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21 results on '"Roh, Jeonghan"'

3. Heterogeneous Structure of Ni–Mo Nanoalloys Decorated on MoOx for an Efficient Hydrogen Evolution Reaction Using Hydrogen Spillover.

Author

Song, DongHoon, Roh, Jeonghan, Choi, Jungwoo, Lee, Hyein, Koh, Gyungmo, Kwon, YongKeun, Kim, HyoWon, Lee, Hyuck Mo, Kim, MinJoong, and Cho, EunAe

Subjects
*HYDROGEN evolution reactions, *ELECTROCHEMICAL analysis, *HETEROGENEOUS catalysts, *DENSITY functional theory, *HYDROGEN atom, *OXYGEN evolution reactions
Abstract

Herein, a heterogeneous structure of Ni–Mo catalyst comprising Ni4Mo nanoalloys decorated on a MoOx matrix via electrodeposition is introduced. This catalyst exhibits remarkable hydrogen evolution reaction (HER) activity across a range of pH conditions. The heterogeneous Ni–Mo catalyst showed low overpotentials only of 24 and 86, 21 and 60, and 37 and 168 mV to produce a current density of 10 and 100 mA cm−2 (η10 and η100) in alkaline, acidic, and neutral media, respectively, which represents one of the most active catalysts for the HER. The enhanced activity is attributed to the hydrogen spillover effect, where hydrogen atoms migrate between the Ni4Mo alloys and the MoOx matrix, forming hydrogen molybdenum bronze as additional active sites. Additionally, the Ni4Mo facilitated the water dissociation process, which helps the Volmer step in the alkaline/neutral HER. Through electrochemical analysis, in situ Raman spectroscopy, and density functional theory calculations, the fast HER mechanism is elucidated. [ABSTRACT FROM AUTHOR]

Published
2024
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6. Tailoring the Electrophilicity of Co Surface for Favorable toward Alkaline Oxygen Evolution Reaction by Metal Cation Doping.

Author

Kim, MinJoong, Song, DongHoon, Lim, JeongHoon, Bak, Junu, Roh, Jeonghan, Oh, SeKwon, Cho, EunAe, and Thirumurugan, Arun

Subjects
OXYGEN evolution reactions, WATER electrolysis, SURFACE properties, OXIDATION states, ELECTRONIC structure
Abstract

The chemical coupling of molybdenum carbide (Mo2C) to cobalt (Co) promotes oxygen evolution reaction (OER) kinetics on the Co surface by making the surface more electrophilic. Here, to gain a deeper understanding of the effects of the surface electrophilic properties on the OER kinetics of Co and to obtain high OER activity, Fe and Ni are additionally incorporated into Co nanoparticles that are coupled with Mo2C nanoparticles (Co‐Mo2C). Considering the oxidation states of Fe (Fe3+), Co (Co2+/Co3+), and Ni (Ni2+) ions, Fe and Ni are expected to affect the electronic structure of Co in the opposite direction. Lewis acidic Fe3+ doping makes the Co surface oxide more electrophilic, promoting the formation of OER‐active CoOOH by strongly attracting hydroxide ions (OH−). Thus, the OER kinetics is facilitated on the Co surface of Fe‐doped Co‐Mo2C, resulting in a significantly lower overpotential for the OER. On the other hand, the Ni2+ doping makes the Co surface oxide less electrophilic, leading to an increase in the overpotential for the OER. Tailoring the electrophilic properties of the Co surface is presented as a key parameter in the design of a Co‐based OER catalyst for alkaline water electrolysis. [ABSTRACT FROM AUTHOR]

Published
2024
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11. Transformation of the Active Moiety in Fe-N-C Electrocatalyst through Invasive P-Doping for Highly Efficient Oxygen Reduction Reaction

Author

Roh, JeongHan, primary, Cho, Ara, additional, Kim, Sungjun, additional, Lee, Kug-Seung, additional, Shin, Jaewook, additional, Bak, Junu, additional, Lee, SangJae, additional, Song, DongHoon, additional, Kim, Eom-Ji, additional, Cho, Yong-Hun, additional, Han, Jeong Woo, additional, and Cho, EunAe, additional

Published
2022
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