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Methods of predicting mineral scale formation have evolved over the years from simple empirical fittings to sophisticated computational programs. Though best practices can now solve complex multi-phase, multi-component systems, they are largely restricted to temperatures below 300 °C. This review examines critical gaps in existing mineral scale modeling approaches as well as strategies to overcome them. Above 300 °C, the most widely used model of standard thermodynamic functions for aqueous species fails when fluid densities are below 0.7 g cm−3. This failure occurs due to the model’s reliance on an empirical form of the Born equation which is unable to capture the trends observed in these high temperature, low density regimes. However, new models based on molecular solvent-solute interactions offer a pathway to overcome some of the deficiencies currently limiting high-temperature and high-pressure mineral scale predictions. Examples of the most common scale prediction methods are presented, and their advantages and disadvantages are discussed.

In this study, we explored the extent to which hydrotropes can be used to increase the aqueous solubilities of redox-active compounds previously used in flow batteries. We measured how five hydrotropes influenced the solubilities of five redox-active compounds already soluble in aqueous electrolytes (≥0.5 M). The solubilities of the compounds varied as a function of hydrotrope type and concentration, with larger solubility changes observed at higher hydrotrope concentrations. 4-OH-TEMPO underwent the largest solubility increase (1.18 ± 0.04 to 1.99 ± 0.12 M) in 20 weight percent sodium xylene sulfonate. The presence of a hydrotrope in solution decreased the diffusion coefficients of 4-OH-TEMPO and 4,5-dihydroxy-1,3-benzenedisulfonate, which was likely due to the increased solution viscosity as opposed to a specific hydrotrope-solute interaction because the hydrotropes did not alter their molecules' hydraulic radii. The standard rate constants and formal potentials of both 4-OH-TEMPO and 4,5-dihydroxy-1,3-benzenedisulfonate remained largely unchanged in the presence of a hydrotrope. The results suggest that using hydrotropes may be a feasible strategy for increasing the solubilities of redox-active compounds in aqueous flow batteries without substantially altering their electrochemical properties.

Prussian blue analogues are used in electrochemical deionization due to their cation sorption capabilities and ion selectivity properties. Elucidating the fundamental mechanisms underlying intercalation/deintercalation is important for the development of ion-selective electrodes. We examined the thermodynamic and kinetic properties of nickel hexacyanoferrate electrodes by studying different temperatures effects on intercalation/deintercalation with monovalent ions (Li

This paper will report on a new membrane-based electrochemical sensor that may provide an important utility in monitoring and characterizing internal corrosion of natural gas pipelines. Using this sensor, the corrosion rate of X65 steel exposed to H2S in humidified environments up to 60°C has been measured. Consistent with the authors’ earlier CO2 study, the membrane’s conductivity did not change when exposed to H2S-containing acidic gas. Introducing H2S consistently increased the measured corrosion rate between testing conditions, though corrosion rates were typically less than 2 μm/y. At 30°C, the corrosion rate doubled from 7.3 nm/y to 14 nm/y below a relative humidity of 30%, and it increased by an order of magnitude (0.19 μm/y to 1.9 μm/y) at 55% relative humidity, showing that the influence of H2S on corrosion increases dramatically with greater humidity. Trends with relative humidity match industry expectations: the corrosion rate is low (

Saline water represents an inexhaustible source of water for hydrogen production from electrolysis. However, direct saltwater splitting faces challenges due to chlorine evolution at the anode and the development of Nernst overpotential due to sodium ion transport competition with protons across the membrane. A new approach to minimize chlorine evolution and improve performance is proposed here by using a humidified gas stream (no liquid electrolyte) for the anode and a liquid saltwater catholyte. Charge repulsion of chloride ions by the proton exchange membrane (PEM) resulted in low chlorine generation, with anodic faradaic efficiencies for oxygen evolution of 100 ± 1% with a synthetic brackish water (50 mM NaCl, 3 g L−1) and 96 ± 2% with synthetic seawater (0.5 M NaCl, 30 g L−1). The enhanced proton transport by the electric field enabled more efficient pH control across the cell, minimizing sodium ion transport in the absence of a liquid anolyte. The vapor-fed anode configuration showed similar performance to a conventional PEM electrolyzer up to 1 A cm−2 when both anode and cathode were fed with deionized water. Much lower overpotentials could be achieved using the vapor-fed anode compared to a liquid-anolyte due to the reduced sodium ion transport through the membranes, as shown by adding NaClO4 to the electrolytes. This vapor-fed anode configuration allows for direct use of saltwater in conventional electrolyzers without additional water purification at high faradaic efficiencies.

