Electrolyte Oxygen Research Articles

Transient response of amperometric solid electrolyte oxygen sensors under high vacuum

This paper determines the response times of amperometric solid electrolyte oxygen sensors under high vacuum conditions in experimental series with varying parameters. Such sensors can be designed with very small sizes and low power consumption and are therefore ideally suited for applications with limited resources. The interpretation of measurements with rapid variations of the oxygen concentration requires knowledge about the transient sensor behavior. It is shown that the response times are significantly reduced by controlling the cathodic overpotential with a potentiostat, compared to an operation with a constant voltage between the electrodes. The response times are a function of the overpotential, and the measured values at pressure levels of 10−5 hPa are in the order of seconds. They increase with lower pressures and decrease with higher temperatures. A model of the reactions at the cathode has been developed in order to explain the findings. It is used for simulations of the transient signal following pressure changes, and the results indicate a significant reduction of the response time by shortening the diffusion length along the electrodes.

Role of Oxygen in Surface Structures of the Solid-Electrolyte Interphase Investigated by Sum Frequency Generation Vibrational Spectroscopy

The solid-electrolyte interphase (SEI) layer on the anode surface is crucial for the operation of lithium-ion batteries. It remains unclear how oxygen in electrolyte influences the SEI formation. W...

Structural engineering of hierarchically hetestructured Mo2C/Co conformally embedded in carbon for efficient water splitting

Developing low-cost and high efficient electrocatalysts for both oxygen and hydrogen evolution reaction in an alkaline electrolyte toward overall water splitting is still a significant challenge. Here, a novel hierarchically heterostructured catalyst composed of ultrasmall Mo2C and metallic Co nanoparticles confined within a carbon layer is produced by a facile phase separation strategy. During thermal reduction of CoMoO4 nanosheets in CO ambient, in-situ generated nanoscale Co and ultrafine Mo2C conformally encapsulated in a conductive carbon layer. In addition, some carbon nanotubes catalyzed by Co nanoparticles vertically grew on its surface, creating 3D interconnected electron channels. More importantly, the integrated C@Mo2C/Co nanosheets assembled into the hierarchical architecture, providing abundant active surface and retaining the structural integrity. Benefiting from such unique structure, the constructed hierarchical heterostructure shows low overpotentials of 280 mV and 145 mV to reach a current density of 10 mA cm−2 for OER and HER in an alkaline electrolyte. Furthermore, the symmetrical electrolyzer assembled with catalyst exhibits a small cell voltage of 1.67 V at 10 mA cm−2 in addition to outstanding durability, demonstrating the great potential as a high efficient bifunctional electrocatalyst for overall water splitting.

Revealing the Impact of Oxygen Dissolved in Electrolytes on Aqueous Zinc-Ion Batteries.

SummaryAqueous zinc-ion batteries (ZIBs) are promising low-cost and high-safety energy storage devices. However, their capacity decay especially at the initial cyclic stage is a serious issue. Herein, we reveal that the dissolved oxygen in aqueous electrolyte has significant impact on the electrochemistry of Zn anode and ZIBs. After removing oxygen, the symmetrical set-up of Zn/Zn is capable of reversible plating/stripping with a 20-fold lifetime enhancement compared with that in oxygen enrichment condition. Taking aqueous Zn-MnO2 battery as an example, although the presence of oxygen can contribute an extra capacity over 20% at the initial cycles due to the electrocatalytic activity of MnO2 with oxygen, the corrosion of Zn anode can be eliminated in the oxygen-free circumstance and thus offering a better reversible energy storage system. The impact of the dissolved oxygen on the cycling stability also exists in other ZIBs using vanadium-based compounds, Birnessite and Prussian blue analog cathodes.

Recent trends in hydrogen and oxygen electrocatalysis for anion exchange membrane technologies

Abstract This review aims at presenting recent findings in the understanding of oxygen and hydrogen electrocatalysis in alkaline electrolytes that are key processes for the emergence of sustainable energy storage and conversion devices such as anion exchange membrane fuel cells and electrolyzers. In these systems, the exchange of electrons through electrochemical reactions provides a unique pathway to reversibly convert the electricity vector into chemical one: hydrogen. A concise and critical review of advances made during the last past years in the design of catalysts is provided. Challenges and opportunities for the development of the next catalyst generation are also addressed.

