• Journal of Surface Science and Engineering
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• v.56 no.6
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• pp.427-436
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• 2023

In the industry, it is recognized that human activities significantly lead to a large amount of wastewater, mainly due to the increased use of water and energy. As a result, the growing field of wastewater resource technology is getting more attention. The common technology for hydrogen production, water electrolysis, requires purified water, leading to the need for desalination and reprocessing. However, producing hydrogen directly from wastewater could be a more cost-effective option compared to traditional methods. To achieve this, a series of first-principle computational simulations were conducted to assess how waste nutrient ions affect standard electrolysis catalysts. This study focused on understanding the adsorption mechanisms of byproducts related to the oxygen evolution reaction (OER) in anion exchange membrane (AEM) electrolysis, using Co₃O₄ as a typical non-precious metal catalyst. At the same time, efforts were made to develop a comprehensive free energy prediction model for more accurate predictions of OER results.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.168.1-168.1
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• 2017

화석연료를 대체하기 위한 에너지원으로서 수소에너지에 대한 연구가 활발히 진행되고 있다. 수전해는 무한 청정한 물을 전기분해하여 수소를 생산하는 기술로써 대표적으로 알칼리 수전해(alkaline water electrolysis, AWE)와 고분자 전해질막 수전해(polymer electrolyte membrane water electrolysis, PEMWE)가 있다. 그 중, AWE는 알칼리 분위기에서 물분해 반응이 진행되어 촉매의 부식 위험성이 비교적 낮기 때문에 상대적으로 저렴한 비귀금속 산화물 촉매를 사용할 수 있다는 장점이 있다. 본 연구에서는 비귀금속인 Cu, Co를 이용하여 $CuCoO_4$를 합성한 후 산소 발생 촉매 물질로 활용하여 산소 발생 반응(Oxygen Evolution Reaction, OER)특성을 고찰하였다.

• Journal of Electrochemical Science and Technology
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• v.6 no.4
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• pp.121-130
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• 2015

The micro emulsion method has been successfully used for preparing perovskite LaCoO₃ with uniform, fine-shaped nanoparticles showing high activity as electro catalysts in oxygen reduction reactions (ORRs). They are, therefore, promising candidates for the air-cathode in metal-air rechargeable batteries. Since the activity of a catalyst is highly dependent on its specific surface area, nanoparticles of the perovskite catalyst are desirable for catalyzing both oxygen reduction and evolution reactions. Herein, LaCoO₃ powder was also prepared by sol-gel method for comparison, with a broad particle distribution and high agglomeration. The electro catalytic properties of LaCoO₃ and LaCoO₃-carbon Super P mixture layers toward the ORR were studied comparatively using the rotating disk electrode technique in 0.1 M KOH electrolyte to elucidate the effect of carbon Super P. Koutecky-Levich theory was applied to acquire the overall electron transfer number (n) during the ORR, calculated to be ~3.74 for the LaCoO₃-Super P mixture, quite close to the theoretical value (4.0), and ~2.7 for carbon-free LaCoO₃. A synergistic effect toward the ORR is observed when carbon is present in the LaCoO₃ layer. Carbon is assumed to be more than an additive, enhancing the electronic conductivity of the oxide catalyst. It is suggested that ORRs, catalyzed by the LaCoO₃-Super P mixture, are dominated by a 2+2-electron transfer pathway to form the final, hydroxyl ion product.

• Journal of Hydrogen and New Energy
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• v.25 no.4
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• pp.436-442
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• 2014

$LaCoO_3$ powders synthesized by Pechini process were pulverized by planetary ball-milling to decrease particle size and characterized as a catalyst in alkaline solution for oxygen reduction and evolution reaction (ORR & OER). The changes of physical properties, such as particle size distribution, surface area and electric conductivity, were analyzed as a function of ball-milling time. Also, the variations of the crystal structure and surface morphology of ball-milled powders were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electrochemically catalytic activities of the intrinsic $LaCoO_3$ powders decreased with increasing ball-milling time, but their electrochemical performance as an electrode improved by the increase of the surface area of the powder.

• Journal of the Korean Electrochemical Society
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• v.23 no.4
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• pp.97-104
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• 2020

One of the main challenges of electrochemical water splitting technology is to develop a high performance, low cost oxygen-evolving electrode capable of substituting a noble metal catalyst, Ir or Ru based catalyst. In this work, CoFe₂O₄ nanoparticles with sub-44 nmsize of a inverse spinel structure for oxygen evolution reaction (OER) were synthesized by the injection of KNO₃ and NaOH solution to a preheated CoSO₄ and Fe(NO₃)₃ solution. The synthesis time of CoFe₂O₄ nanoparticles was controlled to control particle and crystallite size. When the synthesis time was 6 h, CoFe₂O₄ nanoparticles had high conductivity and electrochemical surface area. The overpotential at current denstiy of 10 mA/㎠ and Tafel slope of CoFe₂O₄ (6h) were 395 mV and 52 mV/dec, respectively. In addition, the catalyst showed excellent durability for 18 hours at 10 mA/㎠.

