Disclosed is a method to produce carbonaceous material and hydrogen using a plasma reactor operated at pressures greater than or equal to about 1.5 bar to greater than or equal to 20 bar. One or more electrodes within the reactor are used to generate plasma using either AC or DC. A hydrocarbon, such as natural gas or methane, in either liquid or gaseous form, is injected into the reactor via injectors, the plasma reactor then breaking down the hydrocarbon into hydrogen gas and carbon particles in an oxygen-free process. Additives and sheath gases may further be added to the reactor to improve or change the products.