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. 2023 Sep 19;26(10):107944.
doi: 10.1016/j.isci.2023.107944. eCollection 2023 Oct 20.

Nb-doped NiO nanoflowers for nitrite electroreduction to ammonia

Ying Zhang  1 , Yuying Wan  1 , Xiaoxu Liu  2 , Kai Chen  1 , Ke Chu  1
Affiliations

Nb-doped NiO nanoflowers for nitrite electroreduction to ammonia

Ying Zhang et al. iScience. .

Abstract

Electrocatalytic reduction of nitrite to ammonia (NO2RR) is considered as an appealing route to simultaneously achieve sustainable ammonia production and abate hazardous nitrite pollution. Herein, atomically Nb-doped NiO nanoflowers are designed as a high-performance NO2RR catalyst, which exhibits the highest NH3-Faradaic efficiency of 92.4% with an NH3 yield rate of 200.5 μmol h-1 cm-2 at -0.6 V RHE. Theoretical calculations unravel that Nb dopants can act as Lewis acid sites to render effective NO2- activation, decreased protonation energy barriers, and restricted hydrogen evolution, ultimately leading to a high NO2RR selectivity and activity.

Keywords: Applied chemistry; Electrochemistry; Energy materials.

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Conflict of interest statement

The authors declare no competing interests.

Figures

None
Graphical abstract
Figure 1
Figure 1
Morphology characteristics of Nb−NiO (A) Schematic diagram of the preparation route of NiO and Nb−NiO. (B−G) Characterizations of as-prepared Nb−NiO: (B) XRD patterns, (C and D) SEM images, (E) TEM image, (F) HRTEM image, (G) Elemental mapping images.
Figure 2
Figure 2
Structural characteristics of Nb−NiO (A, B, and D) (A) Nb K−edge XANES, (B) EXAFS spectra, and (D) WT profiles of Nb−NiO, Nb foil and Nb2O5. (C) EXAFS fitting analysis of Nb−NiO. (E) Charge density difference (top half) and electron location function (bottom half), yellow and red: charge accumulation, cyan and blue: charge depletion. (F and G) (F) PDOS profiles and (G) calculated work functions of NiO and Nb−NiO.
Figure 3
Figure 3
Electrochemical NO2RR tsts (A) LSV curves of Nb−NiO in various electrolytes. (B and C) (B) Chronoamperometry test of Nb−NiO at different potentials after 0.5 h electrolysis and (C) obtained NH3 yield rates and FENH3. (D) Comparison of NH3 yield rates and FENH3 between Nb−NiO and reported NO2RR catalysts. (E) Comparison of the NO2RR performance between NiO and Nb−NiO at −0.6 V. (F and G) (F) Cycling and (G) long-term stability tests of Nb−NiO at −0.6 V.
Figure 4
Figure 4
Theoretical analysis (A and B) Charge density difference plots of ∗NO2 on (A) NiO and (B) Nb−NiO. Yellow: charge accumulation, cyan: charge depletion. (C) Free energy profiles of NO2RR process on NiO and Nb−NiO. (D) Free energies of absorbed H and NO2− on Nb-dopant site of Nb−NiO. (E) RDF curves of the interactions between Nb−dopant and NO2−/H+.
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References

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