Materials For Energy Conversion Research Articles

Defect engineering of two-dimensional materials for advanced energy conversion and storage.

In the global trend towards carbon neutrality, sustainable energy conversion and storage technologies are of vital significance to tackle the energy crisis and climate change. However, traditional electrode materials gradually reach their property limits. Two-dimensional (2D) materials featuring large aspect ratios and tunable surface properties exhibit tremendous potential for improving the performance of energy conversion and storage devices. To rationally control the physical and chemical properties for specific applications, defect engineering of 2D materials has been investigated extensively, and is becoming a versatile strategy to promote the electrode reaction kinetics. Simultaneously, exploring the in-depth mechanisms underlying defect action in electrode reactions is crucial to provide profound insight into structure tailoring and property optimization. In this review, we highlight the cutting-edge advances in defect engineering in 2D materials as well as their considerable effects in energy-related applications. Moreover, the confronting challenges and promising directions are discussed for the development of advanced energy conversion and storage systems.

Hydride ion conductor: A key material for innovative energy storage and conversion

Hydride ion conductor: A key material for innovative energy storage and conversion

NiO@CoSe2 nanostructures for high-performance asymmetric supercapacitors and efficient electrocatalysts.

It is very important to design bi-functional materials for sustainable energy storage and conversion. NiO electrodes are promising candidates for supercapacitors and electrocatalysts, but the poor cycling stability limits their practical applications. To solve this issue, we prepared core-shell structured NiO@CoSe2 samples by a multi-step hydrothermal protocol. They exhibit a specific capacitance of 1130 C g-1 at a current density of 1 A g-1. An asymmetric device was assembled using the obtained product as the cathode. It delivers an energy density of 103.8 W h kg-1 at 2700 W kg-1. As an electrocatalyst for hydrogen evolution reactions, the NiO@CoSe2 sample presents an overpotential of 82.8 mV@10 mA cm-2 and a Tafel slope of 72.14 mV dec-1, respectively.

Insights into conduction band flexibility induced by spin polarization in titanium-based metal-organic frameworks for photocatalytic water splitting and pollutants degradation.

Solar energy is becoming the most promising option to mitigate the energy crisis in the future and can be applied in renewable and economical technologies such as water splitting and pollutants degradation. The promotion of the electronic energetic level is considered an efficient method to enhance the photocatalytic performance of semiconductor materials for solar energy conversion. The highly energetic electrons exhibit a remarkable reduction ability by virtue of the electronic spin polarization, which is associated with the conduction band (CB) position. Thus, the regulation of the CB position due to the redistribution of electrons by means of defect engineering presents potential. Here, a series of titanium-based metal-organic frameworks (Ti-based MOFs) named MIL-125-m% containing different extents of defects are reported to enable photocatalytic activity under simulated sunlight and visible light illumination for remarkably enhanced photocatalytic hydrogen evolution and pollutant degradation. The experimental results illustrated that MIL-125-5% exhibited a superior photocatalytic hydrogen evolution rate (16507.27μmol·g-1·h-1), much higher than that of MIL-125-0% (1.444μmol·g-1·h-1). The excellent photocatalytic performance was attributed to upshift of d-band center, which strengthened the adsorption of H*, facilitating the H2 evolution reaction. In addition, the degradation rate of MIL-125-5% was up to twice the original rate, for the highly energetic electrons induced by the CB flexibility alleviated the photoinduced electron recombination in defective MIL-125. The strategy of defect engineering provides a new path to control the flexibility of the CB position by electronic spin polarization on adjustable metal-organic frameworks (MOFs), and the photocatalytic effect is changed accordingly.

Metallene-related materials for electrocatalysis and energy conversion.

As a member of graphene analogs, metallenes are a class of two-dimensional materials with atomic thickness and well-controlled surface atomic arrangement made of metals or alloys. When utilized as catalysts, metallenes exhibit distinctive physicochemical properties endowed from the under-coordinated metal atoms on the surface, making them highly competitive candidates for energy-related electrocatalysis and energy conversion systems. Significantly, their catalytic activity can be precisely tuned through the chemical modification of their surface and subsurface atoms for efficient catalyst engineering. This minireview summarizes the recent progress in the synthesis and characterization of metallenes, together with their use as electrocatalysts toward reactions for energy conversion. In the Synthesis section, we pay particular attention to the strategies designed to tune their exposed facets, composition, and surface strain, as well as the porosity/cavity, defects, and crystallinity on the surface. We then discuss the electrocatalytic properties of metallenes in terms of oxygen reduction, hydrogen evolution, alcohol and acid oxidation, carbon dioxide reduction, and nitrogen reduction reaction, with a small extension regarding photocatalysis. At the end, we offer perspectives on the challenges and opportunities with respect to the synthesis, characterization, modeling, and application of metallenes.

