Two Better Than One: Enhanced Photo-Assisted Li-O₂ Batteries with Bimetallic Fe-UiO-66 Metal-Organic Framework Photocathodes

Li-O-2 batteries, known for their impressive theoretical specific energy, face significant practical challenges, including slow kinetics, voltage hysteresis, and reduced cycle life. In this study, a novel approach is introduced utilizing a bimetallic metal-organic framework known as Fe-UiO-66 as a multifunctional photocatalyst to enhance the oxygen-related reactions in photo-assisted Li-O-2 batteries. In contrast to UiO-66, Fe-UiO-66 exhibits an extended response to visible light, as confirmed through UV-vis and photoluminescence spectra. Electron paramagnetic resonance analysis provides further validation of the pivotal role played by O-2- radicals in the electrochemical processes. Additionally, computations are employed to elucidate the distinct function of Fe centers and the underlying reaction mechanisms. Li-O-2 batteries with Fe-UiO-66 cathodes have a reduced charge/discharge voltage difference of 0.14 V under illumination and operate stably for 500 cycles. This work encourages MOF-based photocathode development for Li-O-2 batteries.