The decreasing cost of electricity produced using solar and wind and the need to avoid CO2 emissions from fossil fuels has heightened interest in hydrogen gas production by water electrolysis. Offshore and coastal hydrogen gas production using seawater and renewable electricity is of particular interest, but it is currently economically infeasible due to the high costs of ion exchange membranes and the need to desalinate seawater in existing electrolyzer designs. A new approach is described here that uses relatively inexpensive commercially available membranes developed for reverse osmosis (RO) to selectively transport favorable ions. In an applied electric field, RO membranes have a substantial capacity for proton and hydroxide transport through the active layer while excluding salt anions and cations. A perchlorate salt was used to provide an inert and contained anolyte, with charge balanced by proton and hydroxide ion flow across the RO membrane. Synthetic seawater (NaCl) was used as the catholyte, where it provided continuous hydrogen gas evolution. The RO membrane resistance was 21.7 ± 3.5 Ω cm2 in 1 M NaCl and the voltages needed to split water in a model electrolysis cell at current densities of 10–40 mA cm−2 were comparable to those found when using two commonly used, more expensive ion exchange membranes.

Increasing interest in spectroelectrochemisty due to its versatility and far-reaching applications has led to its rapid growth in recent years. Attenuated total reflectance (ATR), Fourier transform infrared spectroscopy (FTIR) is one technique that can provide valuable insights into surface interactions provided a viable working electrode can be fabricated. Though ATR working electrodes can be deposited using a range of techniques such as argon sputtering, vapor deposition and electrodeposition, published studies typically do not report electrode thicknesses which are a key in obtaining repeatable signal responses. Here we examine different approaches to quantify ATR electrode thicknesses and screen for optimal electrode configurations. The test system used to assess different approaches for validating electrode performance was the ferri-ferrocyanide redox reaction with an argon sputtered platinum surface. It was found that atomic force microscopy, ellipsometry and optical profilometry had practical limitations operating in the nanometer range and were not adequate for predicting spectroscopic outcomes. In contrast, electrochemical impedance spectroscopy (EIS) measurements accurately predicted high performing ATR working electrodes. For an 11 mm by 9 mm ATR wafer, favorable signal strengths corresponded to cell impedances greater than 500 Ω. Cell constant calculations determined that platinum thickness layers needed to be less than 4 nm to provide consistent spectroelectrochemical responses.

Efforts to reduce the cost of long-duration energy storage systems have drawn increased interest in all-iron redox flow battery systems due to their inexpensive electrolytes. Previous studies have shown that the kinetics of the positive electrode for the Fe(II, III) reaction in these systems are sluggish on carbon surfaces and require significant overpotentials. Here, we identify how changes to the electrode surface and electrolyte composition can influence the electrochemical rate constants to reduce required overpotentials using a rotating disc electrode (RDE) assembly. The impacts of solution composition in terms of pH, chloride content, and cation species were investigated using a range of electrolyte compositions reported for all-iron flow battery systems. The electrode materials studied were glassy carbon, pyrolytic graphite basal plane, and pyrolytic graphite edge plane. Untreated and electrochemically oxidized electrode materials were quantified using X-ray photoelectron spectroscopy (XPS), and the reaction rate constants were quantified using electron impedance spectroscopy (EIS). Rate constants of the Fe(II, III) reaction on untreated electrode materials were largest on platinum and lowest on glassy carbon with pyrolytic materials providing comparable results. For the materials examined, increases electrolyte chloride content generally decreased the obtained rate constant.

Greenhouse gas emissions produced during electricity generation can be reduced by increasing the energy efficiency of power generation systems. One approach to increase generation efficiency is by extracting additional electrical energy from low-grade waste heat (< 100 °C) using thermally regenerative redox flow batteries (TRABs). TRAB chemistries with the largest equilibrium potentials use two different active metals and are referred to as bimetallic TRABs (B-TRAB). In most designs, copper is the positive electrode and zinc is the negative electrode. Using thermal energy, ammonia is moved between battery electrolytes to favorably modify the cell potential of the two electrochemical steps within the cycle. A typical B-TRAB system has four steps to complete a full cycle: 1) high-voltage electrochemical discharge, 2) thermal ammonia separation, 3) low-voltage electrochemical charge, and 4) thermal ammonia separation. During step 1, copper is reduced at the positive electrode and zinc is oxidized at the negative electrode creating aqueous zinc-ammonia complexes. Next, ammonia is separated from the zinc complexes and introduced to the copper electrode electrolyte, thereby increasing the equilibrium potential of the negative electrode, and decreasing the potential of the positive electrode. This creates a smaller cell potential required for electrochemical charging during step 3. After charging, ammonia is thermally separated from the electrolyte and re-introduced to the zinc-containing electrolyte returning the system to step 1. Currently, B-TRAB designs use solid zinc and copper electrodes which lead to low coulombic efficiencies at the copper electrode. Here, we demonstrate how the B-TRAB system can be improved by the addition of ammonium bromide to the positive electrolyte stabilizing Cu(I) species and replacing copper deposition/dissolution reaction with the Cu(I, II) reaction on a carbon felt. As a result, the open circuit potential during charging can be as small as 0.8 V, and as large as 2 V for the discharge step. Polarization curves showed that peak power for the discharge cycle was 98 mW cm-2, a significant improvement over previous B-TRABs.

