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This study presents a comprehensive analysis of the intermolecular interactions and diffusion behavior in deep eutectic solvent (DES)-supported poly(acrylate) (PAA) systems, with a focus on enhancing hydronium (H 3 O + ) ion mobility for proton-exchange membranes (PEMs) in fuel cells. Using classical all-atom molecular dynamics (MD) simulations, we investigated the interactions within pure DES-supported PAA and hydrated DES-supported PAA matrices at hydration levels (HLs) 3 and 9. Radial distribution functions (RDFs) revealed significant interactions between the oxygen atoms of PAA and hydrogen atoms of DES components, with distinct variations at different HLs. Interaction energy calculations highlighted the evolving strengths of PAA-DES interactions, especially with choline, chloride, and urea, under varying hydration conditions. Diffusion coefficients indicated substantial enhancements in the mobility of H 3 O + ions and water molecules with increasing hydration, essential for effective proton transport. These findings underscore the critical role of water in facilitating dynamic restructuring and efficient proton conduction within the DES-supported PAA matrix, offering valuable insights for the development of advanced PEMs with tailored properties for fuel cell applications.

A novel composite material based on poly(acrylate) (PAA) and graphene oxide (GO) has been developed to serve as a proton exchange membrane (PEM). This new material shows great promise in enhancing the mobility of hydronium (H 3 O) ions, particularly under challenging operating conditions. To explore its potential, comprehensive studies were carried out using classical all-atom molecular dynamics (MD) simulations with the Gromacs software to understand the formation mechanism and investigate its application for H 3 O ion transportation in PEM. During the MD simulations, it was observed that an increase in hydration from 3 to 9 in the PAA oligomer and GO-based PEM resulted in the formation of larger water clusters. These clusters facilitated more efficient transportation of H 3 O ions. The study also revealed the development of new interactions between PAA oligomers and GO layers at specific hydration levels (HLs) (3/9) and temperatures (298 K/350 K), as evidenced by the analysis of interaction energies. Furthermore, the mobility of H 3 O ions in the PAA and GO composite–based PEM exhibited behavior comparable to that of the traditional PAA-based PEM at various HLs and temperatures. Additionally, the transportation of H 3 O ions showed a slight increase with higher HL and temperature, as indicated by the diffusion coefficient values for the GO and PAA composite–based PEM. In summary, the newly developed PAA and GO composite material holds promise for improving the mobility of H 3 O ions, making it an excellent candidate for PEM applications. The insights gained from the MD simulations shed light on the material’s formation mechanism and behavior under different conditions, providing a solid foundation for further research and potential real-world applications in the field of membrane technologies.

The limited efficiency of proton exchange membranes under low-humidity conditions remains a major challenge for next-generation fuel cells. Recent studies have explored deep eutectic solvents (DESs) as alternative proton-conducting media to overcome hydration-dependent limitations. In this work, we investigate the effect of solvent hydrophobicity on molecular structure and hydronium ion transport in polyacrylate-based membranes, using three distinct DESs: a hydrophilic system of choline chloride and ethylene glycol (1:2), an amphiphilic system of choline chloride and decanoic acid (1:1), and a hydrophobic system of menthol and lauric acid (1:1), employing density functional theory (DFT) calculations and classical all-atom molecular dynamics (MD) simulations. DFT calculations were used to optimize molecular structures and evaluate electrostatic potential distributions, frontier orbital energies, and hydrogen-bonding capabilities, revealing that the hydrophilic system exhibits the strongest interactions with hydronium ions via stabilized charge delocalization and orbital overlap. MD simulations further elucidated the structural organization of solvent–polymer systems under hydrated conditions, with analyses confirming preferential coordination of hydronium ions with specific functional groups depending on solvent polarity. Interaction energy and diffusion coefficient calculations demonstrated that both water and hydronium mobility are highest in the hydrophilic system, while transport is progressively restricted in amphiphilic and hydrophobic systems. These findings provide fundamental insights into how solvent polarity modulates proton transport, guiding the design of high-performance fuel cell membranes.

