Session K45: Energy - Storage and Conversion at Interfaces

Pristine Cobalt-based 2D metal organic framework for high performance supercapacitor electrodes

2D metal organic frameworks (MOFs) have attracted a significant interest for their applications in energy storage devices. Herein, we report a scalable and low-cost approach for the fabrication of pristine Cobalt-based 2D metal organic framework Co-HAB electrodes using electrophoretic deposition (EPD). We used two different preparations for the Co-HAB solution used in EPD. The morphology of the electrophoretically deposited Co-HAB on Nickel foams characterized by SEM and TEM revealed nanosheets and abundant in-plane pores for both preparations. The resulting symmetric Co-HAB supercapacitors in Na₂SO₄ electrolyte, exhibited excellent electrochemical capacitive performance over a wide cell potential window of 0.0-1.2V. Operating at ultra-high charge-discharge rates, up to 4000mVs^-1, the Co-HAB supercapacitors delivered an excellent areal specific capacitance of 46.3 mFcm^-2. The Co-HAB prepared with the addition of dimethylformamide (DMF) showed a higher areal capacitance, of about twice the areal capacitance obtained for the solution without DMF. Furthermore, the Co-HAB supercapacitors exhibited high cycling stability with a retention of about 98% over 10,000 cycles.

    

Structural and Electronic Properties of Chromium Nitride Thin Films for High Performance Supercapacitor Electrodes

Chromium nitride (CrN) shows interesting structural, electronic, magnetic, and optical properties, which have been studied for potential applications in spintronics, sensors for electric and magnetic fields at low temperatures, and thermoelectrics^1-3. In this project, a complete set of experiments has been designed to study the electronic properties of CrN thin films grown by reactive radio frequency sputtering. Thin films with different Cr, N atomic ratios and layer thicknesses have been prepared to study their effects on the charge carrier concentration, magnetoresistance, and electrode for supercapacitors. These electrodes show high areal specific capacitance, excellent cycling stability and capacitance retention than the published reports. Variable field Hall Effect setup for studying the carrier concentration. The electrodes were investigated by cyclic voltammetry. X-ray photoelectron spectroscopy and Raman spectroscopy have been used for studying the stoichiometry. The optical band gap has been measured by recording transmittance spectra of the films.

 

References

Synthesis, Characterization and Electrochemical Performance of Co and Fe-Doped CuO Nanostructures as Electrode Material

In this research work we will present a facile and cost–effective co-precipitation method to prepare doped (Co & Fe) CuO and undoped CuO nanostructures. The X-ray Diffraction (XRD) analysis of as-prepared samples reveals monoclinic crystal structure of synthesized pure CuO and doped-CuO nanostructures. Field-Emission Scanning Electron Microscopy (FESEM) with Energy Dispersive X-ray Analysis (EDAX) was used to study the morphology and elemental composition of doped (Co & Fe) CuO and undoped CuO nanostructures.  The effect of different morphologies on the electrochemical performance of supercapacitors has been found in CV (cyclic voltammetry) and GCD (galvanic charge discharge) investigations. The specific capacitances have been obtained 156 (±5) Fg^-1, 168(±5) Fg^-1 and 186 (±5) Fg^-1 for CuO, Co-doped CuO and Fe-doped CuO electrodes, respectively at scan rate of 5 mVs^-1, while it is found to be 114 (±5) Fg^-1, 136 (±5) Fg^-1 and 170 (±5) Fg^-1 for CuO, Co-CuO and Fe-CuO, respectively at 0.5 Ag^-1 as calculated from the GCD. The supercapacitive performance of the Fe-CuO nanorods is mainly attributed to the synergism that evolves between CuO and Fe metal ion. The Fe-doped CuO with its nanorods like morphology provides higher specific capacitance value and excellent cyclic stability among all studied nanostructured electrodes. Hence, Fe-doped-CuO nanostructures may be consider as a promising electrode material in supercapacitors.

Keywords: CuO nanostructures; XRD; XPS; FESEM; Raman spectroscopy; Supercapacitors.   

Titanium Oxynitride Thin Film Supercapacitor Decorated with Ruthenium Oxide Nanoparticles

Supercapacitors have attracted a lot of attention as energy storage devices for high power applications such as digital mobile phone device power sources, memory backup devices, and hybrid electric vehicle power sources. Ruthenium oxide has been studied as one of the best electrode material for supercapacitors, owing to its advantages of a wide potential window of highly reversible redox reactions, remarkably high specific capacitance, and a very long cycle life.

