Is the H economy realizable in the foreseeable future? Part III: H usage technologies, applications, and challenges and opportunities.

Energy enthusiasts in developed countries explore sustainable and efficient pathways for accomplishing zero carbon footprint through the H economy. The major objective of the H economy review series is to bring out the status, major issues, and opportunities associated with the key components such as H production, storage, transportation, distribution, and applications in various energy sectors. Specifically, Part I discussed H production methods including the futuristic ones such as photoelectrochemical for small, medium, and large-scale applications, while Part II dealt with the challenges and developments in H storage, transportation, and distribution with national and international initiatives. Part III of the H economy review discusses the developments and challenges in the areas of H application in chemical/metallurgical industries, combustion, and fuel cells. Currently, the majority of H is being utilized by a few chemical industries with >60% in the oil refineries sector, by producing grey H by steam methane reforming on a large scale. In addition, the review also presents the challenges in various technologies for establishing greener and sustainable H society.