The aim of this work is to investigate the natural mineral Montmorillonite (MMT) as catalytic support and to assess the efficiency of the composite MMT-supported Ir toward OER in acidic electrochemical water splitting. MMT is a phyllosilicate layered clay with 2:1 type sheet structure with high cation exchange capacity, high surface area and low cost. Three different catalyst with iridium loadings of 10, 20, and 30 wt% Ir supported on MMT are synthesized. Their phase identification, crystallite size, elemental analysis, and thermal stability are studied by means of XRD, HRTEM, EDX, and TGA, respectively. The catalytic performance is examined in 0.5 M H2SO4 and in electrolysis cell with proton conductive polymer membrane (PEMEC). The results obtained prove that montmorillonite is a promising alternative of the conventional carbon supports with the advantage of being both easily available and cost favourable. Ir/MMT loaded with 30 wt% Ir is the best performed catalyst. In PEMEC operated at 80 degrees C the catalyst loading of 0.5 mgir cm(-2) ensures intensive and sustainable oxygen evolution with current density reaching 200 mA cm(-2) already at 1.6 V. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.