Ultrathin Ni(OH) 2 layer coupling with graphene for fast electron/ion transport in supercapacitor
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Published online 14 September 2020 | https://doi.org/10.1007/s40843-020-1427-0
Ultrathin Ni(OH)2 layer coupling with graphene for fast electron/ion transport in supercapacitor 1
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Xiaoyu Zhang , Hongsen Wang , Lingling Shui , Guofu Zhou , Xin Wang , Ruguang Ma and 3 Jiacheng Wang ABSTRACT Integration of fast electrochemical double-layer capacitance and large pseudocapacitance is a practical way to improve the overall capability of supercapacitor, yet remains challenging. Herein, an effective cyanogel synthetic strategy was demonstrated to prepare ultrathin Ni(OH)2 nanosheets coupling with conductive reduced graphene oxide (rGO) (rGO-Ni(OH)2) at ambient condition. Ultrathin Ni(OH)2 nanosheet with 3–4 layers of edge-sharing octahedral MO6 maximally exposes the active surface of Faradic reaction and promotes the ion diffusion, while the conductive rGO sheet boosts the electron transport during the reaction. Even at −1 30 A g , the optimal sample can deliver a specific capacitance −1 of 1119.52 F g , and maintain 82.3% after 2000 cycles, demonstrating much higher electrochemical capability than bare Ni(OH)2 nanosheets. A maximum specific energy of −1 −1 44.3 W h kg (148.5 W kg ) is obtained, when assembled in a two-electrode system rGO-Ni(OH)2//rGO. This study provides an insight into efficient construction of two-dimensional hybrid electrodes with high performance for the new-generation energy storage system. Keywords: two-dimensional nanomaterials, Ni(OH)2 nanosheet, graphene, cyanogel synthetic strategy, supercapacitor
INTRODUCTION Energy storage system has drawn unprecedented interests in academia and industry, owing to the ever-increasing demand for back-up power sources, large-scale storage of sustainable energy, electric vehicles, and portable electronic devices [1–6]. Among them, supercapacitors with high power density and exceptional cycle stability are
especially attractive for worldwide researchers. Based on the reaction mechanism, two types of supercapacitors are well defined, pseudocapacitors and electrochemical double-layer capacitors (EDLCs) [7,8]. EDLCs store energy by reversible ion adsorption at the electrolyte/electrode surface, which highly depends on the specific surface area. In contrast, pseudocapacitors work through Faradaic redox reactions both on and near the surface of the electroactive materials, which usually have larger capacitance than that of EDLCs [9–11]. However, the relatively low energy density is a common bottleneck for both types of supercapacitors, severely limiting their widespread applications. To address this key issue, extensive studies have been done to develop high-performance electrode materials, including conducting polymers [12,13], heteroatomdoped carbon materials [14–19], transition metal phosphates [20], and transition metal oxides/hydroxides [21– 27]. Lin et al. [28] reported a nitrogen-doped mesoporous carbon, of which the specific capacitance can reach to −1 −1 −1 855 F g at 1 A g in 0.5 mol L H2SO4 solution with the −1 −1 −1 specific energy of 41
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