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Surface alloys using transition metal elements have been regarded as one of the intelligent choices in electrocatalytic hydrogen generation. Herein, hierarchical Ni-Mo bimetallic surface alloy @ microporous 3D Ni support is fabricated by controlled electrodeposition followed by annealing to exhibit hydrogen evolution performance comparable to Pt benchmark, both in the acidic and alkaline media. Precisely controlled formation of Mo-layer on Ni-foam during the electrodeposition through underpotential causes the formation of surface alloy, Ni-Mo. The optimized electrocatalyst shows low overpotentials of 58 mV and 50 mV at a current density of 10 mA cm-2 in 0.5 M H2SO4 and 1 M NaOH solutions, respectively. Moreover, the developed electrocatalyst also shows low Tafel slopes of 58.8 mV dec-1 and 86.8 mV dec-1 in acidic and alkaline media, respectively. The density functional theory based approach suggests that the free-energy of hydrogen adsorption-desorption is lower for a lesser number of Mo layers deposited on the Ni-matrix to keep it very close to that of Pt. [ABSTRACT FROM AUTHOR]