Atomic-Scale Simulation of Electrochemical Processes at Electrode/Water Interfaces under Referenced Bias Potential

Based on constant Fermi-level molecular dynamics and a proper alignment scheme, we perform simulations of the Pt(111)/water interface under variable bias potential referenced to the standard hydrogen electrode (SHE). Our scheme yields a potential of zero charge μ_pzc of ∼0.22 eV relative to the SHE and a double layer capacitance <i>C</i>_dl of ≃19 μF cm^–2, in excellent agreement with experimental measurements. In addition, we study the structural reorganization of the electrical double layer for bias potentials ranging from −0.92 eV to +0.44 eV and find that O_down configurations, which are dominant at potentials above the pzc, reorient to favor H_down configurations as the measured potential becomes negative. Our modeling scheme allows one to not only access atomic-scale processes at metal/water interfaces, but also to quantitatively estimate macroscopic electrochemical quantities

First-Principles Study of Dissociation Processes for the Synthesis of Fe and Co Oxide Nanoparticles

Thermal decomposition is a practical and reliable tool to synthesize nanoparticles with monodisperse size distribution and reproducible accuracy. The nature of the precursor molecules and their interaction with the environment during the synthesis process have a direct impact on the resulting nanoparticles. Our study focuses on widely used transition-metal (Co, Fe) stearates precursors and their thermal decomposition reaction pathway. We show how the nature of the metal and the presence or absence of water molecules, directly related to the humidity conditions during the synthesis process, affect the decomposition mechanism and the resulting transition-metal oxide building blocks. This, in turn, has a direct effect on the physical and chemical properties of the produced nanoparticles and deeply influences their composition and morphology

Organic Cathode for Aqueous Zn-Ion Batteries: Taming a Unique Phase Evolution toward Stable Electrochemical Cycling

Aqueous zinc ion batteries are highly attractive for large-scale storage applications because of their inherent safety, low cost, and durability. Yet, their advancement is hindered by a dearth of positive host materials (cathode) due to sluggish diffusion of Zn²⁺ inside solid inorganic frameworks. Here, we report on a novel organic host, tetrachloro-1,4-benzoquinone (also called: p-chloranil), which due to its inherently soft crystal structure can provide reversible and efficient Zn²⁺ storage. It delivers a high capacity of ≥200 mAh g^–1 with a very small voltage polarization of 50 mV in a flat plateau around 1.1 V, which equate to an attractive specific energy of >200 Wh kg^–1 at an unparalleled energy efficiency (∼95%). As unraveled by density functional theory (DFT) calculations, the molecular columns in p-chloranil undergo a twisted rotation to accommodate Zn²⁺, thus restricting the volume change (−2.7%) during cycling. In-depth characterizations using operando X-ray diffraction, electron microscopy, and impedance analysis reveal a unique phase evolution, driven by a phase transfer mechanism occurring at the boundary of solid and liquid phase, which leads to unrestricted growth of discharged/charged phases. By confining the p-chloranil inside nanochannels of mesoporous carbon CMK-3, we can tame the phase evolution process, and thus stabilize the electrochemical cycling

Revisiting the Electrified Pt(111)/Water Interfaces through an Affordable Double-Reference Ab Initio Approach

The electrified solid–liquid interface plays an essential role in many renewable energy-related applications, including hydrogen production and utilization. Limitations in computational modeling of the electrified solid–liquid interface have held back the understanding of its properties at the atomic-scale level. In this study, we applied the grand canonical density functional theory (GC-DFT) combined with a hybrid implicit/explicit solvation model to reinvestigate the widely studied electrified platinum-water interface affordably. The calculated double-layer capacitances of the Pt(111)–water interface over the applied bias potential closely match the experimental and previous theoretical data from expensive ab initio molecular dynamics simulations. The structural analysis of the interface models reveals that the applied bias potential can significantly affect the Pt(111)–water atomic interface configurations. The orientation of the water molecules next to the Pt(111) surface is vital for correctly describing the potential of zero charge (PZC) and capacitance. Additionally, the GC-DFT results confirm that the absorption of the hydrogen atom under applied bias potential can significantly affect the electrified interfacial properties. The presented affordable GC-DFT approach, therefore, offers an efficient and accurate means to enhance the understanding of electrified solid–liquid interfaces

Evaluating the Critical Roles of Precursor Nature and Water Content When Tailoring Magnetic Nanoparticles for Specific Applications

Because of the broad range of application of iron oxide nanoparticles (NPs), the control of their size and shape on demand remains a great challenge, as these parameters are of upmost importance to provide NPs with magnetic properties tailored to the targeted application. One promising synthesis process to tune their size and shape is the thermal decomposition one, for which a lot of parameters were investigated. But two crucial issues were scarcely addressed: the precursor’s nature and water content. Two <i>in house</i> iron stearates with two or three stearate chains were synthesized, dehydrated, and then tested in standard synthesis conditions of spherical and cubic NPs. Investigations combined with modeling showed that the precursor’s nature and hydration rate strongly affect the thermal decomposition kinetics and yields, which, in turn, influence the NP size. The cubic shape depends on the decomposition kinetics but also crucially on the water content. A microscopic insight was provided by first-principles simulation showing an iron reduction along the reaction pathway and a participation of water molecules to the building unit formation