Energy Storage and Conversion

The following sections are included:

• Contents
• Preface

Bismuth oxide-based electrolyte materials co-doping with yttrium and erbium were synthesized by nitrate combustion method. The crystal structure was analyzed by X-ray diffraction. The data on electrical conductivity were carried out using AC impedance spectroscopy. The results suggested that all of the co-doped bismuth oxide samples obtained δ-phase with cubic fluorite structure. The conductivity of (YO_1.5)_0.2(MoO₃)_0.05(ErO_1.5)_0.05(BiO_1.5)_0.7 ceramic electrolyte sintered at 925°C for 10 h reached 12.26 × 10⁻² S cm⁻¹ at 700°C. It has good thermal stability and is a promising electrolyte material for SOFC.

Aqueous zinc-ion batteries (AZIBs) are the most promising candidates for large-scale energy storage devices due to the advantages of low cost, high safety, environmental friendliness and high energy density. However, the low Coulombic efficiency (CE) and short cycle life of AZIBs caused by dendrite growth, hydrogen evolution reaction and corrosion of Zn anode, are limited the development and application of AZIBs in the future. To solve these problems, many works focused on the modification of Zn anode and electrolyte optimization have been widely reported. The separator–electrolyte interface and the separator– anode interface play a significant part in the behavior of zinc ions. Owing to the importance of separators for batteries, this paper reviews the requirements and optimization strategies of separators for AZIBs. It is mainly based on the surface modification of conventional separators (e.g. glass fiber, cellulose separators), the introduction of an intermediate membrane in the interlayer of the separator and anode, and the preparation of new-type separators to replace the conventional separators. In addition, this review proposes a further outlook on the future development of separators for AZIBs.

Dielectric materials with excellent energy storage performance are crucial to the development of renewable energy. In this work, we prepared 0.95NaNbO₃–0.05Bi(Zn_0.5Zr_0.5)O₃ (0.95NN–0.05BZZ) ceramics using solid state sintering and investigated the effect of sintering temperature on phase structure. We find that the phase transformation of ceramics occurs with the change of sintering temperature. The cubic phase (Pm-3m) and the antiferroelectric phase (Pbma) coexist at 1150°C, the ferroelectric phase (P21ma) appears at 1200°C and its phase proportion decreases with the sintering temperature increasing from 1200°C to 1280°C. Finally, we achieve the high recoverable energy storage density (W_rec) 0.74 J/cm³ and efficiency (η) 71% (at 140 kV/cm) at 1150°C.

Nanoflower-like hollow carbon sphere (CS) materials with two different heteroatoms doping (N, P) were prepared by a simple synthetic method (NPCS). The specific surface area of NPCS can reach a high value of 396 m²/g. The NPCS has a high degree of hollowness and the self-assembled nanosheet of NPCS forms a fast electron transport channel, and also increases active area in contact with electrolyte. The doping of heteroatoms increases the defect level of the carbon-based nanomaterials and changes the local electron state of the material, thus forming storage sites on the surface of the material, which can be used as a station for ions collecting and distributing. The material was studied as an active material for supercapacitors, and the specific capacitance reached 274.9 F/g. After the 4000th cycle stability test, it still maintained 95.2% of the specific capacitance, indicating that the material has excellent properties of supercapacitor materials.

Rapid technological advancements in recent years have necessitated the creation of energy-related devices. Due to their unique properties, including an exceptional cycling life, safe operation, low processing cost, and a higher power density than batteries, supercapacitors (SCs) have been identified as one of the most promising candidates to meet the demands of human sustainability. To increase the energy density of SCs, several advanced electrode materials and cell designs have been researched during the past few years. Utilizing the Faradaic charge storage process of transition metal cations, transition metal compounds have recently received attention as prospective electrode materials for SCs with high energy densities. In this work, the structure, morphology and electrochemical properties of molybdenum oxide (MoO₃) films deposited via thermal evaporation technique and annealed at various temperatures were systematically investigated in order to examine the potential use of MoO₃ for supercapacitors. Electrochemical analysis confirmed the pseudocapacitance characteristics of the synthesized films. The annealing temperature affects the oxidation and reduction observed in the cyclic voltammetry (CV) plots. Areal capacitance of thin films annealed at 150°C was found to be maximum and this could be attributed to the formation of hollow tube-like nanostructures which provided more active sites, than films annealed at higher temperatures. This also influences the charge storage ability of the synthesized films. It would be logical to assume that additional research in this area will result in more interesting discoveries and, eventually, the vi-ability of those promising Mo-based compounds in high-tech energy storage systems.

