Co_0.85Se hollow spheres constructed of ultrathin 2D mesoporous nanosheets as a novel bifunctional-electrode for supercapacitor and water splitting

Hollow spheres of Co_0.85Se constructed by two-dimensional (2D) mesoporous ultrathin nanosheets were synthesized via simple and cost effective approach. Their bifunctional electrocatalytic-supercapacitive properties were obtained simultaneously due to synergistic effects between macroscopic morphological features and microscopic atomic/electronic structure of Co_0.85Se. The as-synthesized hollow spheres of Co_0.85Se that are constructed by 2D mesoporous ultrathin nanosheets exhibit inspiring electrochemical performance for supercapacitor, presenting maximum energy density at high power density (54.66 Wh·kg^-1 at 1.6 kW·kg^-1) and long cycle stability (88% retention after 8, 000 cycles). At the same time, the hollow spheres of Co_0.85Se constructed by 2D mesoporous ultrathin nanosheets display excellent catalytic performance for oxygen evolution reaction (OER) due to special structure, high surface area and mesoporous nature of sheets, which achieve low overpotential (290 mV at 10 mA·g^-1) and low Tafel slope (81 mV·dec^-1) for long-term operation (only 7.8% decay in current density after 9 h). It could be envisioned that the proposed simple approach will pave a new way to synthesize other metal chalcogenides for energy conversion and storage technology.