While nickel phosphide is a highly attractive catalyst for the hydrogen evolution reaction, its preparation requires either high temperature or the use of highly toxic PH3 directly or indirectly. Herein, we demonstrate that H2 plasma activated red phosphorus enables the synthesis of self-supported Ni2P nanosheet (Ni2P/NF) arrays on commercial nickel foam from a NiO/NF precursor at only 250 °C. Highly reactive atomic H in the plasma induces dissociation of the P4 molecules, yielding an acid stable electrode with excellent hydrogen evolution activity and good mechanical strength.