MXenes are a family of two-dimensional materials that could be attractive for use as electrodes in lithium batteries due to their high specific capacity. For this purpose, it is necessary to evaluate magnitudes such as the lithium adsorption energy and the magnitude of the open-circuit voltage for different lithium concentrations. In this paper, we show through first-principles calculations that in a V₂C monolayer, we must consider the high correlation between the electrons belonging to vanadium to obtain correct results of these quantities. We include this correlation employing the Hubbard coupling parameter obtained by a linear response method. We found that the system is antiferromagnetic and that the quantities studied depend on the magnetic phase considered. Indirectly, experimental results could validate the theoretical value of the Hubbard parameter.

Single-atom catalysts (SACs), especially atomically dispersed Fe–N_x–C based SACs, hold great promise to replace Pt-based electrocatalysts for oxygen-reduction reaction (ORR). Currently, synthesizing high-activity ORR electrocatalysts with atomically dispersed Fe–N_x site structures is still challenging due to their high surface free energy, which leads to easy migration and serious aggregation. Herein, we have designed a general graphene quantum dots (GQDs)-anchoring strategy to synthesize a single-iron-atom electrocatalyst (Fe–N-GQDs/PC) applied to ORR through calcining of N-GQDs-Fe³⁺ modified porous carbon (PC) and melamine. Experiments demonstrate the N-GQDs consist of abundant oxygenated groups, which could lead to complexing metal ions and thus facilitating the formation of SACs. Furthermore, the Fe–N-GQDs/PC electrocatalyst exhibits outstanding electrocatalytic ORR activity in 0.1 M KOH media with half-wave potentials of 0.84 versus 0.85 V for Pt/C. This strategy has opened up new feasible ideas to produce SACs for electrochemical energy devices.

In this paper, carbon particles with micro- and nano-particle size were synthesized through a hydrothermal reaction of glucose, namely C-1(123.1 nm), C-2(229.2 nm), C-3(335.1 nm), C-4(456.2 nm) and C-5(534.0 nm) with distinct sizes. We utilized five size carbon particles as individual fillers into the EHS matrix materials to prepare composite eutectic phase change materials (C/EHS PCMs) by melt blending technique. The impact of carbon particle size on the dispersion stability and thermal properties of Na₂SO₄·10H₂O–Na₂HPO₄·12H₂O (EHS) phase change materials was investigated. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) analysis were done to analyze the diameters of carbon particles. The cryogenic-scanning electron microscopy (Cryo-SEM) analysis indicated that the carbon particles resulted in modification in the morphology of the EHS. The results of in situ X-ray diffraction (XRD) and Fourier-transformed infrared (FTIR) analysis showed only simple physical mixing between carbon particles and EHS. It is shown that adding 0.2 wt.% C-2 can decrease the supercooling degree of EHS to 1.5°C. The cyclic stability of C/EHS varies significantly depending on the size of carbon particles. The thermal conductivity of EHS increased by 42.1%, 39.9%, 14.4%, 19.5%, and 18.8% with the addition of C-1, C-2, C-3, C-4, and C-5, respectively, at a mass fraction of 0.2%. The results of differential scanning calorimetry reveal that the incorporation of C-1, C-2, C-3, and C-4 into EHS leads to an enhancement of latent heat. The latent heat capacity of EHS with 0.2 wt.% C-2 is 243.4 J·g⁻¹, and after undergoing 500 cycles of solid-liquid phase transition, the latent heat remained above 200 J·g⁻¹. Through the comprehensive analysis, the C-2/EHS composite phase change material holds significant potential for advancing building insulation and solar energy storage technologies.