Thin Layer Sonoelectrochemistry: Electrocatalysis in Oxygen Reduction Reaction (ORR) and Methanol Electrolysis

In electrochemical energy systems such as fuel cells, important reactions include the oxygen reduction reaction (ORR) and methanol oxidation. Even with platinum catalysts, oxygen reduction kinetics in water at acidic pH are slow. In H₂ proton exchange membrane fuel cells (PEM FCs), ORR is the rate determining kinetic process. In direct reformation fuel cells run on methanol with an oxygen or air cathode, methanol oxidation kinetics are rate limiting. Limitations include slow electron transfer processes coupled to generation of oxidation by-products that adsorb to the electrode and lead to passivation. Sonoelectrochemistry in thin layers of electrolyte enhances electrochemical rates without visible cavitation using low power oscillators [1]. Here, thin layer sonoelectrochemistry coupled with cyclic voltammetry is used to evaluate impacts of sonication in a thin layer on the electrochemical response of oxygen and methanol . For voltammetry at platinum electrodes for saturated oxygen in acidic aqueous electrolyte, the rate of the ORR is enhanced several orders of magnitude as shown by fit of the cyclic voltammetric data. For stoichiometric (50:50) methanol in water with acid electrolyte, oxidation and reduction currents at platinum electrodes are increased almost ten fold as shown in cyclic voltammetric responses. Sonication may increase the rates of electron transfer and remove deposited partial oxidation products. Improved kinetics of oxygen reduction and methanol electrolysis may provide a means to improved electrochemical energy technologies, including hydrogen and direct reformation fuel cells. The energy needed to drive the oscillator represents a low parasitic loss on fuel cell performance. Reference [1] Johna Leddy, Chester G. Duda, Jacob Lyon, and William J. Leddy III, "Thin Layer Sonoelectrochemistry and Sonoelectrochemistry Devices and Methods," published 28 May 2015 as US Patent Application 20150147594 A1.

Oxygen Potential of High-Titania Slag from the Smelting Process of Ilmenite

Oxygen potential of TiO2-FeO-Ti2O3 ternary slags was determined by the electromotive force (EMF) method based on the solid electrolyte oxygen sensor at 2003 K (1730 °C). The effect of FeO content and Ti3+/Ti4+ mass ratio on the oxygen potential of the high-titania slag was also studied. At a fixed Ti3+/Ti4+ mass ratio of 3.11, the oxygen potential increased with increasing FeO content. Increase of Ti3+/Ti4+ mass ratio from 2.29 to 3.60 caused a significant decrease in the oxygen potential of the slag. Comparing measured oxygen potential with the calculated values indicated that the oxygen potential of the slag might be determined by FeO/Fe equilibrium reaction rather than TiO2/Ti2O3 reaction. In addition, the experimentally measured oxygen potential values were modeled by multiple linear regression analysis, and a semi-empirical mathematical correlation was established between the oxygen potential and slag compositions. The iso-oxygen potential distribution diagram based on the mathematical model was obtained for the high-titania slag.

Processes and Their Limitations in Oxygen Depolarized Cathodes: A Dynamic Model-Based Analysis.

Oxygen depolarized cathodes (ODCs) are key components of alkaline fuel cells and metal-air batteries or of chlor-alkaline electrolysis, but suffer from limited oxygen availability at the reaction zone. Dynamic analysis is a highly suitable approach to identify the underlying causes, especially the limiting steps and process interactions in such gas diffusion electrodes. Herein, a one-dimensional, dynamic, three-phase model for analyzing the oxygen reduction reaction in silver-based ODCs is presented. It allows for a detailed evaluation of the electrochemical reaction, the mass transport processes, and their interaction. The model also reveals that the depletion of reactant oxygen in the liquid electrolyte is caused by the current-dependent change of the gas-liquid equilibrium as the limiting subprocess. The phase equilibrium, in turn, depends on the slow mass transport of water and hydroxide ions in the liquid phase. Key parameters are the location or size of the gas-liquid interface within the electrode. Profiles of local concentrations and partial pressures of different species reveal a steep gradient of oxygen in the liquid phase, but no limitation in oxygen mass transport in the gas phase. Dynamic simulations with potential steps allowed the identification of different time constants to separate overlapping processes. Accordingly, the mass transport of water and hydroxide ions was identified as the slowest process that strongly influenced the dynamic response of all species, including oxygen, and of the current. The characteristic time constant of the mass transport of water and hydroxide ions across the liquid phase within the ODC is determined to be τ ≈0.176 s, whereas the time constant of oxygen mass transport into the reaction zone is several magnitudes smaller: τ ≈1.70×10-6 s. Finally, a sensitivity analysis confirms that the overall performance is best improved by adjusting mass transport properties in the liquid phase.

