Performance evaluation of Fe-Ni compound oxygen carriers derived from biochar template for chemical looping hydrogen generation

Fe-Ni oxygen carriers (Fe-Ni/BC) were prepared by using pine biochar as a template, and compared with NiFe₂O₄ oxygen carriers synthesized by sol-gel method. The obtained oxygen carriers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) surface area measurement, hydrogen-temperature programmed reduction (H₂-TPR), and thermos-gravimetric redox-cycling (TG-redox). Furthermore, the performance of chemical looping hydrogen generation was investigated in a fixed-bed reactor. The results show that the prepared Fe-Ni/BC is a mixed crystal of Ni_0.6Fe_2.4O₄ and Fe₂O₃, retaining the framework of biochar and having a macroporous structure. Fe-Ni/BC outperforms NiFe₂O₄/SG in oxygen release, because of small average particle size, high specific surface area and abundant surface absorbed oxygen. In the fixed-bed tests, Fe-Ni/BC exhibits a better capability of hydrogen production and anti-carbon deposition with the maximum rate of hydrogen production for Fe-Ni/BC, 1.58 times that for NiFe₂O₄/SG, and the relative concentration of H₂ produced by Fe-Ni/BC is more than 99.5%.