Sustainable hydrogen generation and storage - a review

Abstract

In 21st century, the energy demand has grown incredibly due to globalization, human population explosion and growing megacities. This energy demand is being mostly fulfilled by fossil-based sources, which are non-renewable and a major cause of global warming. Energy from these fossil-based sources is cheaper, however challenges exist in terms of climate change. This makes renewable energy sources more promising and viable for the future. Hydrogen is a promising renewable energy carrier for fulfilling the increasing energy demand due to its high energy density, non-toxic and environment friendly characteristics. It is a non-toxic energy carrier as combustion of hydrogen produces water as the byproduct whereas other conventional fuels produce harmful gases and carcinogens. Because of its lighter weight, hydrogen leaks are also easily dispersed in the atmosphere. Hydrogen is one of the most abundant elements on Earth, yet it is not readily available in nature like other fossil fuels. Hence, it is a secondary energy source and hydrogen needs to be produced from water or biomass-based feedstock for it to be considered renewable and sustainable. This paper reviews the renewable hydrogen generation pathways such as water splitting, thermochemical conversion of biomass and biological conversion technologies. Purification and storage technologies of hydrogen is also discussed. The paper also discusses the hydrogen economy and future prospects from an Indian context. Hydrogen purification is necessary because of high purity requirements in particular applications like space, fuel cells etc. Various applications of hydrogen are also addressed and a cost comparison of various hydrogen generation technologies is also analyzed. In conclusion, this study can assist researchers in getting a better grasp of various renewable hydrogen generation pathways, it's purification and storage technologies along with applications of hydrogen in understanding the hydrogen economy and its future prospect.

Fig. 1. Energy content of different fuels (drawn using data from ref. 6).

Fig. 2. Schematic of hydrogen economy.

Fig. 3. Renewable hydrogen generation pathways.

Fig. 4. Alkaline electrolysis cell.

Fig. 5. PEM electrolysis cell.

Fig. 6. Schematic diagram of photolysis.

Fig. 7. Two-step cerium oxide water splitting cycle.

Fig. 8. [Fig. 2 influence of temperature process on the syngas characteristics.] Adapted from Molino, A., Chianese, S., & Musmarra, D., Biomass gasification technology: the state of the art overview. Journal of Energy Chemistry, 2016, 25(1), 10–25, DOI: 10.1055/s-0035-1560215.

Fig. 9. Hydrogen production efficiency of different processes.

Fig. 10. A schematic of chemical looping gasification.

Fig. 11. Different applications of hydrogen.

Fig. 12. [Fig. 9 ammonia production via hydrogen electrolysis and H–B process.] Adapted from Valera-Medina, A., Xiao, H., Owen-Jones, M., David, W. I., & Bowen, P. J., Ammonia for power. Progress in Energy and combustion science, 2018, 69, 63–102, DOI: 10.1016/j.pecs.2018.07.001.

Fig. 13. A schematic of PAFC.

Fig. 14. Efficiency of different fuels.

Fig. 15. Hydrogen production costs associated with different technologies.