Research Interest

• Electrochemical Reduction of CO2 Gas into Valuable Products:

Carbon dioxide (CO2) capture, utilization, and storage (CCUS) technology has been considered one of the most promising strategies to resolve CO2 emission problems. The electrochemical CO2 reduction reaction (CO2RR) to valuable chemicals and liquid fuels using renewable electricity is a practically approachable method for carbon neutrality. Electrocatalytic CO2RR catalysts for producing C1 (containing one carbon atom) products, such as carbon monoxide (CO) and formate, have been well established over the past decade and are getting mature enough to be commercialized. However, developing electrochemical systems for generating selective C2+ products, such as ethylene and acetate, still needs to be improved because most reaction pathways overlap with each C2+ product. Diverse and creative strategies for tuning copper (Cu) based electrocatalysts, such as facet, morphology control, dopants, and alloying modification, should be suggested to enhance the single C2+ product selectivity while suppressing the other C2+ product generation. 

Although the electrocatalysts showed improved C2+ product selectivity, achieving commercial-grade fuel liquid products or stable electrocatalytic operation even longer than 20 hours was particularly difficult when using conventional electrolyzers. The purification issue of the collected liquid and CO2RR electrolyzer system's long-term operation stability are major challenges to the industrial application of CO2RR. Alkali cations such as potassium or sodium are demonstrated to be critical in improving CO2RR reaction kinetics. However, the presence of alkali ions in the electrolyzer can cause impurity problems in the liquid collection and salt precipitation (i.e., KHCO3 or K2CO3) on GDE or inside the gas flow channels. Blocking the gas diffusion pathway of CO2 to the electrocatalyst eventually leads to performance degradation and catastrophic failure. Catalyst developments must accompany the electrolyzer/reactor development to boost the system's efficiency. 

Furthermore, targeting carbon chains longer than four carbons (C4+) becomes more difficult due to the intrinsic limitations of electrochemical CO2RR. Engineering a new reaction process design and system integration to promote further upcycling waste/harmful materials into valuable materials (C4+), an important transition pathway into sustainable energy engineering. One of the interesting approaches is to integrate outlet products of CO2RR with other reactors, such as a bioreactor, to further improve them. Still, there could be reaction environment mismatch issues between two connected reactors. Therefore, research on compatibility between reactors or optimizing the reaction environments can open a new field of product upgrading from the waste CO2 gas.

• Material and System Design for Next-Generation Batteries:

Electrolytes/system design (Aqueous, Concentrated organic, hybrid electrolytes, and liquid products from CO2RR) for the efficient redox flow batteries, and materials/system design for the metal-oxide/-sulfur/-air batteries.

Selected Related Papers

Nature Synthesis, 3, 1392–1403 (2024), Nature, 618 959-966 (2023), Nano Letters, 23 (8) 3582-3591 (2023), Energy & Environmental Science, 16 (5) 2003-2013 (2023).

• In-situ transmission electron microscopy (TEM) and Cryogenic TEM analysis:

Direct visualization and observation of nanomaterials and their interface/interphase could be the most straightforward method to understand the nanostructure and its properties. The TEM analysis is a powerful tool for revealing the exact nanostructure including elemental distribution using energy-dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). Above elucidating structural properties of nanomaterials, the demand for understanding reaction mechanisms and finding fundamental correlations is increasing significantly. 

In-situ TEM provides remarkable opportunities for monitoring the real-time reaction evolutions of energy materials, including battery cycling and electrocatalysis. Utilization of battery materials that have theoretically high specific capacity, such as lithium (Li) metal and sulfur (S), has problems due to insufficient understanding of their reaction mechanisms during the charge and discharge process. In electrocatalysis, there are some debates about the degradation mechanism of copper (Cu) catalyst in the electrochemical CO2/CO reduction reaction (CO2/CORR). It is hard to reveal the interfacial evolution of reactions, such as the dissolution of atomic layers or phase transition of Cu, during the reactions using conventional analytic tools. The in-situ TEM can suggest locally generated reaction fronts at the atomic level and then provide some ideas to improve the performance of energy materials. 

Cryogenic TEM enables the observation of metastable materials, such as Li metal and a formed solid electrolyte interphase (SEI), which is difficult to visualize due to the strong electron beam of conventional TEM. It accurately identifies the morphology of plated Li metal and the chemical information of formed SEI. Additionally, it allows the analysis of local interfacial states formed during catalytic reactions without exposure to air, facilitating a better understanding of the precise interfacial reaction. Unlike traditional analysis tools used for interfacial analysis, like X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), it overcomes the ensemble average problem by precisely observing locally formed nanostructures and chemical information. Thereby providing insights for interfacial designs based on a deep understanding of interfacial reactions, such as ionic exchange behavior and pH swing during electrocatalysis.

• Converting Traditional Chemical Engineering to Electrochemical Engineering

Production of green fuels (Hydrogen (H2), Formate (HCOOH), ammonia (NH3), etc.) through eco-friendly (H2O & O2), waste (CO2), and harmful (NOx) reactants 

• Recycling Resources using Electrochemical Systems

Recovery of abundant resources (Li, Ni, …) from seawater or waste materials using efficient electrochemical systems 

• Advanced Techniques to Understand Reaction Chemistry

Liquid cell - 4D STEM and other in-situ spectroscopy studies for understanding fundamental interfacial reaction mechanisms