NASA Langley Research Center has developed a method of depositing arrays of a ferritin protein on a substrate to create a thin-film electrode for a bio-nanobattery. The method is a spin self-assembly procedure by which a first ferritin layer is formed on the substrate, followed by building a second oppositely charged ferritin layer on the top of the first to form a bilayer structure. Oppositely charged ferritin layers are subsequently deposited on top of each other until a desired number of bilayer structures is produced. The result is an ordered, uniform, stable, and robust thin-film electrode material of enhanced packing density that provides optimal charge density for the bio-nanobattery.
Ferritin is an iron storage protein that naturally exists in most biological systems. The ferritin molecule consists of a segmented protein shell with an outer diameter of 12.5 nm and an inner diameter of 7.5 nm, containing up to ~4500 Fe3+ atoms as Fe(OH)3 within its hollow interior. Biomineralization allows ferritins to reconstitute themselves with various metallic cores such as cobalt and manganese.
When the ferritin half-cells are integrated into a complete battery system, the fabrication of well-organized ferritin arrays is very important to enhance the overall battery performance; for example, the battery power density, the power discharge rate, the compactness of battery size, etc.