School of Energy and Chemical Engineering
Ulsan National Institute of Science and Technology (UNIST)
1. Jungki Ryu* and Dong Woog Lee*, Tailoring Hydrophilic and Hydrophobic Microenvironment for Gas-Liquid-Solid Triphase Electrochemical Reactions. Journal of Materials Chemistry A 2024, Accepted.
Electrochemical reactions involving gaseous chemicals as reactants or products have the potential to play a critical role in transitioning to a sustainable, carbon-neutral society. Such reactions include gas-evolving reactions (e.g., hydrogen evolution reaction (HER), oxygen evolution reaction, and chlorine evolution reaction) and gas-consuming reactions (e.g., carbon dioxide reduction reaction, nitrogen reduction reaction, and oxygen reduction reaction). For efficient and stable production of desired chemicals via these reactions, it is imperative to develop rational strategies for managing gaseous chemicals, as well as properly design electrocatalysts. For gas-evolving reactions, efficient gas bubble removal from electrodes is crucial, as gas bubbles can adhere to the electrodes, lowering efficiency and stability due to inefficient mass transport and repeated stress cycles. Conversely, gas-consuming reactions require an effective supply of gaseous reactants and suppression of competing HER for efficient, selective target chemical production. In this review, we summarize recent studies on controlling the hydrophilic and hydrophobic microenvironment of electrodes to address these issues and suggest characterization practices and future perspectives for practical applications. We believe this article provides valuable insights and will inspire researchers in various fields to design innovative electrochemical systems for carbon neutrality.
2. Nayeong Kim, Inhui Lee, Yuri Choi* and Jungki Ryu*, Molecular Design of Heterogeneous Electrocatalysts Using Tannic Acid-Derived Metal-Phenolic Networks. Nanoscale 2021, 13, 20374-20386 (link). Invited to the "Nanoscale 2022 Emerging Investigators" Themed Collection.
Electrochemistry could play a critical role in the transition to a more sustainable society by enabling the carbon-neutral production and use of various chemicals as well as efficient use of renewable energy resources. A prerequisite for the practical application of various electrochemical energy conversion and storage technologies is the development of efficient and robust electrocatalysts. Recently, molecularly designed heterogeneous catalysts have drawn great attention because they combine the advantages of both heterogeneous solid and homogeneous molecular catalysts. In particular, recently emerged metal–phenolic networks (MPNs) show promise as electrocatalysts for various electrochemical reactions owing to their unique features. They can be easily synthesized under mild conditions, making them eco-friendly, form uniform and conformal thin films on various kinds of substrates, accommodate various metal ions in a single-atom manner, and have excellent charge-transfer ability. In this minireview, we summarize the development of various MPN-based electrocatalysts for diverse electrochemical reactions, such as the hydrogen evolution reaction, the oxygen evolution reaction, the CO2 reduction reaction, and the N2 reduction reaction. We believe that this article provides insight into molecularly designable heterogeneous electrocatalysts based on MPNs and guidelines for broadening the applications of MPNs as electrocatalysts.
3. Hyunwoo Kim, Nayeong Kim, Jungki Ryu*, Porous Framework-Based Hybrid Materials for Solar-to-Chemical Energy Conversion: From Powder Photocatalysts to Photoelectrodes. Inorganic Chemistry Frontiers 2021, 8, 4107-4148 (link). Contributed by Invitation.
Solar-to-chemical energy conversion—so-called “artificial photosynthesis”—is one of the ultimate goals of researchers to realize a sustainable future without the use of fossil fuels. Over a couple of decades, there have been intensive efforts to develop efficient artificial photosynthetic devices. Conventional studies have focused on the design and preparation of such devices using inorganic materials. However, these inorganic materials have many inherent problems, resulting in a low efficiency of solar-to-chemical energy conversion devices. These include a low absorption coefficient, severe surface recombination of charge carriers, low electrical conductivity, and poor catalytic activity. In this regard, porous framework materials such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs) can be considered promising materials for solar-to-chemical energy conversion. Their porous, layered, and ordered structure can impart the following characteristics: (i) high absorption coefficients, (ii) efficient charge separation, (iii) long charge carrier lifetime, and (iv) facile access to reactants. Furthermore, their physicochemical properties can be tailored by varying the linker's chain length, introducing additional functional groups, and employing different symmetry combinations even with similar building blocks. As a result, there have recently been intensive studies on the application of MOFs and COFs for solar-to-chemical energy conversion. In this paper, we review recent efforts on their various solar-to-chemical energy conversion applications. In particular, we have organized recent studies on the basis of their function and target reactions in chronological order to help readers readily understand the progress in MOFs and COFs and challenges to their application in artificial photosynthesis. Last, we suggest the future research direction of growing MOF- and COF-based thin films for more efficient utilization of them.
4. Sanghyun Bae, Ji-Eun Jang, Hyun-Wook Lee, Jungki Ryu*, Tailored Assembly of Molecular Water Oxidation Catalysts on Photoelectrodes for Artificial Photosynthesis. European Journal of Inorganic Chemistry 2021, 8, 4107-4148 (link). Invited to the special issue on "Redox Catalysis for Artificial Photosynthesis.
Solar-to-chemical energy conversion, or so-called artificial photosynthesis, is a promising technology enabling sustainable production and use of various chemical compounds such as H2, CO, CH4, HCOOH, CH3OH, and NH3. For practical applications, it is necessary to improve the interfacial properties of light-harvesting semiconductors through modification with proper electrocatalysts, by trying to overcome their intrinsic limitations such as rapid recombination, sluggish reaction kinetics, and photocorrosion. Compared to their heterogeneous counterparts, molecular electrocatalysts have a higher catalytic activity and more flexibility in their design/synthesis and integration with semiconducting materials. In this article, we review recent efforts on the tailored assembly of molecular electrocatalysts to address the above issues for artificial photosynthesis, especially those for oxygen evolution reactions on semiconductor photoelectrodes for photoelectrochemical water oxidation. One can expect that the strategies and methods developed for the tailored assembly and integration of molecular electrocatalysts on water oxidation photoanodes can provide insights for the design and fabrication of various forms of photosynthetic devices due to the similarity between their underlying principles.
