The present invention relates to a catalytically active material for the electrochemical oxidation of water, wherein the catalytically active material comprises an amorphous Ir-oxohydroxide, wherein the catalytically active material has a specific surface area (SBET) of ≥50 m2.g−1; an electrode coated with the catalytically active material; a proton exchange membrane (PEM) based electrolyzer comprising the electrode; the use of the catalytically active material, the electrode or the electrolyzer the electrochemical oxidation of water; and a process for preparing the catalytically active material comprising the microwave-assisted thermal treatment of a basic solution of an Ir(III) or Ir(IV) complex.