Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 11, Issue 2, Pages 2082-2092Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.8b19035
Keywords
nickel cobalt chalcogenide; pseudocapacitance; interface structural design; geometrical-site dependence; all-solid-state asymmetric supercapacitor
Funding
- Fundamental Research Funds for the Central Universities [2018JBZ107, 2018RC022, 2017JBM068, S18I00010, S17I00010, S16C00010]
- 1000 Youth Talents plan project of Beijing Jiaotong University
- Excellent One Hundred project of Beijing Jiaotong University
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Spinel NiCo2X4 (X = O or S), comprising two geometrical cobalt ions, Co2+ in the tetrahedral site (Co-Td(2+)) and Co3+ in the octahedral site (Co-Oh(3+)), has been widely evaluated as a promising pseudocapacitor electrode material. Previous literature mainly demonstrated that much higher specific capacitance of NiCo2S4 than that of NiCo2O4 was ascribed to the higher electronic conductivity. However, we argue that only a small amount of capacitance can be induced by the electronic conductivity, while the significance of electrochemical active species in these system has long been ignored. Here, we propose that geometrical-site-dependent pseudocapacitive activity will generate enhanced specific capacitance through the interface structural design. It reveals that specific capacitance of NiCo2S4 (1862 F g(-1) at 4 A g(-1)) is 50% higher than that of NiCo2O4 (1230 F g(-1) at 4 A g(-1)), which is derived from the designed increase of Co-Td(2+) ions (cobalt ions in the tetrahedral site) in NiCo2S4. These results have significant implications for the design and optimization of the electrochemical properties of transition-metal-based pseudocapacitors.
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