Monolithic electrode integrated of ultrathin NiFeP on 3D strutted graphene for bifunctionally efficient overall water splitting

High-performance earth-abundant electrocatalysts for oxygen and hydrogen evolutions are highly desired for renewable energy but remain challenging. Herein, we have developed ultrathin NiFeP nanosheets, and merged the NiFeP with a 3D support of sponge-like strutted graphenes (SG). The synthesized NiFeP/SG, a porous monolith, shows efficient electrocatalytic activities for oxygen and hydrogen evolutions in alkaline electrolyte with low overpotentials of 218 and 115 mV, respectively. Using NiFeP/SG as direct catalytic electrodes, the overall water splitting requires a low cell voltage of 1.54 V to achieve a current of 10 mA cm−2. The high performances result from the shifted-up d states caused by iron incorporation, the ultrathin NiFeP, and the 3D network structure of SG. Additionally, NiFeP/SG demonstrates excellent gravimetric catalytic activities, meaningful to aerospace and portables. The material opens the way to a universal robust lightweight catalytic electrode for a variety of applications in electrochemical energy storage and conversion.

Electrochemical Properties of Powder Iron/Carbon System in Basic Solution

Electrochemical properties of powder iron/carbon systems in aqueous alkaline solution are discussed. The factors affecting the reversibility of the red-ox reactions on the powder iron/C electrode have been described. The influence of the oxygen and alkali concentration of iron powder surface structures and degrees of iron oxidizing have been performed using electron microscopy. The changes of potential range from -0,56 V to -1,0 V depending on alkali concentration have been fixed by cyclic voltamograms. The formation of new iron hydroxide films in joint presence of oxygen and hydrogen in electrolyte has been proposed. There have been used CVA and EIS studies to elucidate the hydrous oxide films formation on the surface of iron powder electrode. The surface coating by FeO of the iron particles after oxidizing has been validated by SEM.

Pd Nanoparticles Anchored on N-rich Graphdiyne Surface for Enhanced Catalysis for Alkaline Electrolyte Oxygen Reduction

Pd Nanoparticles Anchored on N-rich Graphdiyne Surface for Enhanced Catalysis for Alkaline Electrolyte Oxygen Reduction

Aggregation-Resistant 3D MXene-Based Architecture as Efficient Bifunctional Electrocatalyst for Overall Water Splitting.

The MXene combining high conductivity, hydrophilic surface, and wide chemical variety has been recognized as a rapidly rising star on the horizon of two-dimensional (2D) material science. However, strong tendency to intersheet aggregate via van der Waals force represents a major problem limiting the functionalities, processability, and performance of MXene-based material/devices. We report a capillary-forced assembling strategy for processing MXene to hierarchical 3D architecture with geometry-based high resistance to aggregation. Aggregate-resistant properties of 3D MXene not only double the surface area without loss of the intrinsic properties of MXene but also render the characteristics such as kinetics-favorable framework, high robustness, and excellent processability in both solution and solid state. Synergistically coupling the 3D MXene with electrochemically active phases such as metal oxide/phosphides, noble metals, or sulfur yields the hybrid systems with greatly boosted active surface area, charge-transfer kinetics, and mass diffusion rate. Specifically, the CoP-3D MXene hybrids exhibit high electrocatalytic activity toward oxygen and hydrogen evolution in alkaline electrolyte. As a bifunctional electrocatalyst, they exhibit superior cell voltage and durability to combined RuO2/Pt catalysts for overall water splitting in basic solution, highlighting the great promise of aggregation-resistant 3D MXene in the development of high-performance electrocatalysts.

Highly Graphitic Mesoporous Fe,N-Doped Carbon Materials for Oxygen Reduction Electrochemical Catalysts.

