S-1 Facilitating Pure H ₂ Production over a Spinel NiGa ₂ O ₄ Oxygen Carrier during Water Splitting

Chemical looping steam methane reforming (CL-SMR) offers an attractive pathway for coproducing H2 and syngas (H2 and CO) through two consecutive steps of methane oxidation and water splitting. During this chemical looping process, the oxygen carrier plays an important role in the production of syngas and pure H2. An efficient spinel NiGa2O4 oxygen carrier is successfully designed, achieving high syngas and pure H2 productivity at relatively low temperatures. The introduction of S-1 further enhances the H2 productivity during the water splitting stage. Compared with the H2 productivity of pure NiGa2O4 (6.53 mmol), the H2 productivity of NiGa2O4/S-1 increases to 7.25 mmol at 700 °C and maintains 100% H2 purity during 20 cycles. During redox cycling, partial Ga elements migrate from the NiGa2O4 oxygen carrier to the S-1 surface. This elemental migration process prevents excessive growth of Ga particles, resulting in a superior reactivity and cyclic stability for NiGa2O4/S-1. Due to the strong interactions between silanol groups and H2O, the NiGa2O4/S-1 sample exhibits enhanced H2O absorption capacity, thereby promoting the water splitting reaction. Additionally, the adsorbed OH– groups participate in the water splitting reaction, facilitating H2 production in chemical looping. During 20–100 redox cycles, NiGa2O4/S-1 still exhibits high H2 purity and cycle stability, demonstrating promising scalability potential for industrial-scale hydrogen production. This research provides valuable insights into designing efficient spinel oxygen carriers for pure H2 production at relatively low temperatures during water splitting reaction.