We used density functional theory (DFT) and Car-Parrinello molecular dynamics (CPMD) simulation to investigate the adsorption and bond formation of hydronium ion (H 3 O + ) onto a ( 10 1 ¯ 4 ) calcite surface. For surface coverage of 25% to 100%, the nature of H 3 O + interaction was explored through electron density and energetics in the context of bond critical points. The adsorbate–adsorbent structure was studied by simulation of pair correlation function. The results revealed that dissociation into water molecule(s) and proton(s) complements H 3 O + ion(s) adsorbtion. The H 2 O molecule adsorbs onto the surface via its O atom, and interacts with surface calcium in a closed-shell mode; the H + ion makes a covalent bond to the surface oxygen while maintaining H-bonding with water. Adsorption energies were diminished by 70–90 kJ mol −1 when O bridge -bonded H + ions transferred to the O terminal manually. While dissociative adsorption of H 3 O + ions is spontaneous at all surface coverages tested, the free energy was lowest at 75% coverage. Also, protonation of a completely pre-hydrated calcite surface leads to stronger interaction of water molecules with the surface. This unique outlook on hydrating calcite provides specific insights into biomineralization of this mineral, and helps depict further pH consequences in the field of biomaterial adsorption. Graphical abstract Dissociative adsorption of hydronium ion onto the surface of calcite

Tuning metal–support interaction has been considered as an effective approach to modulate the electronic structure and catalytic activity of supported metal catalysts. At the atomic level, the understanding of the structure–activity relationship still remains obscure in heterogeneous catalysis, such as the conversion of water (alkaline) or hydronium ions (acid) to hydrogen (hydrogen evolution reaction, HER). Here, we reveal that the fine control over the oxidation states of single-atom Pt catalysts through electronic metal–support interaction significantly modulates the catalytic activities in either acidic or alkaline HER. Combined with detailed spectroscopic and electrochemical characterizations, the structure–activity relationship is established by correlating the acidic/alkaline HER activity with the average oxidation state of single-atom Pt and the Pt–H/Pt–OH interaction. This study sheds light on the atomic-level mechanistic understanding of acidic and alkaline HER, and further provides guidelines for the rational design of high-performance single-atom catalysts. Insights into the rational design of single-atom metal catalysts remains obscure in heterogeneous catalysis. Here, the authors establish the atomic-level structure–activity relationship for a wide-pH-range hydrogen evolution reaction through the electronic metal–support interaction modulation.

The idea of spatial confinement has gained widespread interest in myriad applications. Especially, the confined short hydrogen-bond (SHB) network could afford an attractive opportunity to enable proton transfer in a nearly barrierless manner, but its practical implementation has been challenging. Herein, we report a SHB network confined on the surface of ionic covalent organic framework (COF) membranes decorated by densely and uniformly distributed hydrophilic ligands. Combined experimental and theoretical evidences have pointed to the confinement of water molecules allocated to each ligand, achieving the local enrichment of hydronium ions and the concomitant formation of SHBs in water-hydronium domains. These overlapped water-hydronium domains create an interconnected SHB network, which yields an unprecedented ultrahigh proton conductivity of 1389 mS cm −1 at 90 °C, 100% relative humidity. When hydronium ions are enriched in confined water, short hydrogen bonds (SHBs) form due to the constrained space of excess protons between pairs of water molecules. Here authors demonstrate a SHB network confined on the surface of ionic COF membranes with tunable -SO 3 H groups, with proton conductivity of 1389 mS cm -1 at 90 o C.

