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

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.

Unsupported Ni(Pt‐Pd) Electro‐catalysts Synthesized by Hydrazine Reduction under the Assistance of a Magnetic Field

“…The greatest contributions are those associated with the electrostatic field of the Ni 3+ photoelectrons at BEs 857.9 and 875.6 eV for Ni‐SS(PtPd), and 858.0 and 875.8 eV for Ni‐NW(PtPd). These values were in good agreement with those reported in the literature . By contrast, the smallest contributions are related to the corresponding satellites, which are additional indication of the presence of Ni 3+ species.…”

Bifunctional Electrocatalyst of Low-Symmetry Mesoporous Titanium Dioxide Modified with Cobalt Oxide for Oxygen Evolution and Reduction Reactions

“…The mass activity of Co 3 O 4 (3)/lsm-TiO 2 at a potential 1.6 V vs. RHE reaches 42 A g −1 , and the TOF value equals 0.035 s −1 at η = 370 mV. Clearly, the mass activity and TOF values of Co 3 O 4 (3)/lsm-TiO 2 are superior to those of the other investigated electrocatalysts and comparable to those recently reported for the state-of-the-art catalysts [59][60][61][62]. From the data in Table 2, the TOF value of Co 3 O 4 (3)/lsm-TiO 2 catalyst is about~12.5,~17.5, and~1.85 orders of magnitude higher than that of the Co 3 O 4 (3)/hm-TiO 2 (0.0028), Co 3 O 4 (3)/bulk-TiO 2 (0.002), and IrO 2 (0.019) catalysts, respectively.…”

Iron‐Doped Nickel Molybdate with Enhanced Oxygen Evolution Kinetics

“…The proportion of Ni 2+ and Ni 3+ species is calculated to be 44 % and 56 %, respectively. Compared with NiMoO 4 , the appearance of Ni 3+ can be attributed to the electron transfer from Ni to the doped Fe . The Fe 2p XPS spectrum of Ni 0.9 Fe 0.1 MoO 4 in Figure c is deconvoluted into four fitted peaks, indicating the coexistence of Fe 3+ (711.9 and 724.4 eV) and Fe 2+ (716.0 and 726.3 eV) .…”

“…Compared with NiMoO 4 , the appearance of Ni 3+ can be attributed to the electron transfer from Ni to the doped Fe . The Fe 2p XPS spectrum of Ni 0.9 Fe 0.1 MoO 4 in Figure c is deconvoluted into four fitted peaks, indicating the coexistence of Fe 3+ (711.9 and 724.4 eV) and Fe 2+ (716.0 and 726.3 eV) . Figure d shows the Mo 3d XPS spectra of Ni 0.9 Fe 0.1 MoO 4 and NiMoO 4 , in which both of the doublet peaks locate at 235.6 eV and 232.4 eV, corresponding to Mo 3d 3/2 and Mo 3d 5/2 of Mo 6+ species, respectively.…”