Korea University: Gold/Ceria/Graphene Core-Shell Photocatalyst Used to Accomplish the World’s Highest Green Hydrogen Production Rate

Professor Lee In-Hwan’s group of the Department of Materials Science and Engineering in the College of Engineering at KU developed a three-factored Au@CeO2/Gr core-shell photocatalyst for high-efficiency production of green hydrogen. The present study, led by Research Professor Dung Van Dao of Professor Lee In-Hwan’s group at KU, was jointly conducted with Professor Yeon-Tae Yu’ s group at Jeonbuk National University and Professor Hyun You Kim’s group at Chungnam National University.

As a way to address global warming issues and facilitate green economy, developing technologies to efficiently produce hydrogen at a low cost is highly desirable. Hydrogen is classified into gray hydrogen, blue hydrogen and green hydrogen. Among these, green hydrogen refers to clean hydrogen and is considered an environment-friendly energy source. Green hydrogen can be produced by electrolysis, photoelectrochemical decomposition and the photocatalytic decomposition of water. Photocatalytic decomposition in particular is drawing attention as an attractive and promising method of green hydrogen production because it requires a simple system without an electric power supply and can be operated with the solar energy alone.

However, photocatalytic decomposition for converting solar energy into chemical energy in the form of hydrogen is still of low efficiency, and so developing catalytic materials of sufficiently high economic feasibility is a huge challenge. Reasons for the low catalytic efficiency include the low light absorption capability, the fast charge carrier recombination rate, and the misalignment between the redox potential and the energy band.

The photocatalysts often employed include titanium oxide (TiO2), iron oxide (Fe2O3) and ceria (CeO2) based oxide semiconductor materials, because they are less expensive and have high stability in a water system. A photocatalyst suspended in a water system generates electron-hole pairs (EHP) by using the energy from solar light, and the EHP is separated to produce hydrogen through a redox reaction with water. Therefore, the essential conditions of photocatalyst are 1) a suitable band gap for efficiently absorbing the solar light spectrum to generate EHPs (light absorption condition); 2) a structure to prevent the recombination of EHPs and separate them efficiently (EHP separation condition); and 3) a conduction band higher than the redox potential and a valence band lower than the oxidation potential for the redox reaction (band alignment condition).

Faithfully following these photocatalyst requirements, Professor Lee’s group theoretically designed an innovative and creative material structure for a water splitting photocatalyst. The researchers prepared a photocatalyst using an Au@CeO2 core-shell structure wrapped by a graphene network, and then achieved the world’s highest green hydrogen production rate (8.1 µmol/mg·h) using the prepared photocatalyst. In contrast to conventional binary core-shell photocatalysts, the newly developed photocatalyst extends the life time of the hot carrier generated by light energy allowing more of it to be applied to hydrogen production. The hydrogen production mechanism of the newly developed photocatalyst was investigated by finite-difference time-domain (FDTD) simulation. Research Professor Dung Van Dao explained the significance of the research, “Through this study, we developed a three-factored Au@CeO2/Gr photocatalyst for high-efficiency hydrogen production, and we were able to gain deep insights into the operation of the three-factored photocatalytic system for the conversion of light energy into hydrogen.”