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      Unconventional CN vacancies suppress iron-leaching in Prussian blue analogue pre-catalyst for boosted oxygen evolution catalysis

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          Abstract

          The incorporation of defects, such as vacancies, into functional materials could substantially tailor their intrinsic properties. Progress in vacancy chemistry has enabled advances in many technological applications, but creating new type of vacancies in existing material system remains a big challenge. We show here that ionized nitrogen plasma can break bonds of iron-carbon-nitrogen-nickel units in nickel-iron Prussian blue analogues, forming unconventional carbon-nitrogen vacancies. We study oxygen evolution reaction on the carbon-nitrogen vacancy-mediated Prussian blue analogues, which exhibit a low overpotential of 283 millivolts at 10 milliamperes per square centimeter in alkali, far exceeding that of original Prussian blue analogues and previously reported oxygen evolution catalysts with vacancies. We ascribe this enhancement to the in-situ generated nickel-iron oxy(hydroxide) active layer during oxygen evolution reaction, where the Fe leaching was significantly suppressed by the unconventional carbon-nitrogen vacancies. This work opens up opportunities for producing vacancy defects in nanomaterials for broad applications.

          Abstract

          Defect-engineering offers a promising route to vary material properties and reactivities, although the achievable defect types are limited. Here, the authors introduced unusual CN-vacancies in Prussian blue analogue pre-catalysts that can limit Fe leaching and improve oxygen evolution performances.

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          Most cited references40

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          Nickel-iron oxyhydroxide oxygen-evolution electrocatalysts: the role of intentional and incidental iron incorporation.

          Fe plays a critical, but not yet understood, role in enhancing the activity of the Ni-based oxygen evolution reaction (OER) electrocatalysts. We report electrochemical, in situ electrical, photoelectron spectroscopy, and X-ray diffraction measurements on Ni(1-x)Fe(x)(OH)2/Ni(1-x)Fe(x)OOH thin films to investigate the changes in electronic properties, OER activity, and structure as a result of Fe inclusion. We developed a simple method for purification of KOH electrolyte that uses precipitated bulk Ni(OH)2 to absorb Fe impurities. Cyclic voltammetry on rigorously Fe-free Ni(OH)2/NiOOH reveals new Ni redox features and no significant OER current until >400 mV overpotential, different from previous reports which were likely affected by Fe impurities. We show through controlled crystallization that β-NiOOH is less active for OER than the disordered γ-NiOOH starting material and that previous reports of increased activity for β-NiOOH are due to incorporation of Fe-impurities during the crystallization process. Through-film in situ conductivity measurements show a >30-fold increase in film conductivity with Fe addition, but this change in conductivity is not sufficient to explain the observed changes in activity. Measurements of activity as a function of film thickness on Au and glassy carbon substrates are consistent with the hypothesis that Fe exerts a partial-charge-transfer activation effect on Ni, similar to that observed for noble-metal electrode surfaces. These results have significant implications for the design and study of Ni(1-x)Fe(x)OOH OER electrocatalysts, which are the fastest measured OER catalysts under basic conditions.
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            An advanced Ni-Fe layered double hydroxide electrocatalyst for water oxidation.

            Highly active, durable, and cost-effective electrocatalysts for water oxidation to evolve oxygen gas hold a key to a range of renewable energy solutions, including water-splitting and rechargeable metal-air batteries. Here, we report the synthesis of ultrathin nickel-iron layered double hydroxide (NiFe-LDH) nanoplates on mildly oxidized multiwalled carbon nanotubes (CNTs). Incorporation of Fe into the nickel hydroxide induced the formation of NiFe-LDH. The crystalline NiFe-LDH phase in nanoplate form is found to be highly active for oxygen evolution reaction in alkaline solutions. For NiFe-LDH grown on a network of CNTs, the resulting NiFe-LDH/CNT complex exhibits higher electrocatalytic activity and stability for oxygen evolution than commercial precious metal Ir catalysts.
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              Defect Chemistry of Nonprecious-Metal Electrocatalysts for Oxygen Reactions.

              Oxygen electrocatalysis, including the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER), is a critical process for metal-air batteries. Therefore, the development of electrocatalysts for the OER and the ORR is of essential importance. Indeed, various advanced electrocatalysts have been designed for the ORR or the OER; however, the origin of the advanced activity of oxygen electrocatalysts is still somewhat controversial. The enhanced activity is usually attributed to the high surface areas, the unique facet structures, the enhanced conductivities, or even to unclear synergistic effects, but the importance of the defects, especially the intrinsic defects, is often neglected. More recently, the important role of defects in oxygen electrocatalysis has been demonstrated by several groups. To make the defect effect clearer, the recent development of this concept is reviewed here and a novel principle for the design of oxygen electrocatalysts is proposed. An overview of the defects in carbon-based, metal-free electrocatalysts for ORR and various defects in metal oxides/selenides for OER is also provided. The types of defects and controllable strategies to generate defects in electrocatalysts are presented, along with techniques to identify the defects. The defect-activity relationship is also explored by theoretical methods.
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                Author and article information

                Contributors
                mgao@ustc.edu.cn
                shyu@ustc.edu.cn
                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group UK (London )
                2041-1723
                26 June 2019
                26 June 2019
                2019
                : 10
                : 2799
                Affiliations
                [1 ]ISNI 0000000121679639, GRID grid.59053.3a, Division of Nanomaterials & Chemistry, Hefei National Laboratory for Physical Sciences at the Microscale, CAS Center for Excellence in Nanoscience, Hefei Science Center of CAS, Collaborative Innovation Center of Suzhou Nano Science and Technology, Department of Chemistry, , University of Science and Technology of China, ; Hefei, 230026 China
                [2 ]ISNI 0000000121679639, GRID grid.59053.3a, State Key Laboratory of Particle Detection and Electronics, , University of Science and Technology of China, ; Hefei, 230026 China
                [3 ]ISNI 0000000121679639, GRID grid.59053.3a, National Synchrotron Radiation Laboratory, , University of Science and Technology of China, ; Hefei, 230029 China
                [4 ]GRID grid.410752.5, Dalian National Laboratory for Clean Energy, ; Dalian, 116023 China
                Author information
                http://orcid.org/0000-0002-6665-220X
                http://orcid.org/0000-0001-8699-8294
                http://orcid.org/0000-0002-7805-803X
                http://orcid.org/0000-0003-0888-4261
                http://orcid.org/0000-0003-3732-1011
                Article
                10698
                10.1038/s41467-019-10698-9
                6595008
                31243269
                554cfdf6-0bd2-496e-aad0-79832012e183
                © The Author(s) 2019

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 19 March 2019
                : 24 May 2019
                Funding
                Funded by: FundRef https://doi.org/10.13039/501100001809, National Natural Science Foundation of China (National Science Foundation of China);
                Award ID: 21521001
                Award Recipient :
                Categories
                Article
                Custom metadata
                © The Author(s) 2019

                Uncategorized
                catalyst synthesis,electrocatalysis,nanowires
                Uncategorized
                catalyst synthesis, electrocatalysis, nanowires

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