Nanostructured early-transition-metal nitrides possess high capacitances that are consistent with a pseudocapacitive storage mechanism. Prior publications suggest that the mechanism involves the interactions between protons and the metal. This paper describes the use of in-situ small angle neutron scattering as a function of the potential applied to the electrode and ex-situ physical and electrochemical techniques to determine specific details regarding the storage mechanism for high-surface-area Mo nitride (γ-Mo2N) in 0.1 mol dm−3 H2SO4 electrolyte. The results demonstrate that the pseudocapacitance involves a proton-coupled electron transfer (2e- for every H+) via micropores, which is accompanied by the reduction/oxidation of Mo. These results suggest that capacitances in excess of 1500 Fg−1 in 1.2 V could be achieved in aqueous acidic electrolytes.