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One-Step Electrodeposition of Nanocrystalline ZnCo O Films with High Activity and Stability for Electrocatalytic Oxygen Evolution Shan Han, Suqin Liu, Rui Wang, Xuan Liu, Lu Bai, and Zhen He ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 03 May 2017 Downloaded from http://pubs.acs.org on May 5, 2017
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ACS Applied Materials & Interfaces
One-Step Electrodeposition of Nanocrystalline ZnxCo3-xO4 Films with High Activity and Stability for Electrocatalytic Oxygen Evolution Shan Han,†,‡ Suqin Liu,† Rui Wang,† Xuan Liu,†,§ Lu Bai,†,§ and Zhen He†,* †
College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan
410083, P.R. China. ‡
Innovation Base of Energy and Chemical Materials for Graduate Students Training, Central
South University, Changsha, Hunan 410083, P.R. China. KEYWORDS: oxygen evolution reaction, zinc cobaltate, catalyst, water splitting, electrodeposition
ABSTRACT: The development of highly active, environmentally friendly, and long-term stable oxygen evolving catalysts at low costs is critical for efficient and scalable H2 production from water splitting. Here, we report a new and facile one-step electrodeposition of nanocrystalline spinel-type ZnxCo3-xO4 films from an alkaline Zn2+-Co2+-tartrate solution. The electrodeposited ZnxCo3-xO4 electrode could be directly used as the anode for the water electrolysis without any post treatment. The ZnxCo3-xO4 film shows a low and stable overpotential of ~0.33 V at 10 mA
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cm-2 (and ~0.35 V at 20 mA cm-2) for over 10 hours and a Tafel slope of ~39 mV dec-1 toward the oxygen evolution reaction (OER) in 1 M NaOH, comparable to the best performance of the non-precious OER catalysts reported for alkaline media. The enhanced OER activity of ZnxCo3xO4
compared to Co3O4 could be attributed to the surface structural modification and higher
density of the accessible active Co3+ sites induced by the incorporation of Zn2+. The electrodeposition method in this paper could also be used to synthesize other binary and ternary metal oxide-based catalytic electrodes for reactions like the OER and oxygen reduction reaction (ORR).
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ACS Applied Materials & Interfaces
1. INTRODUCTION Solar- or electricity-driven water splitting is regarded as a promising way for the production of H2 fuel as a clean and sustainable energy source to relieve the shortage of fossil fuels and the environmental issues.1,2 The overall efficiency of water splitting is mainly limited by the anodic oxygen evolution reaction (OER) due to the high kinetic overpotential associated with this sluggish four-electron oxidation reaction.3,4 Thus, the development of highly active, environmentally friendly, long-term stable, and low-cost OER catalysts is critical to achieve an efficient and scalable H2 production from water splitting.5,6 In principle, water splitting can be performed in acidic, neutral, and alkaline electrolytes, although alkaline conditions are thought to be the best suited and therefore are most studied.7 Some noble metal oxides, such as RuO2, IrO2, and PtO2, are regarded as the most active OER catalysts in alkaline electrolytes, but their applications are limited due to their scarcity and high costs.8,9 In contrast, the OER catalysts based on the first-row transition metals (e.g., transition metal oxides and (oxy)hydroxides) are inexpensive, earth-abundant, and also quite active in alkaline electrolytes.7,10-16 According to the “volcano plot” for the catalytic activities of metal oxides toward the OER, the spinel Co3O4 is slightly less active than the aforementioned noble metal oxides.17 Recent studies have revealed that in Co3O4 the catalytically active sites for the OER are the Co3+ in the octahedral (Oh) sites but the Co2+ in the tetrahedral (Td) sites.18,19 This result promotes the attempts to prepare Co3O4based OER catalysts with Co2+ partially or completely replaced by other cheaper and more ecofriendly transition metal ions (e.g., Ni, Cu, and Zn ions).18,20-22 In addition to exploring the new efficient catalysts for the OER, the development of facile and economical synthetic methods for these catalysts is also essential for their scalable applications.
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ZnCo2O4 crystallizes in a regular spinel structure, i.e., Zn2+ replaces the Td Co2+ in Co3O4, whereas the Oh sites are still occupied by Co3+ ions. Stoichiometric and nonstoichiometric ZnxCo3-xO4 (0
