Layered transition metal dichalcogenides (TMDs) such as molybdenum diselenides (MoSe2) have raised much research interest for its excellent electrochemical and catalytic properties. In this study, a new nanocomplex (MoSe2/HPCFs) was constructed by anchoring MoSe2 nanosheets onto nitric-acid modified Polyacrylonitrile carbon nanofibers (HPCFs) via one pot hydrothermal treatment, followed by calcination. To target issues triggered by energy storage, lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) and hydrogen evolution reactions (HER) were deployed to comprehensively assess the electrochemical and electrocatalytic performances of the binder-free MoSe2/HPCFs electrodes. When investigated as anode material for LIBs and SIBs, the MoSe2/HPCFs electrodes delivered initial discharge capacities of 862.7 and 586.6 mA h g(-1), respectively, at a current density of 0.1 A g(-1). The MoSe2/HPCFs electrodes also displayed outstanding electrocatalytic activity in HER, requiring only 106 mV of overpotential to reach a current density of 10 mA cm(-2), all the while having a small Tafel slope of 61 mV dec(-1). This study's findings suggest that the synergistic combination of HPCFs fibers and MoSe2 nanosheets could significantly enhance the electrochemical and electrocatalytic performances of Li-ion/Na-ion batteries and HER, which could provide a feasible and easy solution in designing high-performance flexible devices for energy storage and conversion.