Free Energy Pathway Exploration of Catalytic Formic Acid Decomposition on Pt-Group Metals in Aqueous Surroundings

Formic acid is an important platform molecule for hydrogen utilization, where Pt-group metals are the only catalyst candidates to achieve ambient condition formic acid (FA) decomposition (HCOOH → CO2 + H2). However, these catalysts suffer from severe long-term activity loss, the mechanism of which has been highly debated in the past two decades. By combining global structure search with umbrella sampling molecular dynamics based on global neural network potentials, here we quantitatively resolve the whole free energy profile for FA decomposition at the Pt–water and Pd–water interfaces. We show that while the two metals share the same FA decomposition mechanism, their catalytic deactivation rate do differ by more than 2 orders of magnitude─Pt is much more susceptible to CO poisoning due to the kinetics. The physical origin is attributed to the stronger affinity to surface atomic H and the lower adsorption to surface adsorbed bent CO2 (CO2 anion) on Pd, which leads to the slower rate of the secondary CO2 decomposition to the CO molecule, the poisoning species at ambient conditions. After comparing CO generation at the solid–gas and the solid–liquid interface, we propose simple strategies to achieve high activity without CO byproduct formation for FA decomposition.