Investigation of FeOOH for Mechanisms in Water-Splitting Reactions

Electrolysis is at the forefront of methods of producing hydrogen by separating water into oxygen and hydrogen gas. The oxygen evolution reaction (OER) is known for having slower kinetics due to multiple proton-electron coupled transfer steps being involved. Transition metal oxyhydroxides have been demonstrated to have low overpotentials while being composed of abundant and cheap elements and may be an important materials platform in scaled-up hydrogen production.1 This project explores the relationships between structure and OER mechanisms in iron oxyhydroxides (FeOOH). Earth-abundant metals like Fe pose active catalytic sites and can be modeled in a FeOOH structure under alkaline conditions. Studies show that amorphous electrocatalysts exhibit greater catalytic activity compared to crystalline electrocatalysis, a trend which has often been attributed to amorphous electrocatalysts having a greater concentration of electrochemically accessible active sites.2,3 We hypothesize that the lack of long-range order in amorphous electrocatalysts may also introduce novel structural moieties not present in the crystalline form and play a role in enhanced electrocatalytic activity. <br/> <br/>In order to begin testing this hypothesis, we study structure-property relationships between crystalline disorder and OER energetics using density functional theory (DFT) with a Hubbard U correction as implemented in Quantum ESPRESSO.4 We first discuss determining the Hubbard U correction value and constructing a representative adsorbate/surface structure using the crystalline structure. We manually manipulate the crystalline structure to imitate potential local structural distortions of the amorphous structure and compare computed overpotentials with the different structures and previously determined literature values. Finally, we present a rational model to understand the impact of structural distortion on electrocatalytic activity. <br/> <br/>References <br/>(1) D. Friebel et al. Journal of the American Chemical Society 2015, 137 (3), 1305-1313 <br/>(2) W. Cai et al. Nano Lett. 2020, 20 (6), 4278–4285. <br/>(3) S. Anantharaj & S. Noda. Small 2020, 16 (2), 1905779. <br/>(4) TimrovI. et al. Comput. Phys. Comm. 279 (2022), 108455