Interfacial Network Research Articles

Hydrogen Spillover-Bridged Interfacial Water Activation of WCx and Hydrogen Recombination of Ru as Dual Active Sites for Accelerating Electrocatalytic Hydrogen Evolution.

Tungsten carbide (WCx) is a promising alternative to platinum catalysts for hydrogen evolution reaction (HER). However, strong tungsten-hydrogen bond hinders hydrogen desorption while favoring H+ reduction, thus limiting HER kinetics. Inspired by the phenomenon of hydrogen spillover in heterogeneous catalysis, a ruthenium (Ru) doped-driven activated hydrogen migration from WCx surface to Ru is reported. This approach achieved high activity with an ultralow overpotential of 9.0mV at 10 mA·cm-2 and superior stability at an industrial-grade current density of 1.0 A·cm-2 @ 1.65V. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS)and operando electrochemical impedance spectra revealed that this exceptional hydrogen production-which surpasses that of previously reported Pt/C catalysts-is attributable to the outstanding ability of WCx to induce water dissociation and hydrogen spillover from WCx to Ru surface. During the HER process, the rigid interfacial water network negatively affected the HER efficiency under alkaline conditions. The WCx sites disrupted this rigid structure, facilitating the contact between activated hydrogen (H*) and WCx sites. Subsequently, H* migrates to Ru surface, where hydrogen recombination occurs to produce H2. This work paves a new avenue for the construction of coupled catalysts at the atomic scale to facilitate HER electrocatalysis.

Probing atomic-scale processes at the ferrihydrite-water interface with reactive molecular dynamics

Interfacial processes involving metal (oxyhydr)oxide phases are important for the mobility and bioavailability of nutrients and contaminants in soils, sediments, and water. Consequently, these processes influence ecosystem health and functioning, and have shaped the biological and environmental co-evolution of Earth over geologic time. Here we employ reactive molecular dynamics simulations, supported by synchrotron X-ray spectroscopy to study the molecular-scale interfacial processes that influence surface complexation in ferrihydrite-water systems containing aqueous MoO42-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext {MoO}_4}^{2-}$$\\end{document}. We validate the utility of this approach by calculating surface complexation models directly from simulations. The reactive force-field captures the realistic dynamics of surface restructuring, surface charge equilibration, and the evolution of the interfacial water hydrogen bond network in response to adsorption and proton transfer. We find that upon hydration and adsorption, ferrihydrite restructures into a more disordered phase through surface charge equilibration, as revealed by simulations and high-resolution X-ray diffraction. We observed how this restructuring leads to a different interfacial hydrogen bond network compared to bulk water by monitoring water dynamics. Using umbrella sampling, we constructed the free energy landscape of aqueous MoO42-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext {MoO}_4}^{2-}$$\\end{document} adsorption at various concentrations and the deprotonation of the ferrihydrite surface. The results demonstrate excellent agreement with the values reported by experimental surface complexation models. These findings are important as reactive molecular dynamics opens new avenues to study mineral-water interfaces, enriching and refining surface complexation models beyond their foundational assumptions.Graphic

Casein network formation at oil–water interfaces is reduced by [formula omitted]-casein and increased by Ca[formula omitted]

Mixtures of bovine caseins can serve as a benchmark for understanding the functionality of microbial-based recombinant caseins at oil–water interfaces. In this work we show that, in the presence of Ca2+, the individual casein fractions form viscoelastic networks at the oil–water interface with comparable stiffness. In the absence of Ca2+, αs2- and β-casein interfacial network formation was strongly inhibited over the full deformation regime. For αs1-casein, the network stiffness was increased in the absence of Ca2+ at small deformations (<15%), but at large deformations (>50%) it was completely disrupted, to a similar stiffness as αs2- and β-casein. The interfacial structure formed by κ-casein was largely unaffected by Ca2+ due to limited phosphorylation. We hypothesize that the differences between calcium-sensitive caseins lie in the conformation they assume at the interface. Both αs2- and β-casein adsorb in a train-tail conformation with a tail extending into the aqueous bulk phase, whereas αs1-casein adsorbs in a loop-train conformation, with a loop that extends less into the bulk phase. The tail-train configuration is hypothesized to increase the inter-molecular Ca2+ bridging thereby increasing the interfacial stiffness of αs2- and β-casein.Blending the casein fractions revealed a strong negative effect of β-casein on the interfacial modulus, which was more pronounced at a higher concentration. The presence of Ca2+ remained important for interfacial network formation of a casein blend. Without Ca2+, the interfacial network was less stiff, more viscous, and behaved like a 2d polymer solution.With this work we showed that casein interfacial network formation at oil–water interfaces is mediated by Ca2+ bridging. Blending the different casein fractions decreased the interfacial viscoelastic properties through the presence of β-casein. These results indicate that future work on recombinant caseins should focus on single genetic variants, since a blend of variants will likely decrease interfacial functionality.

