## 1 Introduction  
Ambiguous energy storage targets have been announced by international companies as a result of the growing attention to the energy transition as the route of encouraging a green economy. Energy storage is typically applied to store electricity generated by renewable energy devices in huge volumes. The global market size of energy storage is projected to rise at a CAGR of 5.5% during the forecast period of 2021-2026 (GlobeNewswire) [1], creditable to extensive deployment of shifting emphasis towards renewable power, smart grids, and the commercialization of innovative technologies such as solid-state and flow batteries. Redox flow batteries (RFBs) are extensively considered proper for large-scale energy storage [2] because of their attractive features consisting of unlimited capacity, high round trip efficiency, fast responsiveness, depth of discharge, flexible design, and negligible environmental impact [3]. RFBs have 85% efficiency and can be utilized as rechargeable batteries or fuel cells. An RFB is superior to a lithium-ion battery in terms of cycle life (>13,000 cycles), discharge time (1-10 h), energy cost (150-1000 k$/kW), power cost (600-1500 $-kW/h), and capital cost (<70 $ MW/h cycles) [5, 6]. These performances of the redox flow battery are appropriate for stationary energy storage, since the target of a stationary application is anticipated to achieve 0.05 \(\mathrm{\upmu}\)/kW h of cost, 10,000 cycles of durability, and a lifespan of 20 years [7]. RFBs have many possible applications such as power storage, load balancing, uninterruptible power sources to supply continuous power to facilities, electric vehicles' rapid charging, and stand-alone power systems [8]. The functions of RFBs depend upon the depth of discharge (DOD), and the high DOD in RFBs does not negatively impact the lifespan of RFBs [9]. The reactions occurring between the two electrolytes typically overwhelms the activity and durability of the batteries. RFBs have been created depending upon the active redox species in the catholyte and anolyte; thus, there are three major types of RFBs, which are the aqueous system, the hybrid aqueous/non-aqueous system, and the non-aqueous system [10]. VRFBs have emerged as applicable candidates to address large-scale energy storage because the electrochemically active reactants are vanadium species in four different oxidation states in both electrolyte solutions. In other words, they have only vanadium as an active element for the anolyte and catholyte. Applying vanadium as the only active species is principally related to the mitigation of contamination problems between the electrolytes, leading to a longer lifespan, since the cross-contamination of negative and positive electrolytes through the cell separator results in coulombic-efficiency losses [11]. Furthermore, the actively soluble species can be kept without the phase change in the electrodes. The large adoption of RFB systems does not imply that Li-ion batteries will disappear from the market, but the two systems will address different features. Even though VRFBs have reached effective commercial fruition in comparison to other RFBs, the commercialization of vanadium flow battery systems has suffered from the high cost of the vanadium compounds. Therefore, researchers have to either store more electricity in the same amount of vanadium through improved chemistry or improved cell and stack designs [12]. The VRFBs are electrochemical energy storage devices that convert chemical energy into electrical energy through reversible oxidation and reduction of the working fluids, characteristically in two soluble redox couples subsisting in external electrolyte containers sized in concordance with application necessities. A VRFB stack, electrolyte storage, and the balance of the plant part are major compositions of a VRFB system [13]. A VRFB stack typically includes endplates, current collectors, bipolar plates, electrodes, membranes, flow frames, and gaskets.