Facile one-step synthesis of Ir-Pd bimetallic alloy networks as efficient bifunctional catalysts for oxygen reduction and oxygen evolution reactions

Nguyen, Anh Thi Nguyet,Shim, Jun Ho Elsevier 2018 Journal of Electroanalytical Chemistry Vol.827 No.-

<P><B>Abstract</B></P> <P>This paper introduces a facile one-step process to synthesize highly interconnected nanoporous Ir-Pd alloys supported on carbon that exhibit excellent bifunctional electrocatalytic activities for both the oxygen reduction and oxygen evolution reactions with reasonable stability in alkaline electrolytes. Nanoporous Pd networks with crystalline {111} faces were shown experimentally to serve mainly as active sites for the oxygen reduction reaction, whereas the Ir nanoparticles incorporated in the Pd nanoframe networks, where the optimized Ir:Pd ratio was 0.23:0.77 (<I>n</I> = 10), were responsible for the oxygen evolution reaction. Such three-dimensional architectures provide a high density of active sites for the oxygen electrochemical reaction and facilitate electron transport. More importantly, the nanoporous Ir-Pd alloy nanocomposites exhibited similar stability for the oxygen reduction reaction but superior catalytic activity to the commercial Pd catalyst in alkaline solutions. In addition, the materials were also highly active for the oxygen evolution reaction, e.g., a small overpotential at 10 mA cm<SUP>−2</SUP> (1.628 V vs. reversible hydrogen electrode), making it a high-performance bifunctional catalyst for both the oxygen electrochemical reaction. Rotating ring-disk electrode measurements showed that the oxygen reduction and oxygen evolution reactions on the Ir-Pd catalysts proceeded predominantly through the desired 4-electron pathway.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Facile one-step synthesis of a nanoporous Ir-Pd bimetallic alloy network. </LI> <LI> The composites exhibited bifunctional ORR/OER performance compared to Pd/C and Ir/C. </LI> <LI> Ir<SUB>23</SUB>Pd<SUB>77</SUB>/C exhibited the highest activity with good durability and overpotential. </LI> <LI> The properties of Ir<SUB>23</SUB>Pd<SUB>77</SUB>/C were due to its high surface area and high porosity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A highly active bifunctional electrocatalyst for the oxygen reduction and evolution reactions was developed based on a highly interconnected nanoporous Ir-Pd bimetallic alloy network.</P> <P>[DISPLAY OMISSION]</P>

Monitoring oxygen-vacancy ratio in NiFe-based electrocatalysts during oxygen evolution reaction in alkaline electrolyte

Kim, Hyunki,Kim, Junhyeong,Ahn, Sang Hyun Elsevier 2019 Journal of industrial and engineering chemistry Vol.72 No.-

<P><B>Abstract</B></P> <P>High oxygen-vacancy ratio has been recognized as an important criterion for oxygen evolving electrocatalysts to achieve high catalytic performance. Herein, we report changes in the oxygen-vacancy ratio during long-term stability tests. NiFe-based electrocatalysts containing various anions were prepared by a simple electrodeposition. After the fabrication procedure was optimized, the S-doped NiFe oxide electrocatalyst exhibited higher intrinsic activity than others in an alkaline electrolyte because it had the highest oxygen-vacancy ratio. During oxygen evolution at a constant positive potential, the intrinsic activity of the S-doped NiFe oxide electrocatalyst showed a significant correlation with the oxygen-vacancy ratio and surface morphology as a function of time.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Oxygen-vacancy-rich NiFe-based catalyst was simply fabricated by electrodeposition. </LI> <LI> Catalysts with higher oxygen-vacancy ratio showed higher OER intrinsic activity. </LI> <LI> During OER stability test, the oxygen-vacancy rapidly decreased at initial stage. </LI> <LI> The OER intrinsic activity continuously decreased as a function of time. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A simulation of automotive fuel cell system for oxygen starvation trends by compressor surge under load follow-up

Han, Jaeyoung,Hwang, Janghwan,Yu, Sangseok Pergamon 2019 Applied thermal engineering Vol. No.

