The Hydrogen Evolution Reaction on Rhenium Metallic Electrodes: A Selected Review and New Experimental Evidence

The volcano plots reported in the field of electrocatalysis utilize data with a difference of three orders of magnitude between the worst and the best rhenium electrocatalytic activity toward the hydrogen evolution reaction (HER). However, the commonly used mean value of the exchange density current (j(0)) of the HER on rhenium is log j(0)=-2.9 A cm(-2), which is higher than the value used for platinum (log j(0)=-3.3 A cm(-2)). This fact seems to contradict Sabatier's principle and points to the possibility that this value corresponds more to rhenized surfaces than to metallic rhenium. Rhenized surfaces are primarily composed of a mixture of oxides; therefore, the electrocatalytic behavior is attributed to these thin films rather than to metallic rhenium. In addition, a selected review of rhenized electrodes is included herein because these issues have not been considered in the electrocatalysis literature at the present time. We initially believed that the kinetic parameters might have been overestimated due to the formation of rhenide ion or rhenium hydride species; however, no evidence of the formation of these species was found. Our experimental mean value of the exchange current density of the HER on metallic rhenium is 7x10(-5) A cm(-2) in acidic solution. Therefore, our results are in accordance with Sabatier's principle, which states that a weak adsorption energy of hydrogen on rhenium (energy, 6.9 kJ mol(-1)) results in a slow rate of reaction (log j(0)= -4.2 A cm(-2)), whereas an intermediate adsorption energy of hydrogen on platinum (12 kJ mol(-1)) produces a fast reaction (log j(0)=-3.3 A cm(-2)).