Although large lithium-ion batteries like Tesla's construction in South Australia are a way of storing renewable energy, the assembly cost of these batteries is as high as tens of millions of dollars. Redox flow batteries--that is, storing energy in liquid electrolytes in huge tanks--provide a cheaper alternative, and can store energy for several months at a time, just like the world developed in Germany. As planned for the largest redox flow battery.
A popular chemical composition of these types of batteries is to rely on metallic vanadium as the electrolyte, and the most common membrane material for these vanadium redox batteries is perfluorosulfonic acid (PFSA). However, one problem with this is that vanadium ions easily penetrate into the membrane, making the entire battery unstable, affecting its performance and shortening its life.
Researchers from the Chinese Academy of Sciences have already targeted this problem. They fine-tune the function of the membrane through a hybrid material. Tungsten trioxide nanoparticles grow in situ on the surface of very fine graphene oxide sheets. It is reported that graphene oxide is a single-layer graphite sheet that can be made by graphite oxidation.
These sheets are embedded in a new type of PFSA membrane, which has a sandwich structure and is reinforced with a thin layer of PTFE (based on Teflon). Here we see graphene oxide sheets as a barrier to selectively reduce the permeation of vanadium ions, and nanoparticles as active sites, which in turn promote the transport of protons, making the Coulomb efficiency and energy efficiency become very high- -Over 98.1% and 88.9% respectively.
The researchers said that this not only exceeds the efficiency of commercially available membranes, but also solves the stability problem at the same time. In general, the team said that experiments show that the hybrid membrane is very suitable for vanadium redox flow batteries, but its potential may not stop there. They noticed areas such as fuel cell technology and water filtration, which also rely on fine-tuned membranes to allow selective passage of ions, while also benefiting from the design.