<P><B>Abstract</B></P> <P>Oxygen transport analysis is of critical importance during surge evolution for fuel cell systems because it is closely related with the safety and performance of the system. However, research has yet been insufficient on oxygen transport analysis to reaction site surface in catalyst layer under surge evolution. In this paper, an agglomerate model is used to investigate oxygen concentration, local current density, and activation over-potential along catalyst layer thickness under surge evolution. The results are validated versus experimental data from our test. Unlike previous analyses of oxygen transport in the catalyst layer, this study presents an analytic dynamic compressor model that is able to examine the various surge phenomenon. In this study, an agglomerate model is introduced and fuel cell system model including a dynamic compressor is implemented to investigate the influence of surge evolution on the cell performance. At the end, fuel cell system model is simulated during Highway Fuel Economy (HWFET) cycle. The results indicate that oxygen concentration at the GDL/CL interface within the range z = 0 μm to z = 3 μm is most strongly affected by surge evolution, and oxygen concentration changes are strongly affected by surge evolution up to z = 3 μm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dynamic compressor system modeled including a fuel cell system. </LI> <LI> Oxygen reaction reduction was modeled using an agglomerate model. </LI> <LI> Surge was examined by analytical dynamic compressor system model. </LI> <LI> Experiments were conducted to verify the designed agglomerate model. </LI> <LI> Oxygen mass transfer was analyzed in catalyst layer by surge evolution. </LI> </UL> </P>

Design of active bifunctional electrocatalysts using single atom doped transition metal dichalcogenides

Hwang, Jeemin,Noh, Seung Hyo,Han, Byungchan Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.471 No.-

<P><B>Abstract</B></P> <P>Single atom catalyst is designed to achieve high catalytic activity while extremely minimizing precious metal loadings for electrochemical energy conversion and storage applications. Using first-principles density functional theory calculations, we screen 48 combinations of single atom catalysts anchored at defective monolayer transition metal dichalcogenides (A<SUB>1</SUB>/TMD; A = Ni, Cu, Pd, Ag, Pt and Au; TM = Mo, W, Nb and Ta; D = S and Se). With established methodologies, we identify five best catalysts for each of oxygen reduction/evolution and hydrogen evolution reactions among the stable candidates. A scaling relation between the Gibb’s free energy for intermediates is figured out to understand the governing mechanism of single atom catalysts with varying transition metal dichalcogenides supports and to introduce key descriptor. Pt<SUB>1</SUB>/MoS<SUB>2</SUB> is proposed as the best bifunctional catalyst for oxygen reduction/evolution reaction. In addition, Pt<SUB>1</SUB>/NbSe<SUB>2</SUB> and Pt<SUB>1</SUB>/TaS<SUB>2</SUB> are promising candidates for oxygen and hydrogen evolution reactions. Treating the support itself as an active site for hydrogen evolution reaction, Pd<SUB>1</SUB>/NbS<SUB>2</SUB> and Pt<SUB>1</SUB>/NbS<SUB>2</SUB> are proposed as potential bifunctional catalysts toward oxygen reduction and evolution reaction, respectively. Conceptual design principle via high-throughput screening of single atom catalyst is demonstrated as a great approach to determine active and durable bifunctional single atom catalysts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Single atom catalysts with transition metal dichalcogenides supports were screened. </LI> <LI> Five best catalysts were selected for redox reactions of oxygen and hydrogen. </LI> <LI> Pt<SUB>1</SUB>/MoS<SUB>2</SUB> was identified as a great bifunctional single atom catalyst. </LI> <LI> Scaling law was proposed as the key to understand catalytic mechanism. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Ag₂S-CoS hetero-nanowires terminated with stepped surfaces for improved oxygen evolution reaction

Lee, Changsoo,Lee, Chulhee,Shin, Kihyun,Song, Taeyoung,Jeong, Hu Young,Jeon, Duk Young,Lee, Hyuck Mo Elsevier 2019 CATALYSIS COMMUNICATIONS - Vol.129 No.-

