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DOE OSTI2026

Fabrication of Catalytic Distillation Membranes with Atomic Layer Deposition

The integration of catalysts onto the surface of membranes enables simultaneous physical separation and catalytic transformation of constituents in a feed stream, facilitating improved contaminant removal and fouling mitigation. Distillation membranes are a particularly attractive platform for catalytic membranes because they reject nonvolatile species and exhibit exceptional resistance to oxidative and radical-driven degradation. However, imparting catalytic functionality onto hydrophobic, porous distillation membranes has proven challenging since the membranes used are chemically inert and difficult to modify. Furthermore, catalysts on the membrane surface can decrease hydrophobicity and increase the membrane’s susceptibility to pore wetting and failure. In this work, we create a catalytic distillation membrane by coating a polytetrafluoroethylene membrane surface with titanium dioxide (TiO 2 ) via plasma-assisted atomic layer deposition (ALD). By precisely tuning the ALD parameters, we demonstrate localized growth of TiO 2 near (within approximately 1 μm) the surface of polytetrafluoroethylene membranes, forming a catalytically active interface while preserving the underlying hydrophobic pore structure. Localized growth of TiO 2 is confirmed by electron microscopy and spectroscopy techniques, and membranes coated with 500 cycles of ALD show pressure tolerance up to 12.8 bar and higher than 95% salt rejection in pressure-driven distillation. Photocatalytic activity is demonstrated via the degradation of methylene blue dye under UV irradiation, where increasing TiO2 loading leads to an enhancement in dye degradation. These results establish a general strategy for integrating catalytic functionality into chemically inert, hydrophobic membranes without compromising distillation performance, providing a pathway toward multifunctional membranes that couple advanced oxidation with membrane separation for water treatment.

atomic layer deposition↗

DOE OSTI2020

Machine Learning Algorithm Identifies an Antibiotic Vocabulary for Permeating Gram-Negative Bacteria

Drug discovery faces a crisis. The industry has used up the “obvious” space in which to find novel drugs for biomedical applications, and productivity is declining. One strategy to combat this is rational approaches to expand the search space without relying on chemical intuition, to avoid rediscovery of similar spaces. Here, we present proof of concept of an approach to rationally identify a “chemical vocabulary” related to a specific drug activity of interest without employing known rules. We focus on the pressing concern of multidrug resistance in Pseudomonas aeruginosa by searching for submolecules that promote compound entry into this bacterium. By synergizing theory, computation, and experiment, we validate our approach, explain the molecular mechanism behind identified fragments promoting compound entry, and select candidate compounds from an external library that display good permeation ability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Tuning Fabrication Factors for Reduced Graphene Oxide Forward Osmosis Membranes

Forward osmosis (FO) may serve as a near-zero energy approach for wastewater management and selective chemical enrichment with an appropriate FO membrane. There is a need for novel FO membranes with better physical stability, chemical compatibility, and enhanced reverse flux selectivity. In this work, we have systematically studied a variety of factors for fabricating thermally reduced graphene oxide (RGO) FO filtration membranes and have demonstrated that with a comparable water flux, the RGO membranes have an exceptionally large reverse flux selectivity with 1.5 M sodium sulfate draw solution, about 7 times larger than that of cellulose triacetate membranes under the same testing condition. The interlayer spacing of the membranes can be fine-tuned by varying temperatures, so that the free interlayer spacing is less than 0.7 nm after exposure to water. The RGO-based membranes offer a few advantages with high reverse flux selectivity, mechanical robustness with strong adhesion to nylong support membranes without damage after FO tests and tape peel tests, and enhanced chromate and chlorine resistance. Finally, we have further demonstrated that in the FO processes, one can concentrate waste brine while simultaneously harvesting the osmotic energy as electricity, offering potential applications of forward osmosis-based osmotic batteries for powering electronic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Freestanding SrNbO 3 membranes as flexible transparent conductors

