Professor Sanghan Lee's research team presents a new approach to convert water into hydrogen

□ Professor Sanghan Lee' research team at the School of Materials Science and Engineering at the Gwangju Institute of Science and Engineering (GIST, President Seung Hyeon Moon) has developed a new approach to convert water into hydrogen by utilizing the fact that the photocurrent density * increases as the polarization of a ferroelectric * material increases, which suggested another approach for producing hydrogen from water.

* Photocurrent density: The value obtained by dividing the current generated by the electro-separation phenomenon divided by the area of the light-receptor.

* Ferroelectric: A material with spontaneous polarization, which means that the direction of polarization can be changed by an external electric field.

 

□ Most materials on Earth have no electrical poles (+, - electrodes). However, ferroelectric materials, which have been in the spotlight for next generation nonvolatile memory storage, have their own polarity. This characteristic allows efficient separation of electrons * and holes * when light is applied, enhancing solar conversion efficiency. To date, the relationship between the spontaneous polarization of ferroelectric materials and photoconversion efficiency has not been clearly established experimentally.

* Electrons: basic particles with negative charge

* Hole: a basic particle with a positive charge

* Photoelectrode: An electrode made of material that absorbs sunlight to generate electrons and holes

 

□ The team first experimentally correlated the relationship between ferroelectric spontaneous polarization and photoconversion efficiency. As a result of that study, spontaneous polarization values appeared in the same direction of the crystal * in bismuth ferrite * photoelectrode * thin film. In the vertical crystal direction, which is one of the crystal direction types, 65 (μC /cm 2) and 110 (μC /cm 2) appears in the twisted diagonal crystal direction. Because of these spontaneous polarization differences within the same bismuth ferrite material, the photocurrent density was improved five times or more in the diagonal crystal direction *, which was twisted with respect to the vertical crystal direction. The fact that the photocurrent density is high means that the efficiency of converting light energy received from the sunlight into electric energy is also high. The generated electric energy can convert water to produce hydrogen. In other words, by using a ferroelectric material with a higher spontaneous polarization value than the photoelectrode, the hydrogen production efficiency can be increased.

* Bismuth ferrite (BiFeO3) is a material that is considered an important material for the development of room temperature magnetic field devices because it has characteristics of both ferroelectricity and antiferromagnetism at room temperature.

* Photoelectrode: An electrode made of materials that can absorb sunlight to generate electrons and holes.

* Crystal: A solid state material in which atoms and ions are regularly in a regular pattern.

□ Professor Sanghan Lee said, "This research is the first to experimentally prove the correlation between the self-polarization of ferroelectric material with photoconversion efficiency. The spontaneous polarization of the ferroelectric material can increase the solar conversion efficiency. The results of this study are expected to be applied not only to hydrogen production but also to energy production technology, such as solar cells."

 

□ The research was funded by National Research Foundation of Korea and the Korea Institute of Energy Technology Evaluation and Planning, and their paper entitled "Domain-engineered BiFeO3 thin-film photoanodes for highly enhanced ferroelectric solar water splitting" authored by Jaesun Song, Taemin Ludvic Kim, Jongmin Lee, Sam Yeon Cho, Jaeseong Cha, Sang Yun Jeong, Hyunji An, Wan Sik Kim, Yen-Sook Jung, Jiyoon Park, Gun Young Jung, Dong-Yu Kim, Ji Young Jo, Sang Don Bu, Ho Won Jang, and Sanghan Lee and was published by Nano Research on June 9, 2017.