Showing papers in "ACS applied energy materials in 2022"

Engineering of Transition Metal Sulfide Nanostructures as Efficient Electrodes for High-Performance Supercapacitors

Abstract: Supercapacitors (SCs) are highly promising electrochemical energy conversion and storage devices. SCs display an outstanding power performance, excellent reversibility, long-term stability, simple operation, and high feasibility for integration into electronic devices, including consumer electronics, memory backup systems, and industrial power and energy management systems. The electrode materials determine the cell capacitance, operating voltage, power density, energy density, and time constant of SCs. Transition metal-based electrode materials (TMEMs) are among the most promising electrodes for SCs, due to their outstanding energy density, specific capacitance, and quick charging/discharging rates, in addition to their ease of preparation in a high yield from low-cost and earth-abundant resources. Binary transition metal sulfides (BTMSs) possess various advantages relative to other TMEMs, including higher storage capacity, higher electrical conductivity, excellent redox properties, better specific capacitance, quicker electron/ion diffusion, and superior reversibility with long cycle life. Herein, the inventory and the recent progress in the rational design of BTMS electrodes for SCs are deliberated, spaning from the preparation methods to the operative conditions, performance, and mechanism. To help assist in the further development of BTMS electrodes for efficient and durable SCs, current underlying challenges and possible solutions are identified and addressed, with emphasis on device performance vs BTMS type and relative merits.

Deferred Polarization Saturation Boosting Superior Energy-Storage Efficiency and Density Simultaneously under Moderate Electric Field in Relaxor Ferroelectrics

Abstract: High-temperature dielectric Bi0.5Na0.5TiO3 (BNT)-based relaxors near a morphotropic phase boundary are developed with excellent energy storage performance. Random distribution of polar nanoregions induced by composition modulation would disrupt the ferroelectric long-range dipolar alignment and weaken the coupling between the ferroelectric domains, yielding slender and deferred polarization–electric field hysteresis loops with relatively high saturation polarization. The reversible nano-domain orientation and growth in relaxors under a delayed electric field result in negligible remnant polarization and advantageous energy storage properties. Simultaneously, superior recoverable energy storage density and efficiency are gained, significantly surpassing the state-of-the-art dielectric energy storage materials under similar moderate electric fields. Vacancies, defect dipole behavior, and structural evolution that relied on an electric field and temperature are discussed to disclose the underlying mechanism associated with phase transition. Even thermal stability and large electrostrictive strain with low hysteresis are achieved in elevated temperatures. These features demonstrate the promising candidates for dielectric energy-storage application and provide a strategy in designing relaxors.

Dispersions of 1,3,4-Oxadiazole-Linked Conjugated Microporous Polymers with Carbon Nanotubes as a High-Performance Electrode for Supercapacitors

Abstract: In this study, we used classical and simple Sonogashira couplings to construct three 1,3,4-oxadiazole-linked conjugated microporous polymers (OXD-CMPs) through the reaction of 2,5-bis(4-bromophenyl)-1,3,4-oxadiazole (OXD-Br2) as a common partner with the structurally diverse units of ethynyl triphenylamine, tetraphenylethene, and pyrene, respectively. We used several methods, both spectroscopic and microscopic, to characterize the three OXD-CMPs. Each OXD-CMP displayed a high thermal stability. The Py-OXD-CMP possessed pores having sizes in the range 1.20–2.25 nm and a high surface area (298 m2 g–1). These OXD-CMPs interacted with singled-walled carbon nanotubes (CNTs), stabilized through noncovalent π–π interactions, to afford OXD-CMP/CNT composites that were suitable for supercapacitor devices. Among our OXD-CMP/CNT composites, the Py-OXD-CMP/CNT composite offered a specific capacitance of 504 F g–1 and a superior capacitance retention (91.1%) over 2000 cycles.

Structural Changes of Spinel MCo2O4 (M = Mn, Fe, Co, Ni, and Zn) Electrocatalysts during the Oxygen Evolution Reaction Investigated by In Situ X-ray Absorption Spectroscopy

