The first operation for the production of dimensionally stable electrodes based on titanium sheets covered with a layer of RuO2 and/or IrO2 is the treatment of titanium in HCl solution. The surface layer structure of titanium treated in HCl has been determined by X-ray diffraction, electron microscopy and by measurement the double layer capacity. Observation of the surface of etched electrodes by EM has shown the TiH2 (from the X-ray diffraction) formed during dissolution of titanium in an active region is not regularly distributed over all the surface area compared to the regularly distributed TiH2 formed during the cathodic polarization of titanium. The relative content of TiH2 was independently determined by X-ray diffraction and by vacuum desorption of H-2 from the decomposition of TiH2 and these values are directly proportional. The increase of the relative surface content of TiH2 (determined by X-ray diffraction) leads to the decrease of double layer capacity.