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BET stands for Brunauer–Emmett–Teller (BET) theory which is just one of the more common methods to measure and analyze surface area in porous materials. This video shows how to use gas (nitrogen) physisorption to determine the surface area and pore size characteristics of porous carbon materials (in this case carbon felts). Nitrogen gas pressure is gradually increased causing more and more molecules to adhere to the surface. The smaller the pores the larger the surface area available for gas adsorption which is measured by carefully monitoring the volume and pressure of the gas at constant temperature.
One application of this technique is to help improve the capacity of vanadium redox flow batteries (VRBs). VRBs are a type of flow battery that utilize a single electrolyte containing Vanadium ions. VRBs are advantageous to renewable energy storage in that they are capable of being repeatedly charged and discharged with relatively little degradation over very long periods of time, capable of rapidly discharging, and can be scaled to create very large battery systems that compensate for when intermittent energy sources are inactive. On the downside, most current and commercial VRBs use porous carbon (graphite) fiber based electrodes which while inexpensive and robust suffer from relatively low charge storage capacity. The surface analyzer can identify if new surface treatments are effective at increasing the surface area of carbon felts.
Clean Energy Fellow Charles Schmidt demonstrates a surface analyzer.