Construction of hierarchically porous graphitized carbon-supported NiFe layered double hydroxides with a core-shell structure as an enhanced electrocatalyst for the oxygen evolution reaction.

The oxygen evolution reaction (OER) is a vital half-reaction in water splitting and metal-air batteries. Developing earth-abundant, highly efficient and durable OER catalysts has faced huge challenges until now, because OER is a strict kinetic sluggish process. Herein, we report the construction of hierarchically porous graphitized carbon (HPGC) supported NiFe layered double hydroxides (LDHs) with a core-shell structure (denoted as HPGC@NiFe) by a facile strategy. The HPGC was first obtained by pyrolysing phenolic resin nanospheres with FeCl3 and ZnCl2 as the catalyst and the activator, respectively. Then the NiFe LDH arrays were directly grown on the HPGC by a one-step hydrothermal method. The as-synthesized HPGC@NiFe reveals excellent OER properties with a low onset potential, a lower overpotential of 265 mV (corresponding to the current density at 10 mA cm-2) and a small Tafel slope (56 mV per decade). And its catalytic activity is even superior to that of the start-of-the-art noble-metal catalyst IrO2/C. Notably, the HPGC@NiFe electrode shows admirable stability measured by performing 2000 cycle CVs and long-term electrolysis for 50 h. The prominent performance can be attributed to the synergistic effect between the NiFe-LDHs and the hierarchically porous graphitized carbon, in which the former can increase the exposure of the active sites, while the latter can increase the charge transfer efficiency. Our research implies the possibility for the development of low-cost layered double hydroxides as a promising candidate in electrochemical energy storage and conversion equipment.