Nanoparticle Electrodes Trigger Bubble Detachment and Enhance Gas Evolution Efficiency.

Nanobubble formation and binding to nanoelectrodes significantly hinder the efficiency of gas evolution reactions, limiting the potential of hydrogen production technologies. This work uncovers the pivotal role of the nanoelectrode shape in influencing catalytic performance and nanobubble detachment. Using molecular dynamics simulations supported by experimental evidence, we establish that nanoparticle electrodes with convex geometries (e.

Interplay between classical and quantum dissipation in light-matter dynamics.

A quantum-electrodynamics approach is presented to describe the dynamics of electrons that exchange energy with both photon and phonon baths. Our ansatz is a dissipative quantum Liouville equation, cast in the Redfield form, with two driving terms associated with radiative and vibrational relaxation mechanisms, respectively. Remarkably, within the radiative contribution, there is a term that exactly replicates the expression derived from a semiclassical treatment where the power dissipated by the electronic density is treated as the emission from a classical dipole [Bustamante et al.

The smallest electrochemical bubbles.

Many of the relevant electrochemical processes in the context of catalysis or energy conversion and storage, entail the production of gases. This often implicates the nucleation of bubbles at the interface, with the concomitant blockage of the electroactive area leading to overpotentials and Ohmic drop. Nanoelectrodes have been envisioned as assets to revert this effect, by inhibiting bubble formation.

Modeling the electroluminescence of atomic wires from quantum dynamics simulations.

Static and time-dependent quantum-mechanical approaches have been employed in the literature to characterize the physics of light-emitting molecules and nanostructures. However, the electromagnetic emission induced by an input current has remained beyond the realm of molecular simulations. This is the challenge addressed here with the help of an equation of motion for the density matrix coupled to a photon bath based on a Redfield formulation.

Nanobubble Stability and Formation on Solid-Liquid Interfaces in Open Environments.

Are surface nanobubbles transient or thermodynamically stable structures? This question remained controversial until recently, when the stability of gas nanobubbles at solid-liquid interfaces was demonstrated from thermodynamic arguments in closed systems, establishing that bubbles with radii of hundreds of nanometers can be stable at modest supersaturations if the gas amount is finite. Here we develop a grand-canonical description of bubble formation that predicts that nanobubbles can nucleate and remain thermodynamically stable in open boundaries at high supersaturations when pinned to hydrophobic supports as small as a few nanometers. While larger bubbles can also be stable at lower supersaturations, the corresponding barriers are orders of magnitude above , meaning that their formation cannot proceed via heterogeneous nucleation on a uniform solid interface but must follow some alternative path.

Fluorescence in quantum dynamics: Accurate spectra require post-mean-field approaches.

Real time modeling of fluorescence with vibronic resolution entails the representation of the light-matter interaction coupled to a quantum-mechanical description of the phonons and is therefore a challenging problem. In this work, taking advantage of the difference in timescales characterizing internal conversion and radiative relaxation-which allows us to decouple these two phenomena by sequentially modeling one after the other-we simulate the electron dynamics of fluorescence through a master equation derived from the Redfield formalism. Moreover, we explore the use of a recent semiclassical dissipative equation of motion [C.

Tailoring Cooperative Emission in Molecules: Superradiance and Subradiance from First-Principles Simulations.

Cooperative optical effects provide a pathway to both the amplification (superradiance) and the suppression (subradiance) of photon emission from electronically excited states. These captivating phenomena offer a rich variety of possibilities for photonic technologies aimed at electromagnetic energy manipulation, including lasers and high-speed emitting devices in the case of superradiance or optical energy storage in that of subradiance. The employment of molecules as the building pieces in these developments requires a precise understanding of the roles of separation, orientation, spatial distribution, and applied fields, which remains challenging for theory and experiments.

Dissipative Equation of Motion for Electromagnetic Radiation in Quantum Dynamics.

The dynamical description of the radiative decay of an electronically excited state in realistic many-particle systems is an unresolved challenge. In the present investigation electromagnetic radiation of the charge density is approximated as the power dissipated by a classical dipole, to cast the emission in closed form as a unitary single-electron theory. This results in a formalism of unprecedented efficiency, critical for ab initio modeling, which exhibits at the same time remarkable properties: it quantitatively predicts decay rates, natural broadening, and absorption intensities.

Electrochemically Generated Nanobubbles: Invariance of the Current with Respect to Electrode Size and Potential.

Gas-producing electrochemical reactions are key to energy conversion and generation technologies. Bubble formation dramatically decreases gas-production rates on nanoelectrodes, by confining the reaction to the electrode boundary. This results in the collapse of the current to a stationary value independent of the potential.

Mechanisms of Nucleation and Stationary States of Electrochemically Generated Nanobubbles.

Gas evolving reactions are ubiquitous in the operation of electrochemical devices. Recent studies of individual gas bubbles on nanoelectrodes have resulted in unprecedented control and insights on their formation. The experiments, however, lack the spatial resolution to elucidate the molecular pathway of nucleation of nanobubbles and their stationary size and shape.