Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “alkaline electrolyte”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Enhanced stability of silicon for photoelectrochemical water oxidation through self-healing enabled by an alkaline protective electrolyte

Alkaline electrolytes impede the corrosion of Si photoanodes under positive potentials and/or illumination, due to the formation of a SiO x layer that etches 2–3 orders of magnitude more slowly than Si. Hence during water oxidation under illumination, pinholes in protection layers on Si photoanodes result in the local formation of a protective, stabilizing passive oxide on the Si surface. However, operation under natural diurnal insolation cycles additionally requires protection strategies that minimize the dark corrosive etching rate of Si at pinholes. We show herein that addition of [Fe(CN) 6 ] 3- to 1.0 M KOH(aq) results in a self-healing process that extends the lifetime to >280 h of an np + -Si(100) photoanode patterned with an array of Ni catalyst islands operated under simulated day/night cycles. The self-healing [Fe(CN) 6 ] 3- additive caused the exposed Si(100) surface to etch >180 times slower than the Si etch rate in 1.0 M KOH(aq) alone. No appreciable difference in etch rate or facet preference was observed between Si(100) and Si(111) surfaces in 1.0 M KOH(aq) with [Fe(CN) 6 ] 3- , indicating that the surface conformally oxidized before Si dissolved. The presence of [Fe(CN) 6 ] 3- minimally impacted the faradaic efficiency or overpotential of p + -Si/Ni electrodes for the oxygen-evolution reaction.

25 ENERGY STORAGE↗
DOE OSTI2021

Density Functional Theory Investigation of the NiO@Graphene Composite as a Urea Oxidation Catalyst in the Alkaline Electrolyte

Developing efficient and low-cost urea oxidation reaction (UOR) catalysts is a promising but still challenging task for environment and energy conversion technologies such as wastewater remediation and urea electrolysis. In this work, NiO nanoparticles that incorporated graphene as the NiO@Graphene composite were constructed to study the UOR process in terms of density functional theory. The single-atom model, which differed from the previous heterojunction model, was employed for the adsorption/desorption of urea and CO 2 in the alkaline media. As demonstrated from the calculated results, NiO@Graphene prefers to adsorb the hydroxyl group than urea in the initial stage due to the stronger adsorption energy of the hydroxyl group. After NiOOH@Graphene was formed in the alkaline electrolyte, it presents excellent desorption energy of CO 2 in the rate-determining step. Electronic density difference and the d band center diagram further confirmed that the Ni(III) species is the most favorable site for urea oxidation while facilitating charge transfer between urea and NiO@Graphene. Moreover, graphene provides a large surface for the incorporation of NiO nanoparticles, enhancing the electron transfer between NiOOH and graphene and promoting the mass transport in the alkaline electrolyte. Notably, this work provides theoretical guidance for the electrochemical urea oxidation work.

25 ENERGY STORAGE↗
DOE OSTI2024

In Situ and Operando Observation of Zinc Moss Growth and Dissolution in Alkaline Electrolyte for Zinc–Air Batteries

As a promising battery technology, zinc–air batteries still face significant challenges, including the formation of a mossy structure on the zinc metal anode in alkaline electrolyte. Because a similar phenomenon also plagues lithium and sodium metal batteries, elucidating its mechanism has important implications for progress in energy storage. Herein, operando X-ray nanotomography was employed to visualize zinc moss growth and dissolution at the individual colony level. By tracking its microstructure evolution, zinc moss was found to display irreversible plating/stripping behavior. While zinc moss exhibits self-limiting growth and zinc deposition occurs mainly in its outer region, zinc dissolution is more uniformly distributed inside the moss colony upon stripping, leading to the formation of “dead” zinc and capacity loss. A direct correlation is established between the moss amount and zinc plating/stripping efficiency. Finally, results from this study offer new insights into mitigating the unstable zinc plating morphology and improving the cycle life of aqueous zinc–air batteries.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Bifunctional MnO x electrocatalysts for zinc–air batteries in alkaline electrolytes

The growing need for rechargeable zinc–air batteries has led researchers to look for low-cost and robust catalytic candidates. Furthermore, manganese oxides are promising for their low toxicity, natural abundance and low cost. In this review, we summarize the versatility of manganese oxides which is achievable by adjusting synthetic parameters. In addition, we highlight how manganese oxides impact zinc–air electrochemistry.

