CoNi hydroxides functionalized by borate ions with loose porous structure for the boosting of supercapacitor performance.

Developing low-cost and highly efficient electrode is essential for energy storage and conversion device. Herein, CoNi hydroxide nanosheets functionalized by borate ions (denoted as CoNiB) are fabricated via a convenient wet chemical process and subsequent hydrothermal boronization reaction. It is observed that rapid generation of hydrogen in the boronization process favors the formation of nanosheets. Moreover, hydrogen as a gas template is conductive to the formation of 3D loose porous structure which not only facilitates electrolyte penetration, but also exposes more active sites and accelerates the transport of ions and electrons. Resulting from the unique hierarchical microstructure, the optimized CoNi(1:1)B electrode delivers a high specific capacity of 283.25 mAh/g at 1 A g−1 as well as good rate capability (259.38 mAh/g at 20 A g−1) and stability. Besides, the assembled asymmetric supercapacitor (ASC) device with CoNi(1:1)B as positive electrode and activated carbon as negative electrode displays an outstanding energy density of 64.7 Wh kg−1 at 814.7 W·kg−1 with good cyclability (93 % after 15,000 cycles), verifying the great application potential of CoNi(1:1)B in practice. [Display omitted] • CoNiB nanosheets were fabricated by a facile two-step method. • The rate of hydrogen produced during boronization process would affect the morphology of the electrode. • The mesoporous structure of CoNiB enables high exposure of active sites and fast transport of ions and electrons. • BO 2 − functionalized CoNi hydroxides strengthens the electrochemical performance. • The assembled hybrid supercapactor exhibits excellent supercapacitor performance. [ABSTRACT FROM AUTHOR]