Synergistic MXene/LDH heterostructures with extensive interfacing as emerging energy conversion and storage materials

This review covers MXene/LDH heterostructures, including synthesis, growth mechanism, morphology factors, and chemical properties. Synergistic interactions at the heterointerface and their applications are analyzed in-depth.

Accounts of applied molecular rotors and rotary motors: recent advances.

Molecular machines are nanoscale devices capable of performing mechanical works at molecular level. These systems could be a single molecule or a collection of component molecules that interrelate with one another to produce nanomechanical movements and resulting performances. The design of the components of molecular machine with bioinspired traits results in various nanomechanical motions. Some known molecular machines are rotors, motors, nanocars, gears, elevators, and so on based on their nanomechanical motion. The conversion of these individual nanomechanical motions to collective motions via integration into suitable platforms yields impressive macroscopic output at varied sizes. Instead of limited experimental acquaintances, the researchers demonstrated several applications of molecular machines in chemical transformation, energy conversion, gas/liquid separation, biomedical use, and soft material fabrication. As a result, the development of new molecular machines and their applications has accelerated over the previous two decades. This review highlights the design principles and application scopes of several rotors and rotary motor systems because these machines are used in real applications. This review also offers a systematic and thorough overview of current advancements in rotary motors, providing in-depth knowledge and predicting future problems and goals in this area.

Metallic CrP2 monolayer: potential applications in energy storage and conversion.

Phosphorus-rich compounds have emerged as a promising class of energy storage and conversion materials due to their interesting structures and electrochemical properties. Herein, we propose that a metallic CrP2 monolayer, isomorphic to 1H-phase MoS2, is a good prospect as an anode for K-ion batteries and a catalyst for hydrogen evolution through first-principles calculations. The CrP2 monolayer demonstrates not only a desirable high K storage capacity (940 mA h g-1) but also a low K-ion diffusion barrier (0.10 eV) and average open circuit voltage (0.40 V). On the other hand, its Gibbs free energy (0.02 eV)/active site density is superior/comparable to that of commercial Pt, resulting from the contribution of the lone pair electrons of the P atom. Its high structural stability and intrinsic metallicity can ensure high safety and performance during the cyclic process. These interesting properties make the CrP2 monolayer a promising multifunctional material for energy storage and conversion devices.

Rapid dissolution of chitin and chitosan with degree of deacetylation less than 80% in KOH/urea aqueous solution

The rapid dissolution of chitin and chitosan with degree of deacetylation less than 80% in the universal solvent KOH/urea aqueous solution were comprehensively investigated. A desolvation–intercalation dissolution mechanism was proposed.

Uncovering the photoelectronic/catalytic property modulation and applications of 2D MoS2: from the perspective of constructing heterogeneous interfaces

2D polyphase molybdenum disulfide (MoS2) has become a popular material for energy conversion and interdisciplinary applications.

Photoactive and conductive biohybrid films by polymerization of pyrrole through voids in photosystem I multilayer films.

The combination of conducting polymers with electro- and photoactive proteins into thin films holds promise for advanced energy conversion materials and devices. The emerging field of protein electronics requires conductive soft materials in a composite with electrically insulating proteins. The electropolymerization of pyrrole through voids in a drop-casted photosystem I (PSI) multilayer film enables the straightforward fabrication of photoactive and conductive biohybrid films. The rate of polypyrrole (PPy) growth is reduced by the presence of the PSI film but is insensitive to its thickness, suggesting that rapid diffusion of pyrrole through the voids within the PSI film enables initiation at vacant areas on the gold surface. The base thickness of the composite tends to increase with time, as PPy chains propagate through and beyond the PSI film, coalescing to exhibit a tubule-like morphology as observed by scanning electron microscopy. Increasing amounts of PPy greatly increase the capacitance of the composite films in a manner almost identical to that of pure PPy films grown from unmodified gold, consistent with a high polymer/aqueous interfacial area and a conductive composite film. While PPy is not photoactive here, all composite films, including those with large amounts of PPy, exhibit photocurrents when irradiated by white light in the presence of redox mediator species. Optimization of the Py electropolymerization time is necessary, as increasing amounts of PPy lead to decreased photocurrent density due to a combination of light absorbance by the polymer and reduced accessibility of redox species to active PSI sites.

