Carbon nanofibers served as nanoreactors for the design and construction of PtCo alloy carbon core-shell nanostructures with nitrogen doping (PtCo/NCNF) through a combination of electrospinning and nitrogen doping treatments. The PtCo/NCNF hybrid consists of PtCo alloy nanoparticles surrounded by a few of N-doped carbon layers, demonstrating a typical core-shell structures. The PtCo/NCNF hybrid can both served as electrode materials for electrocatalytic water splitting including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). For the HER performance, the PtCo/NCNF exhibits very small onset potential of 20 mV, an overpotential of 50 mV at a j (vs RHE) = 10 mA cm(-2) and Tafel slope of 30 mV dec(-1). The PtCo/NCNF hybrid also exhibits high OER activity with an onset potential of 310 mV, an overpotential of 400 mV at a j of 10 mA cm(-2) and a small Tafel slope of 76 mV dec-1. The high catalytic activities of PtCo alloy for HER and OER originate from the 3D hierarchical structures, well-dispersed PtCo alloy, high conductivity of NCNF, protection from the carbon-encapsulated structure, and the introduction of nitrogen. (C) 2016 Published by Elsevier Ltd.