(Invited) First Principles Studies of Oxygen Cycle Electrocatalysis: Multifunctional Materials and Reactivity Trends
Authors: Zeng Zhenhua , Wang Lei , Dionigi Fabio , Wang Chao , Strasser Peter , Markovic Nenad M , Greeley Jeffrey 
Published: May 2020

Water splitting to generate O2 and H2 fuel has been a major focus of (photo)electrochemical energy storage and conversion efforts, but many challenges remain. 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 in alkaline is over two orders of magnitude slower than that 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. The lack of the atomic-scale details of crystal structure makes it challenging to choose appropriate structural models for first principles-based mechanistic studies. Therefore, it is of significant interest to identify these materials’ in-situ crystal structure and, subsequently, determine the intrinsic catalytic mechanism. Similarly, for alkaline HER, ultrathin (oxy)hydroxide films on precious metal substrates possess impressive activity improvement, 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 introduce the methodologies we have recently developed towards the highly accurate prediction of Pourbaix diagram of transition metal (oxy)hydroxides. Subsequently, using monolayer Ni (oxy)hydroxide films as an example, we will describe a simple scheme to study the structures and the stability of these films on precious metal surfaces. We will show how the ultrathin films can be dramatically stabilized with respect to the corresponding bulk analogs. Then, using the hydrogen evolution reaction as an example, we will demonstrate how these techniques can be applied to understand the steady state, the active phases, and the catalytic mechanism of bi-functional interfaces. We will then demonstrate the extension of the present understanding to real-world catalysts, i.e. precious metal nanoparticles supported on ultrathin transition metal (oxy)hydroxide films. Finally, we will show this understanding can be used to design new bi-functional catalysts with improved performances.

If time permits, we will also show our recent work on tunable intrinsic strain in two-dimensional transition metal electrocatalysts for the oxygen reduction reaction.

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