. The low temperature of the cold-sintering process allows the recovery of composite materials without compromising their chemical properties. Reprocessed composite electrolytes show exceptional electrochemical properties in terms of high conductivities (>10⁻⁴ Scm⁻¹ at room temperature) and long-term stability at 0.1 mAh cm⁻² over 1500 hours. This method provides an insight in the reutilization of battery materials with low energy cost and improved recovery efficiency.   

Direct detection of Na+ diffusion dynamics in Na2Ni2TeO6

The layered honeycomb compound Na₂Ni₂TeO₆ hosts a framework conducive to both complex magnetic interactions and high ionic conductivity. We report on our studies of Na⁺ diffusion dynamics as probed by neutron backscattering spectroscopy. Na₂Ni₂TeO₆ is a promising sodium battery material and has been reported to exhibit ionic conductivities as high as 10.8 S/m at 300 ºC and 3.4 x 10^-3 S/m at room temperature. Despite their weak interaction with matter, neutrons have a particular advantage in the study of diffusive dynamics in that their quasielastic scattering provides a direct probe on length scales comparable to interatomic spacings and time scales typical for diffusive relaxation times. We have utilized the BASIS instrument at the Spallation Neutron Source to perform QENS studies of Na₂Ni₂TeO₆ in a temperature range of room temperature up to 400 ºC, revealing isotropic diffusion above 250 ºC with an activation energy, E_a = 320 ± 40 meV. Results are discussed in the context of the three non-equivalent sites present in the Na layers.   

Effect of Post- Production Thermal Treatment on Electrochemical Energy Storage Properties of Single-Walled Carbon Nanotubes.

In this study, we will present our investigations on the effect of heat treatment on the electrical charge storage capacity of Single-Walled Carbon Nanotubes (SWCNTs) synthesized using direct decomposition of Ferrocene. Electrochemical double-layer capacitors (EDLCs) fabricated using the SWNT sheets as active electrode materials, show substantial improvements in their charge storage capacities after post-production thermal treatment. These findings will be discussed in light of the results obtained from a variety of electrochemical measurements such as cyclic voltammetry (CV), Galvanostatic Charge-Discharge (GCD) as well as Electrochemical Impedance Spectroscopy (EIS).