Redox flow batteries are emerging as a promising method to provide grid-scale power and long-duration energy storage safely and economically. The thermally regenerative ammonia battery (TRAB) is a new redox flow battery category that can be recharged using low-grade waste heat rather than electric energy, adding further flexibility to the applicability of flow battery systems. Recently, a new TRAB with all-aqueous electroactive species (referred to as the Cuaq-TRAB), as opposed to deposition-dissolution reactions, was found to have superior energy and power densities relative to competing TRABs. The use of bromide and ammonia stabilizes for both Cu(I) and Cu(II) oxidation states, while also creating a cell potential of up to 1.0 V. The potential can be recovered by thermally separating ammonia from the electrolyte and adding it back to alternate electrolyte chambers in successive cycles. Potential improvements in overall cell performance are possible by reducing ohmic losses associated with membrane selection. However, the ideal membrane for the Cuaq-TRAB is not obvious and raises interesting transport questions relative to the dominant redox-active copper species being negatively charged in the catholyte but positively charged in the anolyte. Furthermore, membrane crossover of ammonia, a small, uncharged molecule, was previously shown to be a primary source of parasitic losses for TRABs. Therefore, we investigated how different membrane types (cation, anion, and non-selective) affected ion transport and TRAB performance. A batch symmetry cell was used to determine membrane conductivity in the Cuaq-TRAB environment and membrane diffusion coefficients of each species in the electrolytes. Flow cell experiments were also conducted to find peak power, energy density, average power during discharge, and capacity fade over successive electric charge/discharge cycles. Tradeoffs between membrane conductivity and permeability observed in the symmetry cell are manifested in flow cell results as either high peak and average power or high energy density and low capacity fade. These results expand on potential methods for controlling transport in redox flow batteries and demonstrate the potential for non-selective membranes for electrochemical energy technologies.

Attenuated total reflection, surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) is a spectrochemical method that can detect changes in concentrations of electroactive species near an electrode surface as well as adsorbed intermediates. However, its application to heterogeneous redox reactions is still infrequent due to complex working electrode fabrication procedures. This study presents a simple procedure for fabricating ATR-SEIRAS platinum electrodes and demonstrates the effectiveness of the procedure with a successful examination of the Fe(CN)6 3−(aq)/Fe(CN)6 4−(aq) reaction. We found that electrode resistance measurements supported by atomic force microscopy were accurate indicators of ATR-SEIRAS response and ATR electrode thickness. Working electrodes with resistances of 600 Ω were approximately 2.4 ± 0.3 nm in thickness and enabled clear detection of the ferrocyanide peak at 2040 cm−1 with universal wafers. Decreasing electrode thickness to 1.0 ± 0.3 nm improved signal strength by 50%. Polarization tests revealed the formation of adsorbed intermediates at 2070 cm−1 with both positive and negative polarizations consistent with an inner sphere reaction mechanism. Applying large positive polarizations (>900 mV vs SHE) formed additional cyanoplatinate complexes, indicating electrode degradation at large applied potentials.

Models predicting wettability alteration of mineral-brine-oil interfaces during low-salinity-waterflooding (LSW) should account for the elevated temperatures typically found in oil reservoirs. For the first time, high temperature ζ-potential (zeta potential) data for silica are collected and used to interpret surface chemistries and interactions at reservoir-like conditions to predict temperature’s effect on wettability alteration. Mobility data for amorphous silica in varying NaCl(aq) concentrations at 25, 100, and 150 °C and neutral pH were obtained through microelectrophoresis experiments. Calculated ζ-potentials were fit with surface complexation model (SCM) parameters to predict electrical double layer (EDL) parameters based upon the Gouy-Chapman-Stern-Grahame (GCSG) model. ζ-potentials increased with increasing temperature (around 50% increase from 25 to 150 °C) and decreasing NaCl concentrations (10−1–10−4 mol kg−1). These trends, along with Derjaguin-Verwey-Landau-Overbeek (DLVO) theory, suggests that overall repulsive forces extend farther from the surface at low salinity and higher temperatures, implying greater wetting thickness/surface wettability in these environments. The resulting surface concentration calculations suggest that LSW is most impactful up to 10−2 mol kg−1 of salt, and that additional dilution below 10−3 mol kg−1 will negligibly impact oil recovery, particularly at reservoir temperatures above 100 °C. The analysis provides a framework for treating more complex reservoir systems, such as carbonates in multivalent brines.

