This study explores the use of molybdenum phosphide (MoP) as an efficient and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) in both acidic and alkaline media. The research highlights the potential of phosphorization to modify the properties of molybdenum, leading to distinct activities and stabilities. Experimental results and theoretical calculations using density functional theory (DFT) show that MoP exhibits high activity and stability due to its ability to achieve nearly zero binding energy for hydrogen at certain hydrogen coverages. The study also demonstrates that MoP outperforms other catalysts, such as MoS2 and Ni2P, in terms of current density and Tafel slope, making it a promising alternative to noble metals like Pt. The findings suggest that phosphorization can transform molybdenum from a poor catalyst into an active and stable catalyst for HER, opening new avenues for the development of earth-abundant and inexpensive catalysts.This study explores the use of molybdenum phosphide (MoP) as an efficient and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) in both acidic and alkaline media. The research highlights the potential of phosphorization to modify the properties of molybdenum, leading to distinct activities and stabilities. Experimental results and theoretical calculations using density functional theory (DFT) show that MoP exhibits high activity and stability due to its ability to achieve nearly zero binding energy for hydrogen at certain hydrogen coverages. The study also demonstrates that MoP outperforms other catalysts, such as MoS2 and Ni2P, in terms of current density and Tafel slope, making it a promising alternative to noble metals like Pt. The findings suggest that phosphorization can transform molybdenum from a poor catalyst into an active and stable catalyst for HER, opening new avenues for the development of earth-abundant and inexpensive catalysts.