Nonprecious highly active electrocatalysts in water splitting are essential for large-scale storage of renewable hydrogen energy. Two dimensional (2D) layered double hydroxides (LDHs) are commonly regarded as promising electrocatalysts for oxygen evolution reaction (OER), while they are not so efficient for hydrogen evolution reaction (HER). Herein, we propose the NiCo LDHs derived NiCoPx with 2D mesoporous ultrathin nanoplates structure in-situ grown on carbon paper (NiCoPx/CP). The special nanostructure and rich active sites endow the binder-free NiCoPx/CP with excellent bifunctional electrocatalytic performance toward HER and OER with very low overpotentials of 56 mV for HER at 10 mA cm(-2) and 239 mV for OER at 30 mA cm(-2). Moreover, the NiCoPx/CP can be directly used as electrodes for both anode and cathode to construct an efficient alkaline water electrolyzer with a cell votage of 1.58 Vat 10 mA cm(-2), which show even better performance than that of the best known commercial Pt-C&RuO2/CP catalysts. This work presented here can offer a novel guidance for the construction of non-noble metal-based electrocatalysts with 2D nanostructure in energy applications.