Perspective—New Perspectives from Classical Transition State Theory: The Hydrogen Evolution Reaction on Metal Electrodes
Kasun Saweendra Rathnatunga Dadallagei, Daniel Parr, Joshua Richard Coduto, Andrew Lazicki, Sidney J. DeBie, Christian Haas, Johna Leddy
Abstract
New perspectives derive from classical transition state theory applied to hydrogen evolution reactions (HER). Trasatti found exchange current density j 0 increases exponentially with metal electrode work function Φ. The elementary electron transfer step <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>M</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi>e</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>+</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>H</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">ads</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> </mml:msubsup> <mml:mo>⇄</mml:mo> <mml:mi>M</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mo>+</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>H</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">ads</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>•</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> specifies the metal in the transition state and derives rate equations where metal specific physiochemical property Φ is explicit. Linearity of log j 0 with Φ is quantified. Φ raises j 0 because Φ lowers the activation energy for electrocatalysis. Rate expressions that embed material specific physiochemical properties provide opportunities for a priori electrocatalyst design and fundamental insights on electron transfer kinetics. New perspectives derive from revisit of established HER data with classical transition state theory.