Electrolyte Solution Research Articles

Reflection coefficient of a natural sodium bentonite in aqueous mixed electrolyte solutions: positive and negative anomalous osmosis

Reflection coefficient of a natural sodium bentonite in aqueous mixed electrolyte solutions: positive and negative anomalous osmosis

Recovery of antimony from acidic and alkaline leaching solution of low-grade antimony ore by electrowinning process

With regards to the global continuous growth in consumption of base metals such as antimony (Sb), mining companies are currently looking to improve the productivity and extraction of Sb from low grade ore in order to economically process it. With this aim, in this study, an efficient protocol was developed to recover metallic Sb from the low grade Fe3Si2O5(OH)4. Sb3O6(OH). Sb2O3 ore of the Sefid-Abe mine in Zahedan province, Iran, utilizing selective acidic or alkaline leaching followed by Sb electrowinning. A process was developed to recover antimony from an Sb2O3 ore source, using selective acidic or alkaline leaching followed by antimony electrowinning. Sb could be leached with an efficiency of 85 % using 5 M NaOH and 87 % using 5 M hydrochloric acid/5 M sulfuric acid as the digestion solution at 80 °C for 8 h. The electrowinning process plays a significant role in recovery of highly pure Sb metal. Relying on this approach, a high deposition rate and current efficiency have been generated at a deposition potential 2 V at 30 °C (80 °C for alkaline medium). This was achieved by using anode electrode made of graphite and cathode electrode made of steel (two steel electrodes were used for alkaline electrowinning). Additionally, for acidic electrowinning, exploitation of Sb from the electrolyte solution was achieved by applying a current of 0.1 A, resulting in the highest yield equal to 89 %. On the other hand, for alkaline electrowinning, the highest efficiency corresponds to the current intensity of 0.5 A, which resulted in 97 % Sb extraction from the electrolyte solution. The XRD and ICP analysis performed for samples obtained from the electrolysis confirmed that the resulting antimony ingot has an exceptionally high purity.

DNA-Based Conductors: From Materials Design to Ultra-Scaled Electronics.

Photolithography has been the foundational fabrication paradigm in current high-performance electronics. However, due to the limitation in fabrication resolution, scaling beyond a 20-nm critical dimension for metal conductors presents a significant challenge for photolithography. Structural DNA nanotechnology emerges as a promising alternative to photolithography, allowing for the site-specific assembly of nano-materials at single-molecule resolution. Substantial progresses have been achieved in the ultra-scaled DNA-based conductors, exhibiting novel transport characteristics and small critical dimensions. This review highlights the structure-transport property relationship for various DNA-based conductors and their potential applications in quantum/semiconductor electronics, going beyond the conventional scope focusing mainly on the shape diversity of DNA-templated metals. Different material synthesis methods and their morphological impacts on the conductivities are discussed in detail, with particular emphasis on the conducting mechanisms, such as insulating, metallic conducting, quantum tunneling, and superconducting. Furthermore, the ionic gating effect of self-assembled DNA structures in electrolyte solutions is examined. This review also suggests potential solutions to address current challenges in DNA-based conductors, encouraging multi-disciplinary collaborations for the future development of this exciting area.

Droplet Electrophoresis with Internal Free Ions: Effect of Permittivity Changes in the Electric Double Layer.

Droplet electrophoresis (EP) is of interest in biological systems, microfluidics, and separation techniques. We investigate EP of an oil droplet that contains free ions and is stabilized in an electrolyte solution through an amphoteric surfactant. The presence of mobile ions within the droplet leads to the creation of a distinct nonzero space charge density inside the droplet and consequently, formation of an inner EDL inside the droplet in addition to the traditionally considered outside EDL. While we assume the permittivity inside the inner EDL to remain constant, we consider both the case of constant and variable permittivity in the outer EDL. Our findings demonstrate a change in the droplet direction of motion in the electric field when transitioning from acidic to alkaline pH, regardless of permittivity and ionic strength in both oil and electrolyte. We further find a significant reduction in the magnitude of droplet velocity in the case of a variable permittivity due to reduction of the local space charge density within the EDL surrounding the droplet. When decreasing the viscosity ratio of the oil to the electrolyte, in all cases we find a reduction in droplet velocity. This decline is attributed mostly to the formation and strength of a vortex around the droplet. We finally demonstrate that with constant permittivity in the outer EDL, the variation in κaouter has a more significant effect on the droplet's EP velocity than altering κainner. However, in cases where the body forces inside of the droplet dominate, minor changes in the outer electrolyte concentration have no influence on the droplet motion, which is relevant for biological colloids that can contain significant free internal charges. Our results are important for the manipulation of biological colloids, water and waste treatment such as lubricant removal from processing streams.