Single phase ZnV2O6 nanorods with excellent visible light photodetection capability

We report a facile synthetic route for the growth of single phase ZnV2O6 nanorods via a simple acid–base reaction of the Lewis acid forms of ZnCl2 and VCl3 with NaOH in an aqueous solution followed by the thermal treatment of the resulting metal hydroxides on a SiO2 substrate in air. The as-grown ZnV2O6 nanorods exhibited a well-defined rectangular cross-section with a width of approximately 300–350 nm and thickness of 100–150 nm, and they extended in random directions up to a length of 3 µm. The as-grown ZnV2O6 nanorods possessed a single-phase monoclinic brannerite-type structure, as determined via X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopic investigations. The synthesized ZnV2O6 sample exhibited a band gap of ∼2.06 eV and excellent photodetection properties in the visible light region of 635 nm, which is the band-edge wavelength. The new ZnV2O6 synthetic method proposed in this report could be used to develop various photocatalysts and energy conversion materials in the future.

Nonconductive two-dimensional metal−organic frameworks for high-performance electrochemical energy storage

Most metal-organic frameworks (MOFs) cannot be used as electrode materials due to their high cost, poor stability in aqueous solutions, inferior intrinsic electrocatalytic activity, and poor conductivity. The novel application of a nickel (II) cluster-based two-dimensional MOF, Ni-mba ([Ni(II)6Ni(III)2(mba)6(Cl)2(OH−)2(O2−)]n, H2mba is 2-mercaptobenzoic acid), is reported for use as electrode materials. Ni-mba is an insulator and H2mba is an inexpensive chemical raw material. The conductivity of Ni-mba is 2.180 × 10−9 Scm−1 at 30 °C. The electrocatalytic activity of Ni-mba is enhanced by the hexanuclear nickel (II) cluster subunit containing the sulfhydryl group and the mixed valence Ni2+/Ni3+ ions. Ni-mba shows excellent performance, stability in 6 M KOH, and a high inherent density (1.828 gcm−3) and specific capacity (704.4 Fg−1 at 1 Ag−1 and 1088.5 mAhg−1 at the first cycle) for lithium-ion batteries and supercapacitors. This paper provides a novel application of nonconductive two-dimensional MOFs in the energy storage field and the design recommendations of high-performance electrode materials for energy conversion and storage based on its structure and performance differences.

Bioinspired Three-Dimensional Nanoporous Membranes for Salinity-Gradient Energy Harvesting

ConspectusSalinity-gradient energy represents a widespread, clean, environmentally friendly, and sustainable source of renewable energy, which has attracted great attention in the past years. To harness this energy, interdisciplinary efforts from chemistry, materials science, environmental science, and nanotechnology have been made to develop efficient and low-cost approaches and materials for energy conversion. Conventional reverse electrodialysis (RED) systems are generally based on ion-exchange membranes, which usually suffer from ineffective mass transport, high membrane resistance, limited pore size, and concentration polarization, resulting in low output power density and poor energy-conversion efficiency. As one promising material, nanofluidic channels with their unique transport properties, which can be attributed to nanoconfinement effect, enable high-performance reverse electrodialysis to efficiently harvest salinity-gradient energy. Due to the unique porous architectures, three-dimensional (3D) nanoporous membranes demonstrate great potential for harvesting salinity-gradient power. It is generally known that the porous membranes can be prepared by many methods; however, there are some shortcomings such as high costs, poor ion conductance, and fragility limiting the practical application. Several simple and versatile approaches to low-cost fabrication of 3D nanoporous membranes have been developed in recent years. For example, self-assembly provides an effective route of constructing functional materials and organizing them into 3D architectures. In this Account, we mainly review our recent progress in the design and fabrication of bioinspired 3D nanoporous membranes for salinity-gradient energy harvesting. First, we give a brief introduction to bioinspired nanochannel membranes (BNMs) with diverse structural dimensions, and nanofluidic channel membranes may lead to technological breakthroughs and thus act as an emerging platform for harvesting salinity-gradient energy. Subsequently, we discuss the typical preparation approaches for bioinspired 3D nanoporous membranes. To tackle the bottlenecks of the conventional membrane-based power generator and extrapolate single-channel devices to macroscopic materials, our group have developed a series of 3D nanoporous membranes for power generation via various simple and versatile methods. We highlight the design and fabrication of several types of 3D nanoporous membranes, i.e., heterogeneous and homogeneous membranes, with tunable surface charge and porosity. The proof-of-concept demonstration of bioinspired 3D porous membranes shows that these nanofluidic platforms have the potential to overcome the selectivity-permeability trade-off and have impressive osmotic-energy-harvesting performance. Specifically, the scale-up Janus 3D porous membranes maintained high selectivity and rectified current in a hypersaline environment, which benefitted effective energy conversion and high output power density when seawater and river water were mixed. Finally, we give an outlook for future challenges and perspectives on the development of 3D nanofluidics for salinity-gradient energy conversion. We expect that this Account will spark further efforts on the development of bioinspired 3D nanoporous membranes for large-scale (typical side length of more than 10 cm) energy conversion and new opportunities for the applications in water desalination, dialysis, and ionic circuitries.

