https://phys.org/news/2018-07-team-shatters-theoretical-limit-bio-hydrogen.html

A version of the Thermotoga maritima bacterium engineered by Raghuveer Singh, Paul Blum and their colleagues produced 46 percent more hydrogen per cell than a naturally occurring form of the same species. The team's highest reported yield—5.7 units of hydrogen for every unit of glucose fed to the bacterium—easily surpassed the theoretical limit of 4 units.

The feat represents a breakthrough in the global effort to scale up the sustainable production of clean-burning hydrogen for vehicles and heavy industry, Singh said. Most commercial hydrogen comes from refining non-renewable fossil fuels such as natural gas, oil and coal—processes that generate sizable amounts of carbon dioxide.