摘要
Cobalt-based oxygenic compounds Co(OH)2,CoO and Co3 O4 are attractive for electrochemical energy storage owing to their high theoretical capacities and pseudocapacitive properties.Despite the great efforts to their compositional and morphological regulations,the performances to date are still quite limited owing to the low active surface area and sluggish charge transfer kinetics.Herein,different Co-based nanocrystals(Co-NCs)were conveniently anchored on the hierarchical nitrogen-doped carbon nanocages(hNCNCs)with high specific surface area and coexisting micro-meso-macropores to decrease the size and facilitate the charge transfer.Accordingly,a high specific capacity of1170 Fg^-1 is achieved at 2 Ag^-1 for the Co(OH)2/hNCNCs hybrid,in which the capacitance of Co(OH)2(2214 F gco(OH)2)is approaching to its theoretical maximum(2595 Fg^-1),demonstrating the high utilization of active materials by the hybridization with N-doped nanocarbons.This study also reveals that these Co-NCs store/release electrical energy via the same reversible redox reaction despite their different pristine compositions.This insight on the energy storage of Co-based nanomaterials suggests that the commonly-employed transformation of the Co-NCs from Co(OH)2 to CoO and Co3 O4 on carbon supports is unnecessary and even could be harmful to the energy storage performance.The result is instructive to develop high-energy-density electrodes from transition metal compounds.
Co(OH)2、CoO和Co3O4等钴基化合物因具有高理论容量和赝电容性质而备受关注.但受限于活性表面积小、电荷传输缓慢等原因,钴基纳米材料的实际储能性能却有限.本文以我们前期开发的具有大比表面积、高导电性和微孔-介孔-大孔共存的分级结构氮掺杂碳纳米笼(hNCNCs)为载体,成功构建了晶粒尺寸小、电荷转移快的系列钴基纳米晶-hNCNCs复合材料,有效地提高了活性材料的利用率.其中,Co(OH)2/hNCNCs在2 Ag ^-1下表现出1170 F g^-1的高比容量,基于活性物种Co(OH)2的比电容高达2214 Fg^-1,接近其理论值(2595 Fg^-1).研究发现,具有不同组成的Co(OH)2、CoO和Co3O4纳米晶通过相同的可逆氧化还原反应存储/释放电能.这种新的储能机理表明将碳基载体上的活性物种Co(OH)2转化为CoO或Co3O4的操作是非必要的,甚至可能损害其储能性能.本研究可为开发过渡金属化合物基高能量密度电极材料提供借鉴.
基金
jointly supported by the National Key Research and Development Program of China(2017YFA0206500and 2018YFA0209103)
the National Natural Science Foundation of China(21832003,21773111,51571110 and 21573107)
the Fundamental Research Funds for the Central Universities(020514380126)
