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Interfacial engineering is an effective strategy for the design of active oxygen evolution electrode. Yet the intrinsic mechanism of heterogeneous interfaces remains largely unclear for the lack of direct evidence of real active phases. Herein, operando ultraviolet-visible (UV–vis) and Raman spectroscopies were used to probe the surface reconstruction behaviors of FeOOH@NiFe layered double hydroxides (LDH) hybrid catalysts, which revealed that FeOOH@NiFe LDH was converted into highly active FeOOH@ β-Ni(Fe)OOH phases during the OER process. The FeOOH-NiFe LDH interface can promote interfacial charge transfer, delay the Ni oxidation and induce the NiFe LDH phases to highly reactive β-Ni(Fe)OOH. The FeOOH@ β-Ni(Fe)OOH exhibited excellent OER performance (252 mV at 100 mA cm−2) and a 1.6 times increase (at overpotential of 300 mV) in turnover frequency (TOF) with respect to the active phase γ-Ni(Fe)OOH of NiFe LDH. This work clarifies that ration interface engineering can regulate the generation of highly active phases in the OER process. [Display omitted] • Reconstruction of FeOOH@NiFe LDH was study by operando UV–vis and Raman spectroscopies. • FeOOH induced the phase transformation of NiFe LDH to β-Ni(Fe)OOH at the interface. • The interfacial electric field of NiFe LDH and FeOOH promoted the charge transfer. • As-formed FeOOH@ β-Ni(Fe)OOH showed superior OER activity to γ-Ni(Fe)OOH. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) is a key step for electrochemical water splitting and understanding the surface reconstruction of OER pre-catalysts is of vital importance. Herein, hybrid Ni 5 P 4 @FeP nanosheet arrays were evaluated as promising OER pre-catalysts. The dynamic surface evolution was probed by in situ Raman spectroscopy, which revealed that Ni 5 P 4 @FeP was rapidly reconstructed to NiFe 2 O 4 during the anodic scan. The structural instability of amorphous NiFe 2 O 4 led to partial reconstitution to Ni/FeOOH at high oxidation potentials. As-formed Ni/FeOOH@NiFe 2 O 4 hybrid with high structural reversibility was established as a truly active species, which exhibited excellent alkaline OER performance with a low overpotential of 205 and 242 mV under current densities of 10 and 100 mA cm−2, respectively. This work provides a facile strategy to in situ construct an amorphous spinel/oxyhydroxide hybrid structure using electrochemical activation that holds strong promise for potential application in electrochemical water splitting and related energy devices. [Display omitted] • Surface reconstruction of Ni 5 P 4 @FeP was probed by in situ Raman spectroscopy. • Ni 5 P 4 @FeP was oxidized to NiFe 2 O 4 and further to Ni/FeOOH at high potentials. • The real active intermediate was identified as Ni/FeOOH and NiFe 2 O 4 hybrid. • High structural reversibility between NiFe 2 O 4 and Ni/FeOOH was found. • As-formed amorphous NiOOH and NiFe 2 O 4 hybrid showed superior OER activity. [ABSTRACT FROM AUTHOR]