Hanna Lyle, Suryansh Singh, Michael Paolino, Ilya Vinogradov, and Tanja Cuk*
Physical Chemistry Chemical Physics, 2021, 33, 24984 Invited Perspective, DOI: 10.1039/D1CP01760H (Featured Inside Front Cover)
The conversion of diffusive forms of energy (electrical and light) into short, compact chemical bonds by catalytic reactions regularly involves moving a carrier (electron or hole) from an environment that favors delocalization to one that favors localization. While delocalization lowers the energy of the carrier through its kinetic energy, localization creates a polarization around the carrier that traps it in a potential energy minimum. The trapped carrier and its local distortion—termed a polaron in solids—can play a role as a highly reactive intermediate within energy-storing catalytic reactions but is rarely discussed as such. Here, we present this perspective of the polaron as a catalytic intermediate through recent in-situ and time-resolved spectroscopic investigations of photo-triggered electrochemical reactions at material surfaces. The focus is on hole-trapping at metal-oxygen bonds, denoted M-OH*, in the context of the oxygen evolution reaction (OER) from water. The potential energy surface for the hole-polaron defines the structural distortions from the periodic lattice and the resulting “active” site of catalysis. This perspective will highlight how current and future time-resolved, multi-modal probes can use spectroscopic signatures of M-OH* polarons to obtain kinetic and structural information on the individual reaction steps of OER. A particular motivation is to provide the background needed for eventually relating this information to relevant catalytic descriptors by free energies. Finally, the formation of the O-O chemical bond from the consumption of M-OH*, required to release O2 and store energy in H2, will be discussed as the next target for experimental investigations.
