As mentioned before, our flow cell uses Zinc and Nickel oxide, with a flowing solution of ZnO in aqueous KOH. This operates as a normal electrochemical cell, with the zinc dissolving and depositing onto a copper substrate. (Note: the reactions are summarized below) When charging, the electron surplus at the copper anode will cause the Zn(OH)2- ions to form solid Zn and 4 OH- groups. The Zn deposits are said to be dendritic, due to their growth pattern. Dendritic growth is random and very difficult to control, meaning that any unusual growth can come into contact with other cell components and cause an internal short, which is a large obstacle for advancements in flow cell technology.
Not surprisingly, the mechanics of the flow cell are all about the flow of solution through the cell.The electrolyte is caustic and cannot be flown through an ordinary pump, as it would cause corrosion. We therefore use a peristaltic pump with chemical resistant tubing to induce flow in the sytem. The solution’s flowrate will affect dendritic growth and the cell’s efficiency, which is why we are also using a variable power supply. The benefit of this is we can change the voltage going to the pump, which will change the flowrate of solution.
Our cell is made of laser-cut acrylic sheets glued together using acrylic adhesives, which allows us to see what’s going on with the electrodes during operation. This helps us develop our methods of dendrite suppression, and keeps the cell relatively light.
Since this project is focused on energy storage, there is huge potential to include microelectronic technology, such as Arduino boards and printed circuit boards. We haven’t integrated this technology into the project just yet, but we will! Some examples of what we can do include using an Arduino to control the pump’s flow direction, using circuits to display the voltage available in the battery in real-time, or even automating the flow cell’s charge-discharge cycles.
As we’re trying to optimize the cell’s performance, the shape of the cell itself will have an impact on the cell’s electrochemistry. At the moment, our cell is box-shaped, with an inlet and outlet on opposite sides of the cell. Design is one of the most important aspects of engineering, and so we will be incorporating design processes and prototyping technology into the project, to give team members a valuable experience.