• Journal of Electrochemical Science and Technology
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• 제13권1호
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• pp.120-127
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• 2022

Molybdenum disulfide (MoS₂) has been widely used as a catalyst for the bifunctional activities of hydrogen and oxygen evolution reactions (HER and OER). Here, we investigated size dependent HER and OER performance of MoS₂. The smallest size (90 nm) of MoS₂ exhibits the lowest overpotential of -0.28 V at -10 mAcm^-2 and 1.52 V at 300 mAcm^-2 with the smallest Tafel slopes of 151 and 176 mVdec^-1 for HER and OER, respectively, compared to bigger sizes (2 ㎛ and 6 ㎛) of MoS₂. The better HER and OER performance is attributed to high electrochemical active surface area (6 × 10^-4 cm²) with edge sites and low charge transfer resistance (18.1 Ω), confirming that the smaller MoS₂ nanosheets have the better catalytic behavior.

• 한국표면공학회지
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• 제54권4호
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• pp.164-170
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• 2021

Vanadium redox flow batteries (VRFB) have emerged as large-scale energy storage systems (ESS) due to their advantages such as low cross-contamination, long life, and flexible design. However, Hydrogen evolution reaction (HER) in the negative half-cell causes a harmful influence on the performance of the VRFB by consuming current. Moreover, HER hinders V²⁺/V³⁺ redox reaction between electrode and electrolyte by forming a bubble. To address the HER problem, carbon nanotube/graphite felt electrode (CNT/GF) with oxygen functional groups was synthesized through the hydrothermal method in the H₂SO₄ + HNO₃ (3:1) mixed acid solution. These oxygen functional groups on the CNT/GF succeed in suppressing the HER and improving charge transfer for V²⁺/V³⁺ redox reaction. As a result, the oxygen functional group applied electrode exhibited a low overpotential of 0.395 V for V²⁺/V³⁺ redox reaction. Hence, this work could offer a new strategy to design and synthesize effective electrodes for HER suppression and improving the energy density of VRFB.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.87.1-87.1
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• 2017

High functional catalyst to efficiently produce clean and earth-abundant renewable fuels plays a key role in securing energy sustainability and environmental protection of our society. Hydrogen has been considered as one of the most promising energy carrier as represented by focused research works on developing catalysts for the hydrogen evolution reaction (HER) from the water hydrolysis over the last several decades. So far, however, the major catalysts are expensive transition metals. Here using first principles density functional theory (DFT) calculations we screen various pyrites for HER by identifying fundamental descriptor governing the catalytic activity. We enable to capture a strong linearity between experimentally measured exchange current density in HER and calculated adsorption energy of hydrogen atom in the pyrites. The correlation implies that there is an underlying design principle tuning the catalytic activity of HER.

• Journal of Electrochemical Science and Technology
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• 제13권4호
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• pp.417-423
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• 2022

With the emerging importance of catalysts for water electrolysis, developing efficient and inexpensive electrocatalysts for water electrolysis plays a vital role in renewable hydrogen energy technology. In this study, a 1nm thickness of TiC-supported Ru catalyst for hydrogen evolution reaction (HER) has been successfully fabricated using an electron (E)-beam evaporator and thermal decomposition of gaseous CH₄ in a furnace. The prepared Ru/TiC catalyst exhibited an outstanding performance for alkaline hydrogen evolution reaction with an overpotential of 55 mV at 10 mA cm^-2. Furthermore, we demonstrated that the outstanding HER performance of Ru/TiC was attributed to the high surface area of the support and the metal-support interaction.

• 공업화학
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• 제34권6호
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• pp.567-575
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• 2023

물의 전기 분해는 효과적인 그린 수소를 생산하기 위한 유망한 기술 중 하나로서 활발한 연구가 이루어지고 있다. 수전해 시스템의 원료로 해수를 직접 사용하게 되면 지구상에 있는 물의 약 97%를 해수가 차지하고 있으므로, 기존 담수 원료의 제한성에 대한 문제를 해결할 수 있다. 동시에 풍부한 부생 원료를 얻을 수 있는데, 그 성분과 pH 환경에 따라 전기 분해 과정에서 생성되는 Cl₂, ClO^-, Br₂ 및 Mg(OH)₂ 등이 대표적이다. 성공적인 해수 수전해 시스템 개발과 이에 필수적인 산소발생반응(oxygen evolution reaction, OER)과 수소발생반응(hydrogen evolution reaction, HER) 촉매를 개발하기 위해서는 해수 환경에서 일어나는 반응의 원인과 결과에 대해 파악할 필요가 있다. 따라서 본 논문에서는 해수 수전해 시스템의 반응 메커니즘과 특징 및 애노드와 캐소드 전극에 사용되는 전기화학 촉매들의 연구 개발 동향에 대해 살펴보고자 한다.

