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Engineering surface atomic structure of single-crystal cobalt (II) oxide nanorods for superior electrocatalysis

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ABSTRACT

Engineering the surface structure at the atomic level can be used to precisely and effectively manipulate the reactivity and durability of catalysts. Here we report tuning of the atomic structure of one-dimensional single-crystal cobalt (II) oxide (CoO) nanorods by creating oxygen vacancies on pyramidal nanofacets. These CoO nanorods exhibit superior catalytic activity and durability towards oxygen reduction/evolution reactions. The combined experimental studies, microscopic and spectroscopic characterization, and density functional theory calculations reveal that the origins of the electrochemical activity of single-crystal CoO nanorods are in the oxygen vacancies that can be readily created on the oxygen-terminated {111} nanofacets, which favourably affect the electronic structure of CoO, assuring a rapid charge transfer and optimal adsorption energies for intermediates of oxygen reduction/evolution reactions. These results show that the surface atomic structure engineering is important for the fabrication of efficient and durable electrocatalysts.

No MeSH data available.


Analysis of O-vacancies on the pyramidal nanofaceted surface of SC CoO NRs.(a,b) O-K edge and Co-L2,3 edge XANES spectra of SC CoO NRs and reference CoO, respectively. In a the peak at ∼536 eV of SC CoO NRs is assigned to O deficiency. In b the peaks at 781.5 and ∼800 eV of SC CoO NRs shift towards low photon energy relative to the reference CoO, indicating the transfer of electrons from O-vacancies to Co d band. (c) O-vacancy formation energies on {100}, {110} and {111}-O facets of CoO showing a significant reduction in the vacancy formation energy on {111}-O facets.
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f3: Analysis of O-vacancies on the pyramidal nanofaceted surface of SC CoO NRs.(a,b) O-K edge and Co-L2,3 edge XANES spectra of SC CoO NRs and reference CoO, respectively. In a the peak at ∼536 eV of SC CoO NRs is assigned to O deficiency. In b the peaks at 781.5 and ∼800 eV of SC CoO NRs shift towards low photon energy relative to the reference CoO, indicating the transfer of electrons from O-vacancies to Co d band. (c) O-vacancy formation energies on {100}, {110} and {111}-O facets of CoO showing a significant reduction in the vacancy formation energy on {111}-O facets.

Mentions: To further probe the local chemical and electronic environment on the surface of SC CoO NRs, XPS and synchrotron-based X-ray absorption near edge fine structure (XANES) spectroscopy measurements were performed. The XPS O 1s spectrum suggests an enrichment of O-vacancies on the surface of SC CoO NRs (Supplementary Fig. 7a). Further evidence comes from a close inspection of the fine structure of the O-K edge of XANES spectrum (Fig. 3a), in which the peak at ∼536.0 eV assigned to O deficiency4748 in SC CoO NRs is much higher than that of reference CoO. This is also consistent with the observation of a noticeable peak shift in Co-L2,3 edge towards low photon energy and Co 2p XPS spectrum towards low binding energy of SC CoO NRs (Fig. 3b and Supplementary Fig. 8), which is an indicative of electron transfer from O-vacancies to Co d band. Thus, a combination of XANES and XPS results provides a crucial evidence for the presence of abundant O-vacancies on the surface of SC CoO NRs, the quantity of which is even higher than that on the surface of polycrystalline (PC) CoO NRs with threefold larger surface area (Supplementary Table 1). Our DFT computations indeed reveal that the O-vacancy formation energy on the O-terminated {111} facets (hereafter, referred to as ‘{111}-O facet') is by 3 eV lower than the corresponding values of {100} and {110} facets (Fig. 3c). Clearly, such a significant reduction in the vacancy formation energy results in larger concentration of the equilibrium O-vacancies on {111}-O facets of SC CoO NRs. It indicates that the surface defects can be tuned and stabilized through facet engineering.


