A perspective on hydrogen production via high temperature steam electrolysis

High temperature (700–900 °C) steam electrolysis (HTSE) based on solid oxide electrolysis cells (SOECs) has been valued as an efficient and clean path for large scale hydrogen production with nearly zero carbon emissions, compared with the traditional paths of steammethane reforming or coal gasification. The main advantage of HTSE is that energy demand for electrolysis reaction of H2O at gaseous state is less than that for liquid state. Thermodynamically, the electricity for water splitting is reduced by 15%–25% at elevated high temperature. HTSE also serves as a solution to the energy storage problems associated with non-electric application of nuclear power and the supply-and-demand conflictions of renewable energy like wind, hydro and solar power (Figure 1) [1]. A total thermal efficiency above 50% was calculated for large scale HTSE system for hydrogen production using the heat from nuclear reactors or solar. Table 1 compares the features of different hydrogen production paths by electrolysis [2,3]. SOECs, in principle, are reversely operated SOFCs (solid oxide fuel cells), sharing similar material libraries and stack configurations [4,5]. The overall electrolysis reaction is expressed in Eq. (1). The concept was first proposed by Donitz and Erdle [6] in the 1980s as part of the “HotElly” project. However, it did not receive enough attention until 2004, when the energy crisis exacerbated and oil price increased significantly. Hydrogen production based on HTSE has been acknowledged as an important function of GEN IV