A method of producing a pre-selenized (selenium-preloaded) active cathode layer for a rechargeable alkali metal-selenium cell; the method comprising: (a) preparing an integral layer of mesoporous structure having pore sizes from 0.5 nm to 50 nm (preferably from 0.5 nm to 5 nm) and a specific surface area from 100 to 3,200 m2/g; (b) preparing an electrolyte comprising a solvent and a selenium source; (c) preparing an anode; and (d) bringing the integral layer and the anode in ionic contact with the electrolyte and imposing an electric current between the anode and the integral layer (serving as a cathode) to electrochemically deposit nanoscaled selenium particles or coating on the graphene surfaces. The selenium particles or coating have a thickness or diameter smaller than 20 nm (preferably 90% or even >95%).