The hydrogen economy has gained enormous popularity as the means to decarbonise electricity by storing excess renewable power. This recent article by The Times highlights perhaps why, as well as some of the potential pitfalls.
In brief, hydrogen storage involves the conversion of electrical energy to chemical hydrogen energy through electrolysis, the use of additional electrical energy in the compression or liquefication of hydrogen for storage or transport, and the conversion of chemical hydrogen energy to electrical energy in a fuel cell.
As touched upon the by the article, absent large scale CCS, a successful net-zero hydrogen economy is premised on excess renewable energy. The reality is that meaningful excess renewable capacity will not materialise until after 2040, and fuel cells are expensive. Equally, the hydrogen supply chain will take decades to provide sufficiently distributed services for transport owners to switch, and until the renewables/CCS problem is solved, hydrogen production will be a polluter, eliminating any incentive to switch.