(Invited) An Atomically Precise Oxygen Evolution Catalyst

The O2 evolution reaction (OER) is an important anodic process for many aqueous electrochemical applications, including H2 evolution from water and CO2 reduction. Precious metals like Iridium, Ruthenium and/or Platinum are traditionally-used electrochemical anodes because they can efficiently oxidize H2O into O2 with high catalytic activity and good long term stability. However, recent efforts have tried to replace expensive precious-metal anodes with inexpensive and earth-abundant materials. Ni-based materials are promising replacements for precious metal-based OER catalysts because they show high activity and good long-stability. Unfortunately, the literature contains some debate as to the nature of the catalytic reaction center in Ni-based materials. This uncertainty stems from typical catalyst samples containing heterogeneous particle sizes and surface structures, and the literature contains a wide range of reported reaction rates and rate determining steps. My talk describes a combination of experimental and computational techniques to characterize the OER chemistry at an atomically-precise organometallic nickel complex. Single-crystal X-ray diffraction identified the catalyst’s crystal structure as a hexagonal “tiara-like” Ni6(PET) structure (PET = phenylethyl thiol). Laboratory and synchrotron-based X-ray spectroscopies were used to characterize the electronic structure of the Ni6(PET)12 complex (PET = phenylethylthiol). Electrocatalytic testing showed that Ni6(PET)12 outperformed bulk NiO and Pt, and that it had comparable OER performance to that of Ir. Density functional theory (DFT) was used to model the OER at a realistic Ni6(SCH3)12 models to determined Gibbs free energy changes (ΔG) associated OER steps. Computationally predicted potential determining steps and OER onset potentials were in excellent agreement with experimentally-determined values. Interestingly, DFT results suggest subtle changes in adsorbate binding configuration can drastically alter the OER onset potentials. Our results highlight how atomically-precise nanocatalysts can facilitate the development of difficult-to-obtain structure-property relationships because they allow joint experimental and computational studies on nearly identical systems.