Session Y10: Energy Storage

Superior electrochemical capacitive performance of supercapacitors based on pristine Cu3(HAB)2 MOFs electrodes

2D Metal-organic frameworks (MOFs) have recently received increased attention as functional materials for various applications because of their tunable structures and high surface areas. MOFs have been explored as electrodes in electrochemical energy storage devices, but because of their poor conductivity, they have been mixed with conductive additives or binders for these applications. Herein, we use pristine copper hexaaminobenzene Cu₃(HAB)₂ for the fabrication of supercapacitors’ electrodes. The morphology of the Cu₃(HAB)₂ electrodes was characterized by scanning electron microscopy (SEM), and transmission electron microscopy (TEM) and shows a porous three-dimensional structure with a sheet like morphology. The MOF-based symmetric supercapacitor, demonstrated a superior electrochemical capacitive performance over a potential window of 0-1.4V, and displayed an areal capacitance of 16.33 mF cm^-2. Additionally, the MOF-based supercapacitor exhibited a remarkable ultra-high cycling stability with a retention of 80% after 100,000 cycles. These promising results demonstrate the potential of using pristine MOFs as the next generation of materials for supercapacitors applications.   

Dynamics of non-equilibrium nanostructure in a proton-conducting ceramic

Proton-conducting ceramics have attracted interest as moderate-temperature proton conductors for applications such as energy conversion and hydrogen production. Effects of topological defects and interfacial hydrated layers on proton transport and concerns about structural degradation make understanding nanostructure dynamics crucial for improving structural stability and proton transport. However, material polycrystallinity, absorption, and reactive operating conditions have prevented detailed in-situ measurements of the nanostructure dynamics. Here, we find experimentally in-situ in yttrium-doped barium zirconate, an archetypal proton conductor, that contrary to the assumptions of structural stability the nanostructure is unexpectedly dynamic at temperatures as low as 200 °C. We achieve this by applying coherent X-ray diffraction to a BaZr0.8Y0.2O3-d sintered pellet to image in-situ three-dimensional nanostructure inside the constituent grains in a humid nitrogen atmosphere. We directly observe non-equilibrium defect generation and subsequent grain cracking on a timescale of hours, forming new, otherwise energetically unfavorable facets in BaZr0.8Y0.2O3-d. Furthermore, structural rearrangements correlate with dynamic inhomogeneities of the lattice constant within the grains, showing potential heterogeneous H+ transport. We provide an approach to in-depth in-situ studies of nanostructure dynamics in proton-conducting ceramics and demonstrate unexpectedly active evolution of grain boundary and non-equilibrium defect networks, with implications for functional properties from structural stability to proton transport.   

Properties of single and double layer V2O5 polymorphs from first principles

V₂O₅ is a very promising battery electrode material that can intercalate not only Li, but also more abundant alkaline metals such as Na and K, and even multivalent ions such as Mg, Ca, Zn, and Al. V₂O₅ can occur in several polymorphs. Several of these are layered in nature, with both single layer and double layer structural motives occuring. During intercalation phase transitions can take place, and such phase transitions can be detrimental to battery performance. Understanding these transitions requires knowledge of the energetics and structural properties of the various V₂O₅ polymorphs.

We provide such understanding by employing density functional theory (DFT) calculations based on hybrid functionals, with an explicit inclusion of van der Waals interactions. Based on our results we discuss the structural and electronic properties of 8 different single and double layered V₂O₅ polymorphs, and show the role polarons play in electronic transport. The obtained insights can be used to optimize future V₂O₅-based battery electrodes.   

Probing Ion-transport mechansim in lithium based antiperovskite solid-electrolytes

Solid electrolytes are enablers for all-solid-state batteries that incorporate Li metal anodes, promising cell-level energy densities up to 500 Wh/kg and providing a paradigm change to the next-generation battery technology. The significant metrics for a successful solid electrolyte candidate include high ionic conductivity (> 10^-4 S cm^-1), electronic insulation (< 10^-10 S cm^-1), electrochemical stability, and ease in synthesis and processing. Within the last decade, Li-based antiperovskites (LiAP, Li_3-xOH_xX, X = Cl, Br) have emerged as an important emerging class of ion conductors for all-solid-state batteries. Here, Li resides in the traditional O occupancy site, X (typically a halide) is the A site, and O is the B site in classic perovskites, e.g. SrMnO₃). Despite the growing interest, there are two critical unresolved questions about LiAPs, what is the mechanistic effect of protons on Li transport? How does halide substitution affect the structure property correlation to enhance ion transport? Here, we seek to disentangle the coupled effect of structural stability induced by hydroxide-oxide substitution and halide mixing from Li-ion transport, by following proton and halide correlation dynamics with Li hopping.   

Studying Strain Evolution of Platinum Nanograins using Nanopipette Electrochemical Cell Combined with X-ray Bragg Coherent Diffraction Imaging

Understanding the structure of materials under electrochemical polarization is key to developing design principles for electrocatalysts. Probing structural rearrangements in catalytic materials during electrocatalysis is challenging experimentally and further complicated by structural heterogeneities including crystalline defects, strain inhomogeneities, and variations in chemical composition. Nonetheless, in operando measurements are often the most direct ways to improve our understanding of catalytic reactions. To address this challenge, we demonstrate a new approach that combines a nanopipette electrochemical cell with three-dimensional X-ray Bragg Coherent Diffractive Imaging (BCDI) to study how strain in a single Pt grain evolves in response to applied potential. During electrochemical polarization, in-situ BCDI measurements have revealed marked changes in surface strain arising from the Coulombic attraction between the electrode surface and the electrolyte ions in electrochemical double layers, while the strain in the bulk of the crystal remained unchanged. The concurrent surface redox reactions have a strong influence on the magnitude and nature of the strain dynamics under polarization.   