Emerging 2D Copper-Based Materials for Energy Storage and Conversion: A Review and Perspective.

2D materials have shown great potential as electrode materials that determine the performance of a range of electrochemical energy technologies. Among these, 2D copper-based materials, such as Cu-O, Cu-S, Cu-Se, Cu-N, and Cu-P, have attracted tremendous research interest, because of the combination of remarkable properties, such as low cost, excellent chemical stability, facile fabrication, and significant electrochemical properties. Herein, the recent advances in the emerging 2D copper-based materials are summarized. A brief summary of the crystal structures and synthetic methods is started, and innovative strategies for improving electrochemical performances of 2D copper-based materials are described in detail through defect engineering, heterostructure construction, and surface functionalization. Furthermore, their state-of-the-art applications in electrochemical energy storage including supercapacitors (SCs), alkali (Li, Na, and K)-ion batteries, multivalent metal (Mg and Al)-ion batteries, and hybrid Mg/Li-ion batteries are described. In addition, the electrocatalysis applications of 2D copper-based materials in metal-air batteries, water-splitting, and CO2 reduction reaction (CO2 RR) are also discussed. This review also discusses the charge storage mechanisms of 2D copper-based materials by various advanced characterization techniques. The review with a perspective of the current challenges and research outlook of such 2D copper-based materials for high-performance energy storage and conversion applications is concluded.

Controllable Synthesis of 2D Materials by Electrochemical Exfoliation for Energy Storage and Conversion Application

2D materials have captured much recent research interest in a broad range of areas, including electronics, biology, sensors, energy storage, and others. In particular, preparing 2D nanosheets with high quality and high yield is crucial for the important applications in energy storage and conversion. Compared with other prevailing synthetic strategies, the electrochemical exfoliation of layered starting materials is regarded as one of the most promising and convenient methods for the large-scale production of uniform 2D nanosheets. Here, recent developments in electrochemical delamination are reviewed, including protocols, categories, principles, and operating conditions. State-of-the-art methods for obtaining 2D materials with small numbers of layers-including graphene, black phosphorene, transition metal dichalcogenides and MXene-are also summarized and discussed in detail. The applications of electrochemically exfoliated 2D materials in energy storage and conversion are systematically reviewed. Drawing upon current progress, perspectives on emerging trends, existing challenges, and future research directions of electrochemical delamination are also offered.

Negative Poisson's ratio and thickness-dependent optoelectronic response in two-dimensional thermoelectric TlCuSe

In one of the latest accomplishments in the field of materials for energy conversion, layered TlCuSe with a relatively high thermoelectric figure of merit has been designed and successfully fabricated. Inspired by this exciting advance, we herein conduct first-principles calculations to explore the dynamical and thermal stability, mechanical properties, and thickness dependent electronic and optical properties of TlCuSe nanosheets. Analysis of mechanical deformation reveals that TlCuSe monolayer shows a negative in-plane Poisson's ratio of −0.29 and is thus an auxetic material. This novel monolayer also exhibits an intrinsically p-type character with an appreciable hole mobility of 1528 cm2V−1s−1, an HSE06 indirect gap of 1.41 eV, and a multi-valley conduction band. It is found that electronic band gap in TlCuSe considerably decreases with increasing the number of layers and reaches to 0.47 eV for the bulk lattice, indicating strong quantum confinement effects. The mutli-valley character of the conduction and valence bands is also boosted in multilayer TlCuSe systems. Analysis of optical absorption of monolayer to tri-layer TlCuSe indicates that they possess remarkably large absorption coefficients within the visible and UV range of light spectrum. The acquired results provide useful information on physicochemical and electronic properties of TlCuSe nanomaterials for advanced applications.

