Identification of the active sites in NiFe (oxy)hydroxide electrocatalysts for oxygen evolution reaction (OER) is an ongoing challenge due to their largely amorphous and disordered structures, which makes crystalline NiFe layered double hydroxide (LDH) nanosheets structurally more desirable for investigating the structure-activity relationship of the active sites because of their well-defined basal planes and edges. Starting with the example of benchmark bimetallic NiFe LDH nanosheets, we demonstrate the significance of determining electrochemically accessible catalyst loadings based on electrochemical impedance spectroscopy technique for evaluating intrinsic catalyst activities. To understand whether the active sites live on basal planes, edges, or both, we rationally derive edge-rich mesoporous NiFe LDH nanosheets from trimetallic NiZnFe LDH nanosheets by selectively etching amphoteric Zn<sup>2+</sup> cations away from LDH lattices in alkaline media. In-depth comparisons between the trimetallic NiZnFe and the holey NiFe LDH nanosheets suggest basal planes and edges contribute equally to the intrinsic catalyst activity, turnover frequency calculations on LDH catalysts with different Ni to Fe ratios further verify the catalytically active sites are on both basal planes and edges of NiFe LDH catalysts. This work not only provides new insights into the role of Fe in the OER activity of NiFe LDH catalysts, but also builds a reliable experimental platform for determining electrochemically accessible catalyst loadings and evaluating intrinsic catalyst activities, which are directly applicable to a wide variety of OER catalysts for identifying their active sites.

Active sites on both basal planes and edges of NiFe layered double hydroxide oxygen evolution electrocatalysts

256th National Meeting (2018)

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