The synthesis, characterization, and electrocatalytic properties of mesoporous carbon materials doped with nitrogen atoms and iron are reported and compared for the catalyzed reduction of oxygen gas at fuel cell cathodes. Mixtures of common and inexpensive organic precursors, melamine, and formaldehyde were pyrolyzed in the presence of transition-metal salts (e.g., nitrates) within a mesoporous silica template to yield mesoporous carbon materials with greater extents of graphitization than those of others prepared from small-molecule precursors. In particular, Fe,N-doped carbon materials possessed high surface areas (∼800 m2/g) and high electrical conductivities (∼19 S/cm), which make them attractive for electrocatalyst applications. The surface compositions of the mesoporous Fe,N-doped carbon materials were postsynthetically modified by acid washing and followed by high-temperature thermal treatments, which were shown by X-ray photoelectron spectroscopy to favor the formation of graphitic and pyridinic nitrogen moieties. Such surface-modified materials exhibited high electrocatalytic oxygen reduction activities under alkaline conditions, as established by their high onset and half-wave potentials (1.04 and 0.87 V, respectively vs reversible hydrogen electrode) and low Tafel slope (53 mV/decade). These values are superior to many similar transition-metal- and N-doped carbon materials and compare favorably with commercially available precious-metal catalysts, e.g., 20 wt % Pt supported on activated carbon. The analyses indicate that inexpensive mesoporous Fe,N-doped carbon materials are promising alternatives to precious metal-containing catalysts for electrochemical reduction of oxygen in polymer electrolyte fuel cells.

Bi/Bi2O3 sensor for quantitation of dissolved oxygen in molten salts

To quantify the oxygen content in molten salts, we examined the performance of an yttria-stabilized zirconia solid electrolyte oxygen sensor with a Bi/Bi2O3 reference electrode, focusing on its output accuracy. When the above sensor was tested in a flow of gas with known oxygen partial pressure, p_{O_2}, a linear relationship between lgp_{O_2} and the electromotive force (EMF) was observed, and the correlation slope exhibited a positive deviation from Nernstian behavior. EMF measurements performed in molten NaCl–KCl indicated that the oxygen content of this salt mixture increased with increasing oxygen partial pressure in the covering gas, in agreement with Henry’s law. Moreover, the EMF exhibited a linear decrease with increasing melt temperature of molten NaCl–KCl, in agreement with the theoretical model. Finally, a relationship between the structure of molten NaCl–KCl and its oxygen diffusion behavior was established. As a result, the developed sensor was demonstrated to be well suited for determining the oxygen content of molten salts.

An interface-reconstruction effect for rechargeable aluminum battery in ionic liquid electrolyte to enhance cycling performances

Aluminum (Al) metal has been regarded as a promising anode for rechargeable batteries because of its natural abundance and high theoretical specific capacity. However, rechargeable aluminum batteries (RABs) using Al metal as anode display poor cycling performances owing to interface problems between anode and electrolyte. The solid-electrolyte interphase (SEI) layer on the anode has been confirmed to be essential for improving cycling performances of rechargeable batteries. Therefore, we immerse the Al metal in ionic liquid electrolyte for some time before it is used as anode to remove the passive film and expose fresh Al to the electrolyte. Then the reactions of exposed Al, acid, oxygen and water in electrolyte are occurred to form an SEI layer in the cycle. Al/electrolyte/V2O5 full batteries with the thin, uniform and stable SEI layer on Al metal anode perform high discharge capacity and coulombic efficiency (CE). This work illustrates that an SEI layer is formed on Al metal anode in the cycle using a simple and effective pretreatment process and results in superior cycling performances for RABs.

Electrochemical impedance analysis on solid electrolyte oxygen sensor with gas and liquid reference electrodes for liquid LBE

The ionic conductivity of solid electrolyte may insufficient, and the sensor output signal will deviate from the theoretical one in low temperature. The performance of oxygen sensor with Ag/air reference electrode (RE) and liquid Bi/Bi2O3 RE was tested in low-temperature LBE at 300°– 450°C and the charge transfer reactions impedance at the electrode-electrolyte interface was analyzed by electrochemical impedance analysis (EIS). After steady state condition, both of the sensors performed well and can be used at 300°– 450°C. Bi/Bi2O3 RE has lower impedance than Ag/air RE. Therefore, the response time of the oxygen sensor with Bi/Bi2O3 RE is faster than the oxygen sensor with Ag/air RE in the low-temperature region.

