Hydrogen generation from water splitting over polyfunctional perovskite oxygen carriers by using coke oven gas as reducing agent

Abstract

Via redox chemistry, chemical looing water splitting driven by the reduction of coke oven gas (COG) over an oxygen carrier was proposed to co-produce pure H2 and H2-rich syngas without a separation step. We designed an efficient LaFeO3-based perovskite oxygen carriers by doping a small amount of Ni for preferentially oxidizing methane to syngas in the presence of CO and H2 at relatively low temperatures (700–800 ℃), which further improves the H2 yield via water splitting. Compared with pure LaFeO3, the methane conversion and syngas yield for LaNi0.07Fe0.93O3-λ increase from 49.4% and 8.55 mol·kg−1 to 98.6% and 12.58 mol·kg−1 in the COG conversion step at 800 ℃, respectively, and the H2 yield rises from 1.91 mol·kg−1 to 3.30 mol·kg−1 in the water splitting step. Results from combined experimental characterizations and density functional theory (DFT) calculation reveal that the incorporation of Ni cations into LaFeO3 lattice can greatly weaken the Fe-O bond and increase the lattice oxygen mobility, and the exsolved surface Ni species during the early stage of the reduction promote the activation of methane for further conversion. This contributes to the enhanced activity and lowered reaction temperature for syngas and H2 generation. The LaNi0.07Fe0.93O3-λ oxygen carriers also shows high stability in either reaction performance or material structure aspect during the successive redox cycles. This work demonstrates that it is feasible to design a high-performance oxygen carrier to preferentially convert methane in COG into syngas and further produce pure hydrogen via water splitting by using a chemical looping concept.