25 ENERGY STORAGE↗
DOE OSTI2021

Catalytic open-circuit passivation by thin metal oxide films of p-Si anodes in aqueous alkaline electrolytes

Ni and NiO x -based protective thin films are shown to catalyze the oxidation of Si in the presence of O 2 in strongly alkaline KOH(aq) even in the absence of illumination. The O 2 in solution drove the open-circuit potential of the electrode to >0.4 V, which is positive of the Si passivation potential. The elevated electrochemical potential of the surface promoted formation of passive oxides on exposed Si regions of Si/Ni electrodes. Catalytic passivation of Si extended the durability of an np + -Si(100)/NiO x photoanode to >400 h while operating under simulated day/night cycles. In contrast, electrodes without a Ni(O x ) layer and/or without O 2 in solution displayed direct etching of the Si and corrosion pitting during non-illuminated, simulated nighttime episodes of day/night cycling. The O 2 -derived catalyzed passivation of Si using thin films can be generalized to multiple phases of NiO x as well as to materials other than Ni. Finally, relative to operation in aqueous alkaline conditions, decreasing the pH of the electrolyte decreased the dissolution rate of the protective oxide layer formed by the catalyzed passivation process, and consequently increased the durability of the photoanode, but yielded lower photoelectrode fill factors for water oxidation due to the relatively large kinetic overpotentials for the electrocatalyzed oxygen-evolution reaction at near-neutral pH.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Cations Enhance Hydride Transfer to Noncatalytic Metals in Concentrated Alkaline Electrolytes

Alkali metal cations are known to influence the kinetics of the hydrogen evolution reaction (HER), acting as either promoters or inhibitors to the rate-determining step depending on the metal surface, local pH, and cation concentration. Despite the importance of concentrated electrolytes for commercial electrochemical cells, the impact of cations on the HER in concentrated alkaline environments (>1 M) and in mixed cation systems remains poorly understood. Here, this study quantifies the HER kinetics at polycrystalline metal surfaces (Pt, Au, Cu, and Fe) and the equilibrium solvation environment in pure and mixed alkali metal hydroxide electrolytes at concentrations up to 3.0 M. Kinetic analyses of Au, Cu, and Fe revealed a positive cation-concentration-effect that was primarily driven by changes to the charge transfer coefficient. Multinuclear NMR spectroscopy examined the solvation of H 2 O/OH – species and the alkali cations as a function of (mixed) alkali cation concentration(s), and demonstrated rapid exchange between solvent, hydroxide, and solvated cations. Together, these findings support models where HER kinetics on noncatalytic metal surfaces in strongly alkaline conditions are primarily governed by the average polarization and polarizability of the metal/solution interface and that increasing cation activity continues to increase the transfer coefficient at metal-hydroxide concentrations up to 3.0 M. Electrolytes and additives which can outcompete weakly hydrated cations and disrupt the interfacial water structure are expected to suppress parasitic HER at electrodes for energy storage and electroplating.

Cations↗
DOE OSTI2021

Electrochemically active surface area controls HER activity for Fe x Ni 100–x films in alkaline electrolyte

We report the synthesis and electrocatalytic activity of Fe x Ni 100-x electrochemically deposited films were investigated. Films were evaluated for the hydrogen evolution reaction (HER) in alkaline media with respect to composition and electrochemically active surface area (ECSA). Results demonstrate that films of higher or equal Fe content had an ECSA tenfold greater than films with higher Ni. When normalized by geometric surface area, Fe 50 Ni 50 films required the lowest overpotential of -390 mV to reach a current density of -10 mA cm -2 . However, when normalized by the ECSA, intrinsic HER activity increases as Ni content increases. Tafel slope, ECSA, microscopy, and impedance spectroscopy analyses allow a decoupled analysis of surface area versus activity effects on overall measured HER activity. Furthermore, these analyses collectively demonstrate that the increase in electrocatalytic activity is attributed to the increase in ECSA and not to an enhancement in the intrinsic activity by Fe and Ni component interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Platinum and Gold Supported on Transition Metal Nitrides for Hydrogen Evolution in an Alkaline Electrolyte

