Constrained Hybrid Monte Carlo Sampling Made Simple for Chemical Reaction Simulations.

Most electrochemical reactions should be studied under a grand canonical ensemble condition with a constant potential and/or a constant pH value. Free energy profiles provide key insights into understanding the reaction mechanisms. However, many molecular dynamics (MD)-based theoretical studies for electrochemical reactions did not employ an exact grand canonical ensemble sampling scheme for the free energy calculations, partially due to the issues of discontinuous trajectories induced by the particle-number variations during MD simulations.

Unraveling the Dynamic Correlations between Transition Metal Migration and the Oxygen Dimer Formation in the Highly Delithiated LiCoO Cathode.

The voltage-window expansion can increase the practical capacity of LiCoO cathodes, but it would lead to serious structural degradations and oxygen release induced by transition metal (TM) migration. Therefore, it is crucial to understand the dynamic correlations between the TM migration and the oxygen dimer formation. Here, machine-learning-potential-assisted molecular dynamics simulations combined with enhanced sampling techniques are performed to resolve the above question using a representative CoO model.

Impact of the Local Environment on Li Ion Transport in Inorganic Components of Solid Electrolyte Interphases.

The spontaneously formed passivation layer, the solid electrolyte interphase (SEI) between the electrode and electrolyte, is crucial to the performance and durability of Li ion batteries. However, the Li ion transport mechanism in the major inorganic components of the SEI (LiCO and LiF) is still unclear. Particularly, whether introducing an amorphous environment is beneficial for improving the Li ion diffusivity is under debate.

A caveat of the charge-extrapolation scheme for modeling electrochemical reactions on semiconductor surfaces: an issue induced by a discontinuous Fermi level change.

(Photo)electrochemical surface reactions in realistic experimental systems occur under a constant-potential condition, while the simulations of electrochemical reactions are mostly performed under a constant-charge condition. A charge-extrapolation scheme proposed by earlier theoretical studies converts constant-charge reaction energies to constant-potential reaction energies for electrochemical reactions on metal surfaces, which is based on a capacitor-model assumption to approximate the surface electrical double layer. However, the charge-extrapolation approach may be problematic when applied to models of photoelectrochemical reactions on semiconductor surfaces with a cross-bandgap Fermi level change along the reaction path.

Oxidation State of GaP Photoelectrode Surfaces under Electrochemical Conditions for Photocatalytic CO Reduction.

Illuminated GaP electrodes selectively reduce CO to CHOH in aqueous solution. To understand the photoelectrocatalytic mechanism, knowledge of the GaP surface atomic structure in contact with water under relevant electrochemical conditions is essential. However, there remains a debate about the oxidation state of GaP, i.

Optimal functionalization of a molecular electrocatalyst for hydride transfer.

Optimization of hydride transfer (HT) catalysts to enhance rates and selectivities of (photo)electroreduction reactions could be a crucial component of a sustainable chemical industry. Here, we analyze how ring functionalization of the adsorbed transient intermediate 2-pyridinide (2-PyH*)-predicted to form in situ from pyridine (Py) in acidified water at a cathode surface and to be the key to selective CO photoelectroreduction on p-GaP-may enhance catalytic activity. Earlier studies revealed that 2-PyH*'s instability results from a protonation side reaction producing adsorbed dihydropyridine (DHP*), which is relatively HT-inactive.

Balancing Competing Reactions in Hydride Transfer Catalysis via Catalyst Surface Doping: The Ionization Energy Descriptor.

Hydride transfer (HT) is ubiquitous in catalytic reduction reactions. In heterogeneous electrocatalysis, the hydride donor could be a molecular catalytic intermediate adsorbed on an electrode surface. The stability and hydride-donating capability of such an intermediate may determine overall catalytic efficiency.

Theoretical Insights into Heterogeneous (Photo)electrochemical CO Reduction.

Electrochemical and photoelectrochemical CO reduction technologies offer the promise of zero-carbon-emission renewable fuels needed for heavy-duty transportation. However, the inert nature of the CO molecule poses a fundamental challenge that must be overcome before efficient (photo)electrochemical CO reduction at scale will be achieved. Optimal catalysts exhibit enduring stability, fast kinetics, high selectivity, and low manufacturing cost.

Why and How Carbon Dioxide Conversion to Methanol Happens on Functionalized Semiconductor Photoelectrodes.

Functionalization of semiconductor electrode surfaces with adsorbed 2-pyridinide (2-PyH*) has been postulated to enable selective CO photoelectroreduction to CHOH. This hypothesis is supported by recent estimates of sufficient 2-PyH* lifetimes and low barriers for hydride transfer (HT) to CO. However, the complete mechanism for reducing CO to CHOH remained unidentified.

2-Pyridinide as an Active Catalytic Intermediate for CO Reduction on p-GaP Photoelectrodes: Lifetime and Selectivity.

The active intermediate responsible for pyridine (Py)-catalyzed reduction of CO on a p-GaP photoelectrode is currently under debate. Exploration of the proposed intermediates' available pathways for further reaction may yield a deeper understanding of the CO reduction mechanism that will be essential to designing better cocatalysts in such photoelectrochemical systems. Adsorbed 2-pyridinide (2-PyH*) was recently proposed by Carter and co-workers to be an intermediate that facilitates hydride transfer (HT) to CO to produce formate.

Stability of ferrous-iron-rich bridgmanite under reducing midmantle conditions.

Our current understanding of the electronic state of iron in lower-mantle minerals leads to a considerable disagreement in bulk sound speed with seismic measurements if the lower mantle has the same composition as the upper mantle (pyrolite). In the modeling studies, the content and oxidation state of Fe in the minerals have been assumed to be constant throughout the lower mantle. Here, we report high-pressure experimental results in which Fe becomes dominantly Fe in bridgmanite synthesized at 40-70 GPa and 2,000 K, while it is in mixed oxidation state (Fe/∑Fe = 60%) in the samples synthesized below and above the pressure range.

Atomic Layer Deposited MgO: A Lower Overpotential Coating for Li[NiMnCo]O Cathode.

An ultrathin MgO coating was synthesized via atomic layer deposition (ALD) to improve the surface properties of the Li[NiMnCo]O (NMC) cathode. An in-situ quartz crystal sensor was used to monitor the "self-limiting" surface reactions during ALD process and estimate the density of the deposited film. The electrochemical performance of the MgO-coated NMC cathode was evaluated in a half-cell assembly and compared to other ALD-based coatings, such as AlO and ZrO.

Atomic Layer Deposition of Al2O3-Ga2O3 Alloy Coatings for Li[Ni0.5Mn0.3Co0.2]O2 Cathode to Improve Rate Performance in Li-Ion Battery.

Metal oxide coatings can improve the electrochemical stability of cathodes and hence, their cycle-life in rechargeable batteries. However, such coatings often impose an additional electrical and ionic transport resistance to cathode surfaces leading to poor charge-discharge capacity at high C-rates. Here, a mixed oxide (Al2O3)1-x(Ga2O3)x alloy coating, prepared via atomic layer deposition (ALD), on Li[Ni0.

Correction: Ab initio and empirical defect modeling of LaMnO3±δ for solid oxide fuel cell cathodes.

Correction for 'Ab initio and empirical defect modeling of LaMnO3±δ for solid oxide fuel cell cathodes' by Yueh-Lin Lee et al., Phys. Chem.