Hydrogen bonding network in the electrical double layer mediates fast proton skipping to Get Rid of Fenton reaction pH dependence enables highly efficient alkaline water purification

A fundamental scientific quandary in environmental has always been the pH dependence in Fenton reaction, that is, the reaction kinetics decreases by approximately 1–3 orders of magnitude upon transitioning from an acidic to an alkaline state. Here, we discovered that protons significantly contribute to the Fenton reaction through an examination of the reaction's interfacial behavior characteristics. Proton transfer mediated by hydrogen bond network connectivity in the electric double layer is responsible for the pH dependence of Fenton reaction kinetics. On this basis, the surface potential of Fenton reaction catalyst was modified to optimize the distribution of H2O in the electrical double layer, enhancing the connectivity of the interfacial hydrogen bond network and providing a fast channel for rapid proton transfer. The consecutive hydrogen bond network mediates rapid proton hopping, increasing the proton concentration in the Helmholtz layer, and consequently promoting the proton conductivity from 5.38×10−7 S·cm−2 to 4.35×10−6 S·cm−2 in alkaline conditions for Fenton reaction. Meanwhile, the kinetics reaction rate was improved 20 times, and the pH dependence was reduced from 70.9 % to 12.6 %. This discovery clarifies the key role of the interfacial hydrogen bond network and proton transfer in Fenton reaction kinetics pH dependence. It provides new theories and methods for achieving alkaline high Fenton reaction kinetics.

Enhanced colorimetric analysis substrate based on graphene oxide open-close actuator

Traditional colorimetric sensors often suffer from low color resolution and insufficient sensitivity. Therefore, for colorimetric detection to serve as a reliable quantitative analysis technique, an enhanced substrate with high sensitivity and repeatability is required. This strategy employs an interfacial network constructed between two-dimensional graphene oxide (GO) lamellar structures to create a substrate for colorimetric analysis. Under normal conditions, the newly synthesized GO inhibits oxidative activity due to van der Waals forces between the lamellar interfaces, resulting in the GO actuator being in the closed state. During Ag+ colorimetric analysis, the GO interlayer adsorption of silver nanoparticles (AgNPs) disrupts the interlayer van der Waals forces, releasing its oxidase activity and significantly enhancing Ag+ oxidation. The resulting actuator exhibits a faster driving speed (0.045 μM/s), excellent sensitivity, and stability. Additionally, the reducing properties of dopamine (DA) can be utilized to encapsulate the GO actuator with polydopamine, closing the GO actuator. Similarly, the reducing property of ascorbic acid (AA) can be utilized to restore the GO actuator to a closed state. These distinct reduction mechanisms allow for an effective visual distinction between AA and DA. With these advantages, the actuator can be developed into simple analytical tools (such as Ag+ colorimetric test strips and DA and AA test kits), demonstrating significant potential for practical application.

