Energy production by salinity exchange in polyelectrolyte-coated electrodes. Temperature effects

It is now indisputable that clean energy sources must fulfill the increase in the energy demand of all societies. For such a challenge, every small step towards utilizing any renewable source counts. One prominent example is that of blue energy or energy production based on salinity gradients, existing in all kinds of environments, both natural and industrial. Specifically, the present work is based on electric energy that can be extracted when salty and fresh solutions are exchanged in the presence of a pair of electrodes. It has been previously reported that the use of interfaces coated with charged polymers (yielding a deformable or soft interface) offers considerable advantage over bare electrodes, and the combination of Donnan and double layer potentials can play in favour of larger energy and power generation. In this work we show that the temperature dependence of both contributions can produce an even higher performance, and the consideration of this feature is the key point of this work. If the low ionic concentration solution (fresh water) is at higher temperature than that of the high concentration one (salty water), both energy and power increase as compared to those attained at equal temperatures. This behaviour is investigated with activated carbon electrodes coated with cationic and anionic polyelectrolytes to form an electrochemical cell in contact successively with room temperature salt water and warm fresh water. When the difference between the two amounts to about 40 degrees C, the energy and power can increase by almost 80%, a very significant improvement that paves the way to further progress in salinity gradient power production.