• 한국재료학회지
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• 제30권5호
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• pp.217-222
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• 2020

The design and fabrication of catalysts with low-cost and high electrocatalytic activity for the oxygen evolution reaction (OER) have remained challenging because of the sluggish kinetics of this reaction. The key to the pursuit of efficient electrocatalysts is to design them with high surface area and more active sites. In this work, we have successfully synthesized a highly stable and active NiCo₂S₄ nanowire array on a Ni-foam substrate (NiCo₂S₄ NW/NF) via a two-step hydrothermal synthesis approach. This NiCo₂S₄ NW/NF exhibits overpotential as low as 275 mV, delivering a current density of 20 mA cm^-2 (versus reversible hydrogen electrode) with a low Tafel slope of 89 mV dec^-1 and superior long-term stability for 20 h in 1 M KOH electrolyte. The outstanding performance is ascribed to the inherent activity of the binder-free deposited, vertically aligned nanowire structure, which provides a large number of electrochemically active surface sites, accelerating electron transfer, and simultaneously enhancing the diffusion of electrolyte.

• 한국결정성장학회지
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• 제34권3호
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• pp.92-97
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• 2024

수소 생산을 위한 물 분해 시스템의 효율성을 높이려면 산소 발생 반응(OER, Oxygen Evolution Reaction)에서 촉매로 인해 발생하는 전기화학 반응의 높은 과전압을 감소시켜야 한다. 그중 전이금속을 포함하는 LDH(Layered Double Hydroxide)와 같은 화합물은 현재 사용되고 있는 백금 등의 귀금속을 대체할 수 있는 촉매 소재로 주목받고 있다. 본 연구에서는 저렴한 금속 다공성 물질인 니켈 폼을 지지체로 사용하였고, 수열합성 공정을 통해 NiCo LDH 나노결정을 합성하였다. 또한, OER 특성을 향상시키기 위해 Mo를 도핑하여 합성한 Mo 도핑된 NiCo LDH 나노결정 시료의 형태, 결정구조, 물분해 특성의 변화를 관찰하였다.

• Journal of Electrochemical Science and Technology
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• 제10권4호
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• pp.402-407
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• 2019

Water electrolysis is known as the most sustainable and clean technology to produce hydrogen gas, however, a serious drawback to commercialize this technology is due to the slow kinetics in oxygen evolution reaction (OER). Thus, we report on the nanoporous IrNi thin film that reveals a markedly enhanced OER activity, which is attained through a selective etching of Os from the IrNiOs alloy thin film. Interestingly, electrochemical selective etching of Os leads to the formation of 3-dimensionally interconnected nanoporous structure providing a high electrochemical surface area (ECSA, 80.8 ㎠), which is 90 fold higher than a bulk Ir surface (0.9 ㎠). The overpotential at the nanoporous IrNi electrode is markedly lowered to be 289 mV at 10 mA cm^-2, compared with bulk Ir (375 mV at 10 mA cm^-2). The nanoporous IrNi prepared through the selective de-alloying of Os is promising as the anode material for a water electrolyzer.

• Journal of Electrochemical Science and Technology
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• 제7권1호
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• pp.76-81
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• 2016

An anatase TiO₂ nanotube array (NTA) was fabricated by anodization and successive heat treatments. When the anatase TiO₂ NTA was cathodically polarized, its color changed to blue, and it could be used as an electrochemically active anode for an oxygen evolution reaction (OER) in alkaline water electrolysis. The structure of the blue anatase TiO₂ NTA was controlled by the anodization conditions and its catalytic activity increased with an increase of the surface area. The activity of the blue anatase TiO₂ NTA gradually reduced with the continued OER because of the partial oxidation of Ti³⁺ to Ti⁴⁺. However, an intermittent cathodic regeneration process could significantly slow its reduction rate. The blue anatase TiO₂ NTA could be an alternative anode for alkaline water electrolysis.

• 대한금속재료학회지
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• 제47권2호
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• pp.107-113
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• 2009

Molten iron with 2 mass % carbon content was decarbonized at 1823 K~1923 K by bubbling $Ar+O_2$ gas through a submerged nozzle. The reaction rate was significantly influenced by the oxygen partial pressure and the gas flow rate. Little evolution of CO gas was observed in the initial 5 seconds of the oxidation; however, this was followed by a period of high evolution rate of CO gas. The partial pressure of CO gas decreased with further progress of the decarbonization. The overall reaction is decomposed to two elementary reactions: the decarbonization and the dissolution rate of oxygen. The assumptions were made that these reactions are at equilibrium and that the reaction rates are controlled by mass transfer rates within and around the gas bubble. The time variations of carbon and oxygen contents in the melt and the CO partial pressure in the off-gas under various bubbling conditions were well explained by the mathematical model. Based on the present model, it was explained that the decarbonization rate of molten iron was controlled by gas-phase mass transfer at the first stage of reaction, but the rate controlling step was transferred to liquid-phase mass transfer from one third of reaction time.

