Electrochemical water splitting is a promising method for sustainable energy conversion without environmental contamination. Developing active, stable, and low-cost electrocatalysts is important for practical applications with requirements such as scalability and durability. Herein, an efficient method for the electrodeposition of high-activity cobalt iron-phosphorus (CoxFe1-x-P) films as bi-functional electrocatalysts is presented. For films with a cobalt/iron atomic ratio of 1.07, the electrodeposited CoxFe1-x-P films showed outstanding electrocatalytic performance for both the H-2 and O-2 evolution reactions (HER and OER, respectively). In the HER, the overpotential and Tafel slope of the CoxFe1-x-P film on the copper plate were 169 mV at 10 mA/cm(2) and 56.9 mV/dec, respectively. In the case of the OER, the CoxFe1-x-P film on dendritic copper exhibited superior performance with an overpotential of 290 mV and a Tafel slope of 39.2 mV/dec. In the two-electrode system consisting of CoxFe1-x-P film on the copper plate without (HER) and with dendritic copper (OER) for full water splitting, the electrodes exhibited a low overpotential of 1.64 V at 10 mA/cm(2) and excellent long-term stability over several days under alkaline conditions. (C) 2018 The Electrochemical Society.