Low-cost and efficient electrocatalysts for water splitting hold a significant position in future renewable energy system. Herein, we first fabricated a self-standing bimetallic FeCo Prussian blue analogue nanosheet array (FeCo PBA) on Ni foam through ion exchange between K3Fe(CN)6 and hydrothermal synthesized Co3(PO4)2·8H2O nanosheet arrays. Then the obtained FeCo PBA were facilely transformed into FeCo/C and FeCoP/C nanosheet arrays through hydrogenation and phosphidation, respectively. Benefiting from the enhanced mass transfer in porous structure, the intimate contact with Ni framework and the synergistic effect of bimetal sites, the resultant FeCo/C NS and FeCoP/C NS demonstrate superior oxygen and hydrogen evolution activity in alkaline media, respectively. Impressively, a low cell voltage of 1.55 V is sufficient to afford a current density of 10 mA cm−2 by coupling FeCo/C NS and FeCoP/C NS in a two-electrode water splitting electrolyzer, surpassing the performance of PtC based couple (Vcell,10 = 1.60 V). This work provides a new approach to construct highly efficient and cost-effective water splitting electrodes. FeCo/C and FeCoP/C nanosheet arrays for highly efficient water splitting are prepared by facile transformation of self-standing FeCo Prussian Blue Analogous. Display omitted •Self-standing FeCo Prussian blue analogue nanosheet array (FeCo PBA) on Ni foam is fabricated by ion exchange reaction.•Facile conversion of FeCo PBA into efficient water splitting electrodes is achieved by hydrogenation and phosphorization.•A water splitting electrolysor with low cell voltage (1.55 V) is constructed with the as-obtained FeCo/C NS and FeCoP/C NS.