Synthesizing flexible transparent conducting materials is important for applications in flexible optoelectronics. Metallic oxide membranes offer great promise due to their large elasticity and high transparency. Among them, SrNbO 3 , a correlated metal, stands out as a promise transparent conducting oxide. However, synthesizing freestanding SrNbO 3 membranes poses a challenge because it easily undergoes oxidation, resulting in degraded conductivity. To address this, we utilize epitaxial BaTiO 3 capping layers, which effectively prevents SrNbO 3 oxidation. We successfully fabricate millimeter-sized transparent conducting BaTiO 3 /SrNbO 3 /BaTiO 3 membranes using water-soluble sacrificial layers. The obtained SrNbO 3 (10 nm thick) membrane exhibits a room temperature sheet resistance (R S ) of 174 Ω/sq and a transmittance (T) of 92% at a wavelength of 550 nm. The figure of merit (T 10 /R S ) of this transparent conductor reaches 2.2 × 10 −3 Ω −1 in the visible regime, comparable to SrNbO 3 films on rigid substrates. These results open possibilities for applications as flexible transparent conductors.

Ko, Eun Kyo [SLAC National Accelerator Laboratory ↗

DOE OSTI2021

Xylem network connectivity and embolism spread in grapevine( Vitis vinifera L.)

Abstract Xylem networks are vulnerable to the formation and spread of gas embolisms that reduce water transport. Embolisms spread through interconduit pits, but the three-dimensional (3D) complexity and scale of xylem networks means that the functional implications of intervessel connections are not well understood. Here, xylem networks of grapevine (Vitis vinifera L.) were reconstructed from 3D high-resolution X-ray micro-computed tomography (microCT) images. Xylem network performance was then modeled to simulate loss of hydraulic conductivity under increasingly negative xylem sap pressure simulating drought stress conditions. We also considered the sensitivity of xylem network performance to changes in key network parameters. We found that the mean pit area per intervessel connection was constant across 10 networks from three, 1.5-m stem segments, but short (0.5 cm) segments fail to capture complete network connectivity. Simulations showed that network organization imparted additional resistance to embolism spread beyond the air-seeding threshold of pit membranes. Xylem network vulnerability to embolism spread was most sensitive to variation in the number and location of vessels that were initially embolized and pit membrane vulnerability. Our results show that xylem network organization can increase stem resistance to embolism spread by 40% (0.66 MPa) and challenge the notion that a single embolism can spread rapidly throughout an entire xylem network.

Wason, Jay↗

DOE OSTI2024

A High-Ceramic-Loading LATP–PVDF–Al 2 O 3 Composite Film for Lithium-Ion Batteries With Favorable Porous Microstructure and Enhanced Thermal Stability

A separator plays a crucial role in a Li-ion battery to carry liquid electrolytes while preventing short-circuiting between electrodes. Nevertheless, conventional commercial separators often exhibit poor wettability and are prone to shrink at elevated temperatures due to their limited thermal stability. Herein, we report a heat-resistant LATP–PVDF–Al 2 O 3 composite film with outstanding wetting performance. The thin film was prepared using ball mill mixing and tape-casting processes. Two solvents, NMP and glycerol, were applied to prepare the slurry, and a favorable microstructure in the film was created after drying. Here, the ionic conductivity of the film was tested at 1.39 mS cm –1 when paired with liquid electrolyte, almost double that of the commercial counterpart. The high ceramic loading of 70% improved both the thermal shrinkage resistance and dendrite inhibition of the membrane. When assembled in an NMC half-cell, the cycling capacity retentions of 92.8% and 92.1% are achieved after 50 cycles at 0.5 C and 1 C, demonstrating its capability to be used in Li-ion batteries.

25 ENERGY STORAGE↗

DOE OSTI2024

Saccharomyces cerevisiae CellWall Remodeling in the Absence of Knr4 and Kre6 Revealed by Nano-FourierTransform Infrared Spectroscopy

