Recent developments in black phosphorus quantum dots (BPQDs) for energy storage and optoelectronic devices

Black phosphorus quantum dots (BPQDs) have shown promising applications in biosensors and energy storage devices. However, the electrochemiluminescence (ECL) properties of pristine BPQDs in an organic system have rarely been reported. In this paper, N,N'-dimethylformamide passivated BPQDs with a small size of 2.3 nm were obtained by an ultrasonication-assisted liquid exfoliation process, and their ECL properties of BPQDs were studied. A reversible reduction peak was recorded by differential pulse voltammetry, while no apparent oxidation peak was observed. ECL signal was not seen in the annihilation route. Persulfate was proved to be an effective coreactant and yellow emission was observed which was greatly red-shifted in comparison to that of photoluminescence. ECL of BPQDs is believed to be generated from both the surface states and electron promotion over their band gap.

Niobium (Nb) and tantalum (Ta), transition metals with distinct physical and chemical properties, are highly attractive for applications in electrochemical energy storage (EES) devices. Their oxides, dichalcogenides, and MXenes demonstrate significant potential due to effective ion‐diffusion channels and high theoretical capacity. Particularly, Nb‐based dichalcogenides and MXenes offer enhanced electrochemical performance for lithium‐ion batteries (LIBs) and supercapacitors (SCs) applications because of their layered structure. However, the tendency of Nb chalcogenides and Nb‐MXene layers to aggregate or restack impedes electrolyte penetration, diminishing coulombic efficiency and capacity. Moreover, Nb‐ and Ta‐based oxides have intrinsically low electrical conductivity and a slow Li intercalation rate, challenging their application in energy storage devices. To address these issues, strategies such as hierarchical structuring, heteroatom doping, and the development of porous or nanoscale forms, as well as composites incorporating carbon or conductive polymers, have been explored. This review summarizes the impacts of various synthesis techniques, crystal structures, and morphological tunings on the electrochemical properties of Nb and Ta materials in LIBs and SCs and outlines the future directions for enhancing their performance in EES applications.

Over the past decades, the development of porous materials has directly or indirectly affected industrial production methods. Metal-organic frameworks (MOFs) as an emerging class of porous materials exhibit some unique advantages, including controllable composition, a large surface area, high porosity, and so on. These attractive characteristics of MOFs have led to their potential applications in energy storage and conversion devices, drug delivery, adsorption and storage, sensors, and other areas. However, powdered MOFs have limited practical applications owing to poor processability, safety hazards from dust formation, and poor recyclability. In addition, the inherent micro/mesoporosities of MOFs also reduce the accessibility and diffusion kinetics for large molecules. To improve their processability for practical applications, MOFs are often deposited as MOF layers or films (i.e., MOF-coated composites) on supporting materials or are formed into 3D structured composites, such as aerogels and hydrogels. In this article, we review recent researches on these MOF composites, including their synthetic methods and potential applications in energy storage devices, heavy metal ion adsorption, and water purification. Finally, the future outlook and challenges associated with the large-scale fabrication of MOF-based composites for practical applications are discussed.

Black phosphorus quantum dots (BPQDs) exhibit excellent optical and photothermal properties and promising applications in optoelectronics and biomedicine. However, various intrinsic structural defects and oxidation are nearly unavoidable in preparation of BPQDs and how they affect the electronic and optical properties remains unclear. Here, by employing time-dependent density functional theory, we reveal that there are two types of photoabsorption in BPQDs for both point defects and oxidation. A close structure-absorption relation is unraveled: BPQDs are defect-tolerant and show excellent photoabsorption as long as the coordination number (CN) of defective P atoms is 3. By contrast, the unsaturated or oversaturated P atoms with CN ≠ 3 create in-gap-states (IGSs) and completely quench the optical absorption. An effective way to eliminate the IGSs and repair the photoabsorption of defective BPQDs via sufficient hydrogen passivation is further proposed.