Role of pulse globulins and albumins in air-water interface and foam stabilization

Pulse protein isolates are promising substitutes for animal protein in foam preparation, but they typically are complex mixtures of multiple proteins, and the contribution of the individual proteins to the behavior of the mixture in air-water interface stabilization is largely unknown. The major protein fractions in isolates are the globulins and albumins, and this study systematically investigated the molecular properties, and interfacial and foaming properties of these two fractions for three different pulses: lentils, faba beans and chickpeas. The key parameters of these pulse proteins in air-water interface and foam stabilization were investigated by correlation analysis. Based on this, low denaturation enthalpy tends to result in both high foamability and foam stability, most likely due to a greater conformational flexibility that allows for a faster adsorption to the air-water interface, and higher degree of structural rearrangement at the interface, which increases interfacial network stiffness. For globulin-rich pulse protein fractions, vicilins and convicilins tend to introduce high surface hydrophobicity, which increases the affinity of the proteins for the interface, and increases protein-protein in-plane interactions through hydrophobic interactions, resulting in the enhancement of interfacial network connectivity and the level of network branching. These factors increase the interfacial resistance to large deformations and increase foam stability. Vicilins and convicilins also tend to have a high value of the surface charge and further promote foam stability by increasing electrostatic repulsion between air bubbles. Legumins tend to reduce foamability since they adsorb to the air-water interface slowly and tend to disrupt the interfacial network structure. These findings provide deeper insights in the role of pulse globulins and albumins in air-water interface and foam stabilization. The proposed key parameters will benefit the predictability of the interfacial and foaming behavior of pulse proteins.

Dual functional bio-inspired additives reconstruct metal-organic interface stability for wearable energy storage system

Aqueous zinc-ion batteries (AZIBs) hold significant promise across wearable energy storage devices due to their superior safety and cost-effectiveness. However, the instability of the electrode/electrolyte interface leads to severe hydrogen evolution reaction (HER) and dendritic growth. Herein, a bio-inspired additive, keratin (Ker), is introduced to construct a robust interfacial layer. The hydrogen bonding donors homogenize the distribution of interfacial hydrogen bond networks and increases the electron density in Zn2+-OH interaction, stabilizing bound H2O molecules and effectively inhibiting HER. Additionally, electron transfer from the highly reactive thiol (-SH) motivates the formation of Zn-S chemical linkage, enhancing interface stability. These features endow Zn||Zn symmetric cells with an impressive cycle life, reaching up to 3364 h at 1 mA cm−2/1 mAh cm−2. The Zn||α-MnO2 and Zn||VO2 full cells also exhibit a substantial capacity retention after 1000 cycles. Incorporating multi-step laser cutting technology enables the fabrication of flexible, large-area micro-batteries with prolonged cycle life. This study presents an advanced methodology for heralding a promising pathway to improve the reversibility of aqueous energy storage systems.

Characterizing the Orderliness of Interfacial Water through Stretching Vibrations.

Spatial orderliness, which is the orderly structure of molecules, differs significantly between interfacial water and bulk water. Understanding this property is essential for various applications in both natural and engineered environments. However, the subnanometer thickness of interfacial water presents challenges for direct and rapid characterization of its structural orderliness. Herein, through molecular dynamics simulations and infrared spectral analysis of interfacial water in a graphene slit pore, we reveal a hyperbolic tangent relationship between the water ordering and its O-H stretching information in the infrared spectrum. Specifically, O-H symmetric stretching dominated in the highly ordered water structure, while a transition to the asymmetric stretching corresponded to an increase in the degree of disorder. Thus, the O-H stretching behavior could serve as a useful and quick assessment of the orderliness of interfacial water. This work provided insights into interfacial water's unique molecular network and structural dynamics and identified the stretching vibrations' key role in its degree of order, providing insight for fields such as nanotechnology, biology, and material science.

Spatial arrangements and types of dislocations in interfacial networks obtained by Si(001) wafer bonding at low twist angle: A TEM characterization

Two interfacial dislocation networks were obtained in a Si–Si material system by wafer bonding process for low twist angles around 0.2°. For one sample, one of the two initial wafers was rotated with an additional angle of 90° before the bonding. TEM analyses of samples prepared for planar and transverse views show different characteristics in terms of spatial arrangement and dislocation types. Long climbing segments slightly deviated from the [100] axis and short segments a/2<101> are arranged in the dislocation network obtained with an additional rotation and at the lowest twist angle (Ψ = 0.18°) from a <110> axis. Long screw segments a/2<110> and short partial Shockley segments are arranged in the dislocation network obtained without any additional rotation at the highest twist angle (Ψ = 0.27°) from a <110> axis. In both cases, the long and short segments form elongated hexagonal patterns, which are accurately ordered in one set paving the <100> directions or randomly ordered in two perpendicular sets paving the <110> directions, respectively. The results are discussed taking into account the arangement of the surface miscut steps in the initial wafers before the bonding.