The cell wall integrity (CWI) signaling pathway regulates yeast cell wall biosynthesis, cell division, and responses to external stress. The cell wall, comprised of a dense network of chitin, β-1,3- and β-1,6- glucans, and mannoproteins, is very thin, <100 nm. Alterations in cell wall composition may activate the CWI pathway. Saccharomyces cerevisiae, a model yeast, was used to study the role of individual wall components in altering the structure and biophysical properties of the yeast cell wall. Near-field Fourier transform infrared spectroscopy (nano-FT-IR) was used for the first direct, spectrochemical identification of cell wall composition in a background (wild-type) strain and two deletion mutants from the yeast knock-out collection: kre6Δ and knr4Δ. Killer toxin resistant 6 (Kre6) is an integral membrane protein required for biosynthesis of β-1,6-glucan, while Knr4 is a cell signaling protein involved in the control of cell wall biosynthesis, in particular, biosynthesis and deposition of chitin. Complementary spectral data were obtained with far-field (FF)-FT-IR, in transmission, and with attenuated total reflectance (ATR) spectromicroscopy with 3 –10 μm wavelength-dependent spatial resolution. The FF-FT-IR spectra of cells and spectra of isolated cell wall components showed that components of the cell body dominated transmission spectra and were still evident in ATR spectra. In contrast, the nano-FT-IR at ~25 nm spatial resolution could be used to characterize the yeast wall chemical structure. Our results show that the β-1,6-glucan content is decreased in kre6Δ, while all glucan content is decreased in the knr4Δ cell wall. The latter may be thinner than in wild type, since not only are mannan and chitin detectable by nano-FT-IR, but also lipid membranes and protein, indicative of cell interior.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2020

High Performing and Durable Pyrophosphate Based Composite Membranes for Intermediate Temperature Fuel Cells [Slides]

Objective: Develop a novel proton conducting electrolyte operating at >200°C with conductivity σ ≥ 100 mScm –1 and RH < 1%. Fabrication of membranes of less than 40μm thickness while retaining high conductivity will result in ASR <0.04 Ωcm 2 . Evaluate membrane durability in terms of crossover, shorting resistance, and open circuit voltage, as well as against temperature cycling. Relevance: Operating FCs in the intermediate temperature range has the potential to greatly reduce cost and simplify water and thermal management. This effort requires novel materials and approaches to meet DOE membrane performance and durability targets. MPP/Polymer composite membranes show promise in early development for application in IT-FCs for transportation applications. Approach: We have demonstrated that both cation dopants and phosphate precursor influence MPP conductivity and identified the most promising MPP compositions for membrane fabrication. The ceramic MPP materials are fabricated as a composite membrane in a 90:10 wt% ratio with Nafion. We have modified our membrane fabrication procedure to improve the density of our membranes. Accomplishments: We demonstrated through-plane membrane conductivity of 95mScm -1 at T > 200°C and RH<0.04bar with a thickness 50μm. We demonstrated FC performance up to 94hrs at 220°C and <1% RH with a 50μm thick membrane exhibiting an OCV of 0.98V and ASR of 0.08 Wcm 2 . Future work: Further decrease in ASR is expected by decreasing the membrane thickness to <40μm. ITPP with higher P:M ratio will be used to increase the conductivity of the starting material. Long term durability will be assessed against DOE technical targets

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2020

Carbon Nanotube Formation on Cr-Doped Ferrite Catalyst during Water Gas Shift Membrane Reaction: Mechanistic Implications and Extended Studies on Dry Gas Conversions

A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H2 and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H2-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further demonstrated in the synthesis of highly crystalline and dimensionally uniform MWCNTs from a dry gas mixture of CO and CH4, which were the apparent sources for MWCNT growth in the WGS MR. In both the WGS MR and dry gas reactions, the operating temperature was 500 °C, which is significantly lower than those commonly used in MWCNT production by chemical vapor deposition (CVD) method from CO, CH4, or any other precursor gases. Extensive ex situ characterizations of the reaction products revealed that the FeCr catalyst remained in partially reduced states of Fe3+/Fe2+ and Cr6+/Cr3+ in WGS membrane reaction while further reduction of Fe2+ to Fe0 occurred in the CO/CH4 dry gas environments. The formation of the metallic Fe nanoparticles or catalyst surface dramatically improved the crystallinity and dimensional uniformity of the MWCNTs from dry gas reaction as compared to that from WGS reaction in the MR. Reaction of the CO/CH4 mixture containing 500 ppmv H2S also resulted in high-quality MWCNTs similar to those from the H2S-free feed gas, demonstrating excellent sulfur tolerance of the FeCr catalyst that is practically meaningful for utilization of biogas and cheap coal-derived syngas.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Hydrocarbon-based membranes cost-effectively manage species transport and increase performance in thermally regenerative batteries

