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Ta–TiOx nanoparticles as radical scavengers to improve the durability of Fe–N–C oxygen reduction catalysts

Abstract

Highly active and durable platinum group metal-free catalysts for the oxygen reduction reaction, such as Fe–N–C materials, are needed to lower the cost of proton-exchange membrane fuel cells. However, their durability is impaired by the attack of oxidizing radicals such as ·OH and HO2· that form from incomplete reduction of O2 via H2O2. Here we demonstrate that Ta–TiOx nanoparticle additives protect Fe–N–C catalysts from such degradation via radical scavenging. The 5 nm Ta–TiOx nanoparticles were uniformly synthesized on a Ketjenblack substrate using a high-temperature pulse technique, forming the rutile TaO2 phase. We found that Ta–TiOx nanoparticles suppressed the H2O2 yield by 51% at 0.7 V in an aqueous rotating ring disk electrode test. After an accelerated durability test, a fuel cell prepared with the scavengers showed a current density decay of 3% at 0.9 ViR-free (internal resistance-compensated voltage); a fuel cell without scavengers showed 33% decay. Thus, addition of Ta–TiOx provides an active defence strategy to improve the durability of oxygen reduction reaction catalysts.

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Fig. 1: Schematic comparing the PGM-free catalyst durability in the ORR process without and with the Ta–TiOx/Ketjenblack scavengers.
Fig. 2: Morphology of the Ta–TiOx radical scavengers.
Fig. 3: The radical scavenging performance of Ta–TiOx/KB.
Fig. 4: The Fe–N–C catalyst protection and H2O2 suppression performance of the Ta–TiOx/KB scavengers.
Fig. 5: PEM fuel cell performances of the PGM-free cathode with and without Ta–TiOx/KB.
Fig. 6: DFT calculations to understand the radical scavenging performance of the Ta–TiOx/KB.

Data availability

The authors declare that all data supporting the findings of this study are available within the paper and Supplementary Information files. Source data are provided with this paper.

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Acknowledgements

L.H., Y.S., X.X. and H.X. acknowledge support from the US Department of Energy, Office of Energy Efficiency and Renewable Energy and Hydrogen and Fuel Cell Technologies Office through the Electrocatalysis consortium (ElectroCat) and from DOE programme managers D. Papageorgopoulos, S. Thompson, D. Peterson and G. Kleen. R.S.-Y. acknowledges financial support from National Science Foundation DMR-1809439. D.J. acknowledges support from the National Science Foundation CHE-2102191. G.H. acknowledges the financial support from the Queens College, City University of New York. The authors acknowledge the support of the Maryland Nanocenter, its Surface Analysis Center and AIMLab. The views and opinions of the authors expressed herein do not necessarily state or reflect those of the US government or any agency thereof. Neither the US government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.

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L.H. and Y.S. co-supervised the research. L.H., Y.S., V.P. and H.X. conceived the concept. H.X., X.X., Y.S. and L.H. designed the experiment. H.X. and X.X. carried out the experimental works including syntheses and electrochemical measurements. H.X., M.H., M.W. and A.H.P. carried out the characterization of materials. H.X., L.G.-L. and M.I.A.-S. carried out the EPR test. V.P. carried out the fluorescence test. S.S. and V.R. conducted the fuel cell test. G.H. and D.J. carried out the calculation analysis. H.X. and L.H. wrote the paper. G.H, X.X., R.S.-Y. and Y.S. revised the paper. All authors contributed to the discussion of the manuscript.

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Correspondence to Guoxiang Hu, Reza Shahbazian-Yassar, Yuyan Shao or Liangbing Hu.

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Nature Energy thanks Frédéric Jaouen, Ulrike Kramm and Samira Siahrostami for their contribution to the peer review of this work.

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Xie, H., Xie, X., Hu, G. et al. Ta–TiOx nanoparticles as radical scavengers to improve the durability of Fe–N–C oxygen reduction catalysts. Nat Energy 7, 281–289 (2022). https://doi.org/10.1038/s41560-022-00988-w

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