Enhanced Electrochemical and Photocatalytic Performance of Core–Shell CuS@Carbon Quantum Dots@Carbon Hollow Nanospheres

A controlled structural morphology, high specific surface area, large void space, and excellent biocompatibility are typical favorable properties in electrochemical energy storage and photocatalytic studies; however, a complete understanding about this essential topic still remains a great challenge. Herein, we have developed a new type of functionalized carbon hollow-structured nanospheres based on core–shell copper sulfide@carbon quantum dots (CQDs)@carbon hollow nanosphere (CHNS) architecture. This CuS@CQDs@C HNS is accomplished by a simple, scalable, <i>in situ</i> single-step hydrothermal method to produce the material that can be employed as an electrode for electrochemical energy storage and photocatalytic applications. Impressively, the CuS@CQDs@C HNS nanostructure delivers exceptional electrochemical energy storage characteristics with high specific capacitance (618 F g^–1 at a current density of 1 A g^–1) and an excellent rate capability with an extraordinary capacitance (462 F g^–1 at current density of 20 A g^–1) and long cycle life (95% capacitance retention after 4000 cycles). Further, the proposed photocatalyst exhibited superior photocatalytic activity under solar light due to the efficient electron transfer, which was revealed by photoluminescence studies. Such superior electrochemical and photocatalytic performance can be ascribed to the mutual contribution of CuS, CQDs, and CHNS and unique core–shell architecture. These results exhibit that the core–shell CuS@CQDs@C HNS nanostructure is one of the potential candidates for supercapacitors and photocatalytic applications

Hierarchical Heterostructures of Ultrasmall Fe₂O₃‑Encapsulated MoS₂/N-Graphene as an Effective Catalyst for Oxygen Reduction Reaction

In this study, a facile approach has been successfully applied to synthesize a hierarchical three-dimensional architecture of ultrasmall hematite nanoparticles homogeneously encapsulated in MoS₂/nitrogen-doped graphene nanosheets, as a novel non-Pt cathodic catalyst for oxygen reduction reaction in fuel cell applications. The intrinsic topological characteristics along with unique physicochemical properties allowed this catalyst to facilitate oxygen adsorption and sped up the reduction kinetics through fast heterogeneous decomposition of oxygen to final products. As a result, the catalyst exhibited outstanding catalytic performance with a high electron-transfer number of 3.91–3.96, which was comparable to that of the Pt/C product. Furthermore, its working stability with a retention of 96.1% after 30 000 s and excellent alcohol tolerance were found to be significantly better than those for the Pt/C product. This hybrid can be considered as a highly potential non-Pt catalyst for practical oxygen reduction reaction application in requirement of low cost, facile production, high catalytic behavior, and excellent stability

Highly Active and Durable Core–Shell fct-PdFe@Pd Nanoparticles Encapsulated NG as an Efficient Catalyst for Oxygen Reduction Reaction

Development of highly active and durable catalysts for oxygen reduction reaction (ORR) alternative to Pt-based catalyst is an essential topic of interest in the research community but a challenging task. Here, we have developed a new type of face-centered tetragonal (fct) PdFe-alloy nanoparticle-encapsulated Pd (fct-PdFe@Pd) anchored onto nitrogen-doped graphene (NG). This core–shell fct-PdFe@Pd@NG hybrid is fabricated by a facile and cost-effective technique. The effect of temperature on the transformation of face-centered cubic (fcc) to fct structure and their effect on ORR activity are systematically investigated. The core–shell fct-PdFe@Pd@NG hybrid exerts high synergistic interaction between fct-PdFe@Pd NPs and NG shell, beneficial to enhance the catalytic ORR activity and excellent durability. Impressively, core–shell fct-PdFe@Pd@NG hybrid exhibits an excellent catalytic activity for ORR with an onset potential of ∼0.97 V and a half-wave potential of ∼0.83 V versus relative hydrogen electrode, ultrahigh current density, and decent durability after 10 000 potential cycles, which is significantly higher than that of marketable Pt/C catalyst. Furthermore, the core–shell fct-PdFe@Pd@NG hybrid also shows excellent tolerance to methanol, unlike the commercial Pt/C catalyst. Thus, these findings open a new protocol for fabricating another core–shell hybrid by facile and cost-effective techniques, emphasizing great prospect in next-generation energy conversion and storage applications

Plasmonic Effect of Gold Nanostars in Highly Efficient Organic and Perovskite Solar Cells

