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Electrocatalytic oxygen reduction to hydrogen peroxide (H2O2) is one of the most promising methods to replace the conventional anthraquinone route for the green and facile synthesis of H2O2. Owing to the outstanding electrochemical active surface area and fast charge transfer capability of carbon nanomaterials or nanostructures with different dimensions, such as 1D, 2D, and 3D, various strategies including nanostructure engineering, defect engineering, and interface engineering have been proposed to promote the catalytic activity of carbon‐based catalysts toward two‐electron (2e−) oxygen reduction reaction (ORR) for H2O2 generation over the past decade. In this review, the latest progress, major achievements, and prospects of the transition metal‐supported carbon with different dimensions for highly efficient electrochemical H2O2 preparation via the 2e− ORR process are summarized. The rational design principles and synthetic strategies of transition metal‐supported carbon are systematically introduced while the representative advances, the identification of active sites, and their possible catalytic mechanisms toward the H2O2 production are discussed. Finally, according to the current development stage and existing shortcomings of 2e– ORR catalysts for H2O2 production, the challenges and prospects of transition metal‐supported carbon with different dimensions are also summarized. [ABSTRACT FROM AUTHOR]

Transition metal single‐atom catalysts (SACs) are currently a hot area of research in the field of electrocatalytic oxygen reduction reaction (ORR). In this review, the recent advances in transition metal single‐atom supported by 2D materials as catalysts for ORR with high performance are reported. Due to their large surface area, uniformly exposed lattice plane, and adjustable electronic state, 2D materials are ideal supporting materials for exploring ORR active sites and surface reactions. The rational design principles and synthetic strategies of transition metal SACs supported by 2D materials are systematically introduced while the identification of active sites, their possible catalytic mechanisms as well as the perspectives on the future of transition metal SACs supported by 2D materials for ORR applications are discussed. Finally, according to the current development trend of ORR catalysts, the future opportunities and challenges of transition metal SACs supported by 2D materials are summarized. [ABSTRACT FROM AUTHOR]

In this study, nitrogen-rich carbon dots decorated graphene oxide (N- C dots/GO) hybrid, as a metal-free electrocatalyst for oxygen reduction reaction (ORR), is synthesized by a facile and low-cost hydrothermal treatment for the first time. Specifically, as a nitrogen-rich bridge-molecule, urea can trap free citric acid on planar planes, edges, and wrinkle sections of GO through amidation reaction in the initial stage. Then, polymer-like intermediates are in situ formed and carbonized to N- C dots on GO. Owing to the simultaneous N-doping into both C dots and GO characterized by XPS, as well as the formation of defective graphitic structures analyzed by Raman spectra, the as-prepared hybrid displays a remarkable electrocatalytic performance with more positive onset potential (0.13 V vs. Ag/AgCl) and high kinetic current density (up to 18.4 mA cm −2 at −0.70 V) comparable to commercial Pt/C catalyst. Furthermore, it demonstrates significantly higher catalytic efficiency (nearly 100% of four-electron ORR pathway) than those of N- C dots or N- C dots/GO mixture with an outstanding cyclic stability and superior methanol tolerance capability in alkaline solution. [ABSTRACT FROM AUTHOR]

Thermodynamically induced tensile stress in the perovskite film will lead to the formation of atomic vacancies, seriously destroying the photovoltaic efficiency stability of the perovskite solar cells (PSCs). Among them, cations and halide anions vacancies are unavoidable; these point vacancies are considered to be a major source of the ionic migration and perovskite degradation at the crystal boundary and surface of the perovskite films. Here, we use choline bromide to modify the perovskite film by occupying the atomic defects in the CsPbBr 3 perovskite film. The results show that the zwitterion quaternary ammonium ions and bromide ions in choline bromide can simultaneously occupy the Cs + cation and Br - anions vacancies in the perovskite film by the ionic bonding effect, for which the defect-state density on the surface of the perovskite film can be significantly reduced, leading to the effective enhancement of carrier lifetime. In addition, the residual stress at the crystal boundary can be effectively reduced by lowering the Young's modulus in the CsPbBr 3 perovskite film. As a result, the optimized device achieves a photoelectric conversion efficiency (PCE) of 9.06% with an increase of 41.1% compared to the control device with a PCE of 6.42%. Most importantly, the newborn thermal stress due to thermal expansion during heat working conditions can be transferred from the polycrystalline perovskite to the carbon layer by the matched Young's modulus, thus resulting in improved stability perovskite film under environmental conditions. The work provides new insights for preparing high-quality perovskite films with low defect-state density and residual stress.

We demonstrate, for the first time, a new method of fabricating hybrid MoS 2 /poly(ethyleneimine)-modified graphene oxide (PEI-GO) composites assembled through electrostatically charged interaction between the negatively charged MoS 2 nanosheets and positively charged PEI-GO in an aqueous solution. The GO can not only improve the electronic conductivity of the MoS 2 /PEI-GO composites, leading to an excellent charge-transfer network, but also hamper the restacking of MoS 2 nanosheets. The composition ratios between MoS 2 and PEI-GO were also optimized with the highest specific capacitance of 153.9 F g -1 where 96.0% of the initial specific capacitance remains after 6800 cycles. The specific capacitance of only 117.5 F g -1 was observed for the pure MoS 2 nanosheets, and 68.2% of the initial specific capacitance was achieved after 5000 cycles. The excellent electrochemical performance of the hybrid MoS 2 /PEI-GO composites was demonstrated by establishing an asymmetric supercapacitor with a MoS 2 /PEI-GO-based negative electrode and an activated-carbon positive electrode. The asymmetric supercapacitor provided a maximum capacitance of 42.9 F g -1 , and 93.1% of the initial capacitance was maintained after 8000 cycles. Furthermore, a MoS 2 /PEI-GO//activated-carbon asymmetric supercapacitor delivered an energy density of 19.3 W h kg -1 and a power density of 4500 W kg -1 , indicating the potential of the hybrid MoS 2 /PEI-GO composites in electrochemical energy storage applications.