Exploiting low-cost, highly active, and robust oxygen evolution reaction (OER) electrocatalysts based on earth-abundant elements by a simple synthesis approach holds paramount importance for green hydrogen production through water electrolysis. In this work, the NiO, Co3O4 and NiCo2O4 nanoparticle layers with identical surface morphologies are prepared under same deposition conditions by a simple spray pyrolysis method and their OER activities are comparatively investigated. Among all these three electrocatalysts, NiCo2O4 shows the lowest overpotential of 420 mV to drive benchmark current density of 10 mA cm(-2) and the smallest Tafel slope (84.1 mV dec(-1)), which are comparable to the OER performance of the benchmark commercial RuO2 electrocatalyst. The high OER activity of NiCo2O4 is attributed to the synergy effect and the modulation of electronic properties between Co and Ni atoms, which drastically reduces the overpotential required to drive OER activities. Therefore, it is believed that the NiCo2O4 synthesized by this simple method would be a competitive candidate as an industrial electrocatalyst with high-efficiency and low cost for large-scale green hydrogen production via water electrolysis.