Emerging Atomistic Modeling Methods for Heterogeneous Electrocatalysis.

Heterogeneous electrocatalysis lies at the center of various technologies that could help enable a sustainable future. However, its complexity makes it challenging to accurately and efficiently model at an atomic level. Here, we review emerging atomistic methods to simulate the electrocatalytic interface with special attention devoted to the components/effects that have been challenging to model, such as solvation, electrolyte ions, electrode potential, reaction kinetics, and pH. Additionally, we review relevant computational spectroscopy methods. Then, we showcase several examples of applying these methods to understand and design catalysts relevant to green hydrogen. We also offer experimental views on how to bridge the gap between theory and experiments. Finally, we provide some perspectives on opportunities to advance the field.

Activation Energies of Heterogeneous Electrocatalysis: A Theoretical Perspective.

Heterogeneous electrochemistry is important for various applications. However, currently, there is limited information about activation energies. In this invited review, we review the challenges associated with calculating these activation energies. Specifically, we highlight three key difficulties in atomistic modeling: liquid structure, electrode potential, and electrolyte ions, along with state-of-the-art methods to address them. We aim to inspire more studies in the field of activation energies to better understand and design heterogeneous electrocatalysts.

Facet-Defined Dilute Metal Alloy Nanorods for Efficient Electroreduction of CO2 to n-Propanol.

Electroreduction of CO2 into liquid fuels is a compelling strategy for storing intermittent renewable energy. Here, we introduce a family of facet-defined dilute copper alloy nanocrystals as catalysts to improve the electrosynthesis of n-propanol from CO2 and H2O. We show that substituting a dilute amount of weak-CO-binding metals into the Cu(100) surface improves CO2-to-n-propanol activity and selectivity by modifying the electronic structure of catalysts to facilitate C1-C2 coupling while preserving the (100)-like 4-fold Cu ensembles which favor C1-C1 coupling. With the Au0.02Cu0.98 champion catalyst, we achieve an n-propanol Faradaic efficiency of 18.2 ± 0.3% at a low potential of -0.41 V versus the reversible hydrogen electrode and a peak production rate of 16.6 mA·cm-2. This study demonstrates that shape-controlled dilute-metal-alloy nanocrystals represent a new frontier in electrocatalyst design, and precise control of the host and minority metal distributions is crucial for elucidating structure-composition-property relationships and attaining superior catalytic performance.

What Is the Rate-Limiting Step of Oxygen Reduction Reaction on Fe-N-C Catalysts?

Oxygen reduction reaction (ORR) is essential to various renewable energy technologies. An important catalyst for ORR is single iron atoms embedded in nitrogen-doped graphene (Fe-N-C). However, the rate-limiting step of the ORR on Fe-N-C is unknown, significantly impeding understanding and improvement. Here, we report the activation energies of all of the steps, calculated by ab initio molecular dynamics simulations under constant electrode potential. In contrast to the common belief that a hydrogenation step limits the reaction rate, we find that the rate-limiting step is oxygen molecule replacing adsorbed water on Fe. This occurs through concerted motion of H2O desorption and O2 adsorption, without leaving the site bare. Interestingly, despite being an apparent "thermal" process that is often considered to be potential-independent, the barrier reduces with the electrode potential. This can be explained by stronger Fe-O2 binding and weaker Fe-H2O binding at a lower potential, due to O2 gaining electrons and H2O donating electrons to the catalyst. Our study offers new insights into the ORR on Fe-N-C and highlights the importance of kinetic studies in heterogeneous electrochemistry.

Atomistic Understanding of Two-dimensional Electrocatalysts from First Principles.

Two-dimensional electrocatalysts have attracted great interest in recent years for renewable energy applications. However, the atomistic mechanisms are still under debate. Here we review the first-principles studies of the atomistic mechanisms of common 2D electrocatalysts. We first introduce the first-principles models for studying heterogeneous electrocatalysis then discuss the common 2D electrocatalysts with a focus on N doped graphene, single metal atoms in graphene, and transition metal dichalcogenides. The reactions include hydrogen evolution, oxygen evolution, oxygen reduction, and carbon dioxide reduction. Finally, we discuss the challenges and the future directions to improve the fundamental understanding of the 2D electrocatalyst at atomic level.