Low-temperature heat (T<130°C) can be utilized by thermally regenerative batteries (TRBs) for power production, allowing the thermal energy to be converted to storable chemical potential energy. However, TRBs suffer from high ohmic losses and ammonia crossover, which has slowed their development. In this study, we examined how the use of six different membranes influenced TRB performance, determined the most influential membrane parameters, and identified promising membrane candidates that cost-effectively increase TRB performance. Of the six membranes examined, an inexpensive, hydrocarbon CEM (Selemion CMVN) had low ammonia crossover without compromising resistance, resulting in good performance across all metrics studied. A thin anion exchange membrane (Sustainion, 50 microns) showed a high peak power density of 82 mW cm –2 due to low resistance, but the average power density and energy density were low due to high ammonia flux. Full discharge curves using Selemion CMVN provided an average power density of 26 ± 7 mW cm –2 with an energy density of 2.9 Wh L –1 , which were large improvements on previous TRBs. A techno-economic analysis showed that Selemion CMVN had the lowest levelized cost of storage ($410 per MWh) at an applied current density of 50 mA cm –2 .

25 ENERGY STORAGE↗

DOE OSTI2024

A lyotropic liquid crystal-templated nanofiltration membrane with thermo- and pH-responsive 3D transport pathway

We produce controlled nanostructured membranes from cross-linking of self-assembled diacrylated poloxamers. At sufficiently high concentrations, poloxamers form lyotropic liquid crystals (LLCs), such as lamellar (L α ), cubic packing of spherical micelles, and hexagonal packing of rod-like micelles in water (H 1 ). We use the H 1 phase as a template to produce orderly packed nanofibrous membranes. The obtained membrane has a continuous 3D transport pathway and can alter its nanofiltration (NF) properties in response to changes in temperature and pH. The formulation includes Pluronic P84-diacrylate (P84DA), a thermoresponsive component that acts as both macromer and structure-directing amphiphile. P84DA facilitates changes in membrane pore size with temperature due to its thermoresponsiveness when it is in contact with water. Furthermore, the precursor contains acrylic acid (AAc) as the charged component, which upon copolymerization with P84DA, not only enables ion separation through Donnan exclusion but also imparts pH-responsive behavior for the separation of ionic species. The membrane performance is studied and compared with a commercial NF membrane (NF270). We show that the synthesized NF membrane has separation properties adjustable with temperature and pH with exceptional resistance to fouling by various solutes due to its highly hydrophilic surface. Furthermore, the membrane shows an outstanding sulfate over chloride ion selectivity, which is a requirement for salt fractionation applications. Deducted from separate experiments, the ideal chloride/sulfate selectivity for magnesium cation is about 2.38 at low ionic strengths. This study is done on a model system to show the capability of incorporating pH-responsiveness in LLC templated membranes, in which the pH-responsive range can be designed by changing the charged groups of comonomer in the formulation.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Self-assembled nanofiltration membranes with thermo- and pH-responsive behavior

36 MATERIALS SCIENCE↗

DOE OSTI2023

Fast Water Transport through Subnanometer Diameter Vertically Aligned Carbon Nanotube Membranes

Small-diameter carbon nanotubes (CNTs) have outstanding mass-transport properties, especially enhanced water flow. Here, we report on water transport through the first macroscopic membranes with vertically oriented, subnanometer (0.8 nm) CNT pores, made by a scalable, solution-based method with electric-field alignment of bulk-grown single-wall CNTs (SWCNTs). After plasma etching to open pores, vertically aligned CNTs served as the primary pathway for liquid-water transport. The CNT membranes showed fast pressure-driven water transport, with up to 105-fold enhancement compared to no-slip Hagen–Poiseuille flow. Comparing 0.8 and 3 nm CNTs, we found that the hydrodynamic slip lengths increased with decreasing nanotube diameter, reaching 8.5 μm for the smaller-diameter CNTs. Here, the results suggest that pressure-driven water transport in small-diameter CNTs is increasingly dominated by entrance resistance, thus becoming independent of nanotube length. Scalably fabricated membranes incorporating vertically aligned subnanometer CNT pores could have applications in water filtration, desalination, and energy harvesting.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2020

Fabrication of high-performance gas-diffusion-electrode based membrane-electrode assemblies

