Relevance. The search for alternative ways of energy production, including the use of hydrogen as an energy source. The efficient hydrogen production by electrolysis requires catalysts. Molybdenum-based materials, including molybdenum borides, are considered as promising analogs to replace expensive noble metal-based catalysts. In addition, the application of the original vacuum-free electric arc synthesis method allows increasing energy efficiency of molybdenum boride powders production. Aim. To obtain powders in molybdenum–boron system by vacuum-free electric arc method and to evaluate their electrocatalytic properties in the hydrogen evolution reaction. Object. Powder samples of the molybdenum–boron system obtained by varying the atomic ratio of molybdenum to boron from Mo/B=1/1 to 1/15 at fixed current strength of 200 A and arc discharge burning duration of 40 s. Methods. Vacuum-free electric arc synthesis; X-ray diffractometry (X-ray phase analysis); scanning electron microscopy; Raman spectroscopy; specific surface analysis method – BET; voltammetric analysis. Results. The authors have carried out the synthesis of molybdenum boride powders by the original electric arc method based on the arc discharge burning in open air. Scaling of the process was realized by increasing the mass of the processed raw material at constant energy characteristics. The authors investigated the electrocatalytic properties of the powder synthesized by a vacuum-free method in the molybdenum–boride system using an atmospheric DC arc discharge. The obtained characteristics are comparable with analogs and indicate a low catalytic activity in the reaction of hydrogen evolution. It is possible to use insignificant mass additions of platinum for further improvement of parameters of catalytic activity of the samples in terms of reducing the value of overvoltage.