Materials Synthesis for Energy Conversion - Electrochemical Oxygen Evolution Reaction & NO3 Reduction Reaction 

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​The research focuses on developing earth-abundant electrocatalysts and elucidating their reaction mechanisms for two important electrochemical processes: the oxygen evolution reaction (OER) and the nitrate reduction reaction (NO₃RR). A central theme of my work is understanding how catalyst composition, surface reconstruction, and interfacial species regulate proton and electron transfer under realistic operating conditions. By integrating rational materials design with operando spectroscopy and density functional theory (DFT), I aim to establish clear relationships among catalyst structure, dynamic active states, reaction intermediates, and catalytic performance.

For OER, we have investigated spinel oxides, metal sulfides, and layered double hydroxides based primarily on Fe and Co. My early studies demonstrated that cation substitution is an effective strategy for controlling active-site density and interfacial charge transfer. Zn substitution in three-dimensional CuCo₂O₄ and FeCo₂O₄ structures created additional defects, enlarged the electrochemically active surface area, and improved OER kinetics. In Zn-substituted FeCo₂O₄, in situ near-ambient-pressure X-ray photoelectron spectroscopy directly identified the formation of high-valence Co(IV) and cobalt-superoxide species, clarifying their involvement in oxygen formation. I also studied hierarchical FeCo₂S₄ nanospheres using in situ X-ray diffraction and X-ray absorption spectroscopy. These measurements showed that sulfide-assisted charge transfer facilitates the formation of CoOOH, which serves as the catalytically active phase during alkaline OER.

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More recently, our research has shifted from conventional cation engineering toward the active role of interfacial anions. In phosphate-substituted FeCo₂O₄ nanosheets, in situ NAP-XPS revealed that phosphate is not merely a spectator or structural modifier. Instead, it accepts protons from surface Co(OH)₂ and CoOOH species, forming transient hydrogen phosphate and promoting a proton-coupled electron transfer (PCET)-assisted adsorbate evolution mechanism. I further extended this concept to phosphate-modified FeCo layered double hydroxides. Operando Raman spectroscopy, DFT calculations, and molecular-probe experiments consistently demonstrated that phosphate functions as a reversible proton relay. It stabilizes defective surface configurations, assists deprotonation, and lowers the energetic barriers of both adsorbate evolution and lattice-oxygen-mediated pathways.

Building on these OER insights, we apply the same interface-centered approach to NO₃RR for sustainable ammonia production. My current work investigates native phosphate-modulated CoP using operando Raman spectroscopy, in situ NAP-XPS, and DFT calculations. CoP exhibits high nitrate-to-ammonia selectivity and stable operation, while spectroscopic measurements reveal the sequential evolution of NO₃⁻, NO₂⁻, *NO, *NH₂, and NH₃ intermediates. Importantly, persistent and dynamically evolving surface phosphate species appear to facilitate key hydrogenation steps rather than behave as inactive oxidation products. Together, my OER and NO₃RR studies establish interfacial proton management as a unifying principle for controlling complex multielectron electrocatalytic reactions and designing efficient catalysts for renewable hydrogen and ammonia production.

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