Grey Hydrogen Production: The Climate Change Impacts of Steam Methane Reforming (SMR)

Conventional hydrogen production through steam methane reforming (SMR) ('grey') has been found to have the highest climate change impacts in most countries considered. This technology relies on fossil fuel feedstocks, resulting in significant greenhouse gas (GHG) emissions. Moreover, its potential for improvement in the context of the energy transition is limited. To meet climate change mitigation targets, it is necessary to explore alternative technologies to replace SMR.

Currently, over 95% of hydrogen is produced from fossil fuels using processes such as steam reforming, coal gasification, or SMR. In the SMR process, natural gas (primarily CH4) reacts with steam to produce CO and H2 (CH4 + H2O → CO + 3H2). Subsequently, CO reacts with steam in the water gas shift reaction to produce more H2 and CO2 (CO + H2O → CO2 + H2). Thus, for every four molecules of H2 produced via SMR, one molecule of CO2 is released. This means that 5.5 tons of CO2 are emitted into the atmosphere per ton of H2 produced. While it is possible to capture and store around 70% of the released CO2 through carbon capture and sequestration, such practices are not yet widely implemented. Consequently, SMR is not an ideal method for hydrogen production in the hydrogen economy, as it relies on fossil fuels and emits a significant amount of CO2. Thus, the development of alternative technologies for cleaner and renewable hydrogen production is crucial for the advancement of the hydrogen economy.