The electroreduction of pertechnetate ions has been examined in sulfuric acid solutions (0.5 M divided by 4 M H2SO4) using rotating disc electrodes (Au-RDE) and optically transparent thin layer spectroelectrochemical cells (Au/RVC-OTTLE). Soluble Tc(III,IV) species with absorption bands at 502 nm were found to be formed during the reduction of TcO4-. The hydrodynamic experiments (Au-RDE) have shown the influence of the acidity of the solution on the activation energy of the electroreduction of the pertechnetate ions to technetium(III,IV) species. The value of the activation energy calculated for limiting current was found to increase from 12.6 +/- 1.1 kJ mol(-1) for 4 M H2SO4 to 20.1 +/- 0.8 kJ mol(-1) for 0.5 M H2SO4. Such an effect suggests an influence of the acid concentration on the structure of obtained products, which are soluble or insoluble Tc species. Thin layer spectroelectrochemical experiments allowed calculation of the redox standard potentials for Tc2O23+/TcO(OH)((aq)) system which was found to be equal to 0.255 V vs. Ag,AgCl(KClsat). (C) 2014 Elsevier Ltd. All rights reserved.