Monolayer molybdenum disulfide (MoS2), consisting of covalently bonded S-Mo-S sandwiched layers, has high carrier mobility and a direct bandgap of 1.8 eV, offering properties for electronic and optoelectronic devices with high performance. Usually, it is essential to modulate the carrier concentrations and conductivities of monolayer MoS2 for practical applications. In this paper, black phosphorus (BP) quantum dots (QDs) were synthesized by a liquid exfoliation method successfully, and have a diameter of ∼5 nm as confirmed with a transmission electron microscope (TEM). BP QDs were utilized to decorate monolayer MoS2 grown by chemical vapor deposition (CVD). The Raman and PL spectra of the BP QD/MoS2 hybrid structure clearly indicate that BP QDs are an effective n-type doping scheme for monolayer MoS2. Back-gated monolayer MoS2 transistors were fabricated and show an improved source–drain current after BP QD modifications. A high electron concentration of ∼5.39 × 1012 cm−2 in monolayer MoS2 was achieved, which is beneficial for designing FETs and photodetector devices with novel functions.

Over the past decade, carbon quantum dots (CQDs) and graphene quantum dots (GQDs) have emerged as the supreme category of zero‐dimensional (0D) carbonaceous nanostructures having potential applications in energy storage and optoelectronics devices. These zero‐dimensional carbon nanostructures have captivated excellent consideration and have ascended as a substitute to traditional metal‐based semiconductor QDs due to their intriguing estates like excellent photoluminescence, quantum yield, scalability, tuneable emission, biocompatibility, chemical inertness, and excellent hydrophilicity. These unique properties of zero‐dimensional carbon materials have inspired researchers to employ them in bioimaging, optoelectronic, catalytic, and energy storage applications. The last couple of years have perceived an incredible rise in the green synthetic strategies of carbon‐based QDs and their applications and this review familiarizes the reader with the current and significant progress in the synthesis of carbon‐based QDs/GQDs from various natural precursors with their quantum yields as well as intriguing applications in diverse fields. In addition, this communication not only delivers critical perceptions toward the development in the field of advanced energy devices but also highlights the advancements of these nanosized carbonaceous materials in the energy storage devices such as in supercapacitors and batteries. Also, it focuses on the broad scope of carbon nanomaterials and nanotechnology towards cutting‐edge research and expansion in the arena of energy storage applications of carbon‐based QDs.

There has been a significant scope toward the cutting‐edge investigations in hierarchical carbon nanostructured electrodes originating from cellulosic materials, such as cellulose nanofibers, available from natural cellulose and bacterial cellulose. Elements of energy storage systems (ESSs) are typically established upon inorganic/metal mixtures, carbonaceous implications, and petroleum‐derived hydrocarbon chemicals. However, these conventional substances may need help fulfilling the ever‐increasing needs of ESSs. Nanocellulose has grown significantly as an impressive 1D element due to its natural availability, eco‐friendliness, recyclability, structural identity, simple transformation, and dimensional durability. Here, in this review article, we have discussed the role and overview of cellulose‐based hydrogels in ESSs. Additionally, the extraction sources and solvents used for dissolution have been discussed in detail. Finally, the properties (such as self‐healing, transparency, strength and swelling behavior), and applications (such as flexible batteries, fuel cells, solar cells, flexible supercapacitors and carbon‐based derived from cellulose) in energy storage devices and conclusion with existing challenges have been updated with recent findings.

The increasing demand for energy and the reducing supply of conventional energy storage devices have inspired interest to design environmentally-friendly, abundant, and cheap materials for energy storage applications. Graphitic carbon nitride (gCN)-based hybrids have attracted research efforts due to their attractive properties, structures, and performance. In this respect, this chapter addresses the different hybrid gCN-based devices for energy storage applications. The supercapacitance efficiency of gCNs can be improved by incorporating carbon-based materials, metal oxides/hydroxides, or metal sulfides, which increase the surface area and active sites and facilitate the faradaic reaction. The pulverization and aggregation of electrodes and relatively low electrical conductivity demonstrate the major challenges for Li+ storage applications using gCNs. This chapter highlights the recent advances in the rational design of gCN-based devices for energy production and storage applications. This includes fabrication of gCN-hybrids with carbon materials, metal oxides, and metal sulfides for Li-ion batteries (LIBs), Li–S batteries (LSBs), and supercapacitors. The current challenges and future perspectives on gCN-based energy production devices are also discussed.