Photodeposition of catalyst nanoparticles for solar photoelectrochemical reactions: a sustainable fabrication technique.

Photocatalytic and photoelectrochemical phenomena are regarded as attractive options for converting solar energy into chemical energy: solar water splitting, photocatalytic reduction of CO2, water reformation, and CO2 conversion to biomass, all bear a significant impact in solving environmental issues. However, the fabrication of many promising semiconductor materials is in itself an expensive and energy-consuming process, that requires the development of sensibly sustainable techniques. Photodeposition of metal and metal oxide nanoparticles on semiconductor thin films can use solar energy for the electrically unassisted growth of catalyst nanoparticles onto existing photoelectrodes: the catalysts greatly improve the efficiency of the photoelectrodes by facilitating the separation of photogenerated charge carriers. In the present research, gold, platinum and ruthenium dioxide have been photodeposited on titanium dioxide thin films, while ruthenium dioxide has been photodeposited on hematite. Characterization and performances have been assessed, in order to report reliable and scalable processes for the sustainable growth of efficient catalysts.   

Reliable, Neutral-color, Semi-transparent Organic Photovoltaics for Power Generating Windows Applications

Semi-transparent organic photovoltaics (ST-OPVs) can be integrated with windows of buildings and vehicles for the purpose of clean power generation. To fulfill this application, ST-OPVs must be reliable, efficient, and often neutral in color. Recent studies have revealed that, while fullerene-based OPVs are highly reliable¹, they are opaque and thus unsuitable for window applications. The replacement of fullerenes with of non-fullerene acceptors (NFAs) have led to increased power conversion efficiencies, but have considerably shorter lifetimes when used in devices. Recent innovations in the design of NFA-based opaque OPVs have achieved extrapolated lifetimes of at least 30 years². A remaining challenge is the demonstration of long-lived, NFA-based, neutral-color ST-OPVs³. In this work, we optically design an NFA-based ST-OPV for neutral-color, high efficiency, and long operational stability. We demonstrate that these devices maintain > 95 % of their initial electrical and optical properties after 1500 h of exposure to 1 sun intensity, AM 1.5G illumination.   

Impact of Coulomb Scattering on Argon Plasma Based Thermionic Converter Performance

Particle-in-cell (PIC) simulations were performed to study the impact of Coulomb scattering on the performance of argon plasma based thermionic converters. Using a simplified model, studies from the 1970's have concluded that plasma resistance, brought on by Coulomb collisions, causes a shift in the IV-curves of thermionic converters that use an argon plasma to mitigate space charge, thereby strongly limiting their electricity generation capability. In this work the impact of Coulomb collisions in such devices were studied as a function of the relative electrical potential between the electrodes, with higher fidelity through the use of a fully kinetic approach (PIC) which revealed that earlier reports overestimated the negative impact of Coulomb collisions around the flat-band potential. The results of the simulations are also used to comment on the validity of the assumptions made in the simplified model.   

First-principles simulations of catalytic systems for hydrogen production

One way to produce hydrogen more efficiently is by using a catalyst which can increase the rate of the hydrogen evolution reaction (HER). In order to assist the design of new catalytic systems, we perform first-principles density functional theory (DFT) calculations of the electronic structure of several catalysts and attempt to predict their efficiency for HER. We focus on one class of molecular catalysts of the form M(L)₂ composed of an inexpensive transition metal atom (M=Co, Ni, Cu) and coordinated with two organic ligands L which can be bipyridine (bipy) or pyridine DAT (PyDAT). We use the abinit software and the projector-augmented-wave (PAW) methods to compute the structural parameters of the molecules, and the formation energy of each step of the four-step catalytic cycle. Our method accurately reproduces the efficiency of catalysts in the literature. We will also discuss its predictive power for different ligands and their respective hydrogen production.   

Ab initio simulation of the hydrogen absorption of M-Mg-Ni metal hydride.

One of the main challenges to fully utilize hydrogen as a green and renewable energy vector is its storage. Here we employ first principles calculations to study the absorption of hydrogen in ternary compounds of type M-Mg-Ni. We perform density functional theory (DFT) calculations with the Abinit software to study two materials: Nd₃MgNi₁₄ and La₃MgNi₁₄. These compounds occur in two different phases at room temperature: the trigonal phase and the hexagonal phase. We aim to accurately predict the energy of absorption, the desorption temperature and the location of absorption sites. In this talk, we discuss the procedure, its accuracy compared with experimental results from the scientific literature and further possible improvements to reduce the computational resource needed and to improve the accuracy.   

Effect of Substrate-Induced Lattice Strain on the Electrochemical Properties of Pulsed Laser Deposited Nickel Oxide Thin Film

The storage of renewable energy is an important step toward the global effort to combat air contamination and climate change. In this work, the influence of substrate-induced strain on the electrocatalytic properties of nickel oxide (NiO) films toward the hydrogen evolution reaction (HER) is studied. Using pulsed laser deposition, NiO thin films were deposited on strontium titanate, lanthanum aluminate, and sapphire substrates to examine how the substrate–film lattice mismatch influences the electrochemical properties.  X-ray diffraction measurements were carried out to confirm the phases and determine interfacial lattice strain. AFM measurements were used to analyze the topography and surface roughness. The electrochemical analysis was performed in one molar potassium hydroxide solution. It was observed that the electrocatalytic activities of the NiO thin films exhibited a strong sensitivity to strain; the NiO film with the smallest strain recorded the lowest overpotential for the HER. The surface area of the NiO electrocatalyst was explored to estimate the charge storage capacity and surface roughness. This work shows the use of simple thin-film synthesis as a way to evaluate the strain effect in electrocatalysis.