This paper demonstrates the fabrication and processing steps required to produce high performance fuel cell membrane electrode assemblies (MEAs) based on spray-coated gas-diffusion electrodes (GDEs). It is demonstrated that coating the catalyst layer with a thin layer of ionomer and then hot pressing the GDEs to the membrane is required to achieve comparable catalyst activity and air performance to catalyst-coated-membrane MEAs. We show that there is a critical amount of ionomer required to achieve maximized performance. Using electron microscopy, we show that the combination of the ionomer overlayer and hot-pressing bonds the catalyst layer to the membrane, increasing the interfacial contact area and quality of this interface. We also find that the ionomer overlayer smooths the surface of the GDE and provides increased contact area between the GDE and the membrane. Additionally, we demonstrate that much less ionomer is required for high-performance than has been previously reported. Through model fitting of electrochemical impedance spectroscopy, we show that this improvement in the catalyst layer - membrane interface reduces the effective catalyst layer resistance, which reduces Ohmic losses and increases catalyst utilization.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2025

The Effects of Morphology and Hydration on Anion Transport in Self-Assembled Nanoporous Membranes

Ordered nanoporous polymer membranes offer opportunities for systematically probing the mechanisms of ion transport under confinement and for realizing useful materials for electrochemical devices. Here, we examine the impact of morphology and ion hydration on the transport of hydroxide and bromide anions in nanostructured polymer membranes with 1 nm scale pores. We use aqueous lyotropic self-assembly of an amphiphilic monomer, with a polymerizable surfactant to create direct hexagonal (H I ) and gyroid mesophases. UV-induced cross-linking leads to the formation of nanoporous polymers with water continuous channels. The membranes are mechanically robust and chemically durable, resisting degradation during extended exposure to 1 M NaOH solutions. We use a combination of electrochemical impedance spectroscopy, pulsed-field gradient NMR spectroscopy, and molecular simulations to elucidate anion and water transport. The as-prepared hexagonal systems display higher conductivity and lower activation energies for both anions relative to the gyroid system. When compared at equivalent hydration, however, gyroid and hexagonal membranes show similar activation energies, with nearly identical conductivities at ambient temperatures. Both ionic conductivity and water diffusivity increase with increasing hydration. Here, the water uptake as a function of relative humidity for the hexagonal and gyroid mesophases ultimately dictates the water diffusion and magnitude of the ionic conductivity, with the hexagonal system showing overall higher capacity for hydration and thus faster ion transport. The durability of these materials under aggressive alkaline conditions and their relatively high hydroxide ion conductivity suggest that these nanostructured polymers could be of interest as membranes for alkaline fuel cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Scaling of ionic conductance in a fluctuating single-layer nanoporous membrane

Abstract Single-layer membranes have emerged as promising candidates for applications requiring high transport rates due to their low resistance to molecular transport. Owing to their atomically thin structure, these membranes experience significant microscopic fluctuations, emphasizing the need to explore their impact on ion transport processes. In this study, we investigate the effects of membrane fluctuations on the elementary scaling behavior of ion conductance $$G$$ G as a function of ion concentration $$c_{0}$$ c 0 , represented as $$G = \beta c_{0}^{\alpha }$$ G = β c 0 α , using molecular dynamics simulations. Our findings reveal that membrane fluctuations not only alter the conductance coefficient $$\beta$$ β but also the power-law exponent $$\alpha$$ α . We identify two distinct frequency regimes of membrane fluctuations, GHz-scale and THz-scale fluctuations, and examine their roles in conductance scaling. Furthermore, we demonstrate that the alteration of conductance scaling arises from the non-linearity between ion conductance and membrane shape. This work provides a fundamental understanding of ion transport in fluctuating membranes.