<P><B>Abstract</B></P> <P>Water electrolysis has received great attention for producing hydrogen, but sluggish kinetics of oxygen evolution reaction (OER) has remained a big challenge. Recently, cobalt sulfide materials have been widely explored as great choice in highly efficient electrocatalysts due to their good electrical conductivity and bi-functionality toward OER and hydrogen evolution reaction (HER). However, cobalt sulfide shows outstanding HER activity, but its OER activity should be improved. Herein, hexagonal-phase cobalt sulfide (CoS) nanowires with abundant stepped surfaces and defect sites were prepared via a seed-growth approach with silver sulfide (Ag<SUB>2</SUB>S) nanoparticles. The Ag<SUB>2</SUB>S-CoS hetero-nanowires (HNWs) exhibited excellent electrochemical performances for oxygen evolution reaction (overpotential = 275 mV, Tafel slope = 77.1 mVdec<SUP>−1</SUP>, charge transfer resistance = 1.3 Ω) in 1.0 M KOH solution. The origin of superior activity was investigated using a combined experimental and theoretical approach. This work highlights the importance of surface defects for improving oxygen evolution reaction performance of water electrolysis.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hexagonal-phase CoS hetero-nanowires were synthesized using seeded growth with Ag<SUB>2</SUB>S nanoparticles. </LI> <LI> Abundant stepped surface improved catalytic activity toward oxygen evolution reaction. </LI> <LI> Combined experimental and theoretical study for explaining the excellent catalytic performances </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

알칼라인 조건에서의 산소발생반응을 위한 N-doped NiO 촉매

이진구,전옥성,설용건 한국화학공학회 2019 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.57 No.5

Oxygen-evolution reaction (OER) in alkaline media has been considered as a key process for various energy applications. Many types of catalysts have been developed to reduce high overpotential in OER, such as metal alloys, metal oxides, perovskite, or spinel. Nickel oxide (NiO) has high potential to increase OER activity according to volcano plots. The exact mechanisms for OER has not been discovered, but defects such as cation or anion vacancy typically act as an active site for diverse electrochemical reactions. In this study, nitrogen was doped into NiO by using ethylenediamine for formation of Ni vacancy, and the effects of N doping on OER activity and stability was studied. 알칼라인 조건에서의 산소발생 반응(oxygen-evolution reaction: OER)은 다양한 에너지 시스템에 중요한 반응으로여겨지고 있다. 큰 overpotential을 감소시키기 위해 다양한 촉매들이 개발되고 있으며, 그 중 NiO는 높은 활성도에 대한 가능성으로 인해 연구가 활발하게 진행되고 있다. 촉매의 표면에서 OER에 대한 메커니즘은 정확하게 규명되지는않았지만, 산화물 촉매에서 Ni 또는 O vacancy와 같은 결함들은 많은 전기화학반응에서 활성점으로 여겨진다. 따라서, 본연구에서는 nitrogen을 ethylenediamine을 이용하여 NiO의 O위치에 치환하여 Ni vacancy를 형성하고 그로 인해서 OER의activity와 내구성에 어떠한 영향을 미치는지에 대해 분석해 보았다.

Fe-Ni₃S₂ nanoneedles on Ni foam as a Bifunctional Electrocatalyst for Oxygen and Hydrogen Evolution

임동욱,오은택,임채원,백성현 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

Electrocatalytic water splitting is a widely considered as environmentally friendly technology for the extremely pure hydrogen production. Exploring highly efficient, cost-effective, and stable bifunctional electrocatalysts is beneficial for improving the performance of overall water splitting. In this study, Fe-doped Ni₃S₂ nanoneedles directly grown on Ni foam were successfully via two-step processes including hydrothermal reaction and sulfidation method and applied to electrocatalysts for both hydrogen and oxygen evolution reaction. Among the samples, the Fe-doped Ni₃S₂ on Ni foam indicated the best electrochemical performance as a bifunctional electrocatalyst for both OER and HER. Furthermore, when the as-obtained Fe-doped Ni₃S₂ is used as a bifunctional electrocatalyst in an overall water splitting system, a low cell voltage of 1.59 V is required to obtain a current density of 10 mA cm-2 with outstanding long-term stability.

Zeolitic imidazolate frameworks derived novel polyhedral shaped hollow Co-B-O@Co₃O₄ electrocatalyst for oxygen evolution reaction

Kim, Dongwon,Kim, Daekyu,Jeon, Youngmoo,Li, Yong,Lee, Jeongyeon,Kang, Jeongmin,Lee, Lawrence Yoon Suk,Piao, Yuanzhe Elsevier 2019 ELECTROCHIMICA ACTA Vol.299 No.-

