The electroreduction of the pertechnetate ions has been examined in a wide range of sulfuric acid concentrations (0.5-4M) using electrochemical (CV. RRDE) and spectroelectrochemical UV-vis (Au-OTE) techniques. Soluble Tc(IV) and probably Tc(III,IV) species with absorption bands at 502 nm and 670 nm, respectively, were found to be formed during the reduction in 4M H2SO4. The strongly acidic medium was found to stabilize technetium forms with lower oxidation states. Spectroelectrochemical measurements performed in 4M H2SO4 show formation of [Tc(mu-O)(2)](3+/4+). The results indicate existence of mixed chemical and electrochemical pathways of generation of Tc(IV) species, which can be later reduced to Tc(III,IV). Rotating ring disk electrode studies confirm generation of Tc-soluble species with lower oxidation states during pertechnetates reduction. The activation energy calculated for limiting current connected probably with generation of the dimeric structure of Tc in 4 M H2SO4 is equal to 12.56 +/- 1.14 kJ mol(-1) which can indicate a diffusion controlled process. (C) 2012 Elsevier Ltd. All rights reserved.