Transition metal oxides, as newly earth-abundant and low-cost catalysts, have been regarded as promising materials for electrocatalytic oxygen evolution. However, they are rarely used as an electrocatalyst in hydrogen evolution reaction (HER) due to the poor HER activity. Herein, we present a facile two-step method to synthesize P doped CoMoO4/RGO (P-CoMoO4/RGO) with different atomic ratios of Co2+/Co3+ through a simple phosphorization strategy by changing the mass of NaH2PO2. The effective P-doping into CoMoO4/RGO can modify the electronic properties and modulate the atomic ratio of Co2+/Co3+, which promotes the electron transfer and creates more activity sites. Therefore, the optimized P-CoMoO4/RGO with a relatively larger atomic ratio of Co2+/Co3+ shows superior HER performances in alkaline media, which affords a current density of 10 mA cm(-2) at a small overpotential of 90 mV and a low Tafel slope of 62 mV dec(-1 )along with having satisfactory long-term stability. This work provides a valuable route to enhance the HER activity of transition metal oxides. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.