Temperature controlled diffusion of hydroxide ions in 1D channels of Ni-MOF-74 for its complete conformal hydrolyzing to hierarchical Ni(OH)2 supercapacitor electrodes
Temperature controlled diffusion of hydroxide ions in 1D channels of Ni-MOF-74 for its complete conformal hydrolyzing to hierarchical Ni(OH)2 supercapacitor electrodes
复制标题
Ni-MOF-74 的一维通道中氢氧根离子的温度控制扩散，使其完全保形水解为分层 Ni(OH)2 超级电容器电极
DOI：
10.1039/c9nr02555c
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发表时间：
2019
期刊：
影响因子：
6.7
通讯作者：
Daofeng Sun
中科院分区：
文献类型：
--
作者：
Shiyu Zhang;Zhendong Yang;Ke Gong;Ben Xu;Hao Mei;Haobing Zhang;Jiaxin Zhang;Zixi Kang;Youguo Yan;Daofeng Sun
MOF前驱体的共形水解法是一种低成本、高效率、大规模制备分级金属氢氧化物电极材料的方法。然而，由于正常的“由外而内”转换过程，完全的转换是具有挑战性的。在研究了具有规则一维通道的Ni-MOF-74的水解后，我们认为，根据处理温度的不同，前驱体外部和内部都可以同时发生向Ni(OH)2的转变。分子动力学模拟表明，较高的温度削弱了OH-−离子的空间效应，促进了规则通道中的扩散，从而实现了从Ni-MoF-74到Ni(OH)2的完全转变。首次证明了MOF的一维通道被用于Ni-MOF-74到Ni(OH)2电极材料的完全共形水解。同时，我们还做了开创性的工作，说明了完全共形水解是提高MOF衍生的Ni(OH)2电极超级电容器性能的关键。在优化条件下制备的Ni(OH)2电极在1Ag−1电流密度下的比容量为713.2 Cg−1，比在其他温度下制备的Ni(OH)2电极的比容量提高了至少28%。对制得的Ni(OH)2电极的循环伏安和交流阻抗谱分析表明，由于不完全水解，电极内残留的MOF显著影响了OH-−的扩散长度和扩散效率，大大降低了超级电容器的性能。
Conformal hydrolysis of MOF precursors is a promising strategy to prepare hierarchical metal hydroxide electrode materials on a large scale with low cost and high efficiency. However, a complete transformation is challenging due to the normal “outside-in” conversion process. After studying the hydrolysis of Ni-MOF-74, which has regular 1D channels, we suggest that the transformation to Ni(OH)2 can occur simultaneously outside and within the precursor depending on the treatment temperature. Molecular dynamics simulations reveal that a higher temperature weakens the steric effects of OH− ions and facilitates the diffusion in the regular channels, and therefore, a complete transformation from Ni-MOF-74 to Ni(OH)2 is achieved. It is for the first time demonstrated that the 1D channels of MOFs are utilized for the complete conformal hydrolysis of Ni-MOF-74 to Ni(OH)2 electrode materials. Meanwhile, we also perform pioneering work illustrating that the complete conformal hydrolysis is the key to the improved supercapacitor performances of the MOF-derived Ni(OH)2 electrodes. The prepared Ni(OH)2 electrode under the optimized conditions has a specific capacity of 713.2 C g−1 at a current density of 1 A g−1, which is at least 28% larger than those of the Ni(OH)2 prepared at other temperatures. The detailed analyses based on CV and EIS of the obtained Ni(OH)2 electrodes indicate that the residual MOFs within electrodes due to incomplete hydrolysis significantly influence the diffusion length and diffusion efficiency of OH−, drastically lowering the supercapacitor performances.