Hydrogen generation during reverse electrodialysis – The effect of temperature variations from 10 to 40oC

The use of salinity gradient power to generate hydrogen alongside electricity is of increasing interest. In this work the effect of temperature (10–40 °C) on the generation of both forms of energy during reverse electrodialysis is studied using both experiments and mathematical modelling. It is observed that under both short circuit and peak power conditions, increasing the temperature of the entire system has little advantage over an increase in temperature of the electrode rinse solution alone. At peak power conditions, an increase in temperature of the entire system from 20 °C to 40 °C increases power generation from 0.33 to 0.54 W.m⁻²-membrane, while an increase to 40 °C of the electrode alone provides 0.46 W.m⁻²-membrane, when an anode solution of pH 13.7 is used. However, as the electrode rinse solution can be readily recycled and is smaller in volume, the thermal power required to maintain this temperature (21 W.m⁻²-membrane) is two orders of magnitude lower than that required to heat up all streams (2200 W.m⁻²-membrane) as these only pass through the system once. Regardless, this thermal energy demand is significantly higher than that recovered from the reverse electrodialysis process and so this approach would only be viable if waste heat was available. Simulations show that operating with an anode solution of neutral pH further reduces the power generation to 0.13 W.m⁻²-membrane at 20 °C, a third of the value observed experimentally, and even less than the pumping energy required for operation.