Nonaqueous polyelectrolyte solutions have been recently proposed as high Li + transference number electrolytes for lithium ion batteries. However, the atomistic phenomena governing ion diffusion and migration in polyelectrolytes are poorly understood, particularly in nonaqueous solvents. Here, the structural and transport properties of a model polyelectrolyte solution, poly(allyl glycidyl ether-lithium sulfonate) in dimethyl sulfoxide, are studied using all-atom molecular dynamics simulations. We find that the static structural analysis of Li + ion pairing is insufficient to fully explain the overall conductivity trend, necessitating a dynamic analysis of the diffusion mechanism, in which we observe a shift from largely vehicular transport to more structural diffusion as the Li + concentration increases. Furthermore, we demonstrate that despite the significantly higher diffusion coefficient of the lithium ion, the negatively charged polyion is responsible for the majority of the solution conductivity at all concentrations, corresponding to Li + transference numbers much lower than previously estimated experimentally. We quantify the ion–ion correlations unique to polyelectrolyte systems that are responsible for this surprising behavior. These results highlight the need to reconsider the approximations typically made for transport in polyelectrolyte solutions.

Silicon is a promising photocathode for tandem photoelectrochemical water splitting devices, but efficient catalysis and long term stability remain key challenges. Here, it is demonstrated that with appropriately engineered interfaces, molybdenum sulfide nanomaterials can provide both corrosion protection and catalytic activity in silicon photocathodes. Using a thin MoS2 surface protecting layer, MoS2‐n+p Si electrodes that show no loss in performance after 100 h of operation are created. Transmission electron microscopy measurements show the atomic structure of the device surface and reveal the characteristics of the MoS2 layer that provide both catalytic activity and excellent stability. In spite of a low concentration of exposed catalytically active sites, these electrodes possess the best performance of any precious metal‐free silicon photocathodes with demonstrated long term stability to date. To further improve efficiency, a second molybdenum sulfide nanomaterial, highly catalytically active [Mo3S13]2− clusters, is incorporated. These photocathodes offer a promising pathway towards sustainable hydrogen production.

We review the most promising design strategies for enhanced conducting polymer-based supercapacitors, summarizing the challenges and recent progress in optimizing each of the most important metrics of supercapacitor performance.

The theory of transport phenomena in multicomponent electrolyte solutions is presented here through the integration of continuum mechanics, electromagnetism, and nonequilibrium thermodynamics. The governing equations of irreversible thermodynamics, including balance laws, Maxwell's equations, internal entropy production, and linear laws relating the thermodynamic forces and fluxes, are derived. Green-Kubo relations for the transport coefficients connecting electrochemical potential gradients and diffusive fluxes are obtained in terms of the flux-flux time correlations. The relationship between the derived transport coefficients and those of the Stefan-Maxwell and infinitely dilute frameworks are presented, and the connection between the transport matrix and experimentally measurable quantities is described. To exemplify the application of the derived Green-Kubo relations in molecular simulations, the matrix of transport coefficients for lithium and chloride ions in dimethyl sulfoxide is computed using classical molecular dynamics and compared with experimental measurements. K E Y W O R D S electrochemistry, nonequilibrium thermodynamics, thermodynamics/statistical, transport where c i is the concentration of species i and K ij are the Stefan-Maxwell transport coefficients. These equations may be interpreted

Superconcentrated electrolytes for lithium-ion batteries have shown promise in circumventing certain limitations of conventional carbonate electrolytes at lower concentrations while introducing new challenges such as decreased conductivity. We use molecular dynamics simulations with diffusion and residence time analyses to elucidate the main modes of transport of LiPF6 and LiBF4 in propylene carbonate at concentrations ranging from 1 to 3 M. Notably, we find that the Li+ mode of diffusion with respect to its surrounding propylene carbonate solvation shell is a mix of vehicular and structural diffusion at all studied concentrations, exhibiting a small increase toward structural diffusion in the superconcentrated regimes. Furthermore, and important for future strategies toward improved conductivity, we find that the Li+ ions associated with PF6 – anions move in an increasingly vehicular manner as the salt concentration is increased, while the Li+ ions associated with BF4 – anions move in an increasingly structural manner.

Electrolytes featuring negatively-charged polymers such as nonaqueous polyelectrolyte solutions and polymerized ionic liquids are currently under investigation as potential high cation transference number (t +) electrolytes for lithium ion batteries. Herein, we use coarse-grained molecular dynamics simulations to characterize the Onsager transport coefficients of polyelectrolyte solutions as a function of chain length and concentration. For all systems studied, we find that the rigorously computed transference number is substantially lower than that approximated by the ideal solution (Nernst-Einstein) equations typically used to characterize these systems due to the presence of strong anion-anion and cation-anion correlations. None of the polyelectrolyte solutions achieve t + greater than that of the conventional binary salt electrolyte, with some solutions having negative t +. This work demonstrates that the Nernst-Einstein assumption does not provide a physically meaningful estimate of the

The development of next-generation polymer-based electrolytes for energy storage applications would greatly benefit from a deeper understanding of transport phenomena in these systems. In this Perspective, we argue that the Onsager transport equations provide an intuitive but underutilized framework for analyzing transport in polymer-based electrolytes. Unlike the ubiquitous Stefan–Maxwell equations, the Onsager framework generates transport coefficients with clear physical interpretation at the atomistic level and can be computed easily from molecular simulations using Green–Kubo relations. Herein we present an overview of the Onsager transport theory as it applies to polymer-based electrolytes and discuss its relation to experimentally measurable transport properties and the Stefan–Maxwell equations. Using case studies from recent computational work, we demonstrate how this framework can clarify nonintuitive phenomena such as negative cation transference number, anticorrelated cation–anion motion, and the dramatic failure of the Nernst–Einstein approximation. We discuss how insights from such analysis can inform design rules for improved systems.

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