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Transition metal ions regulated oxygen evolution reaction performance of Ni-based hydroxides hierarchical nanoarrays

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ABSTRACT

Nickel-based hydroxide hierarchical nanoarrays (NiyM(OH)x HNAs M = Fe or Zn) are doped with non-noble transition metals to create nanostructures and regulate their activities for the oxygen evolution reaction. Catalytic performance in these materials depends on their chemical composition and the presence of nanostructures. These novel hierarchical nanostructures contain small secondary nanosheets that are grown on the primary nanowire arrays, providing a higher surface area and more efficient mass transport for electrochemical reactions. The activities of the NiyM(OH)x HNAs for the oxygen evolution reaction (OER) followed the order of Ni2.2Fe(OH)x > Ni(OH)2 > Ni2.1Zn(OH)x, and these trends are supported by density functional theory (DFT) calculations. The Fe-doped nickel hydroxide hierarchical nanoarrays (Ni2.2Fe(OH)x HNAs), which had an appropriate elemental composition and hierarchical nanostructures, achieve the lowest onset overpotential of 234 mV and the smallest Tafel slope of 64.3 mV dec−1. The specific activity, which is normalized to the Brunauer–Emmett–Teller (BET) surface area of the catalyst, of the Ni2.2Fe(OH)x HNAs is 1.15 mA cm−2BET at an overpotential of 350 mV. This is ~4-times higher than that of Ni(OH)2. These values are also superior to those of a commercial IrOx electrocatalyst.

No MeSH data available.


High-resolution XPS spectra of the (a) Ni 2p and (b) O 1s regions for the Ni(OH)2, Ni2.1Zn(OH)x, and Ni2.2Fe(OH)x HNAs (from bottom to top); (c) Zn 2p spectra of the Ni2.1Zn(OH)x HNAs, (d) Fe 2p spectra of the Ni2.2Fe(OH)x HNAs.
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f4: High-resolution XPS spectra of the (a) Ni 2p and (b) O 1s regions for the Ni(OH)2, Ni2.1Zn(OH)x, and Ni2.2Fe(OH)x HNAs (from bottom to top); (c) Zn 2p spectra of the Ni2.1Zn(OH)x HNAs, (d) Fe 2p spectra of the Ni2.2Fe(OH)x HNAs.

Mentions: The Ni/M atomic ratios of the NiyM(OH)x HNAs were determined with inductively coupled plasma (ICP) emission spectrometry. The ratios in the HNAs were similar to the reactant ratios (Table S1), indicating that the Ni/M ratios in the hydroxides were similar to those in the precursors. The surface compositions and valence states of the as-prepared NiyM(OH)x HNAs were investigated by X-ray photoelectron spectroscopy (XPS), and the results are shown in Fig. 4. Nickel, Fe, Zn, and O species were observed. Peak fitting analysis of the Ni 2p for Ni(OH)2 revealed one Ni2+ state for Ni at binding energies of 855.5 eV and 873.5 eV. Peak fitting analysis for Ni 2p in the Ni2.2Fe(OH)x and Ni2.1Zn(OH)x HNAs indicated the presence of Ni2+ (855.4 eV and 873.1 eV) and Ni3+ (857.3 eV and 875.5 eV)34. Compared to the un-doped Ni(OH)2 HNAs, the Ni 2p peaks of the M-doped samples were shifted to more positive energies (Ni2.1Zn(OH)x < Ni2.2Fe(OH)x), suggesting that the oxidation of Ni2+ was favored when Fe and Zn were added. This effect was strongest with Fe35. Additional evidence for the presence of Ni2+ was observed in the two intense shakeup satellite peaks (861.8 eV and 880.0 eV)16. The Zn 2p XPS spectrum for the Ni2.1Zn(OH)x HNAs contained 2p3/2 and 2p1/2 doublets, which are characteristic of Zn2+ (1022.7 eV and 1045.7 eV)34. Fe 2p3/2 and Fe 2p1/2 spin-orbital splitting for the Ni2.2Fe(OH)x HNAs was deconvolved into four peaks, indicating the coexistence of Fe2+ (711.5 eV and 723.7 eV) and Fe3+ (716.0 eV and 726.3 eV) in the Ni2.2Fe(OH)x HNAs3637. The O 1s spectrum of the Ni(OH)2 HNAs was fit to a peak at a binding energy of 530.9 eV, which was assigned to the oxygen in hydroxide. The O 1s spectra of the Ni2.2Fe(OH)x and Ni2.1Zn(OH)x HNAs were fit with two peaks at binding energies of 530.1 eV and 531 eV, revealing the presence of lattice and hydroxide oxygens, respectively16. These results confirm that strong electron interactions occurred between Ni and both Fe and Zn in the NiyM(OH)x HNAs.


