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Nickel ferrocyanide as a high-performance urea oxidation electrocatalyst

Abstract

Urea is often present in waste water but can be used in powering fuel cells and as an alternative oxidation substrate to water in an electrolyser. However, an insufficient mechanistic understanding and the lack of efficient catalysts for the urea oxidation reaction have hampered the development of such applications. Here we demonstrate that a nickel ferrocyanide (Ni2Fe(CN)6) catalyst supported on Ni foam can drive the urea oxidation reaction with a higher activity and better stability than those of conventional Ni-based catalysts. Our experimental and computational data suggest a urea oxidation reaction pathway different from most other Ni-based catalysts that comprise NiOOH derivatives as the catalytically active compound. Ni2Fe(CN)6 appears to be able to directly facilitate a two-stage reaction pathway that involves an intermediate ammonia production (on the Ni site) and its decomposition to N2 (on the Fe site). Owing to the different rate-determining steps with more favourable thermal/kinetic energetics, Ni2Fe(CN)6 achieves a 100 mA cm−2 anodic current density at a potential of 1.35 V (equal to an overpotential of 0.98 V).

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Fig. 1: Evaluation of the UOR performance on a Ni2Fe(CN)6 catalyst in a three-electrode cell.
Fig. 2: Comparison of Ni2Fe(CN)6 and conventional NiC2O4 catalysts.
Fig. 3: Reaction mechanism diagrams for UOR on the Ni2Fe(CN)6(011) surface.
Fig. 4: In situ SR-FTIR spectra of catalysts under different conditions.
Fig. 5: OER replacement by the UOR in energy-saving systems for H2 and H2O2 generation.

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Data availability

The datasets analysed and generated during the current study are included in the paper and its Supplementary Information. Source data are provided with this paper.

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Acknowledgements

P.C. acknowledges funding from the National Natural Science Foundation of China (21771002). Q.-H.L. acknowledges funding from the National Natural Science Foundation of China (U1932212). S.-Q.L. acknowledges funding from the Key Project of Educational Department of Anhui Province (KJ2019A0861). Y.Z. acknowledges funding from the Australian Research Council (DP190103472). S.-Z.Q. acknowledges funding from the Australian Research Council (DP160104866 and FL170100154).

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Contributions

P.C. and Y.Z. conceived the project. S.-Z.Q. supervised the project. S.-K.G. performed the material preparations, characterizations and activity tests, with the assistance of J.H. and H.-B.S. H.S., X.Z. and Q.-H.L. performed the in situ XAFS and in situ SR-FTIR tests. S.-Q.L. performed the DFT calculations. P.C., Y.Z. and S.-Z.Q. wrote the manuscript. S.-Z.Q. and M.J. revised the manuscript and discussed the draft submissions.

Corresponding authors

Correspondence to Ping Chen, Qing-Hua Liu or Shi-Zhang Qiao.

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Peer review information Nature Energy thanks Michael Busch, Xinliang Feng and Xuping Sun for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–28, Tables 1 and 2, Notes 1–4 and references.

Supplementary Data 1

Energies of Ni2Fe(CN)6 (011) surface, intermediates and transition states.

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Geng, SK., Zheng, Y., Li, SQ. et al. Nickel ferrocyanide as a high-performance urea oxidation electrocatalyst. Nat Energy 6, 904–912 (2021). https://doi.org/10.1038/s41560-021-00899-2

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