In this work, we demonstrate the synthesis of  pulsed laser deposited titanium oxynitride thin film decorated with RuO₂ nanoparticles as an attractive class of materials for electrochemical charge storage. X ray diffraction analysis of the nanostructure shows that the sharpness and intensity of the TiNO (111) peak decreases with addition of the RuO₂ nanoparticles compared to undecorated TiNO film. The  scanning electron microscopy and  the energy dispersive X-ray spectroscopy analyses of the RuO₂-np/TiNO sample indicate that the RuO₂ nanoparticles are uniformly dispersed on TiNO support with an average particle size of  The X-ray photoelectron spectroscopy survey scan analysis confirms the presence of Ru with the Ru 3d peak at a binding energy of 281.8 eV and elemental percentage loading of 1.21%. The cyclic voltammetry plot has shown that the decorated-TiNO electrode occupies a larger area which is proportional to the charged stored on the electrode. The specific capacitance values calculated from the galvanostatic discharge curves further reveals that the decorated-TiNO showed significant increase in the capacitance value (113 mF.cm^-2) compared to the undercoated-TiNO counterpart (43 mF.cm^-2). This enhancement in the capacitance is related to the synergistic effects of RuO₂ decoration, oxygen doping, and the unique structural properties of the fabricated thin film.

    

Effects of temperature variation on a variable capacitor graphene circuit

The discovery of graphene has inspired extensive research due to the 2D material's multiple novel properties. One such property is the formation of ripples when suspended, that spontaneously invert due to thermal fluctuations. This spontaneous motion makes graphene ripples suitable for the creation of small variable capacitors in graphene energy harvesting (GEH) devices. The motion of a graphene ripple can be modeled using a Langevin equation for a single particle in a double well potential. Simulations of systems with a graphene variable capacitor coupled to a resistor with an applied bias voltage have demonstrated that the power generated by the capacitor is equal to the power dissipated by the resistor when the temperature of the resistor and capacitor are the same. However, research regarding such systems with components at different temperatures is lacking. In this talk, we present one such study, involving two series of Langevin simulations: one where the capacitor temperature is fixed while the higher resistor temperature is varied, and one where the resistor temperature is fixed while the higher capacitor temperature is varied. The temperature difference, as well as the direction of the temperature gradient, play an important role in the time dynamics of the motion and accumulation of charge on the ripple, as well as heat flow and work. While the work done by one component on the other increases linearly in temperature, the efficiency of the system peaks when the absolute temperature of the capacitor is a few times that of the resistor, suggesting that GEH systems could benefit greatly from having the graphene capacitor component in the proximity of a high-temperature heat dump.   

A CORRELATION OF SOLVENT’S MOLE FRACTION TO THE SALT-REDUCED DIFFUSIVITIES OF ORGANICSOLVENTS

Supercapacitors' energy storage capabilities depend on the physical and chemical properties of the electrodes and electrolytes used. The mixing of salt with organic solvents has been adapted to formulate an electrolyte to optimize the electrochemical performances of energy-storing devices. Here, using a combination of two neutron scattering spectrometers and a molecular dynamics simulation, we have investigated the influence of lithium bis(trifluoromethylsulfonyl)amine (LiTFSI) salt on the diffusion of five different organic solvents (acetonitrile, tetrahydrofuran, methanol, dimethyl sulfoxide, and propylene carbonate). A universal reduction in the solvent diffusivity by half and its correlation with solvent mole fraction will be presented.   

Nanophase-segregated Structures and Transport in Aquivion Membrane for Polymer Electrolyte Membrane Fuel Cell

In this study, molecular dynamic simulation method is employed to investigate the structure and transport properties of polymer membrane (Aquivion) consisting of perfluorinated polymers with short side chain in comparison to Nafion. From experimental and computational work, there is a general consensus that the favored properties of polymer electrolyte membrane (PEM) system are a result of nano-phase segregation of hydrophilic clusters in a hydrophobic matrix. Aquivion has a similar chemical structure to Nafion with hydrophobic backbone and hydrophilic sulfonate group. By performing MD simulations of Aquivion and Nafion under the same conditions such as temperature and water content, we compared the nanophase-segregation, transport of water and proton, local structures in water phase, and solvation of sulfonate and hydronium.   