Here, as the urgency to reduce reliance on fossil fuels increases due to carbon dioxide emissions, hydrogen produced by renewably powered water electrolysis has emerged as a promising technology. Alkaline electrolyzers typically exhibit lower current densities than acidic electrolyzers due to the slow kinetics of the hydrogen evolution reaction (HER) under alkaline conditions. This work developed Pt- and Au-modified transition metal nitride (TMN) thin films for improving alkaline HER kinetics. One monolayer Pt–VN, Pt–Mo 2 N, and Pt–TiN were the most promising thin-film catalysts, with alkaline HER activity approaching that of a bulk Pt foil. Additionally, the Gibbs free energy of adsorbed hydrogen was identified as a useful descriptor for alkaline HER activity on TMN and TMN-supported catalysts and has the potential to guide future studies on TMN-based catalysts for enhancing alkaline HER. For practical applications, the thin-film catalysts were then extended to Pt- and Au-modified TMN powders for alkaline HER. Both 5 wt % Pt/TiN and 2 wt % Pt/TiN powders exhibited lower overpotentials at 5 mA/cm 2 when normalized by the Pt electrochemical surface area than the commercial 5 wt % Pt/C benchmark, suggesting a Pt–TiN synergy that creates opportunities for more cost-effective alkaline HER cathodes. Moreover, 20 wt % Au/Mo 2 N also displayed an enhancement in HER activity when compared to the commercial 20 wt % Au/C benchmark.

58 GEOSCIENCES↗
DOE OSTI2020

Bismuth Detection in Alkaline Electrolyte via Anodic Stripping Voltammetry for Battery Separator Evaluation

Abstract Anodic stripping voltammetry (ASV) has been widely used for the detection of several heavy metal ions in neutral and acidic solution, in many cases employing electrodes and/or solutions incorporating Bi. In this work we demonstrate that Bi(OH) 4 − ion concentration can be measured in highly alkaline 8.5 M KOH solution using ASV. The addition of Pb in similar concentrations to the Bi(OH) 4 − being measured is shown to improve both the sensitivity and precision of the method. When the Pb additive is employed, a formal limit of detection of 8.5 ppb is achieved, compared to 17.3 ppb when the Pb additive is not used. Due to the use of Bi additives in alkaline battery chemistries, it follows that separators which limit Bi(OH) 4 − diffusion into the bulk electrolyte and away from the electrodes are of interest. For this purpose, we utilize ASV to determine Bi(OH) 4 − diffusion rates through Celgard 3501, cellophane 350P00, and Nafion 211. Bi(OH) 4 − crossover rates, as determined by ASV, are shown to be repeatable and consistent with expectations from the known separator structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Chapter 7: Recent Advances in Electrocatalysts for Hydrogen Oxidation Reaction in Alkaline Electrolytes

The recent development in electrocatalysts for the hydrogen oxidation reaction (HOR) attracted significant attention. In this sense, this chapter provides a fundamental understanding of the state-of-the-art PGM and non-PGM-based electrocatalysts for the HOR in alkaline conditions. Moreover, a strong focus has been made on the strategies to overcome the slow kinetics of the HOR to commercialize anion-exchange membrane fuel cells.

anion-exchange membrane↗
DOE OSTI2024

Unlocking High Capacity and Reversible Alkaline Iron Redox Using Silicate-Sodium Hydroxide Hybrid Electrolytes

Alkaline iron (Fe) batteries are attractive due to the high abundance, low cost, and multiple valent states of Fe but show limited columbic efficiency and storage capacity when forming electrochemically inert Fe 3 O 4 on discharging and parasitic H 2 on charging. Herein, sodium silicate is found to promote Fe(OH) 2 /FeOOH against Fe(OH) 2 /Fe 3 O 4 conversions. Electrochemical experiments, operando X-ray characterization, and atomistic simulations reveal that improved Fe(OH) 2 /FeOOH conversion originates from (i) strong interaction between sodium silicate and iron oxide and (ii) silicate-induced strengthening of hydrogen-bond networks in electrolytes that inhibits water transport. Furthermore, the silicate additive suppresses hydrogen evolution by impairing energetics of water dissociation and hydroxyl de-sorption on iron surfaces. In conclusion, this new silicate-assisted redox chemistry mitigates H 2 and Fe 3 O 4 formation, improving storage capacity (199 mAh g -1 in half-cells) and coulombic efficiency (94 % after 400 full-cell cycles), paving a path to realizing green battery systems built from earth-abundant materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Toward the Understanding of the Reaction Mechanism of Zn/MnO2 Batteries Using Non-alkaline Aqueous Electrolytes