Abstract: A comparison of the electrochemical and physicochemical behavior of cobalt-based oxides with spinel structure MCo2O4 (M = Mn, Fe, Co, Ni, and Zn) was conducted to investigate the effect of the oxidation state and cation distribution in the spinel on the electrocatalytic activity of the oxygen evolution reaction (OER) in an alkaline solution. Various spinel MCo2O4 electrocatalysts were synthesized by a facile microwave-assisted synthesis and low-temperature annealing. The overpotential of these MCo2O4 electrocatalysts for the OER is comparable to the reported overpotentials of catalysts based on cobalt oxides. From the findings, the catalytic activity of OER decreases in the order of ZnCo2O4 > NiCo2O4 > FeCo2O4 > Co3O4 > MnCo2O4. It was revealed that the active sites are controlled by the balance of M3+/M2+ cation distribution in octahedral and tetrahedral sites and by the bond strength between M and oxygen atoms at the catalyst surface from the direct combination of in situ X-ray absorption fine structure (XAFS) spectroscopy with the electrochemical experiments to track the oxidation state and the structural changes of electrocatalysts before and after the exposure to the OER conditions. This study provides insights into the effects of cation distributions on the OER activity and demonstrates a promising method for determining the fundamental mechanism of cation-substituted cobalt oxides for OER.

Design and Preparation of a CeVO4/Zn0.5Cd0.5S S-Scheme Heterojunction for Efficient Photocatalytic Hydrogen Evolution

Abstract: Improving the separation efficiency of photoinduced electron–hole pairs plays a vital role in preparing high-performance photocatalysts. Here, based on the good light corrosion resistance and excellent visible light response of Zn0.5Cd0.5S, as well as the unique catalytic, optical, and electrical properties of CeVO4, we tightly loaded CeVO4 on Zn0.5Cd0.5S by physical coupling to overcome its severe photogenic carrier recombination and obtained a highly efficient photocatalytic catalyst for hydrogen evolution. One the one hand, the close coupling of Zn0.5Cd0.5S and CeVO4 effectively inhibited the serious aggregation of Zn0.5Cd0.5S, which is conducive to the generation of active sites. On the other hand, an S-scheme heterojunction at the contact interface of Zn0.5Cd0.5S and CeVO4 was successfully built. The formation of the S-scheme heterojunction could consume useless electrons and holes and enable the efficient use of photogenerated electrons to participate in the reaction of reducing water. Finally, the hydrogen yield of Zn0.5Cd0.5S/CeVO4 can reach 695.55 μmol in 5 h. Our work provided an idea for the rational design of heterojunction photocatalysts to obtain excellent hydrogen production performance.

High-Temperature Thermoelectric Monolayer Bi₂TeSe₂ with High Power Factor and Ultralow Thermal Conductivity

Abstract: Because of the quantum confinement effect and the interface/surface effect, the band gap of 0.8–1.5 eV for two-dimensional (2D) bismuth-based material is significantly enlarged relative to that of bulk phase materials (∼0.2 eV), which removes the inhibition effect caused by bipolar transport for the Seebeck coefficients of bulk-phase bismuth-based materials at high temperature. Therefore, the 2D bismuth-based materials exhibit huge application prospects in high-temperature thermoelectric (TE) devices, whereas their figure of merits (ZT) need to be further improved. This work reports the thermal and electrical transport properties of 2D Bi2TeSe2, a new Janus Bi2Te3-based material, from the first-principles calculations. Compared with Bi2Se3/Bi2Te3 monolayers and corresponding Janus materials, the Bi2TeSe2 monolayer exhibits a much lower lattice thermal conductivity (κ) of 0.27 W/mK at 900 K because of stronger phonon anharmonicity and higher frequency phonon scattering. In addition, because the energy pockets around the valence band maximum show convergence character, the Seebeck coefficient (SC) of the p-type system is effectively enhanced. Combined with its intrinsic high electron transport properties, a high power factor of 3.48 mW/mK2 at 900 K is obtained for the p-type Bi2TeSe2 monolayer. The ultralow κ and enhanced SC of the Bi2TeSe2 monolayer eventually result in a significant optimal ZT value of 3.45 at 900 K. Thus, our study provides insights into the thermoelectric properties of the Bi2TeSe2 monolayer and may open up an effective avenue for applying bismuth-based materials to a high-temperature TE field.

Self-Assembled 1T-MoS₂/Functionalized Graphene Composite Electrodes for Supercapacitor Devices

