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Uniform Ni C nanodots dispersed in ultrathin N-doped carbon nanosheets were successfully prepared by carburization of the two dimensional (2D) nickel cyanide coordination polymer precursors. The Ni C based nanosheets have lateral length of about 200 nm and thickness of 10 nm. When doped with Fe, the Ni C based nanosheets exhibited outstanding electrocatalytic properties for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). For example, 2 at % Fe (atomic percent) doped Ni C nanosheets depict a low overpotential (292 mV) and a small Tafel slope (41.3 mV dec ) for HER in KOH solution. An outstanding OER catalytic property is also achieved with a low overpotential of 275 mV and a small Tafel slope of 62 mV dec in KOH solution. Such nanodot-incorporated 2D hybrid structures can serve as an efficient bifunctional electrocatalyst for overall water splitting.

A facile and bottom-up approach has been presented to prepare 2D Ni-MOFs based on cyanide-bridged hybrid coordination polymers. After thermally induced sulfurization and selenization processes, Ni-MOFs were successfully converted into NiS and NiSe2 nanoplates with carbon coating due to the decomposition of its organic parts. When evaluated as anodes of Li-ion batteries (LIBs) and Na-ion batteries (NIBs), NiS and NiSe2 nanoplates show high specific capacities, excellent rate capabilities, and stable cycling stability. The NiS plates show good Li storage properties, while NiSe2 plates show good Na storage properties as anode materials. The study of the diffusivity of Li(+) in NiS and Na(+) in NiSe2 shows consistent results with their Li/Na storage properties. The 2D MOFs-derived NiS and NiSe2 nanoplates reported in this work explore a new approach for the large-scale synthesis of 2D metal sulfides or selenides with potential applications for advanced energy storage.

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Inspired by the remarkable adhesion of mussel, dopamine, a mimicking adhesive molecule, has been widely used for surface modification of various materials ranging from organic to inorganic. However, dopamine and its derivatives are expensive which impede their application in large scale. Herein, we replaced dopamine with low-cost catechol and polyamine (only 8% of the cost of dopamine), which could be polymerized in an alkaline solution and deposited on the surfaces of various materials. By using this cheap and simple modification method, polypropylene (PP) separator could be transformed from hydrophobic to hydrophilic, while the pore structure and mechanical property of the separator remained intact. The uptake of electrolyte increased from 80% to 270% after the hydrophilic modification. Electrochemical studies demonstrated that battery with the modified PP separator had a better Coulombic efficiency (80.9% to 85.3%) during the first cycle at a current density of 0.1 C, while the discharging current density increased to 15 C and the discharge capacity increased by 1.4 times compared to the battery using the bare PP separator. Additionally, the modification allowed excellent stability during manifold cycles. This study provides new insights into utilizing low-cost chemicals to mimic the mussel adhesion and has potential practical application in many fields.

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Transition metal selenides have been attracting significant attention owing to their high conductivity and theoretical capacity. In this article, the N-doped carbon (NDC)-coated Ni 1.8 Co 1.2 Se 4 nanoparticles encapsulated in NDC nanoboxes are prepared from the bi-metal organic framework (Ni 3 [Co(CN) 6 ] 2 ·6H 2 O, Ni-Co BMOF) after the selenization reaction and carbon coating. When used as an anode material for sodium-ion batteries, the prepared anode material delivers excellent rate performance (211 and 153 mA h g −1 at ultrahigh current densities of 30 and 50 A g −1 , respectively) and good cycling performance (379.3 mA h g −1 at 0.5 A g −1 after 100 cycles). More importantly, it also exhibits superior sodium-ion full cell (SIFC) performance when coupled with a high-voltage Na 3 V 2 (PO 4 ) 2 O 2 F cathode recently self-made by the authors. The fabricated SIFC gives an energy density up to 227 W h kg −1 and the capacity retention of above 97.6% even after 60 cycles at 0.4 A g −1 in a voltage range of 1.2-4.3 V at 25 °C. Moreover, the low-temperature (from 25 to −25 °C) Na-storage performance of the fabricated SIFC is also studied.