Research

Overview

The research interests of the Hong lab lie in bioinorganic chemistry, photochemistry, eletrochemistry, and material chemistry. We have a detailed plan for researching the effective use of solar energy for the production of solar fuel. Our research objective is to develop a catalytic system that generates a new paradigm of environmentally friendly renewable energy sources. In particular, the development of a system that converts natural resources (such as water and CO2, which are the most abundant on Earth) to sustainable fuels can provide a solution to overcome not only the depletion of fossil fuels but also the problem of global warming. Therefore, it is very important to establish a basic scientific foundation for developing catalysts that can activate water and CO2. Therefore, We have goals to develop a catalyst system to obtain oxygen and hydrogen peroxide from water oxidation and hydrogen from water reduction with the use of photochemical-electrochemical conversion technology. We have also developed a catalyst system that converts CO2 into sustainable fuels, such as carbon monoxide, formic acid, formaldehyde, and methanol. Moreover, the reduction of CO2 by enzyme analogs can be combined with PSI and PSII model systems to enable the reduction of CO2 by H2O with the use of solar energy, as an artificial photosynthesis model.

Students in the Hong lab have been engaging in synthetic chemistry (organic and inorganic synthesis), physical methods [NMR, EPR, IR, and UV-vis spectroscopy, stopped flow UV-Vis, time-resolved UV-Vis (nano/pico/femto-second laser), mass spectrometry, and X-ray crystallography), as well as photochemical and eletrochemical techniques [CV, DPV, CPE, SHACV, GC, foxy measurement (oxygen sensor), HPLC, Ion chromatography (IC), transient measurement, and fluorescence measurement].

Artificial Photosynthesis

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This project is the first time to achieve the stoichiometry of photosynthesis by combining molecular functional models of PSI and PSII. Even though the photocatalytic system is virtually the same as that of water splitting, the production of NAD(P)H from water like photosynthesis provides a significant breakthrough because once NAD(P)H is produced, CO2 can be readily reduced by NAD(P)H to formic acid, formaldehyde, and methanol by using formate dehydrogenase (FDH), formaldehyde dehydrogenase (FaldDH), alcohol dehydrogenase (ADH), and Carbon monoxide dehydrogenase (CODH), respectively. NAD(P)H can also reduce carbonyl compounds with use of alcohol dehydrogenases with high stereo- and regioselectivities for the production of pharmaceuticals using water as an electron and proton source.

Mechanistic Insight for Catalytic Reaction

This project goal is to achieve the mechanistic insight for the catalytic reaction, such as water oxidation, H2 formation, NADPH formation, CO2 reduction and H2O2 formation. Especially, in water oxidation, the mechanism of O-O bond formation using metal-oxygen intermediates can be elucided. Synthesis, spectroscopic and structural characterization, and reactivity studies of metal intermediates have been done. Moreover, mechanistic studies of metal ion effects or ligand effects on the reactivities of high-valent metal-oxo intermediates have been achieved and thus the efficient inorganic catalysts can be developed.

Generation of Value-added Products

This project goal is to generate vale-added products using natural resources (such as water and CO2, which are the most abundant on Earth). The vale-added products can be easily converted to sustainable fuels and it can provide a solution to overcome not only the depletion of fossil fuels but also the problem of global warming. Catalytic oxidation of organic substrates by metal complexes and mechanisms of oxygen atom transfer from metal-oxygen intermediates to organic compounds have been studied.

Development of Hybrid Catalyst with Efficient Homogeneous Catalyst

This project goal is to develop the efficient hybrid catalyst with homogeneous catalyst. The main studies are (i) synthesis molecular catalyst with anchoring group, (ii) attachement of molecular catalyst on the support , (iii) stability of hybrid catalyst to exposure to a wider range of reaction solution after the photoelectrochemical reaction, (iv) Finding the conditions with the highest efficiency, and (v) application of them to practical use such as fuel cell. We can analyze the hybrid catalyst using FTIR spectroscopy, XPS, SEM, TEM, EDS mapping, and ICP-MS. Homogeneous catalysts often give high selectivity and are easy to tune but have limited stability. Heterogeneous catalysts are typically more stable and easier to separate but give lower selectivity and can be difficult to rationally modify. The immobilization of molecular catalysts on heterogeneous supports potentially provides the benefits of both homogeneous and heterogeneous catalysis as the molecular component can be tuned to give high selectivity, while the heterogeneous nature of the system improves practicality. Further, immobilized systems are especially valuable for photo-, photoelectro- or electrochemical processes where a conductive support can efficiently capture light and subsequently rapidly transport electrons to the immobilized catalyst.

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