Transition metal ions regulated oxygen evolution reaction performance of Ni-based hydroxides hierarchical nanoarrays
High-resolution XPS spectra of the (a) Ni 2p and (b) O 1s regions for the Ni(OH)2, Ni2.1Zn(OH)x, and Ni2.2Fe(OH)x HNAs (from bottom to top); (c) Zn 2p spectra of the Ni2.1Zn(OH)x HNAs, (d) Fe 2p spectra of the Ni2.2Fe(OH)x HNAs.
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f4: High-resolution XPS spectra of the (a) Ni 2p and (b) O 1s regions for the Ni(OH)2, Ni2.1Zn(OH)x, and Ni2.2Fe(OH)x HNAs (from bottom to top); (c) Zn 2p spectra of the Ni2.1Zn(OH)x HNAs, (d) Fe 2p spectra of the Ni2.2Fe(OH)x HNAs.
Mentions: The Ni/M atomic ratios of the NiyM(OH)x HNAs were determined with inductively coupled plasma (ICP) emission spectrometry. The ratios in the HNAs were similar to the reactant ratios (Table S1), indicating that the Ni/M ratios in the hydroxides were similar to those in the precursors. The surface compositions and valence states of the as-prepared NiyM(OH)x HNAs were investigated by X-ray photoelectron spectroscopy (XPS), and the results are shown in Fig. 4. Nickel, Fe, Zn, and O species were observed. Peak fitting analysis of the Ni 2p for Ni(OH)2 revealed one Ni2+ state for Ni at binding energies of 855.5 eV and 873.5 eV. Peak fitting analysis for Ni 2p in the Ni2.2Fe(OH)x and Ni2.1Zn(OH)x HNAs indicated the presence of Ni2+ (855.4 eV and 873.1 eV) and Ni3+ (857.3 eV and 875.5 eV)34. Compared to the un-doped Ni(OH)2 HNAs, the Ni 2p peaks of the M-doped samples were shifted to more positive energies (Ni2.1Zn(OH)x < Ni2.2Fe(OH)x), suggesting that the oxidation of Ni2+ was favored when Fe and Zn were added. This effect was strongest with Fe35. Additional evidence for the presence of Ni2+ was observed in the two intense shakeup satellite peaks (861.8 eV and 880.0 eV)16. The Zn 2p XPS spectrum for the Ni2.1Zn(OH)x HNAs contained 2p3/2 and 2p1/2 doublets, which are characteristic of Zn2+ (1022.7 eV and 1045.7 eV)34. Fe 2p3/2 and Fe 2p1/2 spin-orbital splitting for the Ni2.2Fe(OH)x HNAs was deconvolved into four peaks, indicating the coexistence of Fe2+ (711.5 eV and 723.7 eV) and Fe3+ (716.0 eV and 726.3 eV) in the Ni2.2Fe(OH)x HNAs3637. The O 1s spectrum of the Ni(OH)2 HNAs was fit to a peak at a binding energy of 530.9 eV, which was assigned to the oxygen in hydroxide. The O 1s spectra of the Ni2.2Fe(OH)x and Ni2.1Zn(OH)x HNAs were fit with two peaks at binding energies of 530.1 eV and 531 eV, revealing the presence of lattice and hydroxide oxygens, respectively16. These results confirm that strong electron interactions occurred between Ni and both Fe and Zn in the NiyM(OH)x HNAs.

View Article: PubMed Central - PubMed

ABSTRACT

Nickel-based hydroxide hierarchical nanoarrays (NiyM(OH)x HNAs M&thinsp;=&thinsp;Fe or Zn) are doped with non-noble transition metals to create nanostructures and regulate their activities for the oxygen evolution reaction. Catalytic performance in these materials depends on their chemical composition and the presence of nanostructures. These novel hierarchical nanostructures contain small secondary nanosheets that are grown on the primary nanowire arrays, providing a higher surface area and more efficient mass transport for electrochemical reactions. The activities of the NiyM(OH)x HNAs for the oxygen evolution reaction (OER) followed the order of Ni2.2Fe(OH)x&thinsp;&gt;&thinsp;Ni(OH)2&thinsp;&gt;&thinsp;Ni2.1Zn(OH)x, and these trends are supported by density functional theory (DFT) calculations. The Fe-doped nickel hydroxide hierarchical nanoarrays (Ni2.2Fe(OH)x HNAs), which had an appropriate elemental composition and hierarchical nanostructures, achieve the lowest onset overpotential of 234&thinsp;mV and the smallest Tafel slope of 64.3&thinsp;mV dec&minus;1. The specific activity, which is normalized to the Brunauer&ndash;Emmett&ndash;Teller (BET) surface area of the catalyst, of the Ni2.2Fe(OH)x HNAs is 1.15&thinsp;mA&thinsp;cm&minus;2BET at an overpotential of 350&thinsp;mV. This is ~4-times higher than that of Ni(OH)2. These values are also superior to those of a commercial IrOx electrocatalyst.

No MeSH data available.