Today, most hydrogen is produced through a process called steam methane reformation (SMR). The main uses for hydrogen are as feedstocks to fossil fuel refining and fertilizer via the Haber-Bosch process.
SMR has the net reaction:
CH4 + 2H2O –> 4H2 + CO2
Since the reaction is endothermic, heat input is required which can be done by adding more steam. Therefore, in addition to the CO2 from the reaction, CO2 is produced from combustion to heat steam. This results in hydrogen production contributing about 2% of global greenhouse gas emissions.
An alternative process to make hydrogen without the CO2 is methane pyrolysis, which has the reaction:
CH4 –> C + 2H2
Instead of producing CO2, a powder-like solid carbon is produced.
A number of academic and commercial groups are working on making viable reactors that try to solve the problem of high temperature (~800 – 1400 C depending on catalyst use) required for high conversion rates and the problem of carbon clogging the reactor.
I’ll update this description soon with more details on the challenges associated with methane pyrolysis and how it compares to SMR with carbon capture and electrolysis.