We use ab initio molecular dynamics simulations based on density-functional theory to revisit the enigmatic capacitance peak of the electrified Pt(111)/water interface around the potential of zero charge. We demonstrate that counterbalancing the electronic excess charges with partially charged hydrogen atoms constitutes a computationally efficient approach to converged interfacial water structures. The thus enabled detailed analysis of the interfacial water response clarifies that the peak in the capacitance is predominantly due to structural reorientation, although its magnitude is significantly increased by strong internal electronic polarization, also known as charge transfer (CT). We find that CT is more complex than previously thought, resulting from the interplay between chemisorbed water and depolarization effects from the surrounding water. Finally, we demonstrate that quantitative agreement with the experimental peak can be achieved through inclusion of the interfacial response into an implicit solvent model for the extended part of the double layer. This suggests that such models can accurately reproduce screened interfacial fields as a function of potential, despite their notoriously small native capacitance.
Unraveling the atomistic structures of electric double layers (EDL) at electrified interfaces is of paramount importance for understanding the mechanisms of electrocatalytic reactions and rationally designing electrode materials with better performance. Despite numerous efforts dedicated in the past, a molecular level understanding of the EDL is still lacking. Combining the state-of-the-art ab initio molecular dynamics (AIMD) and recently developed computational standard hydrogen electrode (cSHE) method, it is possible to realistically simulate the EDL under well-defined electrochemical conditions. In this work, we report extensive AIMD calculation of the electrified Pt(111)-Had/water interfaces at the saturation coverage of adsorbed hydrogen (Had) corresponding to the typical hydrogen evolution reaction conditions. We calculate the electrode potentials of a series of EDL models with various surface charge densities using the cSHE method and further obtain the Helmholtz capacitance that agrees with experiment. Furthermore, the AIMD simulations allow for detailed structural analyses of the electrified interfaces, such as the distribution of adsorbate Had and the structures of interface water and counterions, which can in turn explain the computed dielectric property of interface water. Our calculation provides valuable molecular insight into the electrified interfaces and a solid basis for understanding a variety of electrochemical processes occurring inside the EDL.
A series of hydrous salts constructed using AEDPH4 and piperazidine (pip) were synthesized and structurally characterized. A reversible structural transformation circle is observed in single crystals of compounds 1–3.
Electrocatalysis is a decisive factor determining the practicability of green energy technologies. Electric double layers (EDLs) provide suitable chemical environments for electrocatalysis, having direct impact on their activity. However, little is known about EDL structures and dielectric properties. Aiming to address these issues, here we perform ab initio molecular dynamics simulations of electrified Ag(111)/water interfaces, and our calculations are able to reproduce the subtle difference in experimental capacitance curves due to ion effects. It is interesting to find that, on weak binding, Ag(111) water chemisorption can be strengthened when positively charged, contributing to the hump in differential capacitance owing to electronic effects. Bulky ClO4−, compared with small F−, increases the EDL width and decreases the water content at interfaces. Furthermore, steric repulsion between ClO4− forces the formation of a second layer of the ions at very positive potentials. These detailed factors dictate the EDL capacitances that depend on the nature of counter ions.
Abstract A series of hexylamine modified polysuccinimide (PSI–HA) copolymers were synthesized by aminolysis of polysuccinimide (PSI) with hexylamine. FTIR and 1H NMR measurements confirmed the structure of the copolymers and the substitution degree of the N-hexyl aspartamide units ranged from 7 to 92 mol%. Stable nanoparticles formed when the DMF solution of PSI–HA copolymers was dropped into excess water, and the particle size reduced as increasing the substitution degree. 1H NMR analysis indicated that hexyl chain and succinimide units interacted to form the hydrophobic core, while, the nanoparticles were stabilized by the amide groups which formed hydrogen bonds with the surrounding water molecules. The nanoparticles became more compact at higher temperature due to the break of hydrogen bonds between amide groups and water molecules. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) results showed that the nanoparticles were nearly spherical. Larger nanoparticles formed when the dispersion concentration increased from 0.1% to 1.0% according to the DLS and steady-state fluorescence measurements. After the nanoparticles formed in water, a sequential dilution can't influence the particles size of the nanoparticles any longer. Keywords: Amphiphilic copolymersPolysuccinimideHexylamineNanoparticlesBiodegradable Acknowledgment This work was supported by the National Science Foundation of China (Grant No. 50173005) and the Association of Shanghai Science and Technology.
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