The electroreduction mechanism of ReO4- in acidic solution is investigated intensively via experiments and thermodynamic analysis. High acidity and low ReO4- concentration are the advantageous conditions to fabricate metallic rhenium, while under other conditions only small amount of rhenium oxides can be obtained. The reduction of ReO4- to metallic Re is a multi-step process involving the successive reduction of intermediates. When there is no enough hydrion or the rhenium concentration exceeds a certain value, it is apt to produce a detrimental intermediate ReO2, which will benefit the hydrogen evolution reaction and seriously impede the further reduction of low-valent intermediates. (c) 2017 The Electrochemical Society. All rights reserved.