Metal–organic frameworks (MOFs) are increasingly being investigated as electrocatalysts for the oxygen evolution reaction (OER). Despite their promising catalytic activity, many fundamental questions concerning their structure−performance relationships—especially those regarding the roles of active species—remain to be answered. Here we show the structural transformation of a Ni0.5Co0.5-MOF-74 during the OER by operando X-ray absorption spectroscopy analysis and high-resolution transmission electron microscopy imaging. We suggest that Ni0.5Co0.5OOH0.75, with abundant oxygen vacancies and high oxidation states, forms in situ and is responsible for the high OER activity observed. The ratio of Ni to Co in the bimetallic centres alters the geometric and electronic structure of as-formed active species and in turn the catalytic activity. Based on our understanding of this system, we fabricate a Ni0.9Fe0.1-MOF that delivers low overpotentials of 198 mV and 231 mV at 10 mA cm−2 and 20 mA cm−2, respectively.
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The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files.
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We appreciate financial support from the Strategic Priority Research Program of Chinese Academy of Sciences (XDB36000000, Z.T.), the National Key Basic Research Program of China (2016YFA0200700, Z.T.), the National Natural Science Foundation of China (21890381 and 21721002, Z.T.; 11605225, J.D.), the Frontier Science Key Project of Chinese Academy of Sciences (QYZDJ-SSW-SLH038, Z.T.) and K.C. Wong Education Foundation (Z.T.). S.Z. acknowledges financial support from the FH Loxton fellowship of the USYD. J.D. acknowledges support from the Youth Innovation Promotion Association, CAS. C.-T.H. acknowledges support from the Young Elite Scientists Sponsorship Program by CAST. J.Z. thanks the National Key Research and Development Program of China (2017YFA0403400). We sincerely appreciate V. Yachandra and B. Lassalle providing the XAS data for Ni(OH)2 and NiOOH references. We thank R. Chen for help and suggestions.
The authors declare no competing interests.
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Zhao, S., Tan, C., He, CT. et al. Structural transformation of highly active metal–organic framework electrocatalysts during the oxygen evolution reaction. Nat Energy 5, 881–890 (2020). https://doi.org/10.1038/s41560-020-00709-1
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