Elucidation of the Active Site for the Oxygen Evolution Reaction on a Single Pt Atom Supported on Indium Tin Oxide

A tutorial on the modeling of the heterogenous captured CO2 electroreduction reaction and first principles electrochemical modeling

As the energy demands of the world continue to grow, the electroreduction of captured CO2 (c-CO2RR) is an appealing alternative to the traditional CO2 reduction reaction (CO2RR) as it does not include the energetically unfavorable release of CO2 from the capture agent. In this tutorial we cover the motivation behind the c-CO2RR and CO2RR, their respective mechanisms, and computational tools that have been used to model these reactions and to compare their reactivities. Emphasis is given to methods that have already been used to model the c-CO2RR but a comparison to the methods used to explore the more understood CO2RR is covered as well.

Catalytic Activity of an Ensemble of Sites for CO2 Hydrogenation to Methanol on a ZrO2-on-Cu Inverse Catalyst

The significant increase in CO2 emissions from heavy fossil fuel utilization has raised serious concerns, highlighting the need for effective methods to convert CO2 into value-added chemicals. Here, we report a computational investigation on the catalytic activity of ZrO2-on-Cu inverse catalysts for CO2 hydrogenation to methanol, considering highly dispersed ZrO2 trimers on Cu (111). Such clusters present a large ensemble of formate-containing configurations, Zr3On(OH)m(OCHO)l, making the evaluation of the catalytic activity very challenging. We found that the sites on the various catalyst configurations exhibit markedly different activities for formate hydrogenation, despite their similar free energy and composition. To understand these differences in reactivity, we examined the structural and electronic nature of the low free-energy catalyst configurations and identified that the energy of the lowest unoccupied orbital of the reacting formate, modified by its binding with the catalytic site, is a descriptor for the reaction energy of the formate hydrogenation step. From there, we screened an ensemble of catalyst structures using this descriptor to predict highly active metastable catalyst configurations and computed the reaction pathways and transition states for formate hydrogenation. From this investigation, we distinguished reactive from nonreactive sites and formate species on the ZrO2/Cu inverse catalyst based on structural and electronic features. We showed that rare metastable configurations control the activity. Additionally, an efficient method for examining the reactivity of a large number of coexisting catalyst structures was developed.

Probing the Electric Double-Layer Capacitance to Understand the Reaction Environment in Conditions of Electrochemical Amination of Acetone

To elucidate interfacial dynamics during electrocatalytic reactions, it is crucial to understand the adsorption behavior of organic molecules on catalytic electrodes within the electric double layer (EDL). However, the EDL structure in aqueous environments remains intricate when it comes to the electrochemical amination of acetone, using methylamine as a nitrogen source. Specifically, the interactions of acetone and methylamine with the copper electrode in water remain unclear, posing challenges in the prediction and optimization of reaction outcomes. In this study, initial investigations employed impedance spectroscopy at the potential of zero charge to explore the surface preconfiguration. Here, the capacitance of the EDL was utilized as a primary descriptor to analyze the adsorption tendencies of both acetone and methylamine. Acetone shows an increase in the EDL capacitance, while methylamine shows a decrease. Experiments are interpreted using combined grand canonical density functional theory and ab initio molecular dynamics to delve into the microscopic configurations, focusing on their capacitance and polarizability. Methylamine and acetone have larger molecular polarizability than water. Acetone shows a partial hydrophobic character due to the methyl groups, forming a distinct adlayer at the interface and increasing the polarizability of the liquid interface component. In contrast, methylamine interacts more strongly with water due to its ability to both donate and accept hydrogen bonds, leading to a more significant disruption of the hydrogen bond network. This disruption of the hydrogen network decreases the local polarizability of the interface and decreases the effective capacitance. Our findings underscore the pivotal role of EDL capacitance and polarizability in determining the local reaction environment, shedding light on the fundamental processes important for electro-catalysis.

Modeling Interfacial Dynamics on Single Atom Electrocatalysts: Explicit Solvation and Potential Dependence