Polarons and electrical leakage in BaZrO3 and BaCeO3

Barium zirconate (BaZrO₃, or BZO), barium cerate, (BaCeO₃, or BCO), and their alloys have great potential as proton-conducting electrolytes in solid-oxide fuel and electrolysis cells. However, the factors leading to their non-negligible electrical conductivity, which can limit their performance, are not fully understood. We address that question using first-principles calculations based on density functional theory (DFT). First, we study the properties of hole and electron polarons in BZO and BCO. We confirm that hole polarons form favorably in both materials, while electron polarons can only be stabilized in BCO and in Ce-containing alloys. In general, doped BZO and BCO will have low electron concentrations, but larger concentrations of holes and hole polarons may be present. To reduce the resultant risk of p-type electrical leakage, we recommend avoiding extreme O-rich conditions and limiting dopant concentrations as much as possible. Our results provide physical insights into the electronic behaviors of BZO, BCO, and their alloys, which can be used to optimize their pure ionic conductivity in electrolytes.   

Layered monoclinic perrierite oxo-silicate La4Mn5Si4O22+δ: a new family of interstitial oxide ion conductor

Oxide-ion conductors are important for various energy applications such as solid oxide fuel cells, solid oxide electrolyser cells, etc [1]. State-of-the-art stable oxygen active materials often have adequate oxygen ion diffusion and chemical surface exchange only at high temperatures (> 700 ^oC). A promising strategy to improve the oxygen ion transport is to use interstitial oxygen ion conductors as the interstitial hop barriers are often lower than vacancy mediated hops, potentially enabling reduced operation temperatures. However, due to the large size of the oxide ion, the formation of an adequate concentration of interstitials is difficult and hence the number of interstitial oxygen conductors is currently limited to just a handful of compounds, e.g., Ruddlesden-Popper, apatite, and disordered hexagonal perovskites [2-3].

In this work we developed an integrated computational and experimental approach to discover new interstitial oxygen diffusers which might show efficient oxygen transport at low temperature. High-throughput computational screening of the 33,975 oxide materials from the Materials Project revealed the easy formation of interstitial oxygen (ab initio predicted formation energy ~ -0.11 eV at 25 ^oC in air) and high oxide ion diffusivity in a new class of material La₄Mn₅Si₄O_22+δ (LMSO), motivating us to synthesize and study its oxide ion transport properties. Electron probe micro-analyser and iodometric titration revealed the presence of the hyper stoichiometric oxygen (δ ~ + 0.5) in LMSO lattice, consistent with the computational results. Electrical conductivity relaxation study also demonstrated promising self-diffusion and surface exchange coefficients of oxygen ion over the temperature range from 600 to 750 ^oC.

In conclusion, this study introduces layered perrierite LMSO as a new class of interstitial oxide ion conductors and the overall approach may help the rational design of oxide ion conductors-based devices suitable for efficient and stable applications at low temperature.      

References:

[1] M. Coduri, M. Karlsson, L. Malavasi, J. Mater. Chem. A 10 (2022) 5082-5110.

[2] S. Xu, R. Jacobs, D. Morgan, Chem. Mater. 30 (2018) 7166-7177.

[3] M. Yashima, et al., Nat. Com. 12 (2021) 556.

    

Liquid Fuel Cells for Sustainable Energy Production

Liquid fuel cells, which promise to be a clean and efficient energy production technology, have recently attracted worldwide attention, primarily because liquid fuels offer many unique physicochemical properties including high energy density and ease of transportation, storage as well as handling. However, conventional liquid fuel cells, which use acid proton exchange membranes and precious metal catalysts, result in rather low performance. In our research, we use alkaline anion exchange membranes as the solid electrolyte. It is demonstrated that the change from the acid membrane to an alkaline one leads to a significant performance boost. In addition, we also develop a novel hybrid fuel cell, which consists of an alkaline anode and an acid cathode. To further optimize and improve the performance, we develop an integrated model for the liquid fuel cell system. This high performance is attributed not only to the unique design, but also to the use of the integrated model.   

