Assessment of semi-organic electrolytes for redox flow battery: Life cycle assessment as a tool to steer industry toward green chemistry

The world is facing the crucial energy transition and it will require a rapid growth of renewable energy production. Given the intermittency of renewable energy sources, though, the ambitious decarbonization goals cannot be achieved without the implementation of energy storage systems. In this scenario, redox flow batteries (RFBs) stand as promising candidates, where vanadium RFBs have been established as the technological standard. Nevertheless, RFB systems based on metals pose environmental, socio-political and ethical problems; therefore, research is seeking new safer and more sustainable redox materials, shifting attention from metalbased to organic-based electrolytes. To our knowledge, up to now, a complete environmental assessment of an organic or semi-organic electrolyte RFB has not been carried out. In this study, an organic/halogen RFB, based on anthraquinone disulfonic acid (AQDS) and hydrobromic acid (HBr), is analyzed via Life Cycle Assessment (LCA). Influence of materials production on environmental performance of the energy storage system is evaluated via two synthesis scenarios. Organic/halogen battery is compared with an equivalent vanadium-based battery, taken as a standard reference for RFB technology. The analysis shows that the production of a semi-organic RFB may represent a valid environmental alternative to full vanadium RFB, as smaller effects in several impact categories (ReCiPe 2016) are determined. Nevertheless, LCA analysis showed that the results are strongly dependent on the synthetic route adopted to produce AQDS. As a result of such work a greener chemical pathway is open toward the benefits of switching from metal to organic RFBs.