NiCo-Phosphide Bifunctional Electrocatalyst Realizes Electrolysis of Sugar Solution to Formic Acid and Hydrogen.

As a promising liquid hydrogen carrier, formic acid is essential for hydrogen energy. Glucose, as the most widely distributed monosaccharide in nature, is valuable for co-electrolysis with water to produce formic acid and hydrogen, though achieving high formate yield and current density remains challenging. Herein, a nanostructured NiCoP on a 3D Ni foam catalyst enables efficient electrooxidation of glucose to formate, achieving an 85% yield and 200 mA current density at 1.47 V vs RHE. The catalyst forms a NiCoOOH/NiCoP/Ni foam sandwich structure via anodic oxidative reconstruction, with NiCoOOH as the active site and NiCoP facilitating electron conduction. Additionally, NiCoP/Ni foam serves as both an anode and cathode for the production of formate and hydrogen from wood-extracted sugar solutions. At 2.1 V, it reaches a 300 mA current density, converting mixed sugars to formate with a 74% yield and producing hydrogen at 104 mL cm2 h-1 with near 100% Faradaic efficiency.

Electrochemical Recovery of N and P from Municipal Wastewater

Phosphorus, P, is a vital element of paramount importance for both humans and for the Environment. Wastewater contains often relatively high concentrations of P which can be recovered as crystalline struvite (MgNH4PO4·6H2O, MAP). This option is quite attractive in assisting sustainable development because struvite can be used as a slow-release fertilizer. Domestic wastewater is usually high in P and nitrogen, N, but relatively poor in magnesium, Mg. It is necessary to develop low-cost solutions for the enrichment of wastewater with Mg. In the present work, sacrificial magnesium anodes were used, which dissolve upon anodic polarization, releasing sufficient magnesium for the selective precipitation of MAP. The application of constant current between two electrodes of which the anode is a low-cost magnesium cylindrical rod (4 cm2 exposed surface area) and the other a platinum cathode electrode, both immersed in ammonium phosphate solutions, without adjustment of the solution pH, was investigated. Constant current density over the range 10–100 A·m−2, between the Mg- Pt electrodes immersed in solutions of ammonium hydrogen phosphate of exactly known initial concentration, was applied using a potentiostat. In the presence of sodium chloride solutions, on the magnesium anode and in the bulk solution, Mg(OH)2 (brucite) formed because of the passivation of the Mg electrode. In dilute ammonium hydrogen phosphate solutions, the magnesium anode dissolution resulted in struvite precipitation, even at a low applied current (10 mA). Struvite crystals with an average size of 20 μm were precipitated. The behavior of the cell for the electrolyte solutions used was Faradaic as long as the surface coverage of the anode was relatively low. The anodic dissolution of Mg resulted in high pH values (pH 11) eliminating the need for alkali addition.

Statistical‐Mechanical Theory on the Probability Distribution Function for the Net Charge of an Electrolyte Droplet

AbstractDroplets of electrolyte solutions in an insulating medium are ubiquitous in nature. The net charges of these droplets are normally nonzero, and they fluctuate. However, a theory on the probability distribution function for the net charge of droplets is lacking, so far. Thus, a statistical‐mechanical theory of a charged droplet is developed including the effect of the electrostatic energy of charging as well as the random distribution of ions. Then, the probability distribution function for the net charge of an electrolyte droplet is calculated assuming that it is generated from a macroscopic solution with the different cation and anion concentrations. Using the Gaussian approximation and Stirling's formula, the analytic results for the average and variance of the net charge of a droplet are obtained.

All-in-All: Dead Lithium-ion battery to active Lithium-ion Capacitor.

