Current hydrogen production method is mainly steam reforming of hydrocarbons. Regarding sustainability, hydrogen should be ideally produced from H2O without utilization of fossil fuels. However, in the case of current techniques on hydrogen production via water-splitting, more than 800℃ is necessary , suggesting that heat sources are limited.
So far, promising hydrogen systems have been sorted by using thermodynamic database. On the other hand, in this work, we tried to control the chemical reactions from material science point of view to reduce the operating temperature of hydrogen generation. Particularly, the reaction system including alkali metals, which have low melting points, were systematically investigated under nonequilibrium conditions.
From the calculation by using database, it is expected that more than 2000℃ is required to generate hydrogen for all the alkali metal systems. However, the experimental results indicated that the hydrogen production can be operated below 500℃ by using nonequilibrium techniques. The temperature was lower than those of the current hydrogen production techniques. Among them, the sodium Na system experimentally showed the lowest operating temperature, 400℃.
The hydrogen production technique proposed in this work can be operated below 500℃. Thus, renewable energy such as solar heat and unused energy such as exhaust heat from factory can be available. As a future work, we would like to try establishing the bench scale type for practical application.
The current thermochemical hydrogen production via water-splitting requires more than 800℃. On the other hand, in the case of the alkali metal system proposed in this work, the hydrogen can be produced below 500℃ by using nonequilibrium process. Its low operating temperature is recognized as advantage point for the practical use.
Journal: Hiroki Miyaoka, Takayuki Ichikawa, Naoya Nakamura and Yoshitsugu Kojima, International Journal of Hydrogen Energy 37, 17709 (2012)
Patent: Hydrogen Production System, Japanese Patent, Application No.2013-039251