Proton-rich material in a state of nuclear statistical equilibrium (NSE) is one of the least studied regimes of nucleosynthesis. One reason for this is that after hydrogen burning, stellar evolution proceeds at conditions of an equal number of neutrons and protons or at a slight degree of neutron-richness. Proton-rich nucleosynthesis in stars tends to occur only when hydrogen-rich material that accretes onto a white dwarf or a neutron star explodes, or when neutrino interactions in the winds from a nascent proto-neutron star or collapsar disk drive the matter proton-rich prior to or during the nucleosynthesis. In this Letter we solve the NSE equations for a range of proton-rich thermodynamic conditions. We show that cold proton-rich NSE is qualitatively different from neutron-rich NSE. Instead of being dominated by the Fe-peak nuclei with the largest binding energy per nucleon that have a proton-to-nucleon ratio close to the prescribed electron fraction, NSE for proton-rich material near freezeout temperature is mainly composed of and free protons. Previous results of nuclear reaction 56 Ni network calculations rely on this nonintuitive high-proton abundance, which this Letter explains. We show how the differences and especially the large fraction of free protons arises from the minimization of the free energy as a result of a delicate competition between the entropy and nuclear binding energy.

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Applied electrochemistry plays a key role in many technologies, such as Li-ion batteries, fuel cells, supercapacitors, solar cells, etc. It is therefore at the core of many research programs all over the world. However, fundamental electrochemical investigations remain scarce. In particular, electrochemistry is among the fields for which the gap between theory and experiment is the largest. From the computational point of view, there is no classical molecular dynamics (MD) software devoted to the simulation of electrochemical systems while other fields such as biochemistry or material science have dedicated tools. "MetalWalls" (MW), a MD code dedicated to electrochemistry, fills this gap. Its main originality is the inclusion of a series of methods which allow a constant electrical potential to be applied to the electrode materials. It also allows the simulation of bulk liquids or solids using the polarizable ion model and the aspherical ion model. MW is designed to be used on high-performance computers and it has already been employed in a number of scientific publications. It was for example used to study the charging mechanism of supercapacitors, nanoelectrowetting and water desalination devices.

A B S T R A C TUsing a combination of cyclic voltammetry experiments and molecular dynamics simulations, we study the effect of microporous carbon structure on the performance of aqueous supercapacitors using carbide derived carbon (CDC) electrodes. The structures investigated by molecular simulations are compatible with the experimental results for CDC synthesized at 800 C, but not with the other two materials (CDC-1100 and YP-50F), which are more graphitic. In fact, the specific capacitance obtained for the latter two are in good agreement with molecular simulations of graphite electrodes, assuming that all the charge is localized in the first plane in contact with the electrode (a very good approximation). Our molecular simulations further allow to examine the solvation of ions inside the electrodes. Unlike what was observed for large organic ions dissolved in acetonitrile, we find that most Na þ cations remain fully solvated. Overall, microporous carbons such as CDCs are good candidates for applications involving aqueous supercapacitors, in particular the harvesting of blue energy or desalination, but their performance remains to be optimized by tailoring their microstructure. * Corresponding author. Sorbonne Universit e, CNRS, Physico-chimie des electrolytes et nano-syst emes interfaciaux, PHENIX, F-75005,