Simple and cost effective fabrication of 3D porous core-shell Ni nanochains@NiFe layered double hydroxide nanosheet bifunctional electrocatalysts for overall water splitting

Highly efficient, durable and cost-effective electrocatalysts are highly desired for overall water splitting (OWS). Herein, we report the easy fabrication of 3D porous core-shell Ni nanochains@NiFe layered double hydroxide (LDH) nanosheets with extraordinary oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and OWS performance. In specific, a simple magnetic field-assisted method is used for the in situ growth of Ni nanochain cores with large surface areas, allowing the subsequent vertical growth of few-layered NiFe LDH nanosheets to form densely packed shells. Benefiting from the meticulously designed nanoarchitecture, the electrocatalyst possesses rich exposed active sites, plentiful charge transfer channels and high porosity for the release of gas bubbles. The OER performance and durability of the electrocatalyst are far better than those of both commercial RuO₂ and IrO₂, while its HER performance is competitive with the performance of the benchmark Pt/C electrode in alkaline electrolytes. When these catalysts are further employed as anode and cathode electrodes, small cell voltages of 1.53 and 1.78 V can be achieved at current densities of 10 and 100 mA cm^-2 for a long-term OWS reaction. Towards the commercial use, we design an electrolytic overall-water-splitting cell pack, which demonstrates a linear relationship between the numbers of packing cells and the increase of current density under a given voltage.