Methods and devices for generating hydrogen gas with an electrocatalytic energy conversion cell by introducing a tri-transition metal phosphide catalyst at or on an electrode of the electrocatalytic energy conversion cell. The electrocatalytic energy conversion cell includes a first electrode including a tri-transition metal phosphide catalyst, such as Mo.sub.3P, a second electrode of an anodic material, an electrolyte disposed between the first electrode and the second electrode, and an electric potential source connected to both electrodes. Oxidation and reduction reactions, such as hydrogen evolution reactions, occur at the first electrode.