Enhanced hydrogen production and fuel conversion of an iron-based oxygen carrier in the chemical looping process by a small co-addition of CuO and NiO

Abstract

The chemical looping process for hydrogen production is garnering increased attention due to its capability to directly generate high-purity hydrogen (H₂) with minimal energy expenditure. Within the chemical looping hydrogen generation (CLHG) framework, achieving high H₂ yields and fuel conversion rates is crucial for enhancing energy efficiency, thus propelling the innovation of oxygen carriers (OCs). In this study, we decorated Fe₂O₃–Al₂O₃ by incorporating minor amounts of copper oxide (CuO) and nickel oxide (NiO) and assessed its efficacy in the biomass gasification gas-fueled CLHG process. Comprehensive characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), hydrogen/methane temperature-programmed reduction (H₂/CH₄-TPR), and steam temperature-programmed oxidation (H₂O-TPO), were employed to elucidate the underlying reaction mechanisms. Our findings reveal that Fe₂O₃–Al₂O₃, with the co-addition of CuO and NiO (4.55 wt%), outperforms both unmodified Fe₂O₃–Al₂O₃ and those with single metal oxide additions in the CLHG process. Notably, the fuel conversion, H₂ yield, steam conversion, and H₂ energy efficiency were markedly improved, achieving peak values of >99%, 6.35 mmol per g Fe₂O₃, >70%, and 77.9%, respectively. XPS and XRD analyses indicate a robust interaction among Fe₂O₃, CuO, and NiO, leading to the formation of a spinel ferrite phase during OC calcination. Additionally, H₂/CH₄-TPR and H₂O-TPO analyses confirm the enhanced redox reactivity of Fe₂O₃–Al₂O₃ with the co-addition of CuO and NiO. Time-resolved studies on OC conversion and phase evolution during the reduction process highlight the synergistic effects of CuO and NiO in boosting the OC reduction rate. The formation of FeNi and Cu in the early stage of the OC reduction process reduces oxygen vacancy formation energy, further promoting the deep reduction of the OC.