Coordination and Hydrogen Bond Chemistry in Tungsten Oxide@Polyaniline Composite toward High-Capacity Aqueous Ammonium Storage.

Aqueous ammonium ion batteries (AAIBs) have garnered significant attention due to their unique energy storage mechanism. However, their progress is hindered by the relatively low capacities of NH4 + host materials. Herein, the study proposes an electrodeposited tungsten oxide@polyaniline (WOx@PANI) composite electrode as a NH4 + host, which achieves an ultrahigh capacity of 280.3 mAh g-1 at 1 A g-1, surpassing the vast majority of previously reported NH4 + host materials. The synergistic interaction of coordination chemistry and hydrogen bond chemistry between the WOx and PANI enhances the charge storage capacity. Experimental results indicate that the strong interfacial coordination bonding (N: →W6+) effectively modulates the chemical environment of W atoms, enhances the protonation level of PANI, and thus consequently the conductivity and stability of the composites. Spectroscopy analysis further reveals a unique NH4 +/H+ co-insertion mechanism, in which the interfacial hydrogen bond network (N-H···O) accelerates proton involvement in the energy storage process and activates the Grotthuss hopping conduction of H+ between the hydrated tungsten oxide layers. This work opens a new avenue to achieving high-capacity NH4 + storage through interfacial chemistry interactions, overcoming the capacity limitations of NH4 + host materials for aqueous energy storage.

Lewis-base ligand-reshaped interfacial hydrogen-bond network boosts CO2 electrolysis.

Both the catalyst and electrolyte strongly impact the performance of CO2 electrolysis. Despite substantial progress in catalysts, it remains highly challenging to tailor electrolyte compositions and understand their functions at the catalyst interface. Here, we report that the ethylenediaminetetraacetic acid (EDTA) and its analogs, featuring strong Lewis acid-base interaction with metal cations, are selected as electrolyte additives to reshape the catalyst-electrolyte interface for promoting CO2 electrolysis. Mechanistic studies reveal that EDTA molecules are dynamically assembled toward interface regions in response to bias potential due to strong Lewis acid-base interaction of EDTA4--K+. As a result, the original hydrogen-bond network among interfacial H2O is disrupted, and a hydrogen-bond gap layer at the electrified interface is established. The EDTA-reshaped K+ solvation structure promotes the protonation of *CO2 to *COOH and suppressing *H2O dissociation to *H, thereby boosting the co-electrolysis of CO2 and H2O toward carbon-based products. In particular, when 5mM of EDTA is added into the electrolytes, the Faradaic efficiency of CO on the commercial Ag nanoparticle catalyst is increased from 57.0% to 90.0% at an industry-relevant current density of 500mA cm-2. More importantly, the Lewis-base ligand-reshaped interface allows a range of catalysts (Ag, Zn, Pd, Bi, Sn, and Cu) to deliver substantially increased selectivity of carbon-based products in both H-type and flow-type electrolysis cells.

Topological properties of interfacial hydrogen bond networks

Topological properties of interfacial hydrogen bond networks

Role of egg white protein particles’ structure and interface profiles in tailoring high-internal-phase Pickering emulsions with desired applicability

Tailoring food-grade high-internal-phase Pickering emulsions (HIPPEs) with desired applicability has been extremely hindered due to the limited stabilization mechanism deciphering. This study illustrated the specific role of egg white protein (EWP) particlesꞌ structure and interface distribution to the stabilization of HIPPEs. Herein, gelation induced EWP aggregation into its microgel particles (EWPG) with apparent conformation transition (α-helix to β-sheet) and surface activity improvement (e.g., hydrophobicity, interface tension, and wettability). Besides, larger EWPG tended to sparsely absorb on the HIPPEsꞌ interface and achieve admirable long-term stability (6-month storage and 18-days lipid oxidation), owing to higher particle rigidity and steric repulsion. Comparably, EWP (small, soft, and rough) was superior in ready-to-use HIPPEs with centrifugation, freeze-thawing, and nutraceutical delivery demands, accompanied by a stronger rattan-like interfacial network with higher viscoelasticity. Overall, this research would facilitate the facile design of food matrices (e.g., EWP)-based HIPPEs via the gelation-tailored balance of particle structure and interface distribution.