Here, we have developed lithium-ion capacitors (LICs) with all the components, except the electrolyte solution, effectively recycled from the spent Lithium-ion batteries. Hybrid capacitors, such as LICs, are potential breakthroughs in electrochemical energy storage devices, where most research is focused. These devices can simultaneously guarantee high energy and power by hybridizing battery-type and capacitive-type electrodes. We have successfully upcycled the graphite, current collector, separator, etc., from the spent LIBs to fabricate a high-performance LIC. Our LIC consists of recovered graphite (RG) coated over recovered copper foil as an anode, recycled polypropylene as the separator, and reduced graphene oxide (rGO) synthesized from RG as the cathode. The RG half-cell exhibited an specific capacity of 302 mAh/geven after 75 charge-discharge cycles with a coulombic efficiency of >99%. The Li/rGO displayed remarkable cycling performance for over 1000 cycles with high stability and reversibility. Subsequently, the pre-lithiated RG (p-RG) electrode is paired with the rGO electrode under the balanced loading conditions to construct LIC, rGO/p-RG, delivering a maximum energy density of 185 Wh/kgwith ultra-long durability of more than 10,000 cycles. The possibility of LIC under different climatic conditions is also explored, and its remarkable performance under various temperature conditions is worth mentioning.

All colloidal supercapattery: colloid@carbon cloth electrodes meet "water‐in‐salt" electrolyte

The pursuit of excellent electrochemical performance, nonflammability and environmental friendliness of aqueous batteries and supercapacitors has driven efforts to find high‐energy yet reliable electrode materials and electrolyte solutions. Here, all colloidal supercapattery are developed using high‐concentration "water‐in‐salt" electrolytes (LiTFSI‐KOH) and pseudocapacitive colloid@carbon cloth as both positive and negative electrodes, which showed merits of batteries and supercapacitors. Ni/Co‐colloid @carbon cloth positive and Fe‐colloid @carbon cloth negative electrodes can be synthesized by in situ electrochemical reaction. The maximum operating voltage of an aqueous colloidal supercapattery is 1.8 V, and the energy density can reach 73.98 Wh kg−1 at a power density of 1799.5 W kg‐1. The specific capacitance of the aqueous colloidal supercapattery still maintains 74.3% of the initial after 2000 cycles of charge/discharge measurement. The combination of quasi ion colloidal materials and "water‐in‐salt" electrolyte pave a profound way to achieve high energy and power ability simultaneously at the supercapattery device.

Unprecedented electrochemical activity of GdCoO3-gC3N4 nanocomposite for bifunctional oxygen and hydrogen evolution reaction

Development of highly competent and stable electrocatalysts for electrochemical water splitting to attain oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desired. Here in present work, gadolinium cobalt oxide (GdCoO3), graphitized carbon nitride (gC3N4), and their composite is fabricated via hydrothermal method, and then used as electrocatalysts for OER and HER. The prepared electrocatalysts underwent rigorous characterization using X-ray diffraction (XRD) to unravel their structural composition. To further unravel their morphological and textural aspects, scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) techniques were employed. Intriguingly, the synergy of nanoparticles GdCoO3 anchored onto thin nanosheets of gC3N4 exhibited a remarkable surge in OER and HER activities in a 1.0 M KOH electrolyte solution. The composite material showed a remarkable reduction in onset potential of 0.95 V vs Ag/AgCl for OER. On the other hand, impressively it shows the low overpotentials of 210 mV at 10 mA cm−2 with a tafel slope of 44 mV dec−1. Notably, for HER the nanocomposite requires an onset potential of 0.01 V vs Ag/AgCl and 230 mV overpotential to achieve a current density of 10 mA cm−2. The enhanced results are due to that the GdCoO3 nanoparticles integrated onto the nanosheets of gC3N4 shows high surface area and synergistic effect exhibited, which displayed good stability, and are useful for commercial applications. Thus, the exceptional OER performance of the composite combined with its good electrochemical properties, positions it as a viable option for large-scale and sustainable water splitting technologies.

Light Conversion by Electrochemiluminescence at Semiconductor Surfaces.