Performance comparison of protonic and sodium phosphomolybdovanadate polyoxoanion catholytes within a chemically regenerative redox cathode polymer electrolyte fuel cell

The direct reduction of oxygen in conventional polymer electrolyte fuel cells (PEFCs) is seen by many researchers as a key challenge in PEFC development. Chemically regenerative redox cathode (CRRC) polymer electrolyte fuel cells offer an alternative approach via the indirect reduction of oxygen, improving durability and reducing cost. These systems substitute gaseous oxygen for a liquid catalyst that is reduced at the cathode then oxidised in a regeneration vessel via air bubbling. A key component of a CRRC system is the liquid catalyst or catholyte. To date, phosphomolybdovanadium polyoxometalates with empirical formula H3+nPVnMo12-nO40 have shown the most promise for CRRC PEFC systems. In this work, four catholyte formulations are studied and compared against each other. The catholytes vary in vanadium content, pH and counter ion, with empirical formulas H6PV3Mo9O40, H7PV4Mo8O40, Na3H3PV3Mo9O40 and Na4H3PV4Mo8O40. Thermodynamic properties, cell performance and regeneration rates are measured, generating new insights into how formulation chemistry affects the components of a CRRC system. The results include the best CRRC PEFC performance reported to date, with noticeable advantages over conventional PEFCs. The optimum catholyte formulation is then determined via steady state tests, the results of which will guide further optimization of the catholyte formulation.

Fungi residue derived carbon as highly efficient hydrogen peroxide electrocatalyst

In electrochemical devices, the reduction of dissolved oxygen in electrolyte can achieve on-site production of hydrogen peroxide. The industrial viability of the process strongly depends on cathode electrocatalyst. However, current catalysts rely on rare, noble metals and their composite. Thus, it remains a great challenge of cost-effective catalyst with both high activity and selectivity. Herein, we made use of extremely low-cost fungi residue biomass, developing a multi-non-precious metal doped carbon catalyst (named as FRC) for H2O2 electrogeneration by facile in-situ synthesis. The one-step prepared FRC balances the performance of different metal oxides and exhibits not only high activity but also high selectivity at a spacious potential range. Specifically, the current density for ring reaches 0.45mAcm−2 at −0.5V (vs SCE). Besides, the selectivity achieves 98% and remain above 91% in wide potential range (−0.7∼−0.3V), which exceeds almost all metal contained carbon materials to our knowledge. As the first study of fungi residue towards H2O2 electrogeneration, this novel approach provides a highly promising and low cost electrocatalyst for real production, moreover, exploring a new direction for H2O2 electrocatalyst development.

In situ measurements of O<sub>2</sub> and CO eq. in cement kilns

Abstract. The simultaneous in situ measurement of O2 and CO eq. in cement kilns is a great challenge due to the high process temperatures and high dust load. The standard method for measurement for flue gas in cement kilns is extractive. Extractive measurements have a higher response time due to the flue gas conditioning including the length of heated extraction lines for electrochemical or optical analysis. This delayed response is not optimal for fast process control.A probe was developed for this purpose in which the in situ solid electrolyte oxygen sensor and an in situ CO eq. mixed potential sensor are implemented. Due to the high temperatures, the probe is cooled by a water–coolant mixture. In order to prevent deposits of raw material forming and sintering on the probe, it rotates 90° in programmable intervals. In addition, an automated probe plunger pneumatically removes plugging at the probe flue gas entrance, also in programmable intervals. These self-cleaning functions allow the probe to continually stay in the process for combustion optimisation (low excess O2 and CO) and enable the plant operator to measure additional process-related gas components (NO, SO2, HCl etc.) and optimise the SNCR (selective non-catalytic reduction) for NOx reduction. Combustion air supply can be adapted very quickly due to the in situ sensors, which has been demonstrated by a CEMTEC® probe over years (Märker Cement Harburg, 2017).

Functionalized carbon nanotube based hybrid electrochemical capacitors using neutral bromide redox-active electrolyte for enhancing energy density

Abstract A hybrid electrochemical capacitor (EC) with enhanced energy density is realized by integrating functionalized carbon nanotube (FCNT) electrodes with redox-active electrolyte that has a neutral pH value (1 M Na 2 SO 4 and 0.5 M KBr mixed aqueous solution). The negative electrode shows an electric double layer capacitor-type behavior. On the positive electrode, highly reversible Br − /Br 3 − redox reactions take place, presenting a battery-type behavior, which contributes to increase the capacitance of the hybrid cell. The voltage window of the whole cell is extended up to 1.5 V because of the high over-potentials of oxygen and hydrogen evolution reactions in the neutral electrolyte. Compared with raw CNT, the FCNT has better wettability in the aqueous electrolyte and contributes to increase the electric