Herein, a novel strategy is presented for enhancing light absorption by incorporating gold nanostars (Au NSs) into both the active layer of organic solar cells (OSCs) and the rear-contact hole transport layer of perovskite solar cells (PSCs). We demonstrate that the power conversion efficiencies of OSCs and PSCs with embedded Au NSs are improved by 6 and 14%, respectively. We find that pegylated Au NSs are greatly dispersable in a chlorobenzene solvent, which enabled complete blending of Au NSs with the active layer. The plasmonic contributions and accelerated charge transfer are believed to improve the short-circuit current density and the fill factor. This study demonstrates the roles of plasmonic nanoparticles in the improved optical absorption, where the improvement in OSCs was attributed to surface plasmon resonance (SPR) and in PSCs was attributed to both SPR and the backscattering effect. Additionally, devices including Au NSs exhibited a better charge separation/transfer, reduced charge recombination rate, and efficient charge transport. This work provides a comprehensive understanding of the roles of plasmonic Au NS particles in OSCs and PSCs, including an insightful approach for the further development of high-performance optoelectronic devices

Facile Method for the Preparation of Water Dispersible Graphene using Sulfonated Poly(ether–ether–ketone) and Its Application as Energy Storage Materials

A simple and effective method for the preparation of water dispersible graphene using sulfonated poly­(ether–ether–ketone) (SPEEK) has been described. The SPEEK macromolecules are noncovalently adsorbed on the surface of graphene through π–π interactions. The SPEEK-modified graphene (SPG) forms an aqueous dispersion that is stable for more than six months. An analysis of the ultraviolet–visible spectra shows that the aqueous dispersion of SPG obeys Beer’s law and the molar extinction coefficient has been found to be 149.03 mL mg^–1 cm^–1. Fourier transform infrared, Raman, and X-ray photoelectron spectroscopy analyses confirm successful reduction and surface modification of graphene. An atomic force microscopy (AFM) analysis reveals the formation of a single layer of functionalized graphene. Transmission electron microscopy results are also in good agreement with the AFM analysis and support the formation of single-layer graphene. SPG shows good electrochemical cyclic stability during cyclic voltammetry and charge/discharge process when used as a supercapacitor electrode. A specific capacitance of 476 F g^–1 at a current density of 6.6 A g^–1 is observed for SPG materials

Mechanically Strong and Multifunctional Polyimide Nanocomposites Using Amimophenyl Functionalized Graphene Nanosheets

We report an effective way to fabricate mechanically strong and multifunctional polyimide (PI) nanocomposites using aminophenyl functionalized graphene nanosheet (APGNS). APGNS was successfully obtained through a diazonium salt reaction. PI composites with different loading of APGNS were prepared by <i>in situ</i> polymerization. Both the mechanical and electrical properties of the APGNS/PI composites were significantly improved compared with those of pure PI due to the homogeneous dispersion of APGNS and the strong interfacial covalent bonds between APGNS and the PI matrix. The electrical conductivity of APGNS/PI (3:97 w/w) was 6.6 × 10^–2 S/m which was about 10¹¹ times higher than that of pure PI. Furthermore, the modulus of APGNS/PI was increased up to 16.5 GPa, which is approximately a 610% enhancement compared to that of pure PI, and tensile strength was increased from 75 to 138 MPa. The water vapor transmission rate of APGNS/PI composites (3:97 w/w) was reduced by about 74% compared to that of pure PI

CdS-CoFe₂O₄@Reduced Graphene Oxide Nanohybrid: An Excellent Electrode Material for Supercapacitor Applications

CoFe₂O₄ nanospheres ornamented CdS nanorods were successfully assembled over the reduced graphene oxide nanosheets. Such hierarchical morphology established by field emission scanning electron microscopy and transmission electron microscopy studies, with high surface area offered a high specific capacitance of 1487 F g^–1 at a current density of 5 A g^–1 owing to fast diffusion of ions, facile transportation of electrons, and great synergism between the components, which led to reversible redox reactions. Furthermore, the electrode material has specific capacitance retention of 78% up to 5000 cycles, thus demonstrating its good reversibility and cyclic stability. The resulting CdS-CoFe₂O₄@reduced graphene oxide nanohybrid can deliver excellent electrochemical performance and can be a potential candidate for supercapacitor application

In Situ Synthesis of Thermochemically Reduced Graphene Oxide Conducting Nanocomposites

Highly conductive reduced graphene oxide (GO) polymer nanocomposites are synthesized by a well-organized in situ thermochemical synthesis technique. The surface functionalization of GO was carried out with aryl diazonium salt including 4-iodoaniline to form phenyl functionalized GO (I-Ph-GO). The thermochemically developed reduced GO (R-I-Ph-GO) has five times higher electrical conductivity (42 000 S/m) than typical reduced GO (R-GO). We also demonstrate a R-I-Ph-GO/polyimide (PI) composites having more than 10⁴ times higher conductivity (∼1 S/m) compared to a R-GO/PI composites. The electrical resistances of PI composites with R-I-Ph-GO were dramatically dropped under ∼3% tensile strain. The R-I-Ph-GO/PI composites with electrically sensitive response caused by mechanical strain are expected to have broad implications for nanoelectromechanical systems