The various hydrogen species present in a series of synthetic hydroniumjarosite ((H 3 O)Fe 3 (SO 4 ) 2 (OH) 6 ), and ammonioalunite ((NH 4 )Al 3 (SO 4 ) 2 (OH) 6 ) as well synthetic potassium (Cr 3+ and V 3+ ) and hydronium (V 3+ , Cr 3+ , and Ga 3+ ) analogues were identified and quantified by 1 H and 2 H MAS NMR spectroscopy. The results confirm the defect mechanism proposed for alunite Nielsen et al. (Am Miner 92: 587–597, 2007), and allow for identification and quantification of even a few percent structural defects. For the paramagnetic samples, the isotropic shift for G 2 -OH group (V 3+ , Cr 3+ , and Fe 3+ ) span more than 1100 ppm, which is related to different d-electron configuration ( d 2 , d 3 , and d 5 ). Analysis of the 1 H and 27 Al MAS NMR spectra shows that the synthetic ammonioalunite contains small amounts (5–10%) of hydronium. Furthermore, the close structural relationship between of hydronium and gallium alunite is reflected by the 27 Al and 71 Ga quadrupole coupling parameters. Thus, the current work demonstrates the applicability of solid state NMR spectroscopy for identification and quantification of hydrogen species in both dia- and paramagnetic minerals.

Most fundamental studies of electrocatalysis are based on the experimental and simulation results obtained for bulk model materials. Some of these mechanistic understandings are inapplicable for more active nanostructured electrocatalysts. Herein, considering the simplest and most typical electrocatalytic process, the hydrogen evolution reaction, an alternative reaction mechanism is proposed for nanomaterials based on the identification of a new intermediate, which differs from those commonly known for the bulk counterparts. In-situ Raman spectroscopy and electrochemical thermal/kinetic measurements were conducted on a series of nanomaterials under different conditions. In high-pH electrolytes with negligible hydronium (H 3 O + ) concentration in bulk phase, massive H 3 O + intermediates are found generating on the catalytic surface during water dissociation and hydrogen adsorption processes. These H 3 O + intermediates create a unique acid-like local reaction environment on nanostructured catalytic surfaces and cut the energy barrier of the overall reaction. Such phenomena on nanostructured electrocatalysts explain their widely observed anomalously high activity under high-pH conditions. Most of the current understanding on electrocatalysis is obtained on bulk catalysts but has not been fully verified on nanostructured materials. An alternative alkaline hydrogen evolution reaction mechanism is proposed here for nanostructured catalysts.

The reaction of carbon dioxide with hydroxide to form carbonate in near-neutral or alkaline medium severely limits the energy and carbon efficiency of CO 2 electroreduction. Here we show that by suppression of the otherwise predominant hydrogen evolution using alkali cations, efficient CO 2 electroreduction can be conducted in acidic medium, overcoming the carbonate problem. The cation effects are general for three typical catalysts including carbon-supported tin oxide, gold and copper, leading to Faradaic efficiency as high as 90% for formic acid and CO formation. Our analysis suggests that hydrated alkali cations physisorbed on the cathode modify the distribution of electric field in the double layer, which impedes hydrogen evolution by suppression of migration of hydronium ions while at the same time promoting CO 2 reduction by stabilization of key intermediates. Acidic media provide an opportunity to alleviate carbonate formation in electrocatalytic CO 2 reduction but increase competition from H 2 evolution. This study demonstrates that alkali cations in acidic media suppress H 2 evolution leading to high Faradaic efficiency for carbon-based products and models the physical effects that lead to this result.

Chemical reactivity and sorption in zeolites are coupled to confinement and—to a lesser extent—to the acid strength of Brønsted acid sites (BAS). In presence of water the zeolite Brønsted acid sites eventually convert into hydronium ions. The gradual transition from zeolite Brønsted acid sites to hydronium ions in zeolites of varying pore size is examined by ab initio molecular dynamics combined with enhanced sampling based on Well-Tempered Metadynamics and a recently developed set of collective variables. While at low water content (1–2 water/BAS) the acidic protons prefer to be shared between zeolites and water, higher water contents ( n  > 2) invariably lead to solvation of the protons within a localized water cluster adjacent to the BAS. At low water loadings the standard free energy of the formed complexes is dominated by enthalpy and is associated with the acid strength of the BAS and the space around the site. Conversely, the entropy increases linearly with the concentration of waters in the pores, favors proton solvation and is independent of the pore size/shape. The structure of water around Brønsted acid sites in zeolites is shown to influence their catalytic activity. Here the authors shed light on confinement effects in different pores zeolites/water interfaces acidic strength by means of ab-initio molecular dynamics and enhanced sampling metadynamics techniques.