Uneven spatial and temporal distribution of renewable energy necessitates long-term energy storage with large scale conversion. Carbon-free hydrogen production in a low cost and scalable way is a missing piece to fulfilling these requirements. Not only is hydrogen under spotlight as a potential energy resource with high energy density, but also it can be used to store renewable energy (solar, wind, geothermal, etc.) in chemical bonding, or to transform CO2 into useful chemical fuels through the reverse water-gas shift reaction (CO2 + H2 > CO + H2O) and syngas (CO, H2) post-treatment.
A. CO2+H2→CO+H2O. (Reverse water-gas shift reaction)
B. Syngas(CO,H2) post treatment
Currently, more than 90% of hydrogen is being produced through the steam-methane reforming process, in which CO2 is produced as a by-product. While many different carbon-free pathways to producing hydrogen are under development, thermochemical water splitting (TWS) has many advantages that it is scalable due to the volumetric nature of process, that it has the potential to surpass the efficiency limit of photoelectrolyzers, and so on. The two-step TWS is generally regarded as the most promising TWS approach due to its relative simplicity. In such a cycle, a metal oxide (MOx) releases O2 during thermal reduction at high temperature, THigh, to become oxygen deficient (MOx-δ). When exposed to water (steam) at a usually lower temperature, TLow, it enables water splitting to form MOx and thereby produce hydrogen (Fig. 1).
Figure 1. Schematic diagram for two-step thermochemical water splitting
Our lab tries to develop highly efficient two-step thermochemical water splitting processes that can compete with the existing steam methane reforming process. For that, we start from fundamental materials research, where we search for novel material systems which can overcome limitations of the state-of-the-art materials such as ceria (CeO2). We also plan to build laboratory scale reactors and demonstrate water splitting by employing the newly developed materials in the reactors. Potentially, our scope could extend to other water splitting technologies, not limited to the thermochemical processes, whenever we find them interesting and worth for further investigation.