Precious metal free tunable manganese oxides for sustainable anion exchange membrane fuel cells

Abstract

Eliminating platinum group metals from cathode catalysts in low-temperature polymer electrolyte fuel cells is highly important for addressing the sustainability challenge fuel cell systems face. Here, we propose modifying the electronic structure of Li-intercalated layered Mn-oxide as a cathode catalyst to overcome the activity/stability tradeoff in anion exchange membrane fuel cells. To achieve this goal, we deploy a precious metal free catalyst design strategy involving atomically dispersed p -block metal Sn doped in Li 2 MnO 3 , in addition to d -block metals, which has been poorly explored in the research thus far. Operando X-ray absorption spectroscopy and rapid freeze-quench 119 Sn Mössbauer methodology are employed to visualize the catalytic dynamics, revealing that part of Mn 4+ ions are converted into Mn 3+ ions, whereas Sn 4+ ions remain unchanged during the oxygen reduction reaction. Under H 2 /O 2 conditions, anion exchange membrane fuel cells employing Li 2 Mn 0.9 Sn 0.1 O 3 cathodes achieve peak power densities above 1.0 W cm -2 geo and 3.96 W mg -1 Pt . This work demonstrates the beneficial modulation of the electronic structure through p -block metal substitution in earth-abundant Mn-enriched oxide materials.