Recent years have witnessed a dramatic increase in the production of sustainable and renewable energy. However, the electrochemical performances of the various systems are limited, and there is an ...intensive search for highly efficient electrocatalysts by more rational control over the size, shape, composition, and structure. Of particular interest are the studies on single‐atom catalysts (SACs), which have sparked new interests in electrocatalysis because of their high catalytic activity, stability, selectivity, and 100 % atom utilization. In this Review, we introduce innovative syntheses and characterization techniques for SACs, with a focus on their electrochemical applications in the oxygen reduction/evolution reaction, hydrogen evolution reaction, and hydrocarbon conversion reactions for fuel cells (electrooxidation of methanol, ethanol, and formic acid). The electrocatalytic performance is further considered at an atomic level and the underlying mechanisms are discussed. The ultimate goal is the tailoring of single atoms for electrochemical applications.
When less is more: Single‐atom electrocatalysts are characterized by high catalytic activity, selectivity, and maximum metal utilization. They hold great promise in various electrochemical applications, such as the oxygen reduction reaction, the hydrogen evolution reaction, and hydrocarbon conversion reactions for fuel cells.
Development of state-of-the-art electrocatalysts with inexpensive and commercially available materials to facilitate sluggish cathodic oxygen reduction reaction (ORR) is a key issue in the ...development of fuel cells and other electrochemical energy devices. Although great progress has been achieved in this area of research and development, there are still some challenges in both their ORR activity and stability. The emergence of graphene (GN) provides an excellent alternative to electrode materials and great efforts have been made to utilize GN-based nanomaterials as promising electrode materials for ORR due to the high electrical conductivity, large specific surface area, profuse interlayer structure and abounding functional groups involved. It should be noted that rational design of these GN-based nanomaterials with well-defined morphology also plays an important role in their electrochemical performance for ORR. Considerable attempts were achieved to construct a variety of heteroatom doped GN nanomaterials or GN-based nanocomposites, aiming at fully using their excellent properties in their application in ORR. In this critical review, in line with the material design and engineering, some recent advancements in the development of GN-based electrocatalysts for ORR in electrochemical energy devices (fuel cells and batteries) are then highlighted, including heteroatom-doped GN nanomaterials, GN-based nonprecious hybrid nanocomposites (GN/metal oxides, GN/N-M, GN/carbon nitride, etc.) and GN/noble metal nanocomposites.
Due to their unique structures and multifunctionalities, two-dimensional (2D) nanomaterials have aroused increasing interest in the construction of the novel biointerfaces for biosensing ...applications. Efforts in constructing novel biointerfaces led to exploit the more versatile and tunable graphene-like 2D nanomaterials (e.g. graphitic carbon nitride, boron nitride, transition metal dichalcogenides, and transition metal oxides) with various structural and compositional characteristics. This review highlights recent efforts in the design of graphene-like 2D nanomaterials and their derived biointerfaces and exploitation of their research on fluorescent sensors and a series of electrochemical sensors, including amperometric, electrochemiluminescence, photoelectrochemical and field-effect transistor sensors. Finally, we discuss some critical challenges and future perspectives in this field.
•Graphene-like 2D nanomaterials are promising in designing functional biointerfaces.•We review graphene-like 2D nanomaterial-based electrochemical sensors.•We review graphene-like 2D nanomaterial-based fluorescent sensors.•Rational design of novel graphene-like nanomaterial-based biointerfaces is summarized.
In this paper, we developed a green and facile approach to the synthesis of chemically converted graphene nanosheets (GNS) based on reducing sugars, such as glucose, fructose and sucrose using ...exfoliated graphite oxide (GO) as precursor. The obtained GNS is characterized with atomic force microscopy, UV-visible absorption spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and so on. The merit of this method is that both the reducing agents themselves and the oxidized products are environmentally friendly. It should be noted that, besides the mild reduction capability to GO, the oxidized products of reducing sugars could also play an important role as a capping reagent in stabilizing as-prepared GNS simultaneously, which exhibited good stability in water. This approach can open up the new possibility for preparing GNS in large-scale production alternatively. Moreover, it is found that GNS-based materials could be of great value for applications in various fields, such as good electrocatalytic activity toward catecholamines (dopamine, epinephrine, and norepinephrine).