Reference electrodes (RE) are essential to many electrochemical measurements and monitoring technologies. True reference electrodes allow measurement of pH, oxidation-reduction potentials, corrosion potentials, and more. The primary role of these REs is to maintain a stable and predictable potential while withstanding an application environment. When these goals cannot be maintained for a suitable amount of time due to complications like contamination or degradation, a pseudo-reference electrode is often used (e.g., a platinum wire) but diminishes the value of the collected electrochemical data (i.e., potential measurements are no longer traceable to the standard hydrogen scale.) To limit the use of pseudo-reference electrodes, new RE designs are being produced to be more compatible with specific environments, to be more cost-effective, or to exhibit better potential stability for a longer time. Additionally, the operational lifetime/stability of the RE should reflect its application: a small, disposable reference electrode may only need to be stable for a few hours; a reference electrode for daily lab use may need maintenance once every other week; a reference electrode used in a remote location may need to be stable for months or many years without servicing. RE lifetimes are typically determined a posteriori (from observation) and not predicted at the design phase, which can make the process of designing a new RE very inefficient. In this paper, we will discuss key design considerations that impact the stability and lifetime for true reference electrodes.

The vanadium redox flow battery (VRFB) is a promising candidate for use in grid-scale battery applications to support a deeper reliance on intermittent renewable energy. However, it suffers from a sluggish redox reaction at the positive electrode. Previous studies indicate that its performance can be improved by oxidizing a graphene-based carbon electrode and thus increasing the concentration of its oxygen-containing surface sites. While such performance enhancement does not appear to be controversial, the underlying mechanisms is far from being clear. Some authors suggest that this procedure increases the number of electrocatalytically active sites; others simply attribute it to improved wettability. In this ongoing study, we use density functional theory (DFT) to examine the role of hydroxyl and carboxyl groups, as well as free edge carbon atoms, in the oxygen transfer process at the positive electrode. Preliminary results using carefully selected model compounds (with appropriate charge C and spin multiplicity M) indicate that oxygen functional groups are unlikely to be active sites in the electrochemical redox process, which in many respects is analogous to the oxidation reduction reaction (ORR). Both the thermodynamics (less favorable adsorption energy of vanadium oxide) and the kinetics (problematic transition states) are less plausible than in analogous mechanistic steps involving carbene-type active sites. The carbene site was probed through two possible reaction mechanisms: V-down and O-down (see graph below). The former adsorption step is essentially a ‘dead-end’ process. The latter is not only thermodynamically and kinetically more feasible; it is consistent with other oxygen-mediated electron transfer processes occurring on the surface of graphene-based materials, be they catalysts or reactants. Furthermore, it has been shown in such processes that the presence of oxygen functional groups can stabilize and enhance the concentration of free carbene-type sites at graphene edges. Figure 1

A significant amount of the potential energy that is generated during energy harvesting worldwide is discarded as waste heat because of inefficient power generation cycles. Much of this wasted power source goes unused because it is trapped as low-grade thermal energy (< 100 °C), which traditional power cycles cannot viably harness. With the advent of electrochemical power systems such as redox flow batteries and fuel cells, researchers are investigating new methods of providing usable electric power from these unused low-grade thermal energy sources. The thermally regenerative ammonia battery (TRAB) is one promising technology in this space, as it operates with the same principles as a flow battery except that TRABs can be recharged using low-grade waste heat instead of electric power. Of the TRAB chemistries proposed, the all-aqueous copper TRAB chemistry is capable of both large power densities and energy densities, and high coulombic efficiencies. In this presentation, we discuss how key performance metrics relevant to power generation from low grade thermal energy sources are strongly influenced by electrolyte composition and battery operating parameters. Manipulating the ammonia to copper ratio demonstrated clear tradeoffs between achievable energy and power capacities. Increasing ligand concentration had a large impact on electroactive species solubility and cell potential differences, which increased the theoretical energy density limit of the battery. Increasing the amount of ammonia relative to dissolved copper raised peak power density, but adversely affected energy density. Moderate increases in discharge current density did not decrease the energy density due to reduced impact of ammonia crossover which appears to be a dominant source of energy loss in TRABs.

An increasing number of industrial applications rely on controlling solutes in water above and below its critical point. Processes such as hydrothermal synthesis, steam power generation and ultra-high enthalpy geothermal power are all influenced by factors such as mineral precipitation, pH and solute speciation. The supercritical point of water is remarkable in that slight changes in temperature and pressure can cause dramatic changes in some solute properties. Here, it was found that our approach reliant on molecular statistical thermodynamic expressions for hard sphere (HS), ion-dipole and dipole-dipole interactions via mean spherical approximation (MSA) provided excellent agreement to available experimental data. In addition to model parameters having some physical meaning, this approach used less adjustable parameters than the well-known Helgeson-Kirkham-Flowers (HKF) model. Furthermore, the model was used to obtain standard thermodynamic values for HCl0(aq), KCl0(aq) and NaOH0(aq) ion pairs. In total, modeling parameters for 10 different aqueous species were obtained to demonstrate the capabilities of the approach.

