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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]

Developing efficient and nonprecious electrocatalysts for oxygen evolution reaction (OER) is crucial for the hydrogen generation via water splitting. Here we report the direct growth of heterostructural Ni 2 P–Fe 2 P hybrid electrocatalysts on NiFe foams. The redox engineered NiFe foam (rNF) significantly enhances the OER performance. Among prepared catalysts, Ni 2 P–Fe 2 P/rNF performs the highest OER activity, driving the current densities of 10 and 100 mA cm−2 at low overpotentials of 218 and 270 mV in 1 M KOH, respectively. Meanwhile, it can maintain 100 mA cm−2 for 24 h without obvious degradation. The morphology and composition of NFP/rNF after OER test were carefully studied. This work suggests that self-supported bimetal phosphides of NFP/rNF is an efficient and durable electrode material for water oxidation. Heterostructural Ni2P-Fe2P hybrid electrocatalysts were direct grown on NiFe foams, which show excellent oxygen evolution activity and stability. Image 1 • The formation of micro-sized pores on the skeleton of NiFe foam (NF) substrate can enlarge surface area. • The heterogeneous Ni2P-Fe2P structure provides plentiful active sites for OER. • The Ni2P-Fe2P/ rNF foam exhibits an extraordinary electro catalytic performance. [ABSTRACT FROM AUTHOR]