ConspectusElectrochemiluminescence (ECL) is the electrochemical generation of light. It involves an interfacial charge transfer that produces the excited state of a luminophore at the electrode surface. ECL is a powerful readout method that is widely employed for immunoassays and clinical diagnostics and is progressively evolving into a microscopy technique. On the other hand, photoelectrochemistry at illuminated semiconductors is a field of research that deals with the transfer of photogenerated charge carriers at the solid-liquid interface. This concept offers several advantages such as a considerable lowering of the onset potential required for triggering an electrochemical reaction as well as light addressable chemistry, via the spatial confinement of redox reactions at locally illuminated semiconductor electrodes. The combination of ECL with photoelectrochemistry at illuminated semiconductors is termed photoinduced ECL (PECL). It deals with the triggering of an ECL reaction through the transfer of photogenerated minority charge carriers at the illuminated solid/liquid interface. PECL results in the conversion of incident photons (λexc), that are absorbed by the semiconductor photoelectrode to emitted photons (λPECL), produced by the ECL reaction. Although demonstrated in the 1970s by Bard et al. in ultradry organic solvents, PECL remained unexplored until the last five years. Nowadays, as a result of the considerable progress achieved in semiconductor photoelectrodes and ECL systems, a large variety of PECL systems can be designed by combining photoelectrode materials with ECL luminophores, making it a versatile tool for light conversion in aqueous media.In this Account, we introduce the fundamentals of ECL and photoelectrochemistry at illuminated semiconductors and review the recent developments in PECL. We discuss the two main PECL light conversion schemes: downconversion (where λexc < λPECL) and upconversion (where λexc > λPECL). Besides, PECL can be used to simplify considerably the common electrochemical setups employed for ECL. Indeed, by engineering the photoelectrode material and carefully considering the reactivity involved for ECL and its counter-reaction, PECL enables the ultimate concept of all-optical ECL (AO-ECL), i.e., ECL generation at an illuminated monolithic device immersed into the electrolyte solution. As discussed in this Account, AO-ECL is an important breakthrough that allows the simplest ECL experimental configuration ever reported, eliminating constraints such as an electrical power supply, wires, electrodes, connections, and specific electrochemical knowledge. As shown at the end of this Account, due to the robustness of recently manufactured PECL systems, several applications can already be envisioned for microscopy, elucidation of solar conversion mechanisms, near-infrared imaging, and bioanalysis.

Molecularly imprinted Photoelectrochemical sensor for Escherichia coli based on Cu:ZIF-8/KZ3TTz heterojunction

Herein, a signal stable molecularly imprinted photoelectrochemical (MIP-PEC) sensing platform was designed to sensitively detect Escherichia coli by incorporating polythiophene film with Cu: ZIF-8/KZ3TTz heterojunction. Attributed to the formation of a staggered type II heterostructure between KZ3TTz and Cu: ZIF-8 semiconductors, the Cu: ZIF-8/KZ3TTz heterojunction exhibited stable and significant cathode PEC response. Impressively, selective MIP film was grown on the surface of Cu: ZIF-8/KZ3TTz/GCE by electro-polymerization of 2,2-Dimethyl-5-(3-thienyl)-1,3-dioxane-4,6-dione (DTDD) in the presence of E. coli. After removing E. coli, more electrons were transferred to the electrolyte solution through the imprinting cavity on the MIP film, which was eliminated by O2 in the electrolyte, causing further enhancement of the cathode PEC response. On the contrary, when the imprinted cavity was filled with E. coli, the cathodic PEC response gradually decreased due to steric hindrance effect. The sensor showed excellent linearity in the range of 101 to 108 CFU/mL with a detection limit of 4.09 CFU/mL (S/N = 3). This strategy offered a novel approach for pathogenic bacteria detection in food safety and environmental monitoring

Fabrication of Fe-Zr, Co-Zr, and Ni-Zr Catalysts to Boost CNTs Synthesis from Plastic Wastes and the Electrocatalytic Oxygen Evolution Reaction.

The efficient conversion of plastic wastes to high-value carbon materials like carbon nanotubes (CNTs) is one important issue about the rational recycling, reduction, and reuse of solid wastes. Herein, Fe-, Co-, and Ni-Zr catalysts were prepared and used for CNTs synthesis from polyethylene (PE) waste via a two-stage reaction system. At the same time, the effects of the PE/catalyst ratio and reaction temperature on CNTs synthesis have been studied. Compared with Co-Zr and Ni-Zr, Fe-Zr exhibited the best activity in CNTs synthesis from PE, and it achieved the highest CNTs yield of 806.3 mg/g (per gram of Fe-Zr) at 800 °C with a PE/catalyst ratio of 4. Furthermore, the obtained Fe-Zr/CNTs composite exhibited a low overpotential of 267 mV for the electrocatalytic oxygen evolution reaction (OER) at 20 mA/cm2 in 1 M KOH electrolyte solution, which was 21 mV lower than commercial RuO2 (288 mV) and 50 mV lower than Fe-Zr (317 mV). It was deduced that the in situ growth of CNTs reduced the charge transfer resistance and improved the electron transport efficiency of the Fe-Zr/CNTs composite, leading to superior activity in the electrocatalytic OER. This work provided detailed information for the preparation of the metal/CNTs composite from plastic wastes, which contributed positively to alleviate the environment and energy crisis.