Molecular Simulations Probing the Adsorption and Diffusion of Ammonia, Nitrogen, Hydrogen, and Their Mixtures in Bulk MFI Zeolite and MFI Nanosheets

Recent advances in the synthesis of MFI zeolite nanosheets have led to highly selective membranes that are promising candidates for small-scale ammonia separation from ammonia/nitrogen/hydrogen mixtures in distributed green ammonia production plants. Using force-field-based molecular simulations, we evaluate the performance of bulk all-silica MFI zeolite and MFI nanosheet and nanosheet stacks for ammonia/nitrogen/hydrogen separations over a wide range of state points including conditions relevant for a membrane-based

reactor−separator process. Monte Carlo simulations in the isobaric−isothermal Gibbs ensemble (GEMC) are used to probe the selective adsorption behavior for these mixtures. Molecular dynamics simulations in the canonical ensemble are carried out to examine the transport behavior at loadings obtained from the GEMC simulations. Our results show that bulk MFI and the nanosheets with explicit surface silanols are highly selective toward ammonia adsorption, but selectivity decreases with increasing temperature. Conversely, the diffusion selectivities toward ammonia are more favorable at process-relevant temperatures. Analysis of simulation trajectories provides insights on the higher selectivity observed for the nanosheets.   

Ultra-Fast CO2 Gas Absorption Using Bubble-Manipulating Surfaces in Liquid Gas-Absorbing Systems.

Gas absorption by liquid media is an essential part of many large-scale industrial processes. When gas is injected into an absorber unit as discrete bubbles, as is the case for bubble column absorbers or gas sparging systems, the effectiveness of their reaction relies on careful control of the bubbles’ properties and flow. Here we demonstrate an efficient mode of gas absorption into a liquid by using engineered surfaces that manipulate bubbles and enhance the reaction rate between the phases. By integrating these surfaces into a liquid gas-absorbing system, we are able to increase the reaction rate by 2 orders of magnitude compared to a surfaceless gas-absorbing system. Experimentally we use carbon dioxide gas and a moderately alkaline potassium hydroxide absorbent solution. A surfaceless system suffers from two disadvantages: (1) bubble reaction rate decreases as they shrink and (2) the bubbles do not fully absorb due to product aggregation on their surface, blocking the gas/liquid reaction interface. However, our method overcomes the said challenges by (1) demonstrating the highest reaction rates for smaller bubbles, reversing the aforementioned trend, and (2) benefiting from the rapid timescales of bubble-manipulation relative to product aggregation, consequently avoiding the aggregation regime and leading to complete gas absorption. Finally, we offer to integrate bubble-manipulating surfaces in liquid gas-absorbing systems as an absorption technique with advantageous scaling for small-scale or distributed modular absorber designs.

    

How Liquid Ordering Within the Contact Layer Influences Thermal Boundary Conductance at Liquid/Solid Interfaces

Efforts to further miniaturize 3D integrated chips are being stymied by the difficulty in extracting excessive waste heat, which among other deleterious effects, causes thermal runaway and chip failure. Solutions have focused on embedding on chip platforms series of microfluidic channels to convect excess heat away from hot spots. However even in the absence of liquid flow, the fundamental mechanisms which control the thermal flux across a liquid/solid (L/S) interface are not well understood. Fortunately, non-equilibrium molecular dynamics simulations (NEMD) offer the ideal probative tool to help investigate and solve this problem. In this talk, we focus on NEMD studies in planar L/S systems at steady state subject to a fixed temperature difference. We shall discuss numerous correlations between thermal boundary resistance and structural and dynamic properties of the contact liquid layer. The results of this fundamental study may help facilitate improved design of the interfacial layer so as to maximize heat transfer across L/S interfaces.   

Photomolecular Effect Leading to Water Evaporation Exceeding Thermal Limit

We report the discovery of photomolecular effect: cleavage of water clusters off surfaces by photons. This effect is demonstrated through surprising absorption of partially wetted hydrogel in the visible spectrum where both water and hydrogel materials’ absorption are negligible. Illumination of hydrogel under solar or visible-spectrum light-emitting-diode leads to evaporation rates exceeding the thermal evaporation limit, even in hydrogels without additional absorbers. Measurements of temperature and transmission spectrum of vapor above evaporating surfaces show clear signatures of water clusters. The photomolecular effect happens at liquid-vapor interface due to large electrical field gradients and quadrupole force on molecular clusters. This photomolecular evaporation processes might be happening widely in nature, potentially impacting climate and plants growth, and can be exploited for clean water and drying technologies.