We report the evolution of superconductivity in an FeSe thin flake with systematically regulated carrier concentrations by the liquid-gating technique. With electron doping tuned by the gate voltage, high-temperature superconductivity with an onset at 48 K can be achieved in an FeSe thin flake with T_{c} less than 10 K. This is the first time such high temperature superconductivity in FeSe is achieved without either an epitaxial interface or external pressure, and it definitely proves that the simple electron-doping process is able to induce high-temperature superconductivity with T_{c}^{onset} as high as 48 K in bulk FeSe. Intriguingly, our data also indicate that the superconductivity is suddenly changed from a low-T_{c} phase to a high-T_{c} phase with a Lifshitz transition at a certain carrier concentration. These results help to build a unified picture to understand the high-temperature superconductivity among all FeSe-derived superconductors and shed light on the further pursuit of a higher T_{c} in these materials.

Due to the strong reactivity of alkaline metals and the easy formation of the impurity phase, the superconducting transition temperature (T c ) of alkaline metals intercalated FeSe is usually limited to 45 K. To avoid the formation of impurity and improve the T c , we intercalate a more chemically inert organic ion (rather than the chemically reactive alkaline metals) into FeSe single crystal in this report. A new FeSe-based superconductor, namely (TBA) 0.3 FeSe, with T c of 50 K, is synthesized by intercalating FeSe single crystal with organic ion tetrabutyl ammonium (TBA + ) via an electrochemical intercalation method, which has the highest T c among FeSe-based bulk superconductors. The structure of the organic ion intercalated product consists of the alternate stacking of monolayer FeSe and the organic molecule. The superconductivity of (TBA) 0.3 FeSe is confirmed by both the magnetic susceptibility and the transport measurement. It is suggested that the chemically inert organic ion should play a key role in the enhancement of T c by avoiding the formation of impurity and disorder in FeSe plane as possible. We also suggest that the TBA + intercalated FeSe with well defined shape and higher T c offer a good playground for further bulk measurement investigation.

Lattice-oxygen-active (Bi_0.5Co_0.5)₂O₃ was successfully prepared through vacancy modulation and demonstrated great OER activity and performance.