Monitoring simultaneously water-content and corrosion rates in low conductivity natural gas pipeline systems) is carried out using membrane-based electrochemical sensors. An ion conducting membrane improves conductivity in humid natural gas in which electrochemical measurements can be performed. In this study, we monitor corrosion rate and humidity of a gas pipeline through the use of commercial Nafion™ membranes, whose conductivity depends on the partial pressure of water vapor in the gas stream. To improve the accuracy, consistency, and reproducibility of data collection, sensor designs vary between electrode preparation using platinum wires versus nanofabricating flat electrode surfaces and configuration. Data for humidity and corrosion rates within various environments is collected using electrochemical impedance spectroscopy and linear polarization resistance tests. Data for 2-, 3-, and 4-electrode cell tests are presented to compare experimental artefacts among sensor designs.

The silver-based thermally regenerative ammonia battery is a new technology for converting low-grade waste heat (

As the need for a sharp reduction in carbon emissions continues to grow, many researchers are looking to electrochemical technologies to provide sustainable power to the grid. One promising technology is the silver thermally regenerative ammonia battery (Ag-TRAB), which is a new approach for converting low-grade waste heat ( A 2D numerical model was created using COMSOL Multiphysics to study the relationship between fluid flow, electrode structure, and electrodeposition in the porous electrodes using cylinders in cross-flow to represent the internal structure of a porous carbon fiber electrode. Lower void fractions resulted in 2.5% higher power density, but less uniform deposition and the pores clogging 3-5 times faster due to nonuniform deposition normal to the membrane boundary. It was found that the electric field resultant from the void fraction and fiber arrangement was critical to the performance of the electrode. The electrode microstructure can be modified to better distribute the deposition rate relative to the pore size to allow for higher power output for a longer discharge time before the pores begin to clog. An electrode with variable void fraction increased the peak power by 7.5% but the pores clogged 23% faster compared to homogenous void fraction.

Corrosion studies were conducted for martensitic carbon steels in 5 wt% NaCl brine solutions at 4°C and 10 MPa (1,450 psi). These studies simulated different subsurface environments relevant to Arctic drilling. Here, two high-strength martensitic carbon steels, S-135 and UD-165, were studied in three different environments: (1) a CO2-NaCl-H2O solution with a CO2:H2O molar ratio of 0.312 in the whole system, (2) an H2S-NaCl-H2O solution with an H2S:H2O molar ratio of 3.12 × 10−4, and (3) a CO2-H2S-NaCl-H2O solution with the same acid gas to water ratios as environments 1 and 2. Results from the CO2+H2S mixed environment indicated that sour corrosion mechanism was dominant when the CO2:H2S molar ratio was 1,000. This impact of a small amount of H2S on the corrosion mechanism could be attributed to the specific adsorption of H2S on the steel surface. Electrochemical and mass loss measurements showed a distinct drop in the corrosion rate (CR) by more than one order of magnitude when transitioning from sweet to sour corrosion. This inhibiting effect on CR was attributed to the formation of a protective sulfide thin film. Tafel analyses of the anodic reaction showed that the Bockris mechanism was unlikely in the conditions tested. When comparisons were made between modeled and experimental CRs, good agreement was found in the CO2-only and H2S-only environments, but not in the CO2+H2S environment.

A copper-copper sulfate electrode (CSE) was constructed and tested at elevated temperatures. Experimental cell potentials versus a silver-silver chloride electrode were compared against results from Gibbs energy minimization (GEM) calculations. After accounting for irreversible thermodynamic processes, experimental and calculated CSE potentials , were generally within 3% of the observed potential from 25 to 150 °C at 3 MPa. The CSE potentials changed by less than 20 mV with increasing temperature, compared to 120 mV for the silver-silver chloride electrode. With its repeatability and small temperature dependence, the CSE electrode appears to be a viable reference electrode for measuring in-situ real time cell potentials in aqueous phase-containing media at elevated temperature and pressure.