Abstract: Two-dimensional (2D) materials such as graphene and molybdenum disulfide (MoS2) have been investigated widely for applications in energy storage, including supercapacitors, due to their high specific surface area, potential redox activity, and mechanical flexibility. However, electrodes comprising either pure graphene and MoS2 have failed to reach their potential due to restacking of the layered structure and poor electrical conductivity. It has been shown previously that composite electrodes made from a mixture of graphene and MoS2 partially counteract these issues; however, performance is still limited by poor mixing at the nanoscale. Herein, we form a true composite electrode by chemically functionalizing the graphene so that the negatively charged surface can self-assemble with the positively charged 1T-MoS2 to give an alternating layer structure. These alternately restacked 2D materials were then used to produce supercapacitor electrodes, and their energy storage properties were characterized. This stacked structure has increased the interlayer spacing of 1T-MoS2 which was indicated by the increase in the intensity of the (001) peak in the X-ray diffraction spectra. Furthermore, the typically metastable 1T-MoS2 was stabilized by the interaction with the functionalized graphene, preventing it reverting back to the 2H phase, which was observed when pristine graphene was used. The graphene was functionalized using either 4-bromobenzenediazonium or 4-nitrobenzenediazonium, with the latter giving optimal capacitance when mixed with the MoS2. The alternative layer graphene–MoS2 structure was confirmed by Raman spectroscopy and electron microscopy, leading to a high specific capacitance (290 F cm–3 at 0.5 A g–1) and 90% retention of capacitance after 10 000 cycles.

Ultrastable Porous Organic Polymers Containing Thianthrene and Pyrene Units as Organic Electrode Materials for Supercapacitors

Abstract: In this study, we successfully synthesized, designed, and constructed three porous organic polymers (POPs) without or with acetylene as the bridge─Bz-Th, TPA-Th, and P-Th-POPs─through a robust and efficient coupling reaction of 2,8-dibromothianthrene (Th-Br2) as a building unit with 1,3,5-tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene (Bz-3BO), tris(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)amine (TPA-3BO), and 1,3,6,8-tetraethynylpyrene (P-T). Our POP materials displayed exceptional heat stability (char yields of more than 70% for each POP) and superior Brunauer–Emmett–Teller surface areas. According to electrochemical testing, a P-Th-POP-containing acetylene group as a bridge has a specific capacitance of 217 F g–1 at 0.5 A g–1 and an excellent cycling stability of over 5000 times at 10 A g–1. Compared to other porous materials, P-Th-CMP exhibits the highest specific capacitance, which may be attributed to its enormous surface area and extended conjugation system.

Defective Metal–Organic Framework-808@Polyaniline Composite Materials for High Capacitance Retention Supercapacitor Electrodes

Abstract: Among their potential applications, metal–organic frameworks (MOFs) emerge as promising alternative electrode materials to overcome the disadvantages of low energy density supercapacitors. Although the potential of MOFs lies in their adjustable pore structure and high surface areas, they possess poor conductivity. In this context, composites with conductive matrices, including organic conductive polymers, have proved to enhance the electrochemical properties of MOFs and their structural stability in the long-term cycling process compared to the pristine MOF. In this study, we have chosen defective zirconium MOF-808 (d-MOF-808) as a porous material because of its resistance to strong acidic media in a postsynthetic modification process. As a conductive agent, polyaniline (PANI) was selected due to its high stability and facile synthesis. The obtained composites of d-MOF-808@PANI at d-MOF/PANI ratios of 15:1, 30:1, and 60:1 increase the charge transport properties compared to the pristine d-MOF-808 and PANI. Electrochemical evaluation of the new hybrid electrode materials was made to demonstrate the capacitance retention. Among the series of materials prepared, the 60:1 composite shows the highest capacitance (188 F/g at 30 mV s–1) in 1 M KOH and a notable capacitance retention of 99.8% for up to 10,000 cycles with 99.7% coulombic efficiency.

Enhanced Photocatalytic Activity for CO2 Reduction over a CsPbBr3/CoAl-LDH Composite: Insight into the S-Scheme Charge Transfer Mechanism

Abstract: The construction of an S-scheme heterojunction is recognized as a promising approach to developing efficient photocatalytic systems. Herein, a novel S-scheme heterojunction of CsPbBr3 nanocrystals/CoAl layered double hydroxide (LDH) nanosheets was fabricated and applied for photocatalytic conversion of CO2. CsPbBr3/CoAl-LDH composites exhibited superior activity for CO2 photoreduction under visible light. The composite containing 60 wt % CsPbBr3 displayed the optimal photocatalytic performance, which was enhanced by 2.6 and 9.9 times compared to CsPbBr3 and CoAl-LDH, respectively. Moreover, this composite also showed stable photocatalytic activity with no detectable decrease after four cycles. The formation of an S-scheme heterojunction can promote the electron–hole separation and provide a higher redox potential of the composite, thus leading to the remarkable photocatalytic performance toward CO2 reduction. This study provides a new perspective for designing and manufacturing perovskite-based S-scheme photocatalytic systems for CO2 reduction.