How Cation–Silica Surface Interactions Affect Water Dynamics in Nanoconfined Electrolyte Solutions

How Cation–Silica Surface Interactions Affect Water Dynamics in Nanoconfined Electrolyte Solutions

Oxide-Encapsulated Silver Electrocatalysts for Selective and Stable Syngas Production from Reactive Carbon Capture Solutions.

Electrolysis of bicarbonate-containing CO2 capture solutions is a promising approach towards achieving low-cost carbon-neutral chemicals production. However, the parasitic bicarbonate-mediated hydrogen evolution reaction (HER) and electrode instability in the presence of trace impurities remain major obstacles to overcome. This work demonstrates that the combined use of titanium dioxide (TiO2) overlayers with the chelating agent ethylene diamine tetra-acetic acid (EDTA) significantly enhances the selectivity and stability of Ag-based electrocatalysts for bicarbonate electrolysis. The amorphous TiO2 overlayers suppress the HER by over 50 % at potentials more negative than -0.7 V vs. RHE, increasing the CO faradaic efficiency (FE) by 33 % (relative). In situ surface-enhanced Raman spectroscopy (SERS) measurements reveal the absence of near-surface bicarbonate species and an abundance of CO2 reduction intermediates at the Ag|TiO2 buried interface, suggesting that the overlayers suppress HER by blocking bicarbonate ions from reaching the buried active sites. In accelerated degradation tests with 5 ppm of Fe(III) impurity, the addition of EDTA allows stable CO production with >47 % FE, while the electrodes rapidly deactivate in the absence of EDTA. This work highlights the use of TiO2 overlayers for enhancing the CO : H2 ratio while simultaneously protecting electrocatalysts from impurities likely to be present in "open" carbon capture systems.

Sensitive Determination of Alkali Metals by Liquid Anode Glow Discharge-Atomic Emission Spectrometry (LAGD-AES)

Liquid anode glow discharge-atomic emission spectrometry (LAGD-AES) was employed for the determination of alkali metals in brine and bottled drinking water samples. The results demonstrated that the optimum operating conditions are a discharge voltage of 630 V, a flow rate of 2.0 mL min−1, a supporting electrolyte solution of pH 1.7 HNO3, and a discharge gap of 0.5 mm. Alkaline-earth ions (e.g., Ca2+, Mg2+, and Sr2+) and Cr3+ interfere with the determination of alkali metals. The limits of detection (LODs) for the alkali metals, namely cesium (Cs), potassium (K), lithium (Li), sodium (Na), and rubidium (Rb) are 135, 6.21, 3.15, 7.57, and 31.1 µg L−1, respectively. The relative standard deviations are less than 5%, and the power consumption is approximately 13 W. The obtained results are in good agreement with the certified standard value for Li in the certified reference material and are consistent with the values obtained by ICP-OES and reference standards for K and Na in real samples. The concentrations of the Cs and Rb are considerably below the LAGD-AES detection limit. Consequently, they can be considered negligible. The results of the spiked water analysis are broadly consistent with the spiked values, with recoveries from 82% to 112%. LAGD-AES is an excellent technique for the sensitive determination of alkali metals due to its compact design, no requirement for inert gas, and low energy consumption.

