Redox flow devices are described in which at least one of the positive electrode or negative electrode-active materials is a semi-solid or is a condensed ion-storing electroactive material, and in which at least one of the electrode-active materials is transported to and from an assembly at which the electrochemical reaction occurs, producing electrical energy. The electronic conductivity of the semi-solid is increased by the addition of conductive particle to suspensions and the surface modification of the solid in semi-solids: coating the solid with a more electron conductive coating material to increase the power of the device. High energy density and high power redox flow devices are disclosed.