Improving Structural and Moisture Stability of P2-Layered Cathode Materials for Sodium-Ion Batteries

Abstract: P2-type Ni/Mn-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs). However, ground challenges, e.g., irreversible phase transition during cycling, moisture instability, and inferior electrochemical performance, greatly impede their practical applications. Herein, a series of Cu-substituted P2–Na0.6Ni0.3–xMn0.7CuxO2 (0 ≤ x ≤ 0.2) cathode materials for SIBs are fabricated and the mechanisms responsible for their improved electrochemical performances are comprehensively investigated. It is discovered that Cu dopants with strong electronegativity could stabilize the crystal structure by inhibiting the common P2–O2 phase transition, leading to improved cycling stability. The expanded interlayer spacing after Cu doping is facilitated for the charge transfer kinetics, which ensures excellent rate performance. In addition, all Ni, Mn, Cu, and O participate in the charge compensation upon sodiation and desodiation through reversible redox reactions. More importantly, Cu substitution improves the moisture stability of the cathode materials because the Cu2+/Cu3+ redox couple increases the initial charging potential. This work provides a promising guidance for the design of low-cost, high-performance, and air-stable cathode materials with both cationic and anionic redox activities for SIBs.

Rational Construction of ZnCo-ZIF-Derived ZnS@CoS@NiV-LDH/NF Binder-Free Electrodes Via Core–Shell Design for Supercapacitor Applications with Enhanced Rate Capability

Abstract: The improvement of metal–organic framework materials through rational structural design and construction and the construction of core–shell nanostructures to obtain affluent active sites and high redox activity have always been research hotspots in green energy field. In this work, high-quality supported binder-free ZnS@CoS@NiV-LDH/NF was in situ grown on Ni foam by using bimetal ZnCo ZIFs as a template. The designed ZnS@CoS@NiV-LDH/NF electrode material reveals excellent battery-type redox kinetics with the highest specific capacitance of 2918.4 F g–1 (1459.2 C g–1) at 1 A g–1. In addition, ZnS@CoS@NiV-LDH/NF exhibits excellent lifetime maintaining up to 87.5% under 20 A g–1 for 10,000 cycles. Meanwhile, battery–supercapacitor hybrid devices fabricated with the ZnS@CoS@NiV-LDH/NF composite and activated carbon as positive and negative electrodes achieved a remarkable energy density of 71.02 W h kg–1 at a power density of 750 W kg–1. The excellent electrochemical performance of ZnS@CoS@NiV-LDH/NF can be attributed to the synergistic effect of the composite electrode material and its core–shell structure. The ZnS@CoS@NiV-LDH/NF is extremely promising as a functional material for green energy storage.

Efficient Visible-Light Photoreduction of CO2 to CH4 over an Fe-Based Metal–Organic Framework (PCN-250-Fe3) in a Solid–Gas Mode

Abstract: Solar-driven highly efficient CO2 photoreduction by water oxidation to produce high-value-added chemical feedstocks of fuels remains extremely challenging. Over the past few decades, two types of reaction modes (solid–liquid or solid–gas) have been developed by researchers to achieve substrate-based photocatlytic CO2 reduction. In the absence of organic solvents, photosensitizers, and organic sacrificial agents, the solid–gas mode may be more suitable for photocatalytic CO2 reduction. A facile hydrothermal method was used to fabricate a low-cost and photosensitive azobenzene tetracarboxylic acid-based metal–organic framework (MOF), PCN-250-Fe3, which offers the advantages of visible-light and CO2 adsorption and facilitates an electron-coupled proton transition. Notably, PCN-250-Fe3 exhibited a maximum photocatalytic activity of 16.32 μmol g–1 with ca. 77.57% selectivity in 4 h without the use of photosensitizers or organic sacrificial agents under visible-light irradiation. This photocatalytic performance is superior to that of most nonporphyrin-based MOF photocatalysts under solid–gas reaction conditions. This study provides unique insight into enhancing the efficiency of the photoreduction of CO2 to CH4 by pure water.

Macro/Mesoporous Carbon/Defective TiO2 Composite as a Functional Host for Lithium–Sulfur Batteries

Abstract: Lithium–sulfur batteries (LSBs) hold great potential as next-generation electrochemical energy storage and conversion systems owing to their higher theoretical capacity (1675 mAh/g). However, the shuttling of soluble polysulfides with slow redox reaction kinetics has restricted the commercialization of LSBs. The design and synthesis of effective cathode hosts provide a promising solution to improving the electrochemical performances of LSBs. Herein, we report a composite of macro/mesoporous carbon (MMC) coupled with defective TiO2 nanoparticles as a novel functional cathode host for LSBs. The MMC/TiO2 composite has been synthesized using a template-based approach combining simple hydrothermal reactions. Experimental characterizations, electrochemical measurements, and first-principles density functional theory (DFT) calculations disclose that the combination of macro/mesoporous carbon and defective TiO2 (coexistence of oxygen vacancies and Ti3+) effectively suppresses the undesired polysulfide shuttling effect and promotes fast redox conversion of polysulfides during cycling. The resultant LSBs with MMC/TiO2@S as a composite cathode thus exhibit impressive electrochemical properties with high capacity (1420 mAh/g at 0.2C), good rate capability (522 mAh/g at 2C), and cycling ability (65.6% retention at 0.2C over 60 cycles). This work can present some new insights into the rational design and exploration of novel material systems and compositions for applications in LSBs.

