Design Strategies for Oxygen Evolution Reaction Catalysts: Insights from a Kinetic Perspective via Constrained Ab Initio Molecular Dynamics
Authors: Shin Dongyup , Han Sang Soo 
Published: December 2024

Abstract

In the pursuit of sustainable energy, the efficient production of green hydrogen through electrochemical water splitting has emerged as a promising strategy.1 Central to this process is the optimization of the Oxygen Evolution Reaction (OER), where the necessity for a high overpotential at the anodic electrode poses a significant barrier. Among the myriad of catalysts studied, iridium oxides (IrOx) have garnered attention for their superior catalytic activity and stability in acidic environments.2 Yet, the quest for unlocking the full potential of IrOx catalysts necessitates a deeper dive into their operational mechanisms under OER conditions, a challenge that traditional Density Functional Theory (DFT) methodologies have struggled to meet due to their limited representation of the dynamic electrochemical environment intrinsic to OER catalysis.3

Addressing these challenges, our research introduces a novel approach by integrating constant Fermi-level ab initio molecular dynamics (AIMD) simulations with slow-growth kinetic analysis. This methodological innovation captures the complex electrochemical environment of OER catalysis, unveiling reaction pathways and energy barriers with close to actual electrochemical reaction. Through this approach, we explore the impact of the oxygen 2p orbital, Ir–O bond strength, and proton affinity on the Lattice Oxygen Mechanism (LOM) and Adsorbate Evolution Mechanism (AEM), establishing new paradigms for catalyst evaluation and design.
A focal point of our study is the detailed analysis of the elemental phases of LOM and AEM, which provides a granular understanding of the catalytic actions within these mechanisms. In the case of LOM, our focus is on the dynamics and electronic state of lattice oxygen, which play pivotal roles in defining the energy barriers distinct to each elemental phase. This analysis identifies the electronic structure of lattice oxygen and the robustness of Ir–O bonds as key determinants of LOM activity. Similarly, the phase of AEM process is characterized by the sequential proton transfer of water molecules and surface proton, highlighting the importance of the structural arrangement of surface hydrogen and the proton affinity of lattice oxygen in determining AEM activation stages.
Subsequent to the mechanism phase analysis, we present the validation of our theoretical insights through the suggestion and evaluation of E–IrTaO2, a lattice-elongated Ir-Ta bimetallic oxide catalyst designed to enhance LOM selectivity. The design of E–IrTaO2 is informed by kinetic analysis, with its activity evaluation underpinned by kinetic results that consider the thermodynamic energy diagram, including pathways through metastable states. This departure from conventional DFT methodologies signals a paradigm shift towards a kinetic-driven approach, crucial for unraveling the intricate behaviors of IrOx in OER processes and laying the groundwork for the development of sophisticated catalysts.
This study not only provides an in-depth understanding of the catalytic mechanisms in OER processes but also introduces a programmable strategy for catalyst design, paving the way for the rational development of high-performance OER catalysts.

References

Taibi, E., Miranda, R., Carmo, M. & Blanco, H. Green hydrogen cost reduction. (2020).

King, L. A. et al. A non-precious metal hydrogen catalyst in a commercial polymer electrolyte membrane electrolyser. Nature nanotechnology
14, 1071-1074 (2019).

Mefford, J. T. et al. Water electrolysis on La1− x Sr x CoO3− δ perovskite electrocatalysts. Nature communications
7, 11053 (2016)

Figure 1