• 전기화학회지
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• 제26권4호
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• pp.64-70
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• 2023

급격한 온실가스 배출량 증가로 인해 지구 온난화가 심화되고 있다. 이로 인해 탄소중립의 필요성과 이행이 더욱 절실해졌다. 이를 위해 여러 가지 신재생에너지 중 수소에 대한 관심이 부각되고 있다. 수소는 지구 상에 풍부한 자원이며 무탄소 전원으로 친환경적이다. 궁극적으로 물의 전기분해에 의해 친환경 수소를 얻을 수 있다. 하지만 산소 발생 반응에 사용되는 촉매는 고가이며 희귀하고 촉매의 내구성에 문제가 있어 어려움을 겪고 있기 때문에 비귀금속 촉매의 개발이 필요하다. 본 총설에서는 최근 발표된 산소 발생 촉매 중 비귀금속 촉매인 Co와 Mo 기반의 촉매를 정리, 요약하여 소개하고 있다. 이를 통해 비귀금속 촉매의 활성과 내구성을 증가시키기 위한 촉매의 특성 설계를 이해하는 데 도움이 될 것이다.

• 대한화학회지
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• 제68권2호
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• pp.87-92
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• 2024

The commercialization of rechargeable metal-air batteries is extremely desirable but designing stable oxygen reduction reaction (ORR) catalysts with non-noble metal still has faced challenges to replace platinum-based catalysts. The nonnoble metal catalysts for ORR were prepared to improve the catalytic performance and stability by the thermal decomposition of ZIF-8 with optimum cobalt loading. The porous carbon was obtained by the calcination of ZIF-8 and different loading amounts of Co nanoparticles were anchored onto porous carbon forming a Co/PC catalyst. Co/PC composite shows a significant increase in the ORR value of current and stability (500 h) due to the good electronic conductive PCN support and optimum cobalt metal loading. The significantly improved catalytic performance is ascribed to the chemical structure, synergistic effects, porous carbon networks, and rich active sites. This method develops a new pathway for a highly active and advantageous catalyst for electrochemical devices.

• 한국수소및신에너지학회논문집
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• 제32권1호
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• pp.41-52
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• 2021

NiO and Co3O4-doped porous La(CoNi)O3 perovskite oxides were prepared from excess Ni addition by a hydrothermal method using porous silica template, and characterized as bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for Zn-air rechargeable batteries in alkaline solution. Excess Ni induced to form NiO and Co3O4 in La(CoNi)O3 particles. The NiO and Co3O4-doped porous La(CoNi)O3 showed high specific surface area, up to nine times of conventionally synthesized perovskite oxide, and abundant pore volume with similar structure. Extra added Ni was partially substituted for Co as B site of ABO3 perovskite structure and formed to NiO and Co3O4 which was highly dispersed in particles. Excess Ni in La(CoNi)O3 catalysts increased OER performance (259 mA/㎠ at 2.4 V) in alkaline solution, although the activities (211 mA/㎠ at 0.5 V) for ORR were not changed with the content of excess Ni. La(CoNi)O3 with excess Ni showed very stable cyclability and low capacity fading rate (0.38 & 0.07 ㎶/hour for ORR & OER) until 300 hours (~70 cycles) but more excess content of Ni in La(CoNi)O3 gave negative effect to cyclability.

• Journal of Electrochemical Science and Technology
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• 제13권4호
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• pp.497-503
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• 2022

Spinel ferrites (Ni_xFe_3-xO₄; x = 0.25, 0.5, 0.75 and 1.0) have been prepared at 550℃ by egg white auto-combustion route using egg white at 550℃ and characterized by physicochemical (TGA, IR, XRD, and SEM) and electrochemical (CV and Tafel polarization) techniques. The presence of characteristic vibration peaks in FT-IR and reflection planes in XRD spectra confirmed the formation of spinel ferrites. The prepared oxides were transformed into oxide film on glassy carbon electrodes by coating oxide powder ink using the nafion solution and investigated their electrocatalytic performance for OER in an alkaline solution. The cyclic voltammograms of the oxide electrode did not show any redox peaks in oxygen overpotential regions. The iR-free Tafel polarization curves exhibited two Tafel slopes (b₁ = 59-90 mV decade^-1 and b₂ = 92-124 mV decade^-1) in lower and higher over potential regions, respectively. Ni-substitution in oxide matrix significantly improved the electrocatalytic activity for oxygen evolution reaction. Based on the current density for OER, the 0.75 mol Ni-substituted oxide electrode was found to be the most active electrode among the prepared oxides and showed the highest value of apparent current density (~9 mA cm^-2 at 0.85 V) and lowest Tafel slope (59 mV decade^-1). The OER on oxide electrodes occurred via the formation of chemisorbed intermediate on the active sites of the oxide electrode and follow the second-order mechanism.

• 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.