Coupling Ferricyanide/Ferrocyanide Redox Mediated Recycling Spent LiFePO<inf>4</inf> with Hydrogen Production

Abstract

Replacing the oxygen evolution reaction with thermodynamically more favorable alternative oxidation reactions offers a promising alternative to reduce the energy consumption of hydrogen production. However, questions remain regarding the economic viability of alternative oxidation reactions for industrial-scale hydrogen production. Here, we propose an innovative cost-effective, environment-friendly and energy-efficient strategy for simultaneous recycling of spent LiFePO4 (LFP) batteries and hydrogen production by coupling the spent LFP-assisted ferricyanide/ferrocyanide ([Fe(CN)6]4−/[Fe(CN)6]3−) redox reaction. The onset potential for the electrooxidation of [Fe(CN)6]4− to [Fe(CN)6]3− is low at 0.87 V. Operando Raman and UV/Visible spectroscopy confirm that the presence of LFP in the electrolyte allows for the rapid reduction of [Fe(CN)6]3− to [Fe(CN)6]4−, thereby completing the [Fe(CN)6]4−/[Fe(CN)6]3− redox cycle as well as facilitating the conversion of spent LiFePO4 into LiOH ⋅ H2O and FePO4. The electrolyzer consumes 3.6 kWh of electricity per cubic meter of H2 produced at 300 mA cm−2, which is 43 % less than conventional water electrolysis. Additionally, this recycling pathway for spent LFP batteries not only minimizes chemical consumption and prevents secondary pollution but also presents significant economic benefits.