Law of Mass Action Type Chemical Mechanisms for Modeling Autocatalysis and Hypercycles: Their Role in the Evolutionary Race

Counterion Lewis Acidity Determines the Rate of Hexafluorophosphate Hydrolysis in Nonaqueous Battery Electrolytes

The decomposition of LiPF6 in nonaqueous battery electrolytes is a well-studied, deleterious process that leads to hydrofluoric acid (HF) driven transition metal dissolution at the positive electrode and gas production (H2) at the anode, often attributed to the inherent moisture sensitivity of the hexafluorophosphate anion. In this work, we use in situ nuclear magnetic resonance (NMR) spectroscopy to demonstrate that the rate of PF6- hydrolysis significantly decreases in Na and K systems, where the Lewis acidity of the cation dictates the rate of decomposition according to Li+ > Na+ > K+. Despite the remarkable stability of Na and K electrolytes, we show that they are still susceptible to hydrolysis in the presence of protons, which can catalyze the breakdown of PF6-, indicating that these chemistries are not immune from decomposition when paired with solvent/cathode combinations that generate H+ at high voltage. Quantitative in situ multinuclear and multidimensional NMR of decomposed electrolytes shows that after long-term degradation, these systems contain HF, HPO2F2, and H2PO3F as well as a variety of defluorinated byproducts, such as organophosphates and phosphonates, that are structurally similar to herbicides/insecticides and may pose health and environmental risks. Taken together, these results have important implications for Na- and K-ion batteries where hazardous and harmful byproducts like HF, soluble transition metals, organophosphates, and phosphonates can be greatly reduced through cell design. Our results also suggest that next-generation chemistries present a pathway to safer batteries that contain lower quantities of flammable gases, like H2, if properly engineered.

Dynamics of hydroxide-ion-driven reversible autocatalytic networks

In living systems adaptive regulation requires the presence of nonlinear responses in the underlying chemical networks. Positive feedbacks, for example, can lead to autocatalytic bursts that provide switches between two stable states or to oscillatory dynamics. The stereostructure stabilized by hydrogen bonds provides an enzyme its selectivity, rendering pH regulation essential for its functioning. For effective control, triggers by small concentration changes play roles where the strength of feedback is important. Here we show that the interaction of acid-base equilibria with simple reactions with pH-dependent rate can lead to the emergence of a positive feedback in hydroxide ion concentration during the hydrolysis of some Schiff bases in the physiological pH range. The underlying reaction network can also support bistability in an open system.

Thermodynamic Analysis of the Landolt-Type Autocatalytic System

A recent work demonstrated the example of the Landolt-type reaction system and how the simplest autocatalytic loop is described by the kinetic mass action law and proper parametrization of direct and autocatalytic pathways. Using a methodology of non-equilibrium thermodynamics, the thermodynamic consistency of that kinetic model is analyzed and the mass action description is generalized, including an alternative description by the empirical rate equation. Relationships between independent and dependent reactions and their rates are given. The mathematical modeling shows that following the time evolution of reaction rates provides additional insight into autocatalytic behavior. A brief note on thermodynamic driving forces and coupling with diffusion is added. In summary, this work extends and generalizes the kinetic description of the Landolt-type system, placing it within the framework of non-equilibrium thermodynamics and demonstrating its thermodynamic consistency.