Biologically synthesized TiO₂ nanoparticles and their application as lithium-air battery cathodes

Electrocatalysts represent a sustainable solution for lithium-air batteries by eliminating side reactions. Herein, TiO₂ nanoparticles were biosynthesized via the green method and investigated as air cathodes for lithium-air batteries. TiO₂ nanoparticles were also synthesized via the facile sol-gel method to compare the efficiency of this green method. The flower extract of Matricaria chamomilla was utilized to biosynthesize the TiO₂ nanoparticles. The particle size of the biosynthesized TiO₂ nanoparticles was further controlled by manipulating the pH of the solution. In this way, the influence of pH on the nanoparticle’s properties could be evaluated. The phase structures, surface morphology, and elemental composition of the synthesized TiO₂ nanoparticles were characterized as well. Additionally, the TiO₂ cathodes were prepared on nickel foam, and their electrochemical performances were evaluated via an ECC-Air test cell using cyclic voltammetry, electrochemical impedance measurements, and galvanostatic charge-discharge tests. Consequently, the Bio-TiO₂ air cathode showed a full discharge capacity of 2000 mAh g⁻¹ and a specific capacity of 500 mAh g⁻¹ for 30 stable cycles.