Positive and Negative Impacts of Interfacial Hydrogen Bonds on Photocatalytic Hydrogen Evolution.

Understanding the behavior of water molecules at solid-liquid interfaces is crucial for various applications such as photocatalytic water splitting, a key technology for sustainable fuel production and chemical transformations. Despite extensive studies conducted in the past, the impact of the microscopic structure of interfacial water molecules on photocatalytic reactivity has not been directly examined. In this study, using real-time mass spectrometry and Fourier-transform infrared spectroscopy, we demonstrated the crucial role of hydrogen bond (H-bond) networks on the photocatalytic hydrogen evolution in thickness-controlled water adsorption layers on various TiO2 photocatalysts. Under controlled water vapor environments with relative humidity (RH) below 70%, we observed a monotonic increase in the H2 formation rate with increasing RH, indicating that reactive water molecules were present not only in the first adsorbed layer but also in several overlying layers. In contrast, at RH > 70%, when more than three water layers covered the catalyst surface, the H2 formation rate turned to decrease dramatically because of the structural rearrangement and hardening of the interfacial H-bond network induced during further water adsorption. This unique many-body effect of interfacial water was consistently observed for various TiO2 particles with different crystalline structures, including brookite, anatase, and a mixture of anatase and rutile. Our results demonstrated that depositing several water layers in a water vapor environment with RH ∼ 70% is optimal for photocatalytic hydrogen evolution rather than liquid-phase reaction conditions in aqueous solutions. This study provides molecular-level insights into designing interfacial water conditions to enhance photocatalytic performance.

A surface molecular assembly-based composite inhibitor for mitigating corrosion in dynamic supercritical CO[formula omitted] aqueous environment

Supercritical CO2 (sCO2) corrosion is a persistent challenge in carbon capture, utilization, and storage (CCUS) that requires effective inhibition strategies. We present a systematic study using experimentation and modeling to investigate the inhibition behavior of a composite formulation containing Sodium Molybdate (SM), Triethanolamine Borate (TB), and L-Cysteine (LC) on X80 steel. Our in situ electrochemical studies confirm the superior performance of this ternary system, achieving a composite inhibition efficiency of over 99.86%. Surface profilometry measurements showed a roughness value as low as 33.51μm, indicating enhanced corrosion resistance and uniformity. Atomistic simulations provided mechanistic insights, revealing that LC coordinates SM and TB through favorable S-mediated interactions, optimizing the interfacial ligand network. Chemical bonding analysis indicated that this designed interface effectively suppresses corrosion through cooperative interactions, exceeding the performance of individual inhibitors. Overall, the synergistic effects of the optimized multicomponent system surpassed the efficacy expected from simply combining the individual components.

Mechanically Robust, Recyclable, and Highly Thermally Conductive Ethylene–Propylene–Diene Monomer/Boron Nitride Composite Enabled by Multiple Interfacial Cross-Linking Networks

Mechanically Robust, Recyclable, and Highly Thermally Conductive Ethylene–Propylene–Diene Monomer/Boron Nitride Composite Enabled by Multiple Interfacial Cross-Linking Networks

Bioinspired H-Bonding Connected Gradient Nanostructure Actuators Based on Cellulose Nanofibrils and Graphene.

The construction of flexible actuators with ultra-fast actuation and robust mechanical properties is crucial for soft robotics and smart devices, but still remains a challenge. Inspired by the unique mechanism of pinecones dispersing seeds in nature, a hygroscopic actuator with interlayer network-bonding connected gradient structure is fabricated. Unlike most conventional bilayer actuator designs, the strategy leverages biobased polyphenols to construct strong interfacial H-bonding networks between 1D cellulose nanofibers and 2D graphene oxide, endowing the materials with high tensile strength (172MPa) and excellent toughness (6.64MJm-3). Furthermore, the significant difference in hydrophilicity between GO and rGO, along with the dense interlayer H-bonding, enables ultra-fast water exchange during water absorption and desorption processes. The resulted actuator exhibits ultra-fast driving speed (154°s-1), excellent pressure-resistant and cyclic stability. Taking advantages of these benefits, the actuator can be fabricated into smart devices (such as smart grippers, humidity control switches) with significant potential for practical applications. The presented approach to constructing interlayer H-bonding in gradient structures is instructive for achieving high performance and functionalization of biomass nanomaterials and the complex of 1D/2D nanomaterials.

