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Transition-metal phosphides have been identified as effective materials for improving electrocatalytic hydrogen evolution. In this study, Ni2P, Co2P, and NiCoP yolk–shell structures were embedded in N- and P-doped carbon nanofibers (NPNFs) by controlling the heat-treatment procedure of the fiber precursors. The hydrogen evolution reaction (HER) activity of the samples was tested. The formation process of phosphides introduced a large number of surface defects that act as active sites to improve H2 evolution. NPNF embedding composite NiCoP particles exhibited better performance compared with Ni2P–NPNFs and Co2P–NPNF samples in acidic conditions. In the case of a molar ratio Ni : Co : P of 1 : 1 : 1, NiCoP-decorated NPNFs revealed the best HER performance, which is ascribed to the loading of NiCoP composite particles, which greatly increased the specific surface area. NiCoP–NPNFs exhibited overpotentials of 183 and 280 mV at current densities of 1 mA cm−2 and 10 mA cm−2, respectively, with a Tafel slope of 94.5 mV dec−1. [ABSTRACT FROM AUTHOR]