Parallel to this, mixing entropy battery and ionic diode membrane (IDM) are two alternative devices which are also capable of extracting electricity from water salinity difference. Mixing entropy battery may be useful for small scale use, like in a car, in house hold etc., as it is similar to a nano battery which is made of N a2-xM n5O10. This is recharged in sea water and discharged in river water. Energy efficiency is very high (74%) for this method. On the other hand, IDM is an alternate to ion exchange membrane used in RED. IDM is fabricated using mesoporous carbon having pore size nearly 7nm over microporous alumina having pore size nearly 80nm. Using IDM, we may extract energy from salinity gradient with energy density up to 3.46W m -2 which is very high compare to organic membrane based RED (energy density range is 0.35 -0.93W m -2 ). In addition to this, IDM shows better ion selectivity which doesn't deteriorate with time. It is cost effective also.