Zn/MnO 2 systems using non-alkaline aqueous electrolytes have attracted tremendous interest as rechargeable aqueous Zn ion batteries due to their safety and high specific capacities. Despite their promising electrochemical performance, however, their reaction mechanism has remained elusive. Here in this paper, we examined the structural evolution of cryptomelane α-MnO 2 cathode by ex situ transmission electron microscopy after electrochemical testing using two different non-alkaline aqueous Zn electrolytes with acetate and triflate salts of different pH values. We have discovered that the systems tested in both electrolytes exhibit a dissolution–deposition reaction mechanism through dissolution–deposition of Mn 2+ ions from/on the cathodes with a display of similar discharge/charge product formation. We have also found that the cell tested using the acetate electrolyte shows evidence of structural irreversibility that might contribute to its rapid capacity degradation. This finding offers an important insight into optimizing the cathode design for enhanced electrochemical function of aqueous Zn/MnO 2 batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

Investigations of the stability of etched or platinized p-InP(100) photocathodes for solar-driven hydrogen evolution in acidic or alkaline aqueous electrolytes

Here, the stability of p-InP photocathodes performing the hydrogen-evolution reaction (HER) has been evaluated in contact with either 1.0 M H 2 SO 4 (aq) or 1.0 M KOH(aq), with a focus on identifying corrosion mechanisms. Stability for the solar-driven HER was evaluated using p-InP electrodes that were either etched or coated with an electrodeposited Pt catalyst (p-InP/Pt). Variables such as trace O 2 were systematically controlled during the measurements. Changes in surface characteristics after exposure to electrochemical conditions as well as electrode dissolution processes were monitored using X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS). In either H 2 SO 4 or KOH, etched p-InP photoelectrodes corroded cathodically under illumination, forming metallic In 0 at the electrode surface. In contrast, electrodeposition of Pt kinetically stabilized illuminated p-InP photocathodes in both H 2 SO 4 and KOH by inhibiting the cathodic corrosion pathway. Notably, when held at 0 V vs. the reversible hydrogen electrode (RHE) in 1.0 M H 2 SO 4 (aq), p-InP/Pt exhibited a stable current density (J) of ~–18 mA cm –2 for >285 h under simulated 1 Sun illumination. The long-term current density vs. potential (J–E) behavior at pH 0 and pH 14 of p-InP/Pt photocathodes correlated with changes in the surface chemistry as well as the dissolution of p-InP. In acidic media, the J–E behavior of p-InP/Pt photocathodes remained nearly constant with time, but the surface of a p-InP/Pt electrodes gradually turned P-rich via a slow and continuous leaching of In ions. In alkaline electrolyte, the surface of p-InP/Pt electrodes was passivated by formation of an InO x layer that exhibited negligible dissolution but led to a substantial degradation in the J–E characteristics. Consequently, changes in the catalytic kinetics and surface stoichiometry are both important considerations for determining the corrosion chemistry and the long-term operational stability of InP photoelectrodes.

14 SOLAR ENERGY↗
DOE OSTI2021

Electrocatalysts Development for Hydrogen Oxidation Reaction in Alkaline Media: from Mechanism Understanding to Materials Design

Anion exchange member (AEM) fuel cells have gained great attention recently mainly owing to the advantages of non-precious metal catalysts application. Despite of the similar oxygen reduction reaction (ORR) kinetics in acid and base, the reaction kinetics of hydrogen oxidation reaction (HOR) is two orders of magnitude slower in alkaline systems than in acid. To understand the slower kinetics of HOR in base, two major interpretations have been proposed, including 1) hydrogen binding energy as a major descriptor for HOR in both acid and base; and 2) bifunctional theory based on the contributions from both hydrogen and hydroxide adsorption for HOR in alkaline electrolyte. Here, we discuss the possible HOR mechanisms in alkaline electrolytes with the corresponding Tafel behavior change. Besides the discussion of traditional Tafel-Volmer and Heyrovsky-Volmer HOR mechanisms, the recently proposed hydroxide adsorption step is discussed to illustrate the HOR mechanism difference in acid and base. We further correlate the hydroxide adsorption step involved mechanism with HOR catalyst design, and summarize its role in HOR and HER activities improvement in alkaline electrolyte over the same catalyst. The representative works of alkaline HOR catalyst development were briefly introduced, and the strategy of strengthening interaction between H2 desorption and H2O recombination was finally proposed for future HOR catalyst design in alkaline environment.

Hydrogen oxidation reaction, Hydrogen evolution re↗