First Principles Analysis of Oxygen Cycle Electrocatalysis: Multifunctional Materials and Reactivity Trends

Abstract

Water splitting to generate O2 and H2 fuel is an ongoing focus of (photo)electrochemical energy storage and conversion efforts. While water oxidation to generate O2 through the oxygen evolution reaction (OER) accounts for the majority of energy loss in this process, water reduction to generate H2 through the hydrogen evolution reaction (HER) in alkaline is also sluggish, with over two orders of magnitude less activity than in acid. For OER, NiFe layered double hydroxides have attracted significant interest due to their comparable performance with precious metal-based RuO2 and IrO2 catalysts. In spite of extensive study, however, the 3D crystal structure of the active phase under catalytic oxygen evolution reaction conditions remains unclear, and the lack of atomic-scale details concerning the crystal structure makes it challenging to choose appropriate structural models for first principles-based mechanistic studies. Similarly, for alkaline HER, ultrathin (oxy)hydroxide films on precious metal substrates have shown impressive activity improvements compared to pure Pt, but the films’ structure and stability are still largely unknown, and the catalytic mechanism remains unclear.In this presentation, we will begin by showing our recent efforts to elucidate the catalytically active phase and OER mechanism on NiFe layered double hydroxides by combining electrochemical measurements, operando experiments, DFT calculations, and ab initio molecular dynamics simulations. Next, for HER, we will turn to monolayer Ni (oxy)hydroxide films, wherein we will demonstrate that these ultrathin films can be dramatically stabilized with respect to the corresponding bulk analogs and that the bifunctional interface provides ideal sites for water activation. Finally, if time permits, we outline our recent work on oxygen reduction reaction electrochemistry, discussing both tunable intrinsic strain in two-dimensional transition metal electrocatalysts for the ORR, as well as recent developments in the study of stability of PGM-free electrocatalysts.