Hydrogen production using chemical looping technology: A review with emphasis on H2 yield of various oxygen carriers

Natural H2 in useful quantities is negligible, which makes hydrogen unsuitable as an energy resource compared to other fuels. H2 production by solar, biological, or electrical sources needs more energy than obtained by combusting it. Lower generation of pollutants and better energy efficiency makes hydrogen a potential energy carrier. Hydrogen finds potential applications in automobile and energy production. However, the cost of producing hydrogen is extremely high. Chemical-looping technology for H2 generation has caught widespread attention in recent years. This work, presents some recent findings and provides a comprehensive overview of different chemical looping techniques such as chemical looping reforming, syngas chemical looping, coal direct chemical looping, and chemical looping hydrogen generation method for H2 generation. The above processes are discussed in terms of the relevant chemical reactions and the associated heat of reactions to ascertain the overall endothermicity or exothermicity of the H2 production. We have compared the H2 yield data of different Fe/Ni, spinel and perovskites-based oxygen carriers (OC) reported in previous literature. This review is the first comprehensive study to compare the H2 yield data of all the previously reported oxygen carriers as a function of temperature and redox cycles. In addition, the article summarizes the characteristics and reaction mechanisms of various oxygen carrier materials used for H2 generation. Lastly, we have reviewed the application of Density Function Theory (DFT) to study the effect of various dopant addition on the efficiency of H2 production of the oxygen carriers and discussed ASPEN simulations of different chemical looping techniques.