Fouling in boilers has been a problem for decades. In addition to iron oxide deposits on tube walls impeding heat transfer, some forced circulation boilers experience magnetite deposition in lower orifices. These deposits impede flow, cause inefficiencies and lead to boiler tube failures from overheating and corrosion. Particle deposition in some boiler/reactor type environments has been attributed to particle transport and the probability of particle attachment. The attachment is governed by both the inter-particle and particle-substrate interactions, which depend on the aqueous environment. In this study, a novel experimental system is presented, which focusses on the particle attachment aspect of the deposition issues observed in boiler type environments. To identify the effect of boiler water chemistry on the deposition of suspended magnetite on stainless steel, a high temperature high pressure electrophoretic deposition cell with provisions to test metal substrates and different chemistries was developed. Tests were conducted at pH 25 °C of 9.3 in simulated boiler conditions in terms of temperature, pressure and water chemistry. In addition to visual observations, the deposition was investigated using in-situ Electrochemical Impedance Spectroscopy (EIS) and post-test surface analyses including Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). As predicted by Derjaguin-Landau-Verwey- Overbeek (DLVO) theory, deposition was confirmed possible in the above-mentioned aqueous environment at 300 °C. The experimental system presented here was successful in simulating boiler type environments with accelerated deposition. The capability to understand particulate fouling and also to study interfacial phenomena in high temperature, high pressure aqueous environments has been demonstrated.

Low-temperature corrosion relevant to oil and gas wells was investigated. Casing cement was exposed to brine in contact with CO2 at 4 °C and 10 MPa. Pore water was extracted from wet cement using a die press, and a cement simulated pore solution (CSPS) was developed to be used for corrosion studies. High levels of chloride similar to the original brine solution were found. The sodium content was well below that of the original brine, with the change in charge mostly balanced by an increase in dissolved calcium. The calcium content was above predictions for brine-CO2-Ca(OH)2 equilibrium, suggesting that sodium was displaced in favor of calcium. Corrosion measurements were performed on casing steel using linear polarization resistance, electrochemical impedance spectroscopy, and mass loss samples with H2S:CO2 ratios from 0 to 0.001. The corrosion rate was found to decrease slightly with increasing sulfide content from 0.02 to 0.01 mm y-1.

Research efforts on the CuCl(aq)/HCl(aq) electrolyzer would greatly benefit from the ability to quantify the dissipative processes that undesirably increase the cell’s applied potential, E cell , which decreases its efficiency. To date, little is known about what impact further improvements to active surface area, extent of CuCl(aq) conversion and ohmic resistance would exactly have on the electrolyzer performance. To better understand how this electrolyzer can be improved, a model was developed to quantify and separate the effects of electrochemical kinetics, membrane transport and open circuit potential, E OCP, on E cell for a given current density. By employing data obtained from previous studies with electrochemical cells into the developed model, it was possible to calculate E cell values that agreed with data collected from a lab scale electrolyzer using just one adjustable parameter, the Nernst diffusion layer at limiting current. The model was then used to identify the predicted E cell contributions as a function of CuCl(aq) conversion, active electrode area and ohmic resistance. It was found that the extent of CuCl(aq) conversion can dramatically impact the electrolyzer electrode kinetics and E OCP . More importantly, as CuCl(aq) conversion increased, the E cell values needed consistently increased to keep the same current density. Overall, E cell could be most readily reduced by improving R ohm , whereas improvements to electrode kinetics have limited impacts.

Improving power generation of microbial fuel cells (MFCs) requires better methods to quantify the impact of the solution chemistry on performance. While buffer concentration and conductivity have been indicated to impact performance of flat (carbon cloth) anodes, we were able for the first to time to quantitatively determine the impact of the phosphate buffer solution (PBS) concentration separate from conductivity on electrode resistances of commonly used brush anodes and activated carbon cathodes. Using the electrode potential slope (EPS) method, we showed that the anode resistance decreased by 64% (from 14.6 ± 0.1 mΩ m2 to 5.3 ± 0.1 mΩ m2) by increasing the PBS concentration from 50 to 200 mM. There was no appreciable change in the cathode resistance (17.0 ± 0.1 mΩ m2, 50 mM; 18.9 ± 0.2 mΩ m2, 200 mM) although overall performance increased due to a larger cathode experimental working potential (ECat,e0-50 = 268.9 ± 0.9 mV, ECat,e0-200 = 370 ± 1 mV). Adding phosphate buffer to low conductivity synthetic wastewater containing 0.25 g L−1 sodium acetate decreased the anode resistance by 52% (from 59.1 ± 0.2 mΩ m2 to 28.1 ± 0.1 mΩ m2), but increasing only conductivity by adding NaCl or acetate had little impact on electrode resistances. Using electrochemical impedance spectroscopy (EIS), we determined the reasons for these responses. The cathode was limited by oxygen reduction reaction (ORR) kinetics, while the brush anode was limited by mass transfer (proton diffusion), consistent with the impact of buffer concentration on performance. These results have important implications for operation of MFCs as increasing solution conductivity alone, for example, by adding seawater, will not be sufficient to improve anode performance.

