Highly efficient and stable bifunctional electrocatalyst for overall water splitting (OWS) are vital for large-scale hydrogen production. Herein, we demonstrate a novel bifunctional electrocatalyst - Co-3(PO4)(2) nanosheet arrays - prepared by a combined hydrothermal growth and plasma treatment. Owing to the large surface area, enhanced conductivity, the abundance of coordinately unsaturated Co3+ sites and numerous oxygen vacancies, the plasma activated Co-3(PO4)(2) nanosheet arrays exhibit low overpotentials for oxygen evolution reaction (240 mV) and hydrogen evolution reaction (50 mV) at 10 mA cm(-2) with excellent stability. The overall performance is comparable to the best reports for precious-metal-free electrocatalysts. Also, the plasma activated Co-3(PO4)(2) nanosheet arrays show superior kinetics for hydrogen- and oxygen-evolution with Tafel slope values of 35 and 53 mV dec(-1), respectively. The overall-water-splitting, with 10 mA cm(-2) at a low voltage of 1.48 V, is achieved using the nanosheet arrays as both the anode and cathode and the performance surpasses that of the IrO2/C-Pt/C couple for sufficiently high overpotentials. This work presents a promising strategy for designing high-performance electrocatalysts toward overall water splitting.