Electrochemical reactions involve the exchange of electrons and ions at the interfaces between electrodes and an electrolyte allowing supercapacitors to store energy by separating positive and negative charges. Over the past few years, nanowires, as one of the representative one-dimensional (1D) nanomaterials, have demonstrated excellent capability for realizing a variety of applications in the fields of energy storage. Moreover, they offer 1D electronic pathways, which are key in charge transport, a large active interface between the electrolyte and electrode, etc. The high aspect ratio property of nanowires provides high surface area thereby enhancing electrolyte interaction with active electrode sites, resulting in increased material utilization, continuous electron transport, reduced resistance to charge flow, and improving electrode conductivity and kinetics. This chapter presents the theory, synthesis, and application of nanowires for electrochemical energy storage (EES) devices. It also highlights the scientific challenges associated with nanowires’ integration into energy storage devices, including reduced coulombic efficiency, capacity decay, and poor cycling, with possible solutions. Finally, a projection into the future direction of nanowire’s application in energy storage devices is presented and discussed.

Emerging applications of sludge biochar-based catalysts for environmental remediation and energy storage: A review

The research interest in wearable electronics has continuously stimulated the development of flexible energy storage systems with high performance and robustness. However, open problems with respect to energy storage efficiency and device integration are still challenging. Here, we demonstrate the laser fabrication of flexible planar supercapacitors based on graphene oxide (GO) and black phosphorus quantum dot (BPQD) nanocomposites. By combining graphene and BPQDs, the resultant supercapacitors feature high conductivity and activity, demonstrating enhanced specific capacity and superior rate performance, compared to those based on reduced GO (RGO) alone. Furthermore, the as-obtained devices present outstanding flexibility. Their performance shows unobvious degradation after repeated cycles of bending and straightening. Additionally, with the help of direct laser writing (DLW) technology, integration of the supercapacitors has been achieved without the need for any metal interconnection. The integrated devices delivered reasonable performance uniformity with a voltage extension of 3 V, which could easily power a LED. The supercapacitor-based RGO and BPQD nanocomposites demonstrate great potential for practical applications in flexible and wearable electronics.

Chapter 10 - Graphene quantum dots for clean energy solutions

Resorcinol-formaldehyde based carbon aerogel: Preparation, structure and applications in energy storage devices

Black phosphorus quantum dots (BPQDs) show great promise as anode material for sodium‐ion batteries (SIBs) due to their high theoretical capacity and short ion diffusion pathways. However, the challenges of low electronic conductivity and aggregation of BPQDs hinder their performance in SIBs. Loading BPQDs onto MXene nanosheets can address these issues, but the two‐dimensional nanosheets may restack into a dense film during the filtration process, limiting reaction kinetics. Here, we report, for the first time, a bionic strategy for multilayer honeycomb‐like MXene/BPQDs (MLHM/BPQDs) hierarchical architecture anode for SIBs. MXene nanosheets are arranged to ordered honeycomb layers and interlayer channels through the dual‐template method. MXene nanosheets are arranged to ordered honeycomb layers and interlayer channels through the dual‐templates method, and then, BPQDs are uniformly self‐assembled onto the inwalls of the honeycomb. The unique open hierarchical architecture serves as an excellent substrate for rapid electron transport. Its large specific surface area offers more sites for BPQDs loading, preventing aggregation, and provides abundant channels and space for electrolyte infiltration and BPQDs volume change. The ‐O terminal groups increased after annealing, and the abundant ‐O/‐F terminal groups on the surface of MXene can effectively enhance the binding energy and diffusion rate of Na + . The synergy of structure and surface chemistry accelerates the kinetics for MLHM/BPQDs, delivering a high reversible capacity of 653 mAh g −1 after 500 cycles at 2 A g −1 (94.3% capacity retention), which demonstrates its great potential as a SIBs anode material.

An energy storage device is a multi-physic device with ability to store energy in different forms. Energy in electrical systems, so-called ?>electrical energy ?>, can be stored directly or indirectly, depending on the means of the storage medium. Devices that store the electrical energy without conversion from electrical to another form of energy are called direct electrical energy storage devices. Two major energy storage devices are ultra-capacitor energy storage (UCES) and super-conducting magnetic energy storage (SMES). Devices that convert and store the electrical energy in another form of energy are called indirect electrical energy storage devices. Electro-mechanical storage devices are flywheels, compressed air energy storage (CAES) and hydro pumped energy storage (HPES). Electrochemical energy storage devices are electrochemical batteries and fuel cells. Above mentioned energy storage technologies and devices are briefly described in this chapter. Different fields of application are also discussed.