<P><B>Abstract</B></P> <P>The development of highly effective and low-cost non-noble metal electrochemical catalysts for oxygen evolution reactions (OER) is a major challenge for overall water splitting and rechargeable metal-air batteries. In this study, we develop a novel hollow cobalt-borate modified cobalt oxide composite (denoted by Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB>) catalyst derived from zeolitic imidazolate framework-67 (ZIF-67) for electrochemical OER. The Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> was easily synthesized via pyrolysis of ZIF-67 in Ar and air to produce hollow Co<SUB>3</SUB>O<SUB>4</SUB> (denoted by h-Co<SUB>3</SUB>O<SUB>4</SUB>), followed by simple NaBH<SUB>4</SUB> treatment at ambient temperature for 4 h. The unique polyhedral morphology was well preserved during the NaBH<SUB>4</SUB> treatment. Benefiting from its structural and compositional merit, the as-synthesized Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> exhibit excellent electrocatalytic activity and long-term stability for OER. Also, we conducted the OER test using a Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> catalyst in a neutral pH environment for further investigation. Our study can provide an insight into catalyst modification step to enhance the overall performance while keeping its physical structure simultaneously. using metal-organic framework for the electrochemical catalyst thus can be recognized as a method for producing a highly active, long-term working and novel engineered electrocatalyst for OER applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> was prepared using calcination-NaBH<SUB>4</SUB> treatment strategy with a facile and energy efficient method. </LI> <LI> A distinctive polyhedral morphology of Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> was well preserved after the NaBH<SUB>4</SUB> treatment of its precursor material. </LI> <LI> Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> was employed for the electrochemical oxygen evolution reaction. </LI> <LI> Co-B-O@Co<SUB>3</SUB>O<SUB>4</SUB> showed excellent catalytic performance and long-term durability for oxygen evolution reaction in basic media. </LI> </UL> </P>

Electrochemical Oxygen Evolution Reaction on Ni_xFe_3-xO₄ (0 ≤ x ≤ 1.0) in Alkaline Medium at 25℃

Pankaj, Chauhan,Basant, Lal The Korean Electrochemical Society 2022 Journal of electrochemical science and technology Vol.13 No.4

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.

A biomimetic nanoleaf electrocatalyst for robust oxygen evolution reaction

Chen, Bin,Zhang, Zhuo,Kim, Sangkuk,Baek, Minki,Kim, Dokyoung,Yong, Kijung Elsevier 2019 Applied Catalysis B Vol.259 No.-

<P><B>Abstract</B></P> <P>Oxygen evolution reaction (OER) is a key process in various advanced technologies for renewable energy conversion, such as water splitting and metal-air batteries. However, as a four-electron coupled reaction, the OER is kinetically sluggish and limited by its high overpotential and low efficiency. The design of novel nanostructured electrocatalysts is highly desirable to promote OER kinetics. Herein, a bio-inspired nanoleaf electrocatalyst has been successfully achieved for the first time by <I>in situ</I> growing ultrathin NiCo layered double hydroxide (LDH) nanosheets on CuO nanowires. Attributed to the mechanical support of CuO nanowire veins, the NiCo LDH lamina presents a large lateral size (more than 10 μm) and unique hierarchical structure that consisted of ultrathin nanosheets with numerous exposed edges. The CuO veins distributed across the LDH lamina can serve as the fast path for charge transfer and significantly promote the LDH conductivity. Compared to the conventional NiCo LDH nanosheets, the novel nanoleaves with enlarged electrochemical surface area, edge-rich active sites, and improved conductivity exhibit greatly enhanced OER performances with an impressive 9.3 fold enhanced activity, much lower overpotential of 262 mV at 10 mA cm<SUP>−2</SUP>, as well as good stability and flexibility. The biomimetic nanoleaf structures and the corresponding design strategy can be broadly applied to other functional 2D materials for advanced applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A biomimetic nanoleaf with NiCo LDH lamina and CuO veins is designed for the first time. </LI> <LI> The CuO nanowire veins support the ultrathin LDH lamina and promote charge transfer. </LI> <LI> The hierarchical lamina shows a quite large electrochemical surface area and edge-rich active sites. </LI> <LI> This biomimetic nanoleaf exhibits a high activity, good stability and flexibility for OER. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P> <B>A biomimetic nanoleaf electrocatalyst</B> is achieved for the first time by combining ultrathin NiCo layered double hydroxide (LDH) lamina with CuO nanowire veins. The CuO veins support the LDH lamina and serve as fast path for charge transfer. The hierarchical nanoleaves with large surface area, edge-rich active sites, and improved conductivity exhibit superior electrochemical performances for oxygen evolution reaction.</P> <P>[DISPLAY OMISSION]</P>