• 한국수소및신에너지학회논문집
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• 제28권6호
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• pp.610-617
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• 2017

This paper presents a study of the effect of thickness of porous Al-Ni electrodes, on the Hydrogen Evolution Reaction (HER) in alkaline media. As varying deposition time at 300 W DC sputtering power, the thickness of the Al-Ni electrodes was controlled from 1 to $20{\mu}m$. The heat treatment was carried out in $610^{\circ}C$, followed by selective leaching of the Al-rich phase. XRD studies confirmed the presence of $Al_3Ni_2$ intermetallic compounds after the heat treatment, indicating the diffusion of Ni from the Ni-rich phase to Al-rich phase. The porous structure of the Al-Ni electrodes after the selective leaching of Al was also confirmed in SEM-EDS analysis. The double layer capacitance ($C_{dl}$) and roughness factor ($R_f$) of the electrodes were increased for the thicker Al-Ni electrodes. As opposed to the general results in above, there were no further improvements of the HER activity in the case of the electrode thickness above $10{\mu}m$. This result may indicate that the $R_f$ is not the primary factor for the HER activity in alkaline media.

• 한국표면공학회지
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• 제50권5호
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• pp.322-331
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• 2017

Hydrogen evolution reaction(HER) was studied over $Ni_4Cr$ nanofibers(NFs) prepared by electrospinning method and oxidation/reduction heat treatment for alkaline water electrolysis. The physicochemical and electrochemical properties such as average diameter, lattice parameter, HER activity of synthesized $Ni_4Cr$ NFs could be modified by proper electrospinning process condition and reduction temperature. It was shown that $Ni_4Cr$ NFs had average diameter from 151 to 273 nm. Also, it exhibited the overpotential between 0.419 V and 0.526 V at $1mA/cm^2$ and Tafel slope of -334.75 mV to -444.55 mV per decade in 1 M KOH solution. These results indicate that $Ni_4Cr$ NFs with reduction heat treatment at $600^{\circ}C$ show thinnest diameter and highest HER activity among the other catalysts.

• 한국재료학회지
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• 제29권12호
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• pp.798-803
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• 2019

The self-discharge behavior of zinc-air batteries is a critical issue induced by corrosion and hydrogen evolution reaction (HER) of zinc anode. The corrosion reaction and HER can be controlled by a gelling agent and concentration of potassium hydroxide (KOH) solution. Various concentrations of KOH solution and polyacrylic acid have been used for gel electrolyte. The electrolyte solution is prepared with different concentrations of KOH (6 M, 7 M, 8 M, 9 M). Among studied materials, the cell assembled with 6 M KOH gel electrolyte exhibits the highest specific discharge capacity and poor capacity retention. Whereas, 9 M KOH gel electrolyte shows high capacity retention. However, a large amount of hydrogen gas is evolved with 9 M KOH solution. In general, the increase in concentration is related to ionic conductivity. At concentrations above 7 M, the viscosity increases and the conductivity decreases. As a result, compared to other studied materials, 7 M KOH gel electrolyte is suitable for Zn-air batteries because of its higher capacity retention (92.00 %) and specific discharge capacity (351.80 mAh/g) after 6 hr storage.

• 한국재료학회지
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• 제30권12호
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• pp.709-714
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• 2020

For zinc-air batteries, there are several limitations associated with zinc anodes. The self-discharge behavior of zinc-air batteries is a critical issue that is induced by corrosion reaction and hydrogen evolution reaction (HER) of zinc anodes. Aluminum and indium are effective additives for controlling the hydrogen evolution reaction as well as the corrosion reaction. To enhance the electrochemical performances of zinc-air batteries, mechanically alloyed Zn-Al and Zn-In materials with different compositions are successfully fabricated at 500rpm and 5h milling time. Investigated materials are characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), and energy dispersive spectrometer (EDS). Alloys are investigated for the application as novel anodes in zinc-air batteries. Especially, the material with 3 wt% of indium (ZI3) delivers 445.37 mAh/g and 408.52 mAh/g of specific discharge capacity with 1 h and 6 h storage, respectively. Also, it shows 91.72 % capacity retention and has the lowest value of corrosion current density among attempted materials.

• Journal of Electrochemical Science and Technology
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• 제13권1호
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• pp.54-62
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• 2022

The preparation of low-cost, simple, and scalable electrodes is crucial for the commercialization of water electrolyzers for H₂ production. Herein, we demonstrate the fabrication of cathodes through Mo-modified Zn phosphating of Ni foam (NiF) for water electrolysis, which has been largely utilized in surface coating industry. In situ growth of electrocatalytically active layers in the hydrogen evolution reaction (HER) was occurred after 1 min of phosphating to form ZnNiMoP_i, and subsequent thermal treatment and electrochemical activation resulted in the formation of ZnNiMoPO_xH_y. ZnNiMoPO_xH_y exhibited superior HER performance than NiF, primarily because of the increased electrochemically active surface area of ZnNiMoPO_xH_y compared to that of bare NiF. Although further investigations to improve the intrinsic electrochemical activity toward the HER and detailed mechanistic studies are required, these results suggest that phosphating is a promising coating method and will possibly advance the fabrication procedure of electrodes for water electrolyzers with better practical applications.