Extrapolation of world energy consumption between 1990 and 2006 to the future reveals the complete exhaustion of petroleum, natural gas, coal and uranium reserves on the Earth in 2037, 2042, 2055 and 2057, respectively. We are proposing global carbon dioxide recycling to use renewable energy by which all people in the whole world can survive. The electricity will be generated by solar cell in the deserts and used for production of hydrogen by seawater electrolysis at the nearby desert coasts. Hydrogen, for which no infrastructures of transportation and combustion exist, will be converted to methane at the desert coasts by the reaction with carbon dioxide captured by energy consumers. Among systems in global carbon dioxide recycling, seawater electrolysis and carbon dioxide methanation have not been performed industrially. We created energy-saving cathodes for hydrogen production and anodes for oxygen evolution without chlorine formation in seawater electrolysis, and ideal catalysts for methane formation by the reaction of carbon dioxide with hydrogen. The key factors for realization of global carbon dioxide recycling are the activity enhancement and corrosion prevention of those key materials.
Hydrogen accumulated in eutectoid steels with different heat treatments was measured using electrochemical method. This method pulled out about 30% lesser amount of hydrogen than that determined by thermal desorption method. Hydrogen content in steels accumulated during single corrosion cycle was about 0.01 to 0.1 ppm and they depended on microstructure of steels. Hydrogen content in different microstructure of steels decreased in the order of: Martensite > pearlite > spheroidized cementite-ferrite. The amount of hydrogen accumulated during several continuous corrosion cycles was larger than that observed in single cycle, and the difference of hydrogen content between microstructures became also lager.
In order to understand the detailed corrosion process of carbon steel depending on pH in the neutral solution, corrosion film formation reaction on the steel surface in 0.01M NaHCO3 solution has been analyzed as a function of pH, the value of which was adjusted by bubbling a mixture of air and CO2 gas at an atmospheric pressure. It was found that precipitation ratio defined as the amount of precipitated film to the total corrosion loss increases with increase of pH, resulting in decrease of the total corrosion loss with increasing pH in the range between pH=3.5 and 10. Small addition of alloying elements such as Cu and Ni was also found to change the precipitation ratio. The film formation reaction is rationally explained by assuming that precipitation is decided by the solubility product of Fe(OH)2, Fe(OH)3 or FeCO3. The rate of corrosion was found to obey the parabolic low, suggesting that the diffusion of oxygen dissolved in the solution through the film controls the whole process.