Redox Flow Batteries: Materials, Design and Prospects

Abstract

The implementation of renewable energy sources is rapidly growing in the electrical sector. This is a major step for civilization since it will reduce the carbon footprint and ensure a sustainable future. Nevertheless, these sources of energy are far from perfect and require complementary technologies to ensure dispatchable energy and this requires storage. In the last few decades, redox flow batteries (RFB) have been revealed to be an interesting alternative for this application, mainly due to their versatility and scalability. This technology has been the focus of intense research and great advances in the last decade. This review aims to summarize the most relevant advances achieved in the last few years, i.e., from 2015 until the middle of 2021. A synopsis of the different types of RFB technology will be conducted. Particular attention will be given to vanadium redox flow batteries (VRFB), the most mature RFB technology, but also to the emerging most promising chemistries. An in-depth review will be performed regarding the main innovations, materials, and designs. The main drawbacks and future perspectives for this technology will also be addressed.

Tungsten oxide/fullerene-based nanocomposites as electrocatalysts and parasitic reactions inhibitors for VO2+/VO2+ in mixed-acids

“…To further analyze the reversibility (electron transfer rate) of the VO 2+ /VO 2 + redox reaction, Nicholson’s method for quasi-reversible reactions was also used to determine the standard rate constant, k 0 41 , 42 . This was done by plotting a dimensionless kinetic parameter, Ψ, which is a function of ΔE p , against ν −1/2 using equations S2.…”

“…The third generation of vanadium redox flow batteries uses mixed acid electrolyte composed of HCl and H 2 SO 4 to enhance the performance of the batters and increase the solubility and stability of vanadium ions in the electrolyte. However, the parasitic chlorine evolution reaction become one of the drawbacks of the third generation and hence finding a way to suppress the chlorine evaluation reaction became the concern of several research groups 41 .…”

Strategies for Improving Solubility of Redox‐Active Organic Species in Aqueous Redox Flow Batteries: A Review

“…F/m at 20 °C is another important property of water, which characterizes the strong ability of water to solvate solute molecules and separate ions [34] . Because of the hydrophobic nature of organic compounds, the majority of unmodified redoxmers exhibit inferior solubility in aqueous media, thus incorporating a hydrophilic group increases the affinity of redox molecules and water, resulting in high solubility [4,14b,35] . The discussion in this section is organized around different hydrophilic functional groups.…”

“…Despite these advantages, VRFBs also suffer from drawbacks such as high cost (especially the vanadium electrolyte, which accounts for over 40 % of the total cost), corrosion due to the strongly acidic electrolyte, and low energy density [14] . Other RFB systems, such as iron‐chromium, iron‐titanium, vanadium‐bromine, and polysulfide‐bromine, have also been proposed and studied for decades; however, limitations such as poor reversibility, slow reaction rates, and crossover preclude their further application [14b,15] . To alleviate these issues, organic redox compounds have been proposed as alternatives to traditional inorganic electrolytes [1b,c,2c,16] .…”

Organic Electroactive Molecules for Li-Organic Hybrid Redox Flow Battery Application

“…Consequently, an RFB machine's strength density is decided via means of attention, the number of electrons transferred consistent with the redox-lively molecule, and the redox capacity of the redox-lively species pair. As for the strength density, even as the battery voltage and powerful floor vicinity of the electrodes are open without problems decided, the release modern relies on many factors [17], [18], which include the response kinetics of electrolytes, the answer conductivity, electrodes, and operation conditions (such as temperature and low rate). Although stacking a couple of cells presents better strength density, improved cost, and product complexity are capacity consequences.…”