ABSTRACT
Most catalysts cannot accelerate uninterrupted conversion of polysulfides, resulting in poor long-cycle and high-loading performance of lithium-sulfur (Li-S) batteries. Herein, rich p-n junction CoS2 /ZnS heterostructures embedded on N-doped carbon nanosheets are fabricated by ion-etching and vulcanization as a continuous and efficient bidirectional catalyst. The p-n junction built-in electric field in the CoS2 /ZnS heterostructure not only accelerates the transformation of lithium polysulfides (LiPSs), but also promotes the diffusion and decomposition for Li2 S the from CoS2 to ZnS avoiding the aggregation of lithium sulfide (Li2 S). Meanwhile, the heterostructure possesses a strong chemisorption ability to anchor LiPSs and superior affinity to induce homogeneous Li deposition. The assembled cell with a CoS2 /ZnS@PP separator delivers a cycling stability with a capacity decay of 0.058% per cycle at 1.0 C after 1000 cycles, and a decent areal capacity of 8.97 mA h cm-2 at an ultrahigh sulfur mass loading of 6 mg cm-2 . This work reveals that the catalyst continuously and efficiently converts polysulfides via abundant built-in electric fields to promote Li-S chemistry.
ABSTRACT
Amorphous metal-organic framework (MOF) materials have drawn extensive interest in the design of high-performance electrocatalysts for use in the electrochemical oxygen evolution reaction. However, there are limitations to the utilization of amorphous MOFs due to their low electrical conductivity and unsatisfactory stability. Herein, a novel amorphous-crystalline (AC) heterostructure is successfully constructed by synthesizing a crystalline metal sulfide (MS)-embedded amorphous Ni0.67Fe0.33-MOF, namely an MS/Ni0.67Fe0.33-MOF. It exhibits excellent catalytic performance (a low overpotential of 248 mV at 10 mA cm-2 with a small Tafel slope of 50 mV decade-1), durability, and stability (only 8% degradation of the current density at a constant voltage after 24 h). This work thus sheds light on the engineering of highly efficient catalysts with AC heterointerfaces for optimizing water-splitting systems.
ABSTRACT
The preparation of low-cost and high-activity oxygen evolution reaction (OER) catalysts is a technical bottleneck in the field of electrolysis of water to produce hydrogen. Amorphous metal-organic frameworks (MOFs) with low-cost transition metals have attracted increasing attention in the catalytic field, yet metal atoms that are the main active sites are still ambiguous. Here, we synthesized a series of amorphous ternary Fex(NiCu)3-x-MOFs via an ultrasonic method. The optimal amorphous FeNiCu-MOF is found to be able to supply a current density of 10 mA cm-2 merely at a low overpotential of 260 mV with a small Tafel slope of 61 mV dec-1 and exhibits high durability over 24 h. Moreover, density functional theory (DFT) calculations show that the Fe atoms are the main active sites for the OER in the FeNiCu-MOF. This work shows that amorphous ternary MOFs have great potential for application in OER electrocatalysts due to the multiple synergistic effects and amorphous MOF structures.
