Oxygen vacancy engineering of calcium cobaltate: A nitrogen fixation electrocatalyst at ambient condition in neutral ele
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Oxygen vacancy engineering of calcium cobaltate: A nitrogen fixation electrocatalyst at ambient condition in neutral electrolyte Xinyu Chen§, Ke Li§, Xiaoxuan Yang, Jiaqi Lv, Sai Sun, Siqi Li, Dongming Cheng, Bo Li, Yang-Guang Li, and Hong-Ying Zang () Key Laboratory of Polyoxometalate Science of the Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun 130024, China § Xinyu Chen and Ke Li contributed equally to this work. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 25 May 2020 / Revised: 27 July 2020 / Accepted: 7 August 2020
ABSTRACT In order to sustainably transform N2 to ammonia (NRR) using electrocatalysts under mild ambient condition, it is urgent to design and develop non-nobel metal nanocatalysts that are inexpensive and suitable for mass-production. Herein, a calcium metalate catalyst CaCoOx with oxygen vacancies was synthesized and used as an electrocatalyst for NRR for the first time, whose morphology can be controlled by the calcination temperature and the heating rate. Under the optimal conditions, the CaCoOx catalyst achieved the yield of nitrogen conversion to ammonia of 16.25 μg·h−1·mgcat.−1 at the potential of −0.3 V relative to the reversible hydrogen electrode (RHE) with a Faraday efficiency of 20.51%. The electrocatalyst showed good stability even after 12 times recyclability under environmental conditions and neutral electrolyte. Later, the electrocatalytic nitrogen reduction performance of CaFeOx, CaNiOx, CaCuOx was investigated. These earth-rich transition metals also exhibited certain NRR electrocatalytic capabilities, which provided a door for further development of inexpensive and easily available transition metal as nitrogen reduction electrocatalysts.
KEYWORDS nitrogen fixation, oxygen vacancy, electrocatalysis, calcium cobaltate, nanoplates
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Introduction
Nitrogen is one of the important elements that make up all living organisms on earth, which is an essential component of the proteins, nucleic acids and lipids [1, 2]. In nature, a wide range of nitrogen cannot be directly used and only small amount of nitrogen can be transformed to ammonia by slow biological nitrogen fixation and occasional lightning. With the continuous growth of the global population, ammonia and nitric acid have become one of the most demanded chemicals in order to meet the needs for the production of fertilizers, synthetic pharmaceutical raw materials, future generation and storage of hydrogen energy [3, 4]. At present, the harsh Haber- Bosch process is commonly used in the industrial production of ammonia, which requires high-temperature (400–500 °C), highpressure (20–30 MPa) and large-scale centralized production equipment [5]. At present, 1% of global energy consumption is used for large-scale industrial production of ammonia and its derivatives. This continuous energy consumption also emits a large amount of CO2 greenhouse gas [6]. Therefore, the development of environmental-friendly electrocatalytic nitrogen reduction
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