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Developing low-cost and high-efficiency electrocatalytic materials for the oxygen evolution reaction (OER) is crucial and urgent for water splitting. Here, we demonstrate a novel OER electrocatalyst (S–NiFe(CN)5NO) prepared by constructing a bimetallic metal–organic framework (MOF) and in situ doping of sulfur. The generation of Ni–Fe active sites upgrades the structural stability and electronic conductivity of the MOF. The sulfur doping further optimizes the electronic structure, thus lowering the energy barriers for the OER. As a result, the S–NiFe(CN)5NO catalyst possesses excellent catalytic activity towards the OER with an ultralow overpotential of 274 mV at 10 mA cm−2 and a small Tafel slope of 54.4 mV dec−1 in 1.0 M KOH. Moreover, the activity can be well maintained after 1000 cycles, indicating superior electrochemical stability. The electrocatalytic performance of S–NiFe(CN)5NO is far superior to that of pristine NiFe(CN)5NO and the advanced RuO2 catalyst. It is revealed that the improved OER catalytic properties are attributed to the synergetic effect of bimetallic active sites and sulfur species in S–NiFe(CN)5NO. Density functional theory calculations explain that S doping can accelerate electron transport and optimize OER paths. This work is meaningful for the study of many multivariate MOFs as OER catalysts and can be extended to other energy-related fields. [ABSTRACT FROM AUTHOR]

A novel binder-free electrode for lithium–oxygen batteries has been prepared by electrodepositing a Co3O4 layer onto a pretreated TiO2 fiber mesh, formed on nickel foam by an electrospinning method. The Co3O4 depositing layer is composed of Co3O4 nanoflakes, forming a uniform flower-like porous structure. The Co3O4 nanoflakes within the depositing layer provide a large amount of catalytic active sites for oxygen evolution and reduction reactions. The three-dimensional porous network of the Co3O4 depositing layer can not only facilitate the transportation of ions and electrolyte within the electrode, but also provide plenty of space to accommodate Li2O2 species formed during the discharge process. The Co3O4 spheres embedded in the TiO2 fiber mesh, formed by the treatment of a suspension of cobaltammine precipitate, function as anchors to prevent the detachment of the Co3O4 layer from the current collector, resulting in excellent structural and cycling stability. Only a slight specific capacity decay is observed at full discharge/charge after 80 cycles. This work demonstrates the important factors in the preparation of binder-free cathodes for high performance lithium–oxygen batteries. [ABSTRACT FROM AUTHOR]

Iron oxides are regarded as promising anodes for both lithium-ion batteries (LIBs) and potassium-ion batteries (KIBs) due to their high theoretical capacity, abundant reserves, and low cost, but they are also facing great challenges due to the sluggish reaction kinetics, low electronic conductivity, huge volume change, and unstable electrode interphases. Moreover, iron oxides are normally prepared at high temperature, forming large particles because of Ostwald ripening, and exhibiting low electronic/ionic conductivity and unfavorable mechanical stability. To address those issues, herein, we have synthesized ultra-small Fe 3 O 4 nanodots encapsulated in layered carbon nanosheets (Fe 3 O 4 @LCS), using the coordination interaction between catechol and Fe 3+ , demonstrating fast reaction kinetics, high capacity, and typical capacitive-controlled electrochemical behaviors. Such Fe 3 O 4 @LCS nanocomposites were derived from coordination compounds with layered structures via van der Waals's force. Fe 3 O 4 @LCS-500 (annealed at 500 °C) nanocomposites have displayed attractive features of ultra-small particle size (∼5 nm), high surface area, mesoporous and layered feature. When used as anodes, Fe 3 O 4 @LCS-500 nanocomposites delivered exceptional electrochemical performances of high reversible capacity, excellent cycle stability and rate performance for both LIBs and KIBs. Such exceptional performances are highly associated with features of Fe 3 O 4 @LCS-500 nanocomposites in shortening Li/K ion diffusion length, fast reaction kinetics, high electronic/ionic conductivity, and robust electrode interphase stability., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)