Performance of an environmentally benign acid base flow battery at high energy density

Abstract

SummaryAn increasing fraction of energy is generated by intermittent sources such as wind and sun. A straightforward solution to keep the electricity grid reliable is the connection of large-scale electricity storage to this grid. Current battery storage technologies, while providing promising energy and power densities, suffer from a large environmental footprint, safety issues, and technological challenges. In this paper, the acid base flow battery is re-established as an environmental friendly means of storing electricity using electrolyte consisting of NaCl salt. To achieve a high specific energy, we have performed charge and discharge cycles over the entire pH range (0-14) at several current densities. We demonstrate stable performance at high energy density (2.9 Wh L −1 ). Main energy dissipation occurs by unwanted proton and hydroxyl ion transport and leads to low coulombic efficiencies (13%-27%). Although the CGFB has low environmental impact, energy density and power density are too low to be attractive for practical application. KEYWORDSIn this work, we show that the energy density and power density of the CGFB can be improved by implementing a bipolar membrane. The studied system is an energy storage system based on a reversible acid-base reaction. In this system called acid base flow battery (AB-FB), energy is being stored in acid and base solutions created by the bipolar membrane. The charge step of the AB-FB is similar to the well-known bipolar membrane electro dialysis (BPM-ED). BPM-ED converts NaCl solutions into NaOH and HCl solutions by spending electric power to separate protons and hydroxyl ions from water dissociation from the bipolar ----------------------------------------------------This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Electrochemical carbon dioxide capture to close the carbon cycle

“…When a sufficient electric field is applied, the BPM dissociates water into OHand H + , producing a controllable ∆pH over the membrane as shown in Figure (10a) and b [85][86][87][88][89][90]. Using a bipolar membrane, the thermodynamic minimum voltage required for this water dissociation is 0.829 volts for a produced ∆pH = 14.…”

The Acid–Base Flow Battery: Sustainable Energy Storage via Reversible Water Dissociation with Bipolar Membranes

“…Current commercial membranes are designed only for dissociating water, while operating BPMs under water recombination (which occurs during the discharging process in the ABFB), has been so far overlooked by membrane scientists and manufacturers. Hence, when using commercial BPMs in ABFB the discharge current densities of the battery are today limited by membrane delamination [ 25 , 30 ], and are thus relatively low. In particular, van Egmond et al reported successful stable performance (up to 9 cycles) for a 1 M HCl-1 M NaOH battery operated at 15 A/m 2 discharge current density [ 25 ], while Xia et al noted water accumulation in the BPM junction when operating a 0.75 M HCl–0.75 M NaOH battery at discharge current densities above 200 A/m 2 [ 30 ].…”

“…The electrode compartments can be rinsed with a different solution, for example Na 2 SO 4 [ 30 ], to avoid the production of Cl 2 at the anode (i.e., the oxidation product when using only NaCl solutions at the electrodes). The electrodes do not necessarily need to be of metal, but can also be of more environmentally friendly carbon material [ 25 ], in which case an electrode rinse solution with a redox couple must be used. Using such electrode rinse solution has the advantage of opposite electrode reactions occurring at the anode and cathode, meaning that by recirculating the rinse solution no net change of the chemical composition occurs, and the thermodynamic voltage of the electrode reactions is zero.…”

“…Therefore, the ABFB charging step is bipolar membrane electrodialysis (BMED), and the discharging step bipolar membrane reverse electrodialysis (BMRED). Introducing BPMs (and, consequently, an additional pH gradient) in the battery increases the energy density of the battery significantly, i.e., by more than three times compared to the concentration gradient flow battery [ 25 ].…”

“…However, because the electrode compartments were separated from the rest of the cell with CEMs, the battery performance suffered from iron ion migration from the electrode towards the base compartment, thus causing precipitation of iron salts. Van Egmond et al demonstrated stable ABFB operation (at 150 A/m 2 current density during charge, and 15 A/m 2 during discharge) over a wide pH range (pH = 0–14), and analyzed the contribution of different energy loss sources [ 25 ]. They estimated the total energy lost by co-ion transport to be the biggest factor, contributing 39–65% of the total losses.…”