Noncovalent Interactions Induced by Fluorination of the Central Core Improve the Photovoltaic Performance of A-D-A′-D-A-Type Nonfused Ring Acceptors

Abstract: Nonfused ring acceptors (NFRAs) have blazed a trail in achieving high-efficiency organic solar cells (OSCs) from low-cost materials due to their simple synthesis. In this work, two A-D-A′-D-A-type NFRAs, comprising benzotriazole or difluorinated benzotriazole as the electron-deficient core, namely, BTz-HD and ffBTz-HD, were synthesized via direct arylation coupling reaction. The influence of fluorination of the central core on molecular packing and the photovoltaic performance of the nonfused acceptors were investigated by analyzing the single-crystal structures of two model compounds BTz-2T (fluorine free) and ffBTz-2T (fluorinated). Compared with BTz-2T, ffBTz-2T exhibits a more planar molecular skeleton and forms a slip-stack stacking with π–π stacking distances of 3.58 and 3.67 Å owing to the existence of F···S, S···H, and H···F noncovalent interactions. These characteristics favor the ordered and compact stacking of ffBTz-HD in the solid state, which facilitated charge transport and inhibited charge recombination in solar cells. These merits endowed the ffBTz-HD-based OSC with a higher short-circuit current density and fill factor than the BTz-HD-based OSC. As a result, a higher power conversion efficiency of 10.56% has been achieved by ffBTz-HD. The structure–property relationship unraveled in this study is beneficial to the development of more efficient NFRAs for application in OSCs.

Few-Layered MoS2/ZnCdS/ZnS Heterostructures with an Enhanced Photocatalytic Hydrogen Evolution

Abstract: Studies on highly efficient noble-metal-free catalysts are regarded as an important task for H2 production by water-splitting. MoS2/ZnCdS/ZnS dual heterostructures were successfully prepared with respective supernatant MoS2 colloidal solutions (called M/ZC/Z) and MoS2 precipitates (M(p)/ZC/Z). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the M/ZC/Z sample showed that ZnS nanosheets were decorated with ZnCdS nanorods and few-layered MoS2. Then, photocatalytic hydrogen production study was performed and the results showed that the M/ZC/Z sample has a H2 evolution rate of up to 79.3 mmol g–1 h–1 under visible light irradiation with an apparent quantum efficiency of 47.9% at 420 nm with noble-metal-free catalysts, which is nearly 5 times that of the M(p)/ZC/Z sample (15.7 mmol g–1 h–1) and approximately 9 times that of the ZC/Z sample (8.98 mmol g–1 h–1). Cycle tests showed that M/ZC/Z is stable and reusable. Without sacrificial agents, the production rates for hydrogen and oxygen evolution were obtained as 3.15 and 1.55 mmol g–1 h–1, respectively. Time-resolved photoluminescence spectra revealed that the well-matched structure is effective in the separation and transfer of photogenerated electron and hole pairs, leading to the enhancement of the photocatalytic H2 production activity.

Improved Working Temperature and Capacitive Energy Density of Biaxially Oriented Polypropylene Films with Alumina Coating Layers

Abstract: High-temperature dielectric energy-storage properties are crucial for polymer-based capacitors for harsh environment applications. However, biaxially oriented polypropylene (BOPP), a state-of-the-art commercial capacitor dielectric, can work only below 105 °C. Here, we present a versatile method to enhance its working temperature by depositing alumina (Al2O3) layers onto BOPP films via magnetron sputtering. Compared with a pure BOPP film, the sandwiched Al2O3/BOPP/Al2O3 structure shows a higher dielectric constant, a lower electrical conduction loss, stronger mechanical properties, higher thermal conductivity, and especially increased working temperature. As a result, the composite film delivers a high discharged energy density of 0.45 J/cm3 under 200 MV/m (the actual operating electric field in hybrid electric vehicles) at 125 °C. The discharged energy density and energy-storage efficiency (∼97.7%) are highly stable over 5000 cycles at 125 °C. This work provides an effective route to develop high-temperature polymer-based capacitors.