Potassium ion batteries (PIBs) are considered as promising alternatives to sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs), which can be ascribed to the rich abundance of potassium resources, low cost and high safety. Currently, the development of anode materials for PIBs is still confronted with many serious problems, such as low capacity and poor cycling performance. In this work, sheet-like MoSe₂ implanted on the surfaces of carbon nanofibers is successfully synthesized through a simple electrospinning and selenization route. MoSe₂/C-700 (selenization at 700 °C) maintains high structural stability and facilitates the intercalation/deintercalation of K⁺, which benefits from one-dimensional nanofibers with good structural stability and MoSe₂ with an expanded interlayer spacing. As a whole, MoSe₂/C-700 as an anode for PIBs shows a high reversible capacity of 316 mA h g⁻¹ at 100 mA g⁻¹ over 100 cycles. It also displays a specific capacity of 81 mA h g⁻¹ at 100 mA g⁻¹ over 100 cycles when it first serves as an electrode material for nonaqueous potassium-based battery–supercapacitor hybrid (BSH) devices.