Transition-metal doping engineering is an important strategy to adjust the structures of electrode materials (i.e., nickel selenides) for supercapacitors (SCs), and there remain great challenges to seek rational methods for realizing systematical doping. Herein, based on the open-channel structures of Ni_0.85Se and NiSe, a simple hydrothermal process combined with a universal ion exchange reaction was designed to fabricate Ni_0.85–xSe and NiSe nanoflowers doped by a series of 3d-transition-metal M²⁺ ions (M = Co, Cu, and Zn). Structure, morphology, and spectroscopic characterizations as well as Rietveld refinement were employed to research the phases, morphologies, and compositions of Ni_0.85–xSe, NiSe, M_xNi_0.85–xSe, and M_xNi_1–xSe. It was demonstrated that the unique structures of Ni_0.85Se and NiSe reduce the activation energies of M²⁺ ions transported through the interstitial lattice position, and the formation of Ni²⁺ vacancies decreases the steric hindrance of the insertion of divalent cations. Thus, Ni²⁺ was easily substituted by M²⁺ ions via cation exchange reaction at room temperature in water, realizing a 5–7% doping amount. Such transition-metal doping effects, from crystal structure modulation to electronic conductivity improvement, can effectively enhance the supercapacitor properties of Ni_0.85Se and NiSe. The Co_xNi_1–xSe electrode delivers specific capacitances of 918.8, 770.5, 617.5, 496.9, and 437.5 F g^–1 at 1, 2, 5, 7.5, and 10 A g^–1, respectively, which is the best among the eight electrodes. Besides, the “kick-out” cation exchange mechanism for the synthesis of M_xNi_0.85–xSe and M_xNi_1–xSe was discussed in detail. This work gives us feasible guidance to fabricate desired nickel selenides for SCs; moreover, the facile and universal cation exchange route can be expanded to purposefully design other cation-doped transition-metal selenides for energy storage.

中文翻译：

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用于超级电容器的 M2+ 掺杂硒化镍纳米花（M = Co、Cu 和 Zn）

过渡金属掺杂工程是调整超级电容器（SC）电极材料（即硒化镍）结构的重要策略，但寻求实现系统掺杂的合理方法仍面临巨大挑战。在此，基于Ni _0.85 Se和NiSe的开放通道结构，设计了一种简单的水热工艺与通用离子交换反应相结合来制造掺杂一系列3d过渡金属M的Ni _{0.85– x} ^{Se和NiSe纳米花。 2+}离子（M = Co、Cu 和 Zn）。采用结构、形貌和光谱表征以及 Rietveld 精修来研究 Ni _{0.85– x} Se、NiSe、M _x Ni _{0.85– x} Se 和 M _x Ni _{1– x} Se 的物相、形貌和成分。结果表明，Ni _{0.85 Se和NiSe的独特结构降低了通过间隙晶格位置传输的M} ²⁺离子的活化能，并且Ni ²⁺空位的形成降低了二价阳离子插入的空间位阻。因此，室温下在水中通过阳离子交换反应， Ni ^{2+很容易被M 2+}离子取代，实现了5%~7%的掺杂量。这种过渡金属掺杂效应，从晶体结构调制到电子电导率改善，可以有效增强Ni _0.85 Se和NiSe的超级电容器性能。 Co _x Ni _{1– x} Se 电极在 1、2、5、7.5 和 10 A g ^–1时的比电容分别为 918.8、770.5、617.5、496.9 和 437.5 F g ^–1，这是其中最好的。八个电极。此外，还详细讨论了合成M _x Ni _{0.85– x} Se和M _x Ni _{1– x} Se的“踢出”阳离子交换机制。这项工作为我们制造用于 SC 的所需硒化镍提供了可行的指导；此外，可以扩展简便且通用的阳离子交换路线，以有目的地设计其他用于储能的阳离子掺杂过渡金属硒化物。