Deep cuts to global carbon emissions are only possible with a dramatic increase in energy storage capacity. However, the cost of the storage options available hinders the timely deployment of the necessary energy storage. Promising supplements to conventional storage are thermally regenerative ammonia batteries (TRABs), which have an additional advantage of being able to capture low-grade waste heat into dispatchable electricity for the grid. This new battery technology can potentially provide power on demand using low-cost chemistries and waste energy sources relative to their purely electric battery counterparts. Most of the research to date for TRABs has been proof-of-concept in nature. As such, little is known about how the electrolytes used in these devices impact their theoretical energy storage capacity. Here we present the general principles of TRABs from an electrochemical and aqueous chemistry perspective. Energy storage density values and Eh-pH diagrams are presented to highlight key factors that govern these complex but versatile energy storage devices. Ag-based and Cu-based TRABs are discussed, and some experimental data confirming the conclusions of the Eh-pH diagrams are presented.

Internal corrosion monitoring programs are essential for the safe management of natural gas transmission pipelines. Electrochemical technologies can provide reliable, real-time monitoring of key risk factors, such as solution conductivity, corrosion rates, and localized corrosion risk. A novel, membrane-based sensor is being developed to perform electrochemical tests in both aqueous and gaseous environments, allowing for continuous operation and data collection within a pipeline environment. This sensor can be used to determine water content in the presence of a number of gases (CH4, H2S, CO2), to monitor the pipeline’s corrosion rate with and without a condensed phase, and to provide localized corrosion data in the presence of a pitting agent. Here, we explore the sensor’s design, validation through finite-element analysis, and performance data for general and localized forms of corrosion.

As the need for a sharp reduction in carbon emissions continues to grow, many researchers are looking to electrochemical technologies to provide sustainable power to the grid. One promising technology is the silver thermally regenerative ammonia battery (Ag-TRAB), which takes advantage of low-grade waste heat (

One aspect of effective steam/water cycle chemical treatment programs is their ability minimize corrosion and corrosion related failures. In this study, we examine how corrosion product layers on the surface of tubing samples impact corrosion rate for a series of test specimens prepared from boiler/steam piping provided from operating power plants. Corrosion rates were estimated using the following electrochemical techniques: linear sweep voltammetry (LSV), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). Two sources of Tafel slopes were the standard assumptions used if the corrosion mechanism is not known and those obtained from LSV curves. In total, five variations of corrosion rate measurements were compared. For these corrosion tests, water chemistries representative of conditions that induced online hydrogen damage and offline pitting were used. Field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDS/EDX) were the electron microscopy techniques applied to examine the corrosion product layers. Using these techniques, the microstructure and elemental composition of the tubing sample corrosion product layers were examined. These techniques could be utilized to evaluate the effectiveness or reduction in corrosion rates with the application of film forming products.

For meeting ambitious carbon-free electricity goals, low-cost electrical energy storage solutions are needed. Although redox flow batteries are a promising option to satisfy this need, the cost of these devices must decrease before widespread adoption can take place. As the electrolytes are the most significant expense for MW-scale flow batteries, new chemistries derived from inexpensive metals is one approach that may alleviate this bottleneck towards a carbon-free power grid. Here we use an electrochemical approach by applying a rotating disc electrode (RDE) to quantify how ligand chemistries can favorably manipulate the electrochemical parameters of the Cu(I/II) redox reaction, progressing these chemistries forward as potential low-cost electrolytes for redox flow batteries. In this research, multiple ligands were used to analyze such impacts on aqueous copper metal complexes by using both a platinum and carbon tipped electrode installed into the RDE. Electrochemical Impedance Spectroscopy (EIS), Linear Sweep Voltammetry (LSV) and Open Circuit Potential (OCP) were the three techniques utilized to analyze the effects of these metal complexes. The experimental data was analyzed using the Butler-Volmer and Nernst equations. As step reactions are mostly unknown for these reactions, LSV and EIS data gave insights into what may be occurring at the electrode interfaces. OCP data quantified how different ligands modified the standard electrode potentials of the Cu(I/II) redox reaction.

A phenomenological model describing the transport processes across a cation exchange membrane was developed. Using data obtained from conductivity, permeability and transport number experiments, the model quantified the direct and indirect influences of CuCl(aq) chemical potential and electric potential gradients on the fluxes of H+(aq), CuCl(aq) and charged species across a pressed Nafion 117 membrane in contact with 7 mol L-1 HCl(aq). This system is of particular interest for the CuCl(aq)/HCl(aq) electrolytic cell, a key component in the Cu-Cl hybrid thermochemical cycle. It was found that in highly reduced CuCl(aq) solutions, the flux of protons and charged species were influenced by the presence of copper species.

