Mg batteries have potential advantages in terms of safety, cost, and reliability over existing battery technologies, but their practical implementations are hindered by the lack of amenable high-voltage cathode materials. The development of cathode materials is complicated by limited understandings of the unique divalent Mg2+ ion electrochemistry and the interaction/transportation of Mg2+ ions with host materials. Here, it is shown that highly dispersed vanadium oxide (V2O5) nanoclusters supported on porous carbon frameworks are able to react with Mg2+ ions reversibly in electrolytes that are compatible with Mg metal, and exhibit high capacities and good reaction kinetics. They are able to deliver initial capacities exceeding 300 mAh g(-1) at 40 mA g(-1) in the voltage window of 0.5 to 2.8 V. The combined electron microscope, spectroscopy, and electrochemistry characterizations suggest a surface-controlled pseudocapacitive electrochemical reaction, and may be best described as a molecular energy storage mechanism. This work can provide a new approach of using the molecular mechanism for pseudocapacitive storage of Mg2+ for Mg batteries cathode materials.