Coaxial titanium vanadium nitride core-sheath nanofibers (VN@TiN) with mesoporous structure are fabricated and explored as efficient Pt-free counter electrodes (CEs) for Dye-sensitized Solar Cells (DSCs). For these nanofibers, the TiN core is covered with a sheath of VN, and their boundary is a continuous series of TiVN solid solutions. Both electrochemical tests and density functional theory computations indicate that the combination of core-sheath nanofibers structure design and the formation of TiVN solid solutions significantly enhance the triiodide reduction activity of parental TiN and VN. Impressively, the devices employing VN@TiN core-sheath nanofibers CEs yield 8.98%, which is 17% higher than that device with Pt CE (7.64%). The design strategy developed in this study may promote a boom in a promising alternative CE for future large-scale application of DSCs. (C) 2018 Elsevier Ltd. All rights reserved.