Brightly red fluorescent carbon dots are synthesized hydrothermally and dissolved in diluted hydrochloric acid solution. Such carbon dots exhibit excitation-independent emission at about 620 nm with quantum yield over 10%, which is visible in daylight. After the carbon dots solution is sprayed to the fingerprints on various solid substrates and dried in air, clear fingerprints can be seen under an ultraviolet lamp and stay stable for 1 day. Detailed characterizations suggest that during the drying process, the coffee-ring effect and the electrostatic interactions between the carbon dots and the fingerprint residues prevent the typical aggregation-induced fluorescence quenching of carbon dots.

3-5 folds or more amounts of carbon materials are required to fill the capacitance gap between the positive/negative electrodes, which finally restrict the whole energy densities of the devices. To improve electrochemical capacitances of carbon materials, three main strategies have been investigated thoroughly: enlarging specific surface areas, [19] constructing porous structures, [20,21] and introducing pseudocapacitive reactions. [22] But each strategy is not perfect. When the surface areas and the pore volumes are improved, the tap densities of electrodes will be reduced. Moreover, enhancing pseudocapacitance by modifying too many functional groups will decrease the whole conductivity and stability of electrode materials. [23] In the present work, we suggest a new concept of building electron-rich regions on the electrode surface, so as to adsorb more cations and accelerate the charge transfer. As a result, the capacitance of carbon materials will be increased reasonably without sacrificing the density, conductivity, and stability of the whole electrode. However, this idea brings a new challenge because the desired groups with abundant electrons (like phosphate groups) are usually difficult to be modified on the carbon materials. In order to resolve this problem, we used carbon dots (CDs, sub-10 nm) [24,25] with desired groups as the guest, and the commercial polyacrylamide (PAM) hydrogel as the host. After calcination on the host-guest composites, we obtained new carbon frameworks which have abundant electron-rich regions, large surface areas, and appropriate porous structures in the meantime. The optimal sample exhibits a specific capacitance up to 468, 510, and 438 F g −1 in alkaline, acidic, and neutral electrolytes, respectively. When it is fabricated into a hybrid supercapacitors with the positive electrode material Ni(OH) 2 /CNTs using an alkaline electrolyte, the mass ratio of positive/negative electrodes is less than 2, an energy density over 90 Wh kg −1 is realized successfully, and 100% of capacity retention rate is recorded after 10 000 cycles. This material also shows excellent performances in both acidic (PbO 2 as positive electrode) and neutral (LiMn 2 O 4 as positive electrode) systems. Detailed structural characterizations and theoretical calculations prove that the well-preserved phosphate/nitrogen groups from the CDs precursors can effectively modulate the electronic structure and form electron-rich regions on the electrode Hybrid supercapacitors generally show high power and long life spans but inferior energy densities, which are mainly caused by carbon negative electrodes with low specific capacitances. To improve the energy densities, the traditional methods include optimizing pore structures and modifying pseudocapacitive groups on the carbon materials. Here, another promising way is suggested, which has no adverse effects to the carbon materials, that is, constructing electron-rich regions on the electrode surfaces for absorbing cations as much as possible. For this aim, a series of hi...

Development and comparison of the latent fingerprints (LFPs) are two major studies in detection and identification of LFPs, respectively. However, integrated research studies on both fluorescent materials for LFP development and digital-processing programs for LFP comparison are scarcely seen in the literature. In this work, highly efficient red-emissive carbon dots (R-CDs) are synthesized in one pot and mixed with starch to form R-CDs/starch phosphors. Such phosphors are comparable with various substrates and suitable for the typical powder dusting method to develop LFPs. The fluorescence images of the developed LFPs are handled with an artificial intelligence program. For the optimal sample, this program presents an excellent matching score of 93%, indicating that the developed sample has very high similarity with the standard control. Our results are significantly better than the benchmark obtained by the traditional method, and thus, both the R-CDs/starch phosphors and the digital processing program fit well for the practical applications.

Non-noble metal-based bifunctional electrocatalysts for both oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) are an essential component of high-performance rechargeable Zn−air batteries (ZABs). Herein, we report a novel and simple method for preparing Co 9 S 8 nanoparticles embedded in N and S codoped carbon materials with aid of carbon dots (CDs). CDs play a key role in distributing Co 9 S 8 nanoparticles in the matrix uniformly and enhancing the specific surface area and the electric conductivity simultaneously. The obtained Co 9 S 8 / CD@NSC exhibits an excellent ORR and OER bifunctional catalytic activity and a great long-term durability, with a half-wave potential of 0.84 V versus reversible hydrogen electrode (RHE) for the ORR and a low potential of 1.62 V versus RHE at 10 mA cm −2 , which outperform the popular Pt/C and RuO 2 commercial catalysts. Moreover, the Co 9 S 8 /CD@NSC catalyst also displays a superior activity and cycling stability as a cathode material in ZABs, which is far better than Pt/C + RuO 2 mixture catalysts. Such a ZAB shows a low charge/discharge voltage gap of 0.62 V and great cycling stability over 125 h at 10 mA cm −2 .

Rational design and fabrication of advanced sulfur cathode is highly desirable for development of high performance lithium-sulfur (Li-S) batteries. Herein, we report Co(OH) 2 as a new stabilizer for the sulfur cathode by constructing cobalt hydroxidecovered sulfur/conductive carbon black (CCB) electrode with the help of thermal and hydrothermal treatments. In this composite (Co(OH) 2 @S/CCB), the sublimed sulfur is anchored in the CCB, followed by a uniform coating of Co(OH) 2 nanosheets. As cathode materials of lithium-sulfur batteries, the as-prepared Co(OH) 2 @S/CCB electrode exhibits remarkable electrochemical performances with a high capacity of 1026 mAh g -1 at 0.1 C (1 C=1675 mA g -1 ) and 829 mAh g -1 at 1 C. Moreover, it keeps high coulombic efficiencies above 97% after 200 cycles at 1 C, much higher than those of the S/CCB counterpart electrode (85%). After 200 cycles at 1 C, a high capacity retention of 71.2% is remained, better than that of the S/CCB electrode (20.2%). The enhanced performance is mainly due to Co(OH) 2 layer which helps to inhibit the shuttle diffusion of polysulfide, resulting in improved capacity retention and cycling life.

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This review summarizes the recent progress in the design and preparation of multiple electrochemical energy storage devices utilizing carbon dots, and elaborates the positive effects of carbon dots on the resulting electrodes and devices.

Tailored sulfur cathode is vital for the development of a high performance lithium-sulfur (Li-S) battery. A surface modification on the sulfur/carbon composite would be an efficient strategy to enhance the cycling stability. Herein, we report a nickel hydroxide-modified sulfur/conductive carbon black composite (Ni(OH)2@S/CCB) as the cathode material for the Li-S battery through the thermal treatment and chemical precipitation method. In this composite, the sublimed sulfur is stored in the CCB, followed by a surface modification of Ni(OH)2 nanoparticles with size of 1-2 nm. As a cathode for the Li-S battery, the as-prepared Ni(OH)2@S/CCB electrode exhibits better cycle stability and higher rate discharge capacity, compared with the bare S/CCB electrode. The improved performance is largely due to the introduction of Ni(OH)2 surface modification, which can effectively suppress the "shuttle effect" of polysulfides, resulting in enhanced cycling life and higher capacity.