A holistic insight on stability and transport of hematite colloid: Role of various environmental factors

Hematite colloids (Hem) could carry pollutants into deep underground environments and its potential ecological risk needs to be evaluated. This study investigated the aggregation and transport behavior of Hem under different solution pH, electrolyte concentration and humic acid (HA) concentration. Rising the electrolyte concentration would shrink the double electric layer of Hem, weaken the electrostatic repulsion and promote the aggregation of Hem. The critical coagulation concentration (CCC) of Hem was higher at pH 5 (48.83 mM) than pH 10 (24.70 mM), implying that Hem were more stable under acidic conditions than under alkaline conditions. The addition of HA increased the negative charge of Hem and improved the electrostatic repulsion between colloid and sand surface, thus intensifying the stability and mobility of Hem. High HA concentration (≥ 0.5 mg/L) had little effect on the surface charge of Hem, indicating that electrostatic repulsion was not the dominant, however increasing HA significantly improve the stability and transport of Hem by stimulating the steric hindrance interaction. The effect of HA on the transport of Hem under acidic condition was significantly higher than that under alkaline condition because HA changed the surface charge of Hem from positive to negative under acidic condition, so that the electrostatic repulsion between the colloid and sand surface increased sharply and accompanied by a significant penetration. This study exhibited a holistic view on the aggregation and transport behavior of Hem in typical soil environment, and extended the understanding of co-transport potential mechanisms of colloids with contaminants and/or nutrients.

60 Years of Betaine 30─From Solvatochromic Discovery to Future Frontiers.

Betaine-30 (B30) was reported by Karl Dimroth and Christian Reichardt et al. in 1963 as a solvatochromic probe that can be easily synthesized, shows good solubility, and remains stable in various organic solvents and solutions. Its strongly negatively solvatochromic behavior arises from differential solvation between its electronic ground and excited states, making it a valuable tool for assessing solvent polarity using the ET(30) polarity scale, also devised by Dimroth and Reichardt. In addition, advancements in femtosecond laser spectroscopy in the 1990s greatly improved the understanding of B30's relaxation dynamics following photoexcitation. In solvents capable of hydrogen bonding, such as alcohols, intermolecular hydrogen-bond rearrangement contributes to the multiple relaxation components observed. Since the 1990s, the applications of B30 have expanded beyond simple organic solvents to include complex solvent mixtures, such as electrolyte solutions for battery technologies and eutectic solvent mixtures. Given the growing importance of these complex solvent mixtures, B30 is becoming an increasingly valuable tool for studying previously unexplored solvation properties.

Liquid‐Solid Combination Memristors with Switchable Resistance

AbstractHere a reconfigurable memristor is demonstrated by connecting ZnO film to a fluidic channel. The memristive characteristics are successfully demonstrated with an electrolyte solution. The benefit of using a microfluidic channel is that the memristive characteristics can be adjusted by changing the electrolyte solution in real‐time. The neuromorphic functions such as long‐term plasticity, Spiking‐Rate‐Dependent Plasticity (SRDP), and behavior associated with “learning experiences”are demostrated in the devices. The capability of real‐time manipulating of memristive characteristics enables diverse manipulations on memristive characteristics of the devices, by doping of different concentrated and type of ions in the ZnO film. The electrolyte solution will open new possibilities for resistance switch manipulations, for the next generation neuromorphic computing.

Accelerating QM/MM simulations of electrochemical interfaces through machine learning of electronic charge densities.

A crucial aspect in the simulation of electrochemical interfaces consists in treating the distribution of electronic charge of electrode materials that are put in contact with an electrolyte solution. Recently, it has been shown how a machine-learning method that specifically targets the electronic charge density, also known as SALTED, can be used to predict the long-range response of metal electrodes in model electrochemical cells. In this work, we provide a full integration of SALTED with MetalWalls, a program for performing classical simulations of electrochemical systems. We do so by deriving a spherical harmonics extension of the Ewald summation method, which allows us to efficiently compute the electric field originated by the predicted electrode charge distribution. We show how to use this method to drive the molecular dynamics of an aqueous electrolyte solution under the quantum electric field of a gold electrode, which is matched to the accuracy of density-functional theory. Notably, we find that the resulting atomic forces present a small error of the order of 1 meV/Å, demonstrating the great effectiveness of adopting an electron-density path in predicting the electrostatics of the system. Upon running the data-driven dynamics over about 3ns, we observe qualitative differences in the interfacial distribution of the electrolyte with respect to the results of a classical simulation. By greatly accelerating quantum-mechanics/molecular-mechanics approaches applied to electrochemical systems, our method opens the door to nanosecond timescales in the accurate atomistic description of the electrical double layer.