Coupling Ferricyanide/Ferrocyanide Redox Mediated Recycling Spent LiFePO₄ 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.