Evaluation of hydrogen evolution reaction activity of molybdenum nitride thin films on their nitrogen content

We report preparation and electrochemical properties of molybdenum nitride Mo_xN (x from 1 to 2) and Mo thin films prepared by the magnetron sputtering. We adjusted amount of nitrogen during reactive sputtering, to achieve different ratios of Mo:N in the films. We could prepare well-defined and extremely smooth films. We determined hydrogen evolution reaction (HER) activity and other kinetics parameters such as Tafel slopes and exchange current densities. Corrosion stability at anodic potentials was also evaluated from onset potentials of dissolution of prepared films. We found that Mo_xN thin film HER activity dependence on nitrogen content in the film exhibits volcano-like diagram. From XRD measurements we identified several phases present in the films from pure Mo to β-Mo₂N and δ-MoN. We find that β-Mo₂N phase has the highest HER activity. Stability of studied nitrides at anodic potentials increases with increasing content of nitrogen. Mo films sputtered at high substrate temperatures exhibit higher HER activity than Mo_xN systems. In addition, with increasing substrate temperature during sputtering, HER activity of pure Mo thin films increases.