# A challenge to the Delta G~0 interpretation of hydrogen evolution

## TL;DR

This paper challenges the traditional view that platinum's high catalytic activity in hydrogen evolution is due to its near-zero hydrogen binding energy, revealing instead that kinetically active hydrogens have weaker binding energies similar to gold.

## Contribution

The study introduces a fully potential-dependent ab initio microkinetic model to explain platinum's high activity, highlighting the kinetic inertness of G~0 hydrogens and the importance of on-top hydrogens with weaker binding.

## Key findings

- Kinetically active hydrogens on platinum have weaker G values similar to gold.
- On-top hydrogens with low barriers explain platinum's high reaction rates.
- Conventional Sabatier analysis misses the kinetic factors critical for platinum's activity.

## Abstract

Platinum is a nearly perfect catalyst for the hydrogen evolution reaction, and its high activity has conventionally been explained by its close-to-thermoneutral hydrogen binding energy (G~0). However, many candidate non-precious metal catalysts bind hydrogen with similar strengths, but exhibit orders-of-magnitude lower activity for this reaction. In this study, we employ electronic structure methods that allow fully potential-dependent reaction barriers to be calculated, in order to develop a complete working picture of hydrogen evolution on platinum. Through the resulting ab initio microkinetic models, we assess the mechanistic origins of Pt's high activity. Surprisingly, we find that the G~0 hydrogen atoms are kinetically inert, and that the kinetically active hydrogen atoms have G's much weaker, similar to that of gold. These on-top hydrogens have particularly low barriers, which we compare to those of gold, explaining the high reaction rates, and the exponential variations in coverages can uniquely explain Pt's strong kinetic response to the applied potential. This explains the unique reactivity of Pt that is missed by conventional Sabatier analyses, and suggests true design criteria for non-precious alternatives.