The traditional luminol–H2O2 electrochemiluminescence (ECL) sensing platform suffers from self‐decomposition of H2O2 at room temperature, hampering its application for quantitative analysis. In this ...work, for the first time we employ iron single‐atom catalysts (Fe‐N‐C SACs) as an advanced co‐reactant accelerator to directly reduce the dissolved oxygen (O2) to reactive oxygen species (ROS). Owing to the unique electronic structure and catalytic activity of Fe‐N‐C SACs, large amounts of ROS are efficiently produced, which then react with the luminol anion radical and significantly amplify the luminol ECL emission. Under the optimum conditions, a Fe‐N‐C SACs–luminol ECL sensor for antioxidant capacity measurement was developed with a good linear range from 0.8 μm to 1.0 mm of Trolox.
Boosting luminescence: The traditional luminol–H2O2 electrochemiluminescence (ECL) sensing platform suffers from self‐decomposition of H2O2 at room temperature, hampering its application for quantitative analysis. Single‐atom iron boosts luminol ECL by in situ generating reactive oxygen species, achieving sensitive detection of antioxidants.
Display omitted
Recent years have witnessed a rapid development of the fluorescent carbon dots (CDs), due to their distinctive advantages of straightforward synthesis, excellent biocompatibility, low ...cost, and tunable optical properties. However, the widespread applications of CDs in biomedical theranostics, light harvesting, and photocatalysis are limited by the lack of emission and/or excitation in the red/near-infrared (NIR) region. Extensive explorations have been conducted to synthesize CDs with intensive red/NIR emission/excitation (red CDs) by rational design and ingenious synthesis to broaden their applications. This review emphasizes the most recent efforts in the development of CDs with intensive emission at a long wavelength, with a focus on the regulation methods for the optical properties of CDs, including particle size, surface state, and heteroatom doping. Key factors in processing red CDs, such as reaction solvent and precursors, are demonstrated. More importantly, employing polyaromatic and dye molecules as carbon sources is highlighted, which could further expand emission/excitation to the NIR region. The boosting applications of red CDs in white light-emitting diodes (WLEDs), biosensing, bioimaging, theranostics, and photocatalysis are demonstrated. Finally, the challenges and perspectives of red CDs are also discussed.
We propose an ingenious method for synthesizing cross-linked hollow fluorescent carbon nanoparticles (HFCNs) with green emission by simply mixing acetic acid, water, and diphosphorus pentoxide. This ...is an automatic method without external heat treatment to rapidly produce large quantities of HFCNs, in contrast to other syntheses of fluorescent carbon nanoparticles that required high temperature, complicated operations, or long reaction times. Characterizations of HFCNs through high-resolution transmission electron microscopy, infrared/Raman spectroscopy, and X-ray diffraction indicate that abundant small oxygenous graphite domains existed and endowed the HFCNs with fluorescent properties. After simple post-treatments, the cross-linked HFCNs can be used for cell-imaging applications. Compared with traditional dyes and CdTe quantum dots, HFCNs are the superior fluorescent bioimaging agent according to their low toxicity, stability, and resistance to photobleaching. The HFCNs were also applied to watermark ink and fluorescent powder, showing their promising potentials for further wide usage.
Highlights
Secondary-atom-doped strategy was proposed to synthesize single-atom electrocatalyst.
The increase in both the density of active sites and their intrinsic activity was achieved ...simultaneously.
The resultant single-atom catalyst shows outstanding ORR activity in acidic media.
Single-atom catalysts (SACs) with nitrogen-coordinated nonprecious metal sites have exhibited inimitable advantages in electrocatalysis. However, a large room for improving their activity and durability remains. Herein, we construct atomically dispersed Fe sites in N-doped carbon supports by secondary-atom-doped strategy. Upon the secondary doping, the density and coordination environment of active sites can be efficiently tuned, enabling the simultaneous improvement in the number and reactivity of the active site. Besides, structure optimizations in terms of the enlarged surface area and improved hydrophilicity can be achieved simultaneously. Due to the beneficial microstructure and abundant highly active FeN
5
moieties resulting from the secondary doping, the resultant catalyst exhibits an admirable half-wave potential of 0.81 V versus 0.83 V for Pt/C and much better stability than Pt/C in acidic media. This work would offer a general strategy for the design and preparation of highly active SACs for electrochemical energy devices.
PDF
