Optimised electrolyte, membrane, and electrode to be integrated in the prototype (July 2022 – Month 33/43)

Result from partners CIC energiGUNE, UAM, CNRS, CTECH, UWB, and PFES.

Result has been achieved in July 2022 in month 33 of the project

The HIGREEW project sets out to design, build, and demonstrate a prototype of a new high energy density generation of Aqueous Organic Redox Flow Battery (AORFB) based on a water-soluble low-cost organic electrolyte and featuring low-cost components and long service life.

  • Objective: The development of high-performance materials and the combination of those in a single cell set-up as a demonstrator to confirm the compatibility of the components to be later employed in the following WPs.
  • Research1-electrolytes) The electrolyte plays a key role in the definition of the redox flow battery and system. In addition, to define completely the energy module of the system, the physico-chemical properties of the electrolyte determine to a large extent the characteristics and the cost of the power module. Different active materials and electrolyte formulations have been screened before final selection. For the final selection of materials to be implemented in the HIGREEW prototype not only performance aspects have been considered, but also the availability of raw materials, the production process, the environmental impact, the cell performance, and the lifetime have been taken into account. 2-membrane) membranes are a critical component of RFBs as they largely determine the economic viability of these devices. Different membranes have been evaluated. Both commercial and modified commercial membranes have been considered. The availability of materials, the environmental impact and cost, the cell performance, and the durability of the membranes have been considered for the selection. 3-electrodes) Electrodes suitable for the HIGREEW prototype are carbon and graphite felts, materials exhibiting high void space fraction (>90%) and high specific surface area. However, these materials’ electrochemical properties have been known to be extremely sensitive to their surface state, which is altered via activation treatments. In order to target the best possible operating conditions for the batteries, it is therefore of interest to be able to thoroughly quantify and characterize the kinetics of redox couples promoted in HIGREEW project on a wide selection of carbon felts. The ultimate selection of the electrodes is based on the good compatibility with the active materials
  • Result: 1-electrolytes) Organic compounds have been studied to be applied as active materials based on their electrochemical properties and large-scale application, including safety and cost. Thus, viologen and ferrocyanide derivatives have been chosen. Aiming at cost-effective electrolyte formulations based on environmentally sustainable materials, a mixed electrolyte solution that meet all operational requirements in terms of viscosity (< 10 cP), thermal stability (0-50 ºC) and stability has been selected. Using a mixed electrolyte has a disadvantage on the consumption of extra active materials (sleeping active materials) but allows for remixing and rebalancing of the battery. The effect of permeability over time has been considered over the use of additional material which to some extent is mitigated by the low cost of those compounds. The exact electrolyte formulation, active material concentration, and supporting electrolyte content, have been defined based on cell performance results. 2-membrane) Membrane FS830 has been selected for the prototype based on the availability of the material for the prototype and the low ASR of this membrane for the combination with mixed electrolyte. 3-electrodes) SGL GFD4.6 EA with thermal activation provided by Sigracell has been selected for the prototype considering the robustness of the material, the good response to electrolyte active materials, and the availability and cost of the felts. Evaluation of HIGREEW membranes and electrodes stability was confirmed attending to the lack of degradation evidence in the performed experiments.
    Finally, selected materials were incorporated into a flow battery, and the single cell demonstrator with optimized felt compression was tested for more than 1000 cycles. Results from cell testing show good performance and promising stability for further development of the technology.
  • What will it be used for:the indicated materials are considered optimal to progress toward prototype development.
  • Impact:It has been confirmed that a set of components electrolyte-electrode-membrane developed in the first stage fulfils the project targets. A highly stable system, with negligible capacity decay based on low-cost electrolyte-membrane-electrode tandem has been achieved.