Full-text paper:
Behling, N.H., Managi, S. & Williams, M.C. Mining, Metallurgy & Exploration (2019) 36: 181. https://doi.org/10.1007/s42461-018-0022-x
Whatever the social, political and environmental implications, carbon remains the world’s primary energy carrier and energy source. Coal, petroleum and natural gas, all sources of carbon, are extracted, refined and transported — energy carriers (carrying their energy) — to the electric power and transportation industries that use them as their energy source or fuel. The chemical energy of carbon is transformed through energy conversion networks (ECNs) into other energy forms, such as electricity, kinetic energy, heat, light, other fuels and energy carriers. For example, coal is combusted to make steam for steam turbine generators, which provide electricity. Fuel cells are one type of ECN that can operate directly on hydrogen, ammonia, methanol, methane and other fuels or energy carriers. In a fuel cell, most of the chemical energy in these fuels is directly, electrochemically converted to electrical energy. Most fuel-cell development has centered on developing fuel cells that operate on hydrogen or reformed methane. Most of the world’s hydrogen comes from the steam reforming of methane into hydrogen and carbon dioxide. This steam reforming process is only 85 percent efficient. The hydrogen fuel cell itself is theoretically only 80 percent efficient in extracting the chemical energy of hydrogen into electricity. The overall efficiency is 65 percent. It would be much more efficient to directly convert solid carbon to carbon dioxide in a direct carbon fuel cell (DCFC). The maximum intrinsic efficiency of the solid carbon to carbon dioxide is nearly 100 percent. This would be a 40 percent fundamental improvement in thermal efficiency if fuel cells could directly operate on carbon (see Fig. 1).
