Amorphous nickel-cobalt bimetal-organic framework nanosheets with crystalline motifs enable efficient oxygen evolution reaction: Ligands hybridization engineering

Development of high-efficiency and low-cost electrocatalyst for oxygen evolution reaction(OER) is very important for use at alkaline water electrolysis.Metal-organic frameworks(MOF) provide a rich platform for designing multi-functional materials due to their controllable composition and ultra-high surface area.Herein,we report our findings in the development of amorphous nickel-cobalt bimetal-organic framework nanosheets with crystalline motifs via a simple "ligands hybridization engineering" strategy.These complexes' ligands contain inorganic ligands(H_2 O and NO_3) and organic ones,hexamethylenetetramine(HMT).Further,we investigated a series of mixed-metal with multi-ligands materials as OER catalysts to explore their possible advantages and features.It is found that the Ni doping is an effective approach for optimizing the electronic configuration,changing lattice ordering degree,and thus enhancing activities of HMT-based electrocatalysts.Also,the crystalline-amorphous boundaries of various HMTbased electrocatalyst can be easily controlled by simply changing amounts of Ni-precursor added.As a result,the optimized ultrathin(Co,0.3 Ni)-HMT nanosheets can reach a current density of 10 mA cm^(-2)at low overpotential of 330 mV with a small Tafel slope of 66 mV dec^(-1).Our findings show that the electronic structure changes induced by Ni doping,2 D nanosheet structure,and MOF frameworks with multiligands compositions play critical roles in the enhancement of the kinetically sluggish electrocatalytic OER.The present study emphasizes the importance of ligands and active metals via hybridization for exploring novel efficient electrocatalysts.

Crystalline and amorphous Mn0_(2)cathodes with open framework enable high-performance aqueous zinc-ion batteries

Currently,δ-Mn0_(2)is one of the popularly studied cathode materials for aqueous zinc-ion batteries(ZIBs)but impeded by the sluggish kinetics of Zn^(2+)and the Mn cathode dissolution.Here,we report our discovery in the study of crystalline/amorphous Mn0_(2)(disordered Mn0_(2)),prepared by a simple redox reaction in the order/disorder engineering.This disordered Mn0_(2)cathode material,having open framework with more active sites and more stable structure,shows improved electrochemical performance in 2 mol L^(-1)ZnSO_(4)/0.1 mol L^(-1)MnS0_(4)aqueous electrolyte.It delivers an ultrahigh discharge specific capacity of 636 mA·h·g^(-1)at 0.1 A·g^(-1)and remains a large discharge capacity of 216 mA·h·g^(-1)even at a high current density of 1 A·g^(-1)after 400 cycles.Hence disordered Mn0_(2)could be a promising cathode material for aqueous ZIBs.The storage mechanism of the disordered Mn0_(2)electrode is also systematically investigated by structural and morphological examinations of ex situ,ultimately proving that the mechanism is the same as that of the δ-Mn0_(2)electrode.This work may pave the way for the possibility of using the order/disorder engineering to introduce novel properties in electrode materials for high-performance aqueous ZIBs.