According to this wikipedia page, hydrogen can combine with the carbon found in carbon steel to form some methane inside the steel, weakening it. Is is possible to convert hydrogen to methane by putting it through graphite powder or activated carbon?
Note that I mainly want the reaction to occur at STP. The flow of the gas through the graphite will be very slow (at the speed it is generated by electrolysis), so maybe catalysts not needed?
The purpose of this is to form a more energy-dense fuel than pure hydrogen. Also, it will be much safer since methane is less flammable.