• Journal of Electrochemical Science and Technology
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• v.14 no.1
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• pp.96-104
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• 2023

Synergistically increased oxygen evolution reaction (OER) of manganese oxide (MnO₂) catalyst is introduced with surface-modified halloysite nanotube (Fe₃O₄-HNTs) structure. The flake shaped MnO₂ catalyst is attached on the nanotube template (Fe₃O₄-HNTs) by series of wet chemical and hydrothermal method. The strong interaction between MnO₂ and Fe₃O₄-HNTs maximized active surface area and inter-connectivity for festinate charge transfer reaction for OER. The synergistical effect between Fe₃O₄ layer and MnO₂ catalyst enhance the Mn³⁺/Mn⁴⁺ ratio by partial replacement of Mn ions with Fe. The relatively increased Mn³⁺/Mn⁴⁺ ratio on MnO₂@FHNTs induced 𝜎^* orbital (e_g) occupation close to single electron, improving the OER performances. The MnO₂@FHNTs catalyst exhibited the reduced overpotential of 0.42 V (E vs. RHE) at 10 mA/cm² and Tafel slope of (99 mV/dec), compared with that of MnO₂ with unmodified HNTs (0.65 V, 219 mV/dec) and pristine MnO₂ (0.53 V, 205 mV/dec). The present study provides simple and innovative method to fabricate nano fiberized OER catalyst for a broad application of energy conversion and storage systems.

• Journal of Hydrogen and New Energy
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• v.32 no.1
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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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• v.10 no.4
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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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• v.7 no.1
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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.

• Journal of Electrochemical Science and Technology
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• v.13 no.4
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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.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.46-46
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• 2014

알칼리 수전해는 신재생에너지를 이용하여 오염물질 없이 효율적으로 수소를 생산할 수 있는 방법 중의 하나이다. 알칼리 수전해 시스템의 산화전극으로 불용성전극이 많이 사용되고 있으나 높은 과전압과 제조 공정이 복잡한 문제점을 가지고 있다. 본 연구에서는 전기변색을 이용해 짙은 파란색의 $TiO_2$ 나노튜브를 알칼리 수전해 시스템의 산화전극으로 이용하고자 하였다. 양극산화법을 이용해 $TiO_2$ 나노튜브를 만드는 과정에서 양극산화 시간과 인가전압에 따라 Blue $TiO_2$의 산소발생반응(Oxygen evolution reaction, OER) 활성 변화를 측정하였고 나노튜브 길이가 길고 직경이 클수록 OER활성과 내구성이 향상되는 것을 확인하였다.

• Journal of Hydrogen and New Energy
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• v.27 no.6
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• pp.677-684
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• 2016

Various commercially available gas diffusion layers (GDLs) from different manufacturers were used to prepare an air electrode using $La_{0.8}Sr_{0.2}CoO_3$ perovskite (LSCP) as the catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in an alkaline solution. Various GDLs have different physical properties, such as porosity, conductivity, hydrophobicity, etc. The ORR and OER of the resulting cathode were electrochemically evaluated in an alkaline solution. The electrochemical properties of the resulting cathodes were slightly different when compared to the physical properties of GDLs. Pore structure and conductivity of GDLs had a prominent effect and their hydrophobicities had a minor effect on the electrochemical performances of cathodes for ORR and OER.

• Journal of Hydrogen and New Energy
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• v.27 no.3
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• pp.276-282
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• 2016

The effects of conductive additives in a $La_{0.8}Sr_{0.2}MnO_3$ perovskite bifunctional electrode for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were investigated in an alkaline solution. Highly porous carbon black (CB) and Ni powder were added to the bifunctional electrodes as conductive additives. The surface morphologies of electrodes containing CB and Ni were observed by scanning electron microscopy (SEM). The current densities for both ORR and OER were changed by the addition of CB. The conductive additive changed physical properties of bifunctional electrodes such as the sheet conductance, gas permeability and contact angle. It was observed that the air permeability of electrode was most effective to enhance the currents for ORR and OER.

• Korean Journal of Materials Research
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• v.32 no.5
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• pp.237-242
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• 2022

Designing and producing a low-cost, high-current-density electrode with good electrocatalytic activity for the oxygen evolution reaction (OER) is still a major challenge for the industrial hydrogen energy economy. In this study, nanostructured Fe-doped CuCo(OH)₂ was discovered to be a precedent electrocatalyst for OER with low overpotential, low Tafel slope, good durability, and high electrochemically active surface sites at reduced mass loadings. Fe-doped CuCo(OH)₂ nanosheets are made using a hydrothermal synthesis process. These nanosheets are clumped together to form a highly open hierarchical structure. When used as an electrocatalyst, the Fe-doped CuCo(OH)₂ nanosheets required an overpotential of 260 mV to reach a current density of 50 mA cm^-2. Also, it showed a small Tafel slope of 72.9 mV dec^-1, and superior stability while catalyzing the generation of O₂ continuously for 20 hours. The Fe-doped CuCo(OH)₂ was found to have a large number of active sites which provide hierarchical and stable transfer routes for both electrolyte ions and electrons, resulting in exceptional OER performance.

• Journal of Surface Science and Engineering
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• v.49 no.6
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• pp.539-548
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• 2016

The non-noble 1D nanofibers(NFs) prepared by electrospinning and calcination method were used as oxygen evolution reaction (OER) electrocatalyst for water electrolysis. The electrospinning process and rate of solution composition was optimized to prepare uniform and non-beaded PVP polymer electrospun NFs. The diameter and morphology of PVP NFs changed in accordance with the viscosity and ion conductivity. The clean metal precursor contained electrospun fibers were synthesized via the optimized electrospinning process and solution composition. The calcined $CuCo_2O_4$ NFs catalyst showed higher activity and long-term cycle stability for OER compared with other $Co_3O_4$, $NiCo_2O$ NF catalysts. Furthermore, the $CuCo_2O_4$ NFs maintained the OER activity during long-term cycle test compared with commercial $CuCo_2O_4$ nanoparticle catalyst due to unique physicochemical and electrochemical properties by1D nanostructure.