CoxFe1-xFeAlO4-δ as highly active oxygen carriers for enhanced chemical looping hydrogen production

Abstract

The oxygen carrier is a key factor to enable efficient and high-quality chemical looping hydrogen production. Here, we prepared several oxygen vacancies engineered CoxFe1-xFeAlO4-δ spinel by tuning Co loading of and investigated the performance for hydrogen production through chemical looping. The results show that Co0.4Fe0.6FeAlO4-δ displays a high hydrogen yield of 10.56 mmol.g−1 with a stable trend for 100 cycles at 600 °C. Mechanism studies demonstrate that doping Co decreases the energy barriers for oxygen vacancy formation, resulting in a high oxygen vacancy concentration on the surface. The high oxygen vacancy concentration accelerates the bulk oxygen diffusion, which is the rate-limiting step of the redox reaction. The enhanced bulk oxygen diffusion improves the oxygen release and redeposition of the lattice oxygen during redox cycles, thus promoting the chemical looping hydrogen production performance. No obvious phase separation can be found for Co0.4Fe0.6FeAlO4-δ during 100 cycles. The observed doping effect can pave way to developing more advanced oxygen carriers with high reactivity and stability for chemical looping applications.