With rising energy consumption in the world and the negative environmental and human health impacts of fossil fuels, the demand for renewable energy sources is increasing. The energy generated by renewable energy sources can be stored either in a chemical (water splitting) or an electrochemical (battery or supercapacitor) form, that are two distinct processes. Here, we introduce an integrated solar-powered system for both electrochemical energy storage and water electrolysis. A nickel-cobalt-iron layered double hydroxide (Ni-Co-Fe LDH) was successfully synthesized on nickel foam as a substrate using a fast, one-step electrodeposition approach. The Ni-Co-Fe LDH exhibited excellent electrochemical properties both as an active electrode material in supercapacitors, and as a catalyst in the oxygen evolution reaction (OER). When employed as the positive electrode in a supercapacitor, along with activated carbon as the negative electrode in an asymmetric configuration, the ultrathin and porous Ni-Co-Fe LDH nanoplatelets delivered an ultrahigh specific energy of 57.5 W h kg−1 with an outstanding specific power of 37.9 kW kg−1 and an excellent cycle life. As an OER electrocatalyst, Ni-Co-Fe LDH exhibited superior electrocatalytic performances with a very low overpotential of 0.207 V versus a reference hydrogen electrode (RHE) at 10.0 mA cm−2, and a small Tafel slope of 31 mV dec−1. The superior energy storage and catalytic OER properties of the Ni-Co-Fe LDH nanoplatelet array can be attributed to both the synergistic effects among the metal species and the unique mesoporous structure of the LDH that provides facilitated charge/ion diffusion pathways and more available active sites.