Phase transition hysteresis at the antiferroelectric-ferroelectric boundary in PbZr1−xTixO3

$\mathrm{Pb}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ exhibits an antiferroelectric-ferroelectric phase boundary at the composition $x\ensuremath{\sim}0.06$. Around this boundary, several questions need to be answered, such as the stabilizations of different phases with a small amount of compositional difference, the sequence of phase transitions, the coexistence of crystal structures, and potential applications. In this work, we have carried out systematic structural investigations of single crystals and ceramics with several compositions across the phase boundary. The phase diagram for $x\ensuremath{\le}0.07$ has been established. A complex phase coexistence is found near the phase boundary, which leads to an unusual transition sequence. It is confirmed that $Pbam$ and $R3c$ structures maintain a subtle balance at the phase boundary, which may be perturbed by a slight change in the concentration or external stimuli. These findings provide unique insights into understanding the antiferroelectric-ferroelectric competition and, hence, into designing alternative materials for energy storage and conversion.

Four-point bending piezoelectric energy harvester with uniform surface strain toward better energy conversion performance and material usage

Improving the energy conversion efficiency of piezoelectric energy harvesters is of great importance, and one approach is to make more uniform use of the working material by ensuring a uniform strain state. To achieve better performance, this paper presents a four-point bending piezoelectric energy harvester with extensive investigation and modeling to identify the influential parameters. An electromechanical analytical model is presented and verified by experimental data. The frequency-domain method extracts the solutions for a general time-variable force and impact. Four-point bending is compared with the standard cantilever harvesters regarding voltage generation, mechanical strain, and figure of merit. Strain contours are analyzed and interpreted for this innovative approach, and the power generation by the optimal resistance load is studied. Dimensionless parameters are introduced and investigated to find the optimal operating conditions for the four-point bending harvester. Finally, the four-point bending performance and the best figure of merit are discussed with a view to the long-term fatigue life of the harvester. The results show that in the best four-point bending energy conversion conditions; the energy conversion coefficient is more than three times higher than that of typical cantilever energy harvesters. The results also illustrate that the axial strain experienced in a standard cantilever harvester is more than three times higher than that of the four-point bending harvester, suggesting the latter device may have favorable fatigue performance. Overall, the presented piezoelectric harvester has improved energy conversion efficiency and experiences a reduced and uniform surface strain, making it appropriate for high-efficiency energy harvesting systems.

Fe7Se8 nanoparticles encapsulated by CNT reinforced fibrous network with advanced sodium ion storage and hydrogen evolution reaction

Sodium ion batteries (SIBs) has been regarded as one of the most promising large scale energy storage devices. Besides, hydrogen production by water splitting is the green, safe and low cost long-term energy conversion and storage technology. Rare studies have reported advanced electrode materials for both SIBs and HER. Herein, Fe7Se8 nanoparticles have been successfully encapsulated into CNT reinforced fibrous network (Fe7Se8/CNT/C) by electrospinning combined with in situ selenide process. When utilized as flexible anodes for SIB, the Fe7Se8/CNT/C delivers superior rate capabilities (524 mAh g−1 even at 5000 mA g−1) and cycling stability (610 mAh g−1 at 500 mA g−1 after 1000 cycles). Moreover, the Fe7Se8/CNT/C also delivers considerable hydrogen evolution reaction (HER) activity (an overpotential of 138 mV at a current density of 10 mA cm−2 and a Tafel slope of 114 mv dec−1). Ex-situ electrochemical mechanism studies including EIS, GITT, CV and ECSA reveal that the graphitized CNT reinforced fibers can accelerate the ions/electrons transportations and the robust fibrous network structure guarantees excellent structural stability, thereby, preventing the aggregations of Fe7Se8 nanoparticles, facilitating electrolyte penetration and creating numerous catalytic active sites. Therefore, the Fe7Se8/CNT/C is one of the most promising energy storage and conversion materials. The fabrication strategy in this work could give an insight in exploring advanced functional materials.