42 ENGINEERING↗

DOE OSTI2025

Mineral Scale Formation during Crossflow Reverse Osmosis at Constant Flux and Constant Transmembrane Pressure Conditions

Mineral scale formation on membrane surfaces is a significant challenge in reverse osmosis water purification. Laboratory fouling experiments are typically run such that the transmembrane pressure (TMP) is fixed, and the permeate flux decreases over time as scales accumulate on the membrane surface. However, this change in flux means that the hydrodynamic conditions at the membrane surface are continuously changing, which could affect crystallization and foulant deposition processes. Operating under constant permeate flux conditions, in contrast, is advantageous because it keeps the hydrodynamic conditions relatively consistent, making it possible to compare how membrane properties (e.g., surface chemistry) affect fouling propensity. Industrial reverse osmosis operations are not run strictly in either constant TMP or constant flux mode; while they may start at a constant TMP, feed pressure may be periodically adjusted to maintain permeate water production within a specified range. Here, the scarcity of constant permeate flux reverse osmosis scaling experiments reported in the literature frustrates efforts to compare membrane fouling processes under constant TMP and constant flux conditions. For the first time, the evolution of the fouling layer resistance was compared as a function of cumulative permeate volume per membrane area during constant TMP and constant flux reverse osmosis filtrations. Scaling experiments were conducted by challenging commercial reverse osmosis membranes with a model feed solution nearly saturated with calcium sulfate dihydrate (gypsum). At low fluxes, the increase in fouling layer resistance was quantitatively similar for the two operational modes. In contrast, at high fluxes, the fouling layer resistance increased more rapidly in constant flux filtration than in constant TMP filtration. The mechanism of scale formation in constant TMP and constant flux operation was self-limiting and self-reinforcing, respectively.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Effect of electrode rinse solutions on the electrodialysis of concentrated salts

The data presented indicate that modest attention to the chemistry of the electrode rinse solution can yield as much as 56% improvement in process efficiency. When operating electrodialysis (ED) with salt concentrations greater than 10,000 mg/l (as NaCl) the amperage can be relatively high even at low voltages. To maximize the overall rate of ion transport from diluate to concentrate, there is a need to minimize resistances in the electrode cells since these can represent as much as 30% of the total resistances in the entire process and in this particular ED unit, represented resistance roughly equivalent to that within the membrane stack. This work describes the performance of a 10-cell pair, 200 cm 2 (0.02 m 2 ) per membrane, pilot ED unit operated in batch mode at 5 V potential. The feedstock to the stack was varied from 0.5% to 6% NaCl. Results from Volt-amp profiles (2.0–15 V) were used as the rationale for choosing the preferred electrode rinse solution, 90 g/l (kg/m 3 ) disodium sulfate at pH 12.5. The recommended solution of 30 g/l (kg/m 3 ) disodium sulfate at neutral pH was tested against stronger solutions (60, 90, and 120 g/l (kg/m 3 ) disodium sulfate) at neutral pH and with 1 g/l (kg/m 3 ) sodium hydroxide added to yield solutions at pH 12.5. There were stark differences in the performance of the ED unit between the solutions at pH 7 and those at pH 12.5. The slopes of the Volt-amp profiles improved indicating less resistance to ion flow at pH 12.5. Most of the difference can be attributed to the greater conductivity of sodium hydroxide compared to disodium sulfate, where even a modest addition of 1 g/l (kg/m 3 ) sodium hydroxide increased the conductivity of the solution between 8 and 20% depending on the concentration of disodium sulfate. Most notably, the initiation voltage was 2.39 ± 0.08 V with solutions at pH 7 and 1.99 V ± 0.04 V when the rinse solutions were around pH 12.5, a difference of around 0.42 V. Since the full batch runs were performed at 5.0 V, this 0.42 V differential represented a loss of 8% in process efficiency. A series of tests showed a shift in initiation voltage occurred between pH 11.5 and 12.5. Nernst equations for water electrolysis are coupled with a simple flux model that estimates the concentration of hydroxide and hydronium ions at the electrode surfaces. This model indicates that the potential demanded by the electrodes is directly linked to the current. Furthermore, there is a steep drop in the potential demanded by the anode when there is sufficient hydroxide available to generate oxygen from hydroxide as opposed to generation from water. The voltage demand is minimal at pH 12.5 and reflective of the reference standard voltage (just over 1.23 V predicted at 0.1 amps). However, the flux model predicts that the voltage demanded by the electrodes at pH 7 is 1.61 V at 0.1 amps (the lowest amperage measurable with the power pack). In conclusion, comparing this result to the reference standard (E 0 = -1.23 V) yields a satisfactory explanation for the observed difference below reference standard of 0.42 V.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