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A new family of perovskite catalysts for oxygenevolution reaction in alkaline media: BaNiO and BaNi O 3
0.83
2.5
Jin Goo Lee, Jeemin Hwang, Ho Jung Hwang, Ok Sung Jeon, Jeongseok Jang, Ohchan Kwon, Yeayeon Lee, Byungchan Han, and Yong-Gun Shul J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b00036 • Publication Date (Web): 24 Feb 2016 Downloaded from http://pubs.acs.org on February 25, 2016
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Journal of the American Chemical Society
A new family of perovskite catalysts for oxygen-evolution reaction in alkaline media: BaNiO3 and BaNi0.83O2.5 Jin Goo Lee,1† Jeemin Hwang,1† Ho Jung Hwang,2 Ok Sung Jeon,1 Jeongseok Jang,1 Ohchan Kwon,1 Yeayeon Lee,2 Byungchan Han1* and Yong-Gun Shul1* 1
Department of Chemical and Bio-molecular Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749, Republic of Korea
2
Department of Graduate Program in New Energy and Battery Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749, Republic of Korea KEYWORDS. oxygen-evolution reaction, hexagonal perovskite, metal-air battery, water splitting, catalysis
ABSTRACT: Establishment of sustainable energy society has been strong driving force to develop cost-effective and highly active catalysts for energy conversion and storage devices such as metal-air batteries and electrochemical water splitting systems. This is because the oxygen evolution reaction (OER), a vital reaction for the operation, is substantially sluggish even with precious metalsbased catalysts. Here, we show for the first time that a hexagonal perovskite BaNiO3 can be highly functional catalyst for OER in alkaline media. We identify that the BaNiO3 performs OER activity at least an order of magnitude higher than an IrO2 catalyst. Using integrated density functional theory calculations and experimental validations we unveil the underlying mechanism is originated from structural transformation from BaNiO3 to BaNi0.83O2.5 (Ba6Ni5O15) over the OER cycling process.
INTRODUCTION Oxygen evolution reaction (OER) is a vital process for diverse energy storage devices. For instance, the rechargeable metal-air batteries (MxO2 → Mx + O2) (1, 2) and fuel generation through water splitting reactions (H2O → H2 + ½O2) (3) are two archetype examples. The efficiency of the systems is critically dependent on the OER but even with precious metallic catalysts the low activity is still a major concern leading to significant overpotential. Recently, it was proposed that perovskite oxides performed high OER activity comparable to stateof-the-art IrO2, ever since numbers of researches have been focused on the development of the perovskite structure catalysts and to identification essential descriptor of the OER activity from fundamental aspect (4-13). A perovskite oxide (crystal structure: ABO3 where A is a rareearth or alkaline-earth metal and B is a transition metal) is more cost-effective and highly active catalysts compared to conventionally utilized noble metals and pliable in physical, chemical and catalytic properties. Recently, using corner-shared pseudocubic perovskites in an alkaline solution (4OH– → O2 + 2H2O + 4e–) Suntivich et al.(5) suggested that the filling of eg level electrons of the surface cation can be a descriptor for OER activity. They proposed that the OER activity is high as the occupancy is close to one and the degree of the covalency in the chemical bond between the transition metal and oxygen is high (5). We realized that few studies have been published on hexagonal perovskite catalysts for the OER
in spite of numerous reports on the perovskite catalysts (6-12). Grimaud et al. reported the OER activity and stability of hexagonal perovskite oxides (Ba6Mn5O16 and Sr6Co5O15) (13). They suggested that the electronic structure of transition metal oxides, such as face-shared (f-s) and prism (P) in hexagonal perovskites, plays a critical role in the OER activity and stability. We focused on a BaNiO3 (Ba6Ni5O15) material (t=~1.13, t refers to Goldschmidt’s tolerance factor), which has a hexagonal perovskite structure with the face-shared (f-s) [NiO6] octahedral oriented to chain units (NiO3)∞∞-. The Ni oxidation states are crystallographically equivalent in BaNiO3, but it has been suggested that intermediate phases, BaNiOx (2.3