ConspectusSingle atom electrocatalysts, with noble metal-free composition, maximal atom efficiency, and exceptional reactivity toward various energy and environmental applications, have become a research hot spot in the recent decade. Their simplicity and the isolated nature of the atomic structure of their active site have also made them an ideal model catalyst system for studying reaction mechanisms and activity trends. However, the state of the single atom active sites during electrochemical reactions may not be as simple as is usually assumed. To the contrary, the single atom electrocatalysts have been reported to be under greater influence from interfacial dynamics, with solvent and electrolyte ions perpetually interacting with the electrified active center under an applied electrode potential. These complexities render the activity trends and reaction mechanisms derived from simplistic models dubious.In this Account, with a few popular single atom electrocatalysis systems, we show how the change in electrochemical potential induces nontrivial variation in the free energy profile of elemental electrochemical reaction steps, demonstrate how the active centers with different electronic structure features can induce different solvation structures at the interface even for the same reaction intermediate of the simplest electrochemical reaction, and discuss the implication of the complexities on the kinetics and thermodynamics of the reaction system to better address the activity and selectivity trends. We also venture into more intriguing interfacial phenomena, such as alternative reaction pathways and intermediates that are favored and stabilized by solvation and polarization effects, long-range interfacial dynamics across the region far beyond the contact layer, and the dynamic activation or deactivation of single atom sites under operation conditions. We show the necessity of including realistic aspects (explicit solvent, electrolyte, and electrode potential) into the model to correctly capture the physics and chemistry at the electrochemical interface and to understand the reaction mechanisms and reactivity trends. We also demonstrate how the popular simplistic design principles fail and how they can be revised by including the kinetics and interfacial factors in the model. All of these rich dynamics and chemistry would remain hidden or overlooked otherwise. We believe that the complexity at an electrochemical interface is not a curse but a blessing in that it enables deeper understanding and finer control of the potential-dependent free energy landscape of electrochemical reactions, which opens up new dimensions for further design and optimization of single atom electrocatalysts and beyond. Limitations of current methods and challenges faced by the theoretical and experimental communities are discussed, along with the possible solutions awaiting development in the future.

Nature of Zirconia on a Copper Inverse Catalyst Under CO2 Hydrogenation Conditions

The growing concern over the escalating levels of anthropogenic CO2 emissions necessitates effective strategies for its conversion to valuable chemicals and fuels. In this research, we embark on a comprehensive investigation of the nature of zirconia on a copper inverse catalyst under the conditions of CO2 hydrogenation to methanol. We employ density functional theory calculations in combination with the Grand Canonical Basin Hopping method, enabling an exploration of the free energy surface including a variable amount of adsorbates within the relevant reaction conditions. Our focus centers on a model three-atom Zr cluster on a Cu(111) surface decorated with various OH, O, and formate ligands, noted Zr3Ox (OH)y (HCOO)z/Cu(111), revealing major changes in the active site induced by various reaction parameters such as the gas pressure, temperature, conversion levels, and CO2/H2 feed ratios. Through our analysis, we have unveiled insights into the dynamic behavior of the catalyst. Specifically, under reaction conditions, we observe a large number of composition and structures with similar free energy for the catalyst, with respect to changing the type, number, and binding sites of adsorbates, suggesting that the active site should be regarded as a statistical ensemble of diverse structures that interconvert.

A First-Principles Study of Regulating Spin States of MoSi2N4 Supported Single-Atom Catalysts Via Doping Strategy for Enhancing Electrochemical Nitrogen Fixation Activity

Regulating the spin states of catalysts to enhance activity is fascinating but challenging. Herein, by using first-principles calculations, single transition-metal (TM) atoms Mo, Re, and Os embedded in nitrogen vacancy of the MoSi2N4 monolayer (TM1/VN-MoSi2N4) were screened out as potential catalysts for electrochemical nitrogen reduction reaction to ammonia. Our findings suggest that the spin states of these active centers can be precisely and gradually tuned through a simple doping strategy. Additionally, doping one O atom into the Mo1/VN-MoSi2N4 system as an example significantly improves catalytic activity. The spin state of Mo1 transitions from high to intermediate while simultaneously breaking the C3v symmetry of the supported atom. These factors synergistically lead to better orbital overlap between the catalyst and intermediates, facilitating subsequent protonation processes and overall catalytic activity. This work provides novel insight into designing, precisely controlling, and revisiting the spin-related catalytic performance in heterogeneous catalysis.

Sodium Tartrate-Assisted Synthesis of High-Purity NiFe2O4 Nano-Microrods Supported by Porous Ketjenblack Carbon for Efficient Alkaline Oxygen Evolution

Herein, a simple two-step synthetic method was developed for the synthesis of NiFe₂O₄ nano-microrods supported on Ketjenblack carbon (NiFe₂O₄/KB). A sodium tartrate-assisted hydrothermal method was employed for the synthesis of a NiFe-MOF/KB precursor, which was then pyrolyzed under N₂ at 500 °C to yield NiFe₂O₄/KB. Benefiting from the presence of high-valence Ni³⁺ and Fe³⁺, high conductivity, and a large electrochemically active surface area, NiFe₂O₄/KB delivered outstanding OER electrocatalytic performance under alkaline conditions, including a very low overpotential of 258 mV (vs RHE) at 10 mA cm^-2, a small Tafel slope of 43.01 mV dec^-1, and excellent durability in 1.0 M KOH. Density functional theory calculations verified the superior alkaline OER electrocatalytic activity of NiFe₂O₄ to IrO₂. While both catalysts possessed a similar metallic ground state, NiFe₂O₄ offered a lower energy barrier in the rate-determining OER step (*OOH → O₂) compared to IrO₂, resulting in faster OER kinetics.