The hydrogen reaction in concentrated HCl(aq) solutions is a key reaction for the CuCl(aq)/HCl(aq) electrolytic cell. Here, electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) were used to obtain new data for the hydrogen reaction on platinum submerged in highly concentrated acidic solutions at 25 °C and 0.1 MPa. LSV and EIS data were collected for Pt in 0.5 mol/L H2SO4(aq), 1 mol/L HCl(aq) and 7.71 mol/L HCl(aq) solutions. It was found that exchange current density (j0) values varied between 1 and 2 mA/cm2. An equivalent circuit model was used to obtain comparable j0 and limiting current density values from EIS data relative to values obtained with LSV data. It was found that as the concentration of acid increased, a noticeable decrease in the performance was observed. Keywords: Hydrogen reaction on platinum, Concentrated HCl(aq) solutions, Electrochemical kinetics, Exchange current density, Electrochemical impedance spectroscopy, Linear sweep voltammetry

Suspended magnetite particles in boiler waters were found to deposit in orifice headers, impeding flow and causing inefficiencies and boiler tube failures from overheating. Particle interactions due to the zeta potential developed on the colloidal magnetite particles could also be a factor in deposition. To study the mechanism behind the deposition of suspended magnetite on stainless steel, a high temperature high pressure electrophoretic deposition cell with provisions to test 304 stainless steel substrates has been developed. The tests, conducted at pH25 °C of 9.3 in simulated boiler conditions in terms of temperature, pressure and water chemistry. The deposition was monitored using in-situ Electrochemical Impedance Spectroscopy (EIS) and post-test surface analyses were carried out on the substrate. The results of the tests concurred with the theory on oxide particle behavior in aqueous systems and colloidal stability. The specific conditions in the boiler that favor deposition have been successfully replicated.

A state-of-health test of a CuCl/HCl electrolytic cell was carried out by maintaining a constant current density of 0.3 A cm −2 for 168 h at 80 °C and ambient pressure. While the most common method used to characterize the electrochemical performance of a CuCl electrolytic cell is to record current–voltage ( I–V curves), it is also essential to separate the electrochemical and ohmic components of the polarization curve. In our study, the AC impedance characteristics of a single cell were studied along with the DC polarization curves. After the durability test, the potential required to maintain the cell at 0.3 A cm −2 increased from 630 mV of the fresh membrane electrode assembly (MEA) to 710 mV due to some degradation processes in the electrolytic cell. Quantitative analysis of the performance decay was carried out by Electrochemical Impedance Spectroscopy (EIS). EIS measurements showed an increase in the area specific ohmic resistance of the MEA from 0.6 Ω cm 2 to 0.85 Ω cm 2 and area specific charge-transfer resistance from 0.61 Ω cm 2 to 0.8 Ω cm 2 measured at an overpotential of 0.2 V. The degradation in the cell is attributed to the decrease in membrane conductivity and an increase in the charge-transfer resistance.

The high ionic strength and complex speciation of the anolyte solution within the CuCl(aq)/HCl(aq) electrolytic cell have impeded predictions of the energy requirements for the cell's electrolytic reaction at 25 °C and 1 bar. After collecting experimental open circuit potential (OCP) data and comparing the values obtained with predictions from prospective thermodynamic models, an approach to predict thermodynamic values and the overall efficiency was formulated. The compositions of the experimental measurements ranged from 2-2.5 mol of CuCl(aq) with 8-9 mol of HCl(aq) per kilogram of water in anolyte solution and 8-9 mol of HCl(aq) per kilogram of water in catholyte solution. From the OCP data, it was found that activity coefficient and speciation effects were critical in predicting the Gibbs energy, entropy and thermodynamic (intrinsic maximum) efficiency of the electrolytic cell. At equilibrium, all thermodynamic functions of the anolyte redox reactions were the same after activity coefficients and speciation effects were taken into account. The electrochemical reactions’ Gibbs energy and entropy were found to be 9700 J/mol and 2.18 J/(mol K) at 25 °C and 1 bar, which indicated that the reactions required a small amount of electrical and thermal energy to proceed. With thermodynamic values for the electrolytic reaction and experimental data from a CuCl(aq)/HCl(aq) electrolytic cell, the voltage, current, thermodynamic and overall efficiency were calculated. The overall efficiency ranged from 15 to 95% depending on the current density.

Monitoring the internal corrosion of natural gas transmission lines is required for safe management of natural gas infrastructures. Internal corrosion programs can be strengthened by real-time monitoring of key risk factors such as relative humidity and corrosion rates of the pipeline material. We have developed a membrane-based electrochemical sensor, which functions in gaseous environments, to provide this real-time monitoring capability. The design is based on the sensitivity of the membrane’s conductivity to gaseous water content. We match relative humidity curves to 4-electrode, electrochemical impedance spectroscopy results, and use 3-electrode, linear polarization resistance tests to calculate corrosion rates. Due to the membrane’s atypical current pathways, precise estimation of the sensor’s cell constant was required to interpret the impedance results into relative humidity. We utilize finite-element analysis to obtain our cell constant (14.84 cm-1), and the resulting membrane conductivity values were in good agreement with published data. The sensor was tested in H2S environments to gauge how these results may change with acidic gases that may be present in the natural gas stream.