Gray hydrogen is a high-emissions form of hydrogen produced using steam methane reforming
Gray hydrogen is produced through steam methane reforming (SMR), a process where natural gas, mainly methane (CH4), reacts with steam (H2O) at high temperatures (700–1,000°C) in the presence of a catalyst. This reaction yields hydrogen (H2) and carbon monoxide (CO), which is subsequently converted to carbon dioxide (CO2) through the water-gas shift reaction 1. The CO2 produced is typically released into the atmosphere, making gray hydrogen a significant source of greenhouse gas emissions.