Interfacial network formation by casein blends in the presence of Ca2+ is dominated by β- and κ-casein

With the increasing interest in precision fermentation for food purposes, the opportunity arises to produce individual casein fractions or specific blends based on the requirements of an application. Therefore, the functionality of individual casein fractions has gained attention in academia and industry.This study focused on the air-water interfacial functionality of individual bovine casein fractions in casein blends, to serve as a benchmark for precision fermented casein fractions. With oscillating bubble tensiometry, we showed that the interfacial behavior of a milk-like casein blend of αs1-, αs2-, β-, &κ-casein (ratio 4:1.1:3.8:1.3) was dominated by the β- and κ-casein fractions through the formation of a disordered solid-like viscoelastic interface. The presence of Ca2+ in the buffer was essential; Without Ca2+, the casein blend formed a weak interfacial microstructure where the viscoelastic modulus was dominated by exchange between bulk and interface. The interfacial microstructure was imaged with Langmuir-Blodgett deposition followed by atomic force microscopy. Here we showed that the interfacial structure of β+κ-casein was highly similar to the milk-like casein blend. In the presence of Ca2+ in the buffer, the interfacial microstructure of the casein blend was shown to be more connected and homogeneous compared to a buffer without Ca2+. Thereby highlighting the importance of the phosphoserine residues in β-casein.These results show the opportunity to mimic the interfacial functionality of a milk-like casein blend with only a blend of β+κ-casein but that the presence of phosphoserine residues in β-casein is essential for the formation of a stiff interfacial network.

Stretchable Electrodes with Interfacial Percolation Network.

Stretchable electrodes are an essential component that determines the functionality and reliability of stretchable electronics, but face the challenge of balancing conductivity and stretchability. This work proposes a new conducting concept called the interfacial percolation network (PN) that results in stretchable electrodes with high conductivity, large stretchability, and high stability. The interfacial PN is composed of a 2D silver nanowires (AgNWs) PN and a protruding 3D AgNWs PN embedded on the surface and in the near-surface region of an elastic polymer matrix, respectively. The protruded PN is obtained by changing the arrangements of AgNWs from horizontal to quasi-vertical through introducing foreign polymer domains in the near-surface region of the polymer matrix. The resulting electrode achieves a conductivity of 13500 S cm-1 and a stretchability of 660%. Its resistance changes under stretched conditions are orders of magnitude lower than those of conventional 2D PN and 2D + 3D PN. An interfacial PN electrode made from liquid metal remained its conductivity at46750 S cm-1 after the electrode underwent multiple stretch-release cycles with a deformation of >600%. The concept of interfacial PN provides fruitful implications for the design of stretchable electronics.

Controlling Interfacial Hydrogen Bonding at a Gold Surface: The Effect of Organic Cosolvents.

Water often serves as both a reactant and solvent in electrocatalytic reactions. Interfacial water networks can affect the transport and kinetics of these reactions, e.g., hydrogen evolution reaction and CO2 reduction reaction. Adding cosolvents that influence the hydrogen-bonding (H-bonding) environment, such as dimethyl sulfoxide (DMSO), has the potential to tune the reactivity of these important electrocatalytic reactions by regulating the interfacial local environment and water network. We investigate interfacial H-bonding networks in water-DMSO cosolvent mixtures on gold surfaces by using surface-enhanced infrared absorption spectroscopy and molecular dynamics simulations. Experiments and simulations show that the gold surface is enriched with dehydrated DMSO molecules and the mixture phase-separates to form water clusters. Simulations show a "buckled" water conformation at the surface, further constraining interfacial H-bonding. The small size of these water clusters and the energetically unfavorable H-bond conformations might inhibit H-bonding with bulk water, suppressing the proton diffusion required for efficient hydrogen evolution reaction processes.