Tuning Carbon Defect in Copper Single-Atom Catalysts for Efficient Oxygen Reduction.

Defect chemistry in carbon matrix shows great potential for promoting the oxygen reduction reaction (ORR) of metal single-atom catalysts. Herein, a modified pyrolysis strategy is proposed to tune carbon defects in copper single-atom catalysts (Cu-SACs) to fully understand their positive effect on the ORR activity. The optimized Cu-SACs with controllable carbon defect degree and enhanced active specific surface area can exhibit improved ORR activity with a half-wave potential of 0.897 VRHE , ultrahigh limiting current density of 6.5 mA cm-2 , and superior turnover frequency of 2.23 e site-1 s-1 . The assembled Zn-air batteries based on Cu-SACs can also show well-retained reversibility and voltage platform over 1100 h charge/discharge period. Density functional theory calculations reveal that suitable carbon defects can redistribute charge density of Cu-N4 active sites to weaken the O-O bond in adsorbed OOH* intermediate and thus reduce its dissociation energy. This discovery offers a universal strategy for fabricating superior single-atom catalysts with high-efficiency active sites toward energy-directed applications.

General metal-organic framework-derived strategy to synthesize yolk-shell carbon-encapsulated nickelic spheres for sodium-ion batteries.

Transition-metal compounds have attracted enormous attention as potential energy storage materials for their high theoretical capacity and energy density. However, the most present transition-metal compounds still suffer from severe capacity decay and limited rate capability due to the lack of robust architectures. Herein, a general metal-organic framework-derived route is reported to fabricate hierarchical carbon-encapsulated yolk-shell nickelic spheres as anode materials for sodium-ion batteries. The nickelic metal-organic framework (Ni-MOF) precursors can be in situ converted into hierarchical carbon-encapsulated Ni2P (Ni2P/C), NiS2 (NiS2/C) and NiSe2 (NiSe2/C) by phosphorization, sulfuration, and selenation reaction, respectively, and maintain their yolk-shell sphere-like morphology. The as-synthesized Ni2P/C sample can deliver much lower polarization and discharge platform, smaller voltage gap, and faster kinetics in comparison with that of the other two counterparts, and thus achieve higher initial specific capacity (3222.1/1979.3 mAh g-1) and reversible capacity of 765.4 mAh g-1 after 110 cycles. This work should provide new insights into the phase and structure engineering of carbon-encapsulated transition-metal compound electrodes via MOFs template for advanced battery systems.

A facile and simple microwave-assisted synthesis method for mesoporous ultrathin iron sulfide nanosheets as an efficient bifunctional electrocatalyst for overall water splitting.

The engineering of inexpensive, high-efficiency and stable electrodes related to both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desired for full water splitting devices to promote future advances in this energy technology. Therefore, a large surface area, rich in exposed surface atoms, and mesoporosity are very effective parameters in electrochemical reactions. Herein, we have, for the first time, synthesized free-standing mesoporous Fe3S4 nanosheets with a large surface area of 129.65 m2 g-1 through a microwave-assisted synthetic technique. Our present synthesis strategy demonstrates a facile and cost-effective method to overcome the obstacles of fabricating ultrathin two-dimensional graphene-like transition metal sulfide nanosheets. The as-synthesized Fe3S4 nanosheets are applied as both cathodic and anodic electrodes for full water electrolysis. Remarkably, Fe3S4 nanosheets can exhibit a small overpotential (η = 103 mV) to provide the required 10 mA cm-2 current density during the HER process. Meanwhile, a low overpotential of 230 mV is also exhibited for the OER process to allow a 10 mA cm-2 current density. Furthermore, the assembled full water splitting device can achieve potentials of 1.43 and 1.65 V at 10 and 100 mA cm-2 current densities, respectively, in an alkaline electrolyte with excellent cycling stability over 24 h. Our current study may provide an advanced channel for transition metal sulfide catalysts towards commercial water splitting applications.

Fluorophosphorus derivative forms a beneficial film on both electrodes of high voltage lithium-ion batteries.

Layered lithium-rich oxides, as a series of highly promising cathode material for lithium-ion batteries, attract extensive attention due to their high specific capacity and high working potential (4.6 V vs Li/Li+). However, the poor interface stability of the cathode and electrolyte seriously restricts their practical application. In this article, theoretical calculations, linear sweep voltammetry and cyclic voltammetry results indicate that tris (pentafluorophenyl) phosphine (TPFPP) is a potential dual-functional electrolyte additive to solve interface problems. The TPFPP additive can decompose preferentially on the surface of both electrodes and form uniform and stable protective films, which effectively inhibit the continuous decomposition of the electrolyte and significantly alleviate the dissolution of transition metal ions during cycling. Owing to the above effects, the capacity retention and coulombic efficiency of Li1.17Ni0.25Mn0.58O2 (LLO)/graphite (Gr) cells are improved from 62.6% and 97.7% to 90.6% and 99.8% after 200 cycles at 0.3 C (1 C = 300 mA g-1), respectively. This study provides a wide prospect for the application of lithium-rich materials in the future.