Solid materials with special atomic and electronic structures are deemed desirable platforms for establishing clear relationships between surface/interface structure characteristics and electrochemical activity. In this work, nickel boride (Ni_xB) and nickel boride/graphene (Ni_xB/G) are chosen as positive materials of supercapacitors. The Ni_xB/G displays higher specific capacitance (1822 F g^–1) than that of Ni_xB (1334 F g^–1) at 1 A g^–1, and it still maintains 1179 F g^–1 at 20 A g^–1, suggesting the high rate performance. The asymmetric supercapacitor device (Ni_xB/G//activated carbon) also delivered a very high energy density of 50.4 Wh kg^–1, and the excellent electrochemical performance is ascribed to the synergistic effect of Ni_xB, Ni(BO₂)₂, and graphene that fully enhances the diffusion of OH^– and the electron transport. During the cycles, the prepared ultrafine Ni_xB nanoparticles will be gradually in situ converted into β-Ni(OH)₂ which has a smaller particle size than that prepared by other methods. This will enhance the utilization of Ni(OH)₂ and decrease the ion diffusion distance. The electron deficient state of B in Ni(BO₂)₂ amorphous shell will make it easy to accept extra electrons, enhancing the adsorption of OH^– at the shell surface. Moreover, Ni(BO₂)₂ makes strong adhesion between Ni_xB (or β-Ni(OH)₂) and graphene and protects the core structure in a stable state, extending the cycle life. The above properties of Ni_xB/G endow the electrode good capacitive performance.

中文翻译：

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硼化镍/金属硼酸盐的界面工程及其对高能量密度不对称超级电容器的影响

具有特殊原子和电子结构的固体材料被认为是在表面/界面结构特征与电化学活性之间建立明确关系的理想平台。在这项工作中，选择硼化镍（Ni _x B）和硼化镍/石墨烯（Ni _x B / G）作为超级电容器的正极材料。Ni _x B / G在1 A g ^–1处比Ni _x B（1334 F g ^–1）表现出更高的比电容（1822 F g ^–1），在20 A g时仍保持1179 F g ^–1的比电容。^–1，表示高速率性能。非对称超级电容器装置（Ni _xB / G ///活性炭）还提供了非常高的50.4 Wh kg ^–1能量密度，并且出色的电化学性能归因于Ni _x B，Ni（BO ₂）₂和石墨烯的协同作用，充分增强了OH的扩散^–和电子传输。在循环过程中，制得的超细Ni _x B纳米颗粒将逐渐原位转化为比其他方法制得的粒径更小的β-Ni（OH）₂。这将提高Ni（OH）₂的利用率并减少离子扩散距离。Ni（BO ₂）₂中B的电子缺乏态无定形壳将可以很容易地接受额外的电子，提高OH的吸附^-在外壳表面。而且，Ni（BO ₂）₂使Ni _x B（或β-Ni（OH）₂）与石墨烯之间具有很强的附着力，并以稳定的状态保护芯结构，从而延长了循环寿命。Ni _x B / G的上述特性赋予电极良好的电容性能。