• Journal of Powder Materials
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• v.29 no.5
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• pp.411-417
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• 2022

Environmental issues such as global warming due to fossil fuel use are now major worldwide concerns, and interest in renewable and clean energy is growing. Of the various types of renewable energy, green hydrogen energy has recently attracted attention because of its eco-friendly and high-energy density. Electrochemical water splitting is considered a pollution-free means of producing clean hydrogen and oxygen and in large quantities. The development of non-noble electrocatalysts with low cost and high performance in water splitting has also attracted considerable attention. In this study, we successfully synthesized a NiCo₂O₄/NF electrode for an oxygen evolution reaction in alkaline water splitting using a hydrothermal method, which was followed by post-heat treatment. The effects of heat treatment on the electrochemical performance of the electrodes were evaluated under different heat-treatment conditions. The optimized NCO/NF-300 electrode showed an overpotential of 416 mV at a high current density of 50 mA/cm² and a low Tafel slope (49.06 mV dec^-1). It also showed excellent stability (due to the large surface area) and the lowest charge transfer resistance (12.59 Ω). The results suggested that our noble-metal free electrodes have great potential for use in developing alkaline electrolysis systems.

• Journal of Surface Science and Engineering
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• v.57 no.4
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• pp.325-330
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• 2024

When seawater is used in electrochemical devices, issues arise such as the adsorption of chloride ions blocking the active sites for Oxygen reduction reactions (ORR) in seawater batteries, and the occurrence of Chlorine evolution reactions (ClER) in seawater electrolysis due to chloride anions (Cl^-) competing with OH^- for catalytic active sites, potentially slowing down Oxygen evolution reactions (OER). Consequently, the performance of components used in seawater battery and seawater electrolysis may deteriorate. Therefore, conventional alloys are often used by coating or plating methods to minimize corrosion, albeit at the cost of reducing electrical conductivity. This study thus designed a corrosion-resistant layer by doping carbon with Nitrogen (N) and Sulfur (S) to maintain electrical conductivity while preventing corrosion. Optimal N,S doping ratios were developed, with corrosion experiments confirming that N,S (10:90) carbon exhibited the best corrosion resistance performance.

• Journal of Surface Science and Engineering
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• v.56 no.4
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• pp.243-249
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• 2023

Urea oxidation reaction (UOR) via electrochemical oxidation process can replace oxygen evolution reaction (OER) for green hydrogen production since UOR has lower thermodynamic potential (0.37 V_RHE) than that of OER (1.23 V_RHE). However, in the case of UOR, 6 electrons are required for the entire UOR. For this reason, the reaction rate is slower than OER, which requires 4 electrons. In addition, it is an important challenge to develop catalysts in which both oxidation reactions (UOR and OER) are active since the active sites of OER and UOR are opposite to each other. We prove that among the NiFe₂O₄ nanoparticles synthesized by the hydrothermal method at various synthesis temperatures, NiFe₂O₄ nanoparticle with properly controlled particle size and crystallinity can actively operate OER and UOR at the same time.

• Environmental Engineering Research
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• v.19 no.4
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• pp.299-308
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• 2014

This study presents a review on Chemical looping combustion (CLC) development, design aspects and modeling. The CLC is in fact an unmixed combustion based on the transfer of oxygen to the fuel by a solid oxygen carrier material avoiding the direct contact between air and fuel. The CLC process is considered as a very promising combustion technology for power plants and chemical industries due to its inherent capability of $CO_2$ capturing, which avoids extra separation costs of the of $CO_2$ from the rest of flue gases. This review covers the issues related to oxygen carrier materials. The modeling works are reviewed and different aspects of modeling are considered, as well. The main drawbacks and future research and prospects are remarked.

• Korean Journal of Materials Research
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• v.29 no.2
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• pp.92-96
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• 2019

Transition metal oxide is widely used as a water electrolysis catalyst to substitute for a noble metal catalyst such as $IrO_2$ and $RuO_2$. In this study, the sol-gel method is used to synthesize the $Cu_xCo_{3-x}O_4$ catalyst for the oxygen evolution reaction (OER),. The CuxCo3-xO4 is synthesized at various calcination temperatures from $250^{\circ}C$ to $400^{\circ}C$ for 4 h. The $Cu_xCo_{3-x}O_4$ synthesized at $300^{\circ}C$ has a perfect spinel structure without residues of the precursor and secondary phases, such as CuO. The particle size of $Cu_xCo_{3-x}O_4$ increases with an increase in calcination temperature. Amongst all the samples studied, $Cu_xCo_{3-x}O_4$, which is synthesized at 300?, has the highest activity for the OER. Its onset potential for the OER is 370 mV and the overpotential at $10mA/cm^2$ is 438 mV. The tafel slope of $Cu_xCo_{3-x}O_4$ synthesized at $300^{\circ}C$ has a low value of 58 mV/dec. These results are mainly explained by the increase in the available active surface area of the $Cu_xCo_{3-x}O_4$ catalyst.