Active and durable acid medium electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are of critical importance for the development of proton exchange membrane (PEM) water electrolyser or Fuel cells. Herein, we report a facile method for the synthesis of 3D-hierarchical porous iridium oxide/N-doped carbon hybrid (3D-IrO2/N@C) and its superior OER and HER activity in acid. In 0.5 M HClO4, this catalyst exhibited remarkable activity towards OER with a low overpotential of 280 mV at 10 mA/cm(2) current density, a low Tafel slope of 45 mV/dec and similar to 98% faradaic efficiency. The mass activity (MA) and turnover frequency (TOF) are found to be 833 mA/mg and 0.432 s(-1) at overpotential of 350 mV which are similar to 32 times higher than commercial (comm.) IrO2. The HER performance of this 3D-IrO2/N@C is comparable with comm. Pt/C catalyst in acid. This 3D-IrO2/NOC catalyst requires only 35 mV overpotential to reach a current density 10 mA/cm(2) with Tafel slope 31 mV/dec. Most importantly, chronoamperometric stability test confirmed superior stability of this catalyst towards HER and OER in acid. This 3D-IrO2/NCPC catalyst was applied as both cathode and anode for over-all water splitting and required only 1.55 V overpotential to achieve a current density of 10 mA/cm(2) in acid. The outstanding activity of the 3D-IrO2/N@C catalyst can be attributed to a unique hierarchical porous network, high surface area, higher electron and mass transportation, synergistic interaction between IrO2 and carbon support. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.