The development of cheap, high activity and stability catalysts for oxygen evolution reaction (OER) is of great significance because of its important role in energy storage technology. Herein, flower-like CoSe₂-Co₃O₄-Ag with enhanced electrochemical performance was synthesized by simple methods. The CoSe₂-Co₃O₄-Ag exhibits lower overpotential and higher current density, with an overpotential of 324 mV at the current density of 10 mA·cm⁻² and a Tafel slope of 65.69 mA·dec⁻¹. From the ECSA normalized LSV curves, higher electrocatalytic activity for OER is mainly due to the increase of ESCA and conductivity, minor due to adjusting the electronic configuration. These strategies to improve electrochemical active area and conductivity have valuable reference for designing cheap, high activity and stability catalysts.

Nanostructured thin-film electrode materials are proposed for supercapacitors due to their outstanding performance over bulk materials. In this work, we fabricated a TiO₂ nanotube film over a titanium foil using a top-down approach for supercapacitor electrodes. We noticed that the fabricated nanotubes are uniform and well aligned, confirmed by FESEM; the TiO₂ nanotube parameters were further simulated using COMSOL Multiphysics. Simulations show an areal capacitance of 1.19393 pF/cm² with oxidation and reduction peak currents of 6.18921 × 10⁻¹⁵ A and −6.0320 × 10⁻¹⁵ A, respectively, at 10 mV/s scan rate. The as-prepared nanotubes show a poor areal capacitance of 1.0193 F/cm², which is improved to 12.8764 F/cm² at a scan rate of 10 mV/s, that is approximately 12.63 times with oxidation and reduction peak currents of 0.129 mA/cm² and −0.105 mA/cm², respectively, by performing an electrochemical etching. Further, the surface roughness of both as-prepared and etched samples is studied to comment on their surface area changes. The effect of the etched sample is studied, compared and validated with simulation, which reveals that the etched TiO₂ nanotubes thin-film sample shows considerable similarity with the simulation results.

Single-crystal nickel (Ni)-rich cathode materials (Li[Ni_xCo_yMn_1−x−y]O₂, (NCMs)) of lithium ion batteries (LIBs) have displayed promising application potential due to the merits of stable structure, minor side reaction, and high energy density. The Ni_xCo_yMn_1−x−y(OH)₂ as the precursor of single-crystal NCM faces the issues of tedious preparation process and serious pollutant emission for traditional preparation methods during the industrial preparation. Herein, an improved continuous two-step spray pyrolysis strategy is adopted to prepare the precursor of single-crystal NCM. Combining with the industrial devices, ton-scale preparation of single-crystal NCM is realized after dynamic lithiation post-treatment. This improved strategy not only shortens the preparation process, but also reduces metal segregation and sintering temperature, effectively balancing the cost control and production efficiency. The samples sintering at 850°C show uniform morphology with a diameter of 4.5 µm and delivers an initial discharge capacity of 169 mAh/g at 0.1 C after 100 cycles. This work provides a new route for the industrial preparation single-crystal NCM cathode materials of LIBs.

Ternary compound Cd_1−xZn_xS thin films with different zinc compositions were deposited by the chemical bath deposition method, as a window layer for CdTe solar cells. The influence of Zn content on the structural, optical, morphological and electrical properties of Cd_1−xZn_xS was studied from X-ray diffraction (XRD), SEM and UV-vis spectroscopy. We have considered the transformation of the crystal phase, change in the crystallite size and lattice parameters of Cd_1−xZn_xS thin film with the change of Zn content through XRD studies. SEM measurement revealed that the size of Cd_1−xZn_xS particles and surface roughness of thin film decreases with the increase of Zn composition. It was found that the band gap value obtained from transmittance spectrum became wider with the increase of Zn contents, which indicates the increase of film transmittance. The electrical resistivity of Cd_1−xZn_xS thin films increased as Zn content x increases. Finally, we measured the performances of CdTe solar cells using Cd_1−xZn_xS thin films as a window layer and confirmed that desirable Zn content was in the range x = 0.5–0.6.

The following section is included:

• Index