Novel Approach of Diffusion‐Controlled Sequential Reduction to Synthesize Dual‐Atomic‐Site Alloy for Enhanced Bifunctional Electrocatalysis in Acidic and Alkaline Media
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Abstract The tailoring of active sites is closely related to the substrate. Dual‐atom catalysts (DACs) have been achieved on doped carbon, oxides, and 2D materials, but are rarely reported on metals, due to the challenges of sintering and alloying using metal as the host. Herein, an innovative approach to anchor isolated single atoms as dual‐atomic‐site alloy (DASA) through two‐step pyrolysis of porous structure is proposed. Firstly, the role of Zn and Co in generating pores during the pyrolysis of zeolite imidazolate framework (ZIFs) is revealed, and a hierarchical porous structure with self‐supported Co particles is achieved by the first‐step pyrolysis. Diffusion‐controlled reduction of precursors containing target metals is then allowed through hierarchical structures by second‐step pyrolysis, so to address the challenge of sintering and alloying at pyrolysis of high temperatures. The approach is demonstrated by synthesizing Ir 1 Ni 1 @Co/N‐C DASA, with outstanding bifunctional oxygen reduction/evolution reaction (ORR/OER) performance in both acidic and alkaline media, which is rarely reported. The density functional theory (DFT) calculations represent that adsorption‐free energies of intermediates OH and O are regulated to nearly 0 eV by Ir 1 and Ni 1 on Co. This work demonstrates a new path of constructing DASA using the designed porous structure, inspiring catalysts design in a related field.Keywords:
Zeolitic imidazolate framework
Imidazolate
A bifunctional electrocatalyst based on heteroatoms doped VS 2 was developed for electrocatalytic water splitting.
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The development of green energy conversion technologies and sophisticated energy storage devices are crucial for a sustainable future. Currently, metal-air batteries and fuel cells promise cost-effective, efficient and clean operation. However, highly active bifunctional noble-metal-free catalyst materials are needed to boost sluggish kinetics of oxygen electrode reactions for replacing conventional benchmark catalysts (Pt/C; RuO 2 /IrO 2 ). Herein, we report highly active manganese and cobalt containing metal-organic framework (MOF)-derived bifunctional electrocatalyst with rich porous and well-dispersed structure. Mn/Co-containing material displayed excellent electrocatalytic performance toward both oxygen evolution and reduction reactions (E j=10 =1.66 V; E 1/2 = 0.85 V vs RHE, 0.1 M KOH) due to the desired active sites and architecture. Proposed bifunctional electrocatalyst was also tested in Zn-air battery setup and demonstrated outstanding durability within 10 h cycling without any noticeable degradation and great efficiency with high power density.
Oxygen evolution
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금속유기구조체(metal-organic frameworks, MOF)는 넓은 비표면적, 규칙적인 구조 및 높게 분산된 금속 성분 등 뛰어난 물리화학적 특성으로 인해 활발한 연구가 이뤄지고 있는 다공성 물질이며, 특히 가스의 흡착, 분리 매체로서 뛰어난 성능이 보고되고 있다. MOF를 이용한 온실가스 이산화탄소의 흡착 연구는 상온 고압 영역에서 이산화탄소 저장 공정과 상온 저압 영역에서 이산화탄소 흡착 공정의 두 범주로 나눌 수 있으며, MOF의 넓은 비표면적 외에도 (1) MOF의 빈 배위결합 자리, (2) MOF의 기능화, (3) MOF의 상호 침투 효과, 및 (4) 이온 교환 효과를 이용한 연구 결과가 보고되고 있다. MOF 물질들은 비교적 낮은 수분 및 열에 대한 안정성이 문제로 제기되고 있으며, 제올라이트 유사 구조체(zeolitic imidazolate frameworks, ZIF) 또는 유기 골격 구조체(covalent organic frameworks, COF) 물질의 이산화탄소 흡착 특성이 거론되고 있다. 본 소고에서는 MOF를 이용한 이산화탄소 흡착에 대한 최근의 연구 결과를 본 연구실의 실험 결과를 중심으로 간략히 소개하고자 한다. Metal organic frameworks (MOFs) are a class of crystalline organic-inorganic hybrid compounds formed by coordination of metal clusters or ions with organic linkers. MOFs have recently attracted intense research interest due to their permanent porous structures, large surface areas and pore volume, high-dispersed metal species, and potential applications in gas adsorption, separation, and catalysis. $CO_2$ adsorption in MOFs has been investigated in two areas of $CO_2$ storage at high pressures and $CO_2$ adsorption at atmospheric pressure conditions. In this short review, $CO_2$ adsorption/separation results using MOFs conducted in our laboratory was explained in terms of four contributing effects; (1) coordinatively unsaturated open metal sites, (2) functionalization, (3) interpenetration/catenation, and (4) ion-exchange. Zeolitic imidazolate frameworks (ZIFs) and covalent organic frameworks (COFs) were also considered as a candidate material.
Zeolitic imidazolate framework
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Oxygen evolution
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A coordinately unsaturated MOF for bifunctional oxygen electrocatalysis with a potential gap ΔE (OERj=10–ORR1/2) as small as 0.79 V.
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A highly active bifunctional electrocatalyst for oxygen reduction and evolution reactions was developed based on nanocarbon-intercalated and Fe–N-codoped graphene materials.
Oxygen evolution
Noble metal
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In article number 1700369, Yizhong Lu, Zexiang Shen, and co-workers report a novel MoP nanoflake array grown on nickel foam, which can act as high-performance bifunctional electrocatalyst for water splitting. The bifunctional electrocatalyst behaves like two hands, one for the hydrogen evolution reaction (HER) and another for the oxygen evolution reaction (OER), respectively. With the two hands, the whole water splitting can be fulfilled efficiently.
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La 0.6 Ca 0.4 CoO 3 perovskite electrocatalyst had been synthesized by organic acid-aided method. The impact of the cal-cining conditions on the electrocatalyst preparation was studied by XRD, TEM and optimal results were given. The perfor-mance of bifunctional oxygen electrode electrocatalyst was evaluated preliminarily by galvanostatic polarization curve method. The results show that the electrocatalyst synthesized at 700 ℃for 2h has the characteristics of single phase, single crystal and smaller grain size, so the condition is optimal for preparing the electrocatalyst. The electrocatalyst made under that condition has better bifunctional oxygen electrode electrocatalytic activity and stability, which is promising as bifunctional oxygen elec-trode electrocatalyst for the MH-Air secondary battery application.
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We present an interface coupling strategy using Cu nanoclusters and NiFe LDH nanosheets to form a heterostructure electrocatalyst (Cu/NiFe LDH) and apply it as both NO 3 − RR and OER bifunctional electrodes under ambient conditions.
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