Co0.85Se hollow spheres constructed of ultrathin 2D mesoporous nanosheets as a novel bifunctional-electrode for supercapacitor and water splitting

Hollow spheres of Co0.85Se con structed by two-dime nsional(2D)mesoporous ultrathi nnanosheets were synthesized via simple and costeffective approach.Their bifunctional electrocatalytic-supercapacitive properties were obtained simultaneously due to synergistic effects betweenmacroscopic morphological features and microscopic atomic/electronic structure of Co0.85Se.The as-synthesized hollow spheres of Co0.85Sethat are con structed by 2D mesoporous ultrathin nanosheets exhibit in spiring 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).Atthe same time,the hollow spheres of Co0.85Se constructed by 2D mesoporous ultrathin nanosheets display excellent catalytic performaneefor oxygen evolution reaction(OER)due to special structure,high surface area and mesoporous nature of sheets,which achieve lowoverpotential(290 mV at 10 mA·g^-1)and low Tafel slope(81 mV·dec^-1)for Iong-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 chalcoge nides for energy conversionand storage technology.