Engineering surface atomic structure of single-crystal cobalt (II) oxide nanorods for superior electrocatalysis
Analysis of O-vacancies on the pyramidal nanofaceted surface of SC CoO NRs.(a,b) O-K edge and Co-L2,3 edge XANES spectra of SC CoO NRs and reference CoO, respectively. In a the peak at ∼536 eV of SC CoO NRs is assigned to O deficiency. In b the peaks at 781.5 and ∼800 eV of SC CoO NRs shift towards low photon energy relative to the reference CoO, indicating the transfer of electrons from O-vacancies to Co d band. (c) O-vacancy formation energies on {100}, {110} and {111}-O facets of CoO showing a significant reduction in the vacancy formation energy on {111}-O facets.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5035995&req=5

f3: Analysis of O-vacancies on the pyramidal nanofaceted surface of SC CoO NRs.(a,b) O-K edge and Co-L2,3 edge XANES spectra of SC CoO NRs and reference CoO, respectively. In a the peak at ∼536 eV of SC CoO NRs is assigned to O deficiency. In b the peaks at 781.5 and ∼800 eV of SC CoO NRs shift towards low photon energy relative to the reference CoO, indicating the transfer of electrons from O-vacancies to Co d band. (c) O-vacancy formation energies on {100}, {110} and {111}-O facets of CoO showing a significant reduction in the vacancy formation energy on {111}-O facets.
Mentions: To further probe the local chemical and electronic environment on the surface of SC CoO NRs, XPS and synchrotron-based X-ray absorption near edge fine structure (XANES) spectroscopy measurements were performed. The XPS O 1s spectrum suggests an enrichment of O-vacancies on the surface of SC CoO NRs (Supplementary Fig. 7a). Further evidence comes from a close inspection of the fine structure of the O-K edge of XANES spectrum (Fig. 3a), in which the peak at ∼536.0 eV assigned to O deficiency4748 in SC CoO NRs is much higher than that of reference CoO. This is also consistent with the observation of a noticeable peak shift in Co-L2,3 edge towards low photon energy and Co 2p XPS spectrum towards low binding energy of SC CoO NRs (Fig. 3b and Supplementary Fig. 8), which is an indicative of electron transfer from O-vacancies to Co d band. Thus, a combination of XANES and XPS results provides a crucial evidence for the presence of abundant O-vacancies on the surface of SC CoO NRs, the quantity of which is even higher than that on the surface of polycrystalline (PC) CoO NRs with threefold larger surface area (Supplementary Table 1). Our DFT computations indeed reveal that the O-vacancy formation energy on the O-terminated {111} facets (hereafter, referred to as ‘{111}-O facet') is by 3 eV lower than the corresponding values of {100} and {110} facets (Fig. 3c). Clearly, such a significant reduction in the vacancy formation energy results in larger concentration of the equilibrium O-vacancies on {111}-O facets of SC CoO NRs. It indicates that the surface defects can be tuned and stabilized through facet engineering.

View Article: PubMed Central - PubMed

ABSTRACT

Engineering the surface structure at the atomic level can be used to precisely and effectively manipulate the reactivity and durability of catalysts. Here we report tuning of the atomic structure of one-dimensional single-crystal cobalt (II) oxide (CoO) nanorods by creating oxygen vacancies on pyramidal nanofacets. These CoO nanorods exhibit superior catalytic activity and durability towards oxygen reduction/evolution reactions. The combined experimental studies, microscopic and spectroscopic characterization, and density functional theory calculations reveal that the origins of the electrochemical activity of single-crystal CoO nanorods are in the oxygen vacancies that can be readily created on the oxygen-terminated {111} nanofacets, which favourably affect the electronic structure of CoO, assuring a rapid charge transfer and optimal adsorption energies for intermediates of oxygen reduction/evolution reactions. These results show that the surface atomic structure engineering is important for the fabrication of efficient and durable electrocatalysts.

No MeSH data available.