The hydrogen economy is using hydrogen to decarbonize economic sectors which are hard to electrify, essentially, the "hard-to-abate" sectors such as cement, steel, long-haul transport, etc. In order to phase out fossil fuels and limit climate change, hydrogen can be created from water using renewable sources such as wind and solar, and its combustion only releases water vapor into the atmosphere. Hydrogen is an energetic fuel, frequently used as rocket fuel, but numerous technical challenges prevent the creation of a large-scale hydrogen economy. These include the difficulty of developing long-term storage, pipelines, and engine equipment; a relative lack of off-the-shelf engine technology that can currently run safely on hydrogen; safety concerns regarding the high reactivity of hydrogen fuel with oxygen in ambient air; the expense of producing it by electrolysis; and a lack of efficient photochemical water splitting technology. Hydrogen can also react in a fuel cell, which efficiently produces electricity in a process that is the reverse of the electrolysis of water. The hydrogen economy is nevertheless slowly developing as a small part of the low-carbon economy. , hydrogen is mainly used as an industrial feedstock, primarily for the production of ammonia and methanol, and in petroleum refining. Although initially hydrogen gas was thought not to occur naturally in convenient reservoirs, it is now demonstrated that this is not the case; a hydrogen system is currently being exploited near Bourakebougou, Koulikoro Region in Mali, producing electricity for the surrounding villages. More discoveries of naturally occurring hydrogen in continental, on-shore geological environments have been made in recent years and open the way to the novel field of natural or native hydrogen, supporting energy transition efforts. , almost all (95%) of the world's 70 million tons of hydrogen consumed yearly in industrial processing, significantly in fertilizer for 45% of the world's food, are produced by steam methane reforming (SMR) that also releases the greenhouse gas carbon dioxide. A possible less-polluting alternative is the newer technology of methane pyrolysis, though SMR with carbon capture and storage (CCS) may also greatly reduce carbon emissions. Small amounts of hydrogen (5%) are produced by the dedicated production of hydrogen from water, usually as a byproduct of the process of generating chlorine from seawater. there is not enough cheap clean electricity (renewable and nuclear) for this hydrogen to become a significant part of the low-carbon economy, and carbon dioxide is a by-product of the SMR process,