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Developing efficient oxygen evolution reaction (OER) electrocatalysts with earth-abundant elements is very important for sustainable H 2 generation via electrochemical water splitting. Here we design a crystalline-amorphous Ni–Fe–Al hybrid phosphides nanosheet arrays grown on NiFe foam for efficient OER application. Dynamic surface reorganization of phosphides at anodic/cathodic polarizations is probed by in situ Raman spectroscopy. The reconstructed amorphous Ni(Fe)OOH species are determined as the active phases that facilitate the OER process. This unique electrode shows highly catalytic activity toward water oxidation, achieving the current densities of 10 and 100 mA cm−2 at 181 and 214 mV in 1 M KOH, respectively. Meanwhile, it also exhibits excellent stability at a large current density of 100 mA cm−2 for over 60 h. This work reveals the dynamic structural transformation of pre-catalyst in realistic conditions and highlights the important role of oxyhydroxides as real reactive species in OER process with high activity. [Display omitted] • Ni–Fe–Al hybrid phosphides nanosheet arrays were synthesized for OER. • Dynamic self-reconstruction was revealed by in situ Raman spectroscopy. • Amorphous Ni(Fe)OOH species act as the real active phases. • Regenerated pre-catalyst shows excellent OER activity. [ABSTRACT FROM AUTHOR]

Metal foams with high surface/volume ratio and excellent electrical conductivity are widely used in water splitting. Herein, we report a redox process sculpturing commercial NiFe foams with dual-scale porosities as high efficient catalysts for water oxidation reactions. Through the oxidation-reduction process, many pores of few micrometres in size were formed on a porous NiFe backbone with a pore size of 50–300 μm. The pore morphology can be reasonably controlled by varying the oxidation temperature. Electrochemical measurement demonstrates that redox-NiFe foam exhibits greatly enhanced activity towards oxygen evolution reaction. Specifically, the redox-NiFe foam oxidized at 900 °C yields the best catalytic activity with an overpotential of 294 ± 3 mV to achieve the current density of 100 mA cm−2 in 1 M KOH, which is much lower than 402 ± 2 mV of initial NiFe foam. This work highlights the formation of highly porous microstructure in the original skeleton of NiFe foam. Furthermore, the redox sculptured NiFe foams can also function as effective skeletons for the loading of active catalysts, which thus can find wide applications in electrocatalysis and energy storage. • NiFe foams with dual-scale porosities were fabricated by a redox process. • Micropore structure can be engineered by controlling oxidation temperature. • Redox-NiFe foams exhibited greatly enhanced water oxidation activity. • Redox NiFe foam showed excellent durability. [ABSTRACT FROM AUTHOR]

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]