Towards a more sustainable hydrogen energy production: Evaluating the use of different sources of water for chloralkaline electrolyzers

Water scarcity is becoming a serious threat for the implementation of energy storage devices based on hydrogen in the inland of dry regions, because of the difficulties in finding appropriate sources of water and the important environmental problem associated with the discharge of rejection saline streams produced during the purification of water. This becomes an opportunity for chloralkaline technology in which the quality of water used is lower than the required in other hydrogen production technologies. This work compares the performance of chloralkaline electrolyzers fed with different solutions of NaCl (from brackish water to brines) with that obtained feeding two natural water samples (seawater and porewater) and three processed waters (rejections streams of the electrodialysis, reverse osmosis of the porewater and a real rejection of the reverse osmosis of a vineyard). All tests were made with a lab-scale 3-D printed cell where, in addition, the performance of Ti/RuO2 and Pb/PbO2 anodes were compared, being always better the results obtained in the tests made with the Ti/RuO2 electrode. Results obtained indicate that efficiencies reached using these alternative sources are lower than those which can be reached using synthetic brines that, in turn, were very near to the standards reached in the chloralkaline industry. In the case of hydrogen production, the maximum values were obtained for seawater, reaching efficiencies proximate to 8.0 mg H2 (Wh)−1. Rejection streams of desalination processes were found to be less efficient, attaining values in the range 2 and 4 mg H2 (Wh)−1. Regarding the production of chlorine and caustic soda, better performances were reached again with seawater (161.7 mg Cl2 (Wh)−1 and 0.092 mg OH− (Wh)−1) and with the rejection of the electrodialysis, which also reached sound values of 90.4 mg Cl2 (Wh)−1 and 0.107 mg OH− (Wh)−1. Results obtained are promising and indicate a path that must be further worked for the implementation of a greener water management strategy in the hydrogen -based energy storage technology.