Hybrid capacitive deionization (HCDI) has emerged to address the shortcomings of CDI in high-salinity solutions. Cathodes for HCDI with active Faradaic reaction ability are desirable. In this work, we propose a facile method to prepare hollow echinus-like NiCo₂O₄ nanocrystals as high-performance cathodes for HCDI. It was determined that the specific surface area of NiCo₂O₄ is ∼70.74 m² g⁻¹ with the mean pore diameter of 20.72 nm. The electrochemical analysis demonstrated that NiCo₂O₄ possesses high specific capacity, remarkable capacitance retention and low impedance. As a cathode for HCDI, NiCo₂O₄ exhibited high salt removal capacity of 44.3 mg g⁻¹ with charge efficiency of 98.7% at 1.2 V in an NaCl solution with initial conductivity of 1000 μS cm⁻¹. This is attributed to the definite redox reaction between NiCo₂O₄ and sodium ions during the charge/discharge process. Moreover, the HCDI behavior of NiCo₂O₄ in various solutions containing K⁺, Na⁺ and Mg²⁺ was explored, illustrating that the ionic radius has priority in HCDI. Furthermore, the salt removal capacity of the NiCo₂O₄ electrode after 20 cycles was still ∼42.9 mg g⁻¹, which was 97.5% of the initial value, proving its prominent regeneration.

中文翻译：

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空心棘手类NiCo2O4纳米晶体用于混合电容去离子的可行性

混合电容去离子（HCDI）已经出现，以解决高盐度解决方案中CDI的缺点。具有主动法拉第反应能力的HCDI阴极是理想的。在这项工作中，我们提出了一种简便的方法来制备空心的像海chin一样的NiCo ₂ O ₄纳米晶体作为HCDI的高性能阴极。经测定，NiCo ₂ O ₄的比表面积为〜70.74m ² g ^-1，平均孔径为20.72nm 。电化学分析表明，NiCo ₂ O ₄具有较高的比容量，显着的电容保持率和低阻抗。NiHC ₂ O作为HCDI的阴极_图4在NaCl溶液中在初始电导率为1000μScm ^{-1的情况下}在1.2V下显示出44.3mg g ^-1的高除盐能力和98.7％的充电效率。这归因于在充电/放电过程中NiCo ₂ O ₄和钠离子之间的确定的氧化还原反应。此外，探索了NiCo ₂ O ₄在含K ⁺，Na ⁺和Mg ^2+的各种溶液中的HCDI行为，表明离子半径在HCDI中具有优先权。此外，经过20个循环后，NiCo ₂ O ₄电极的除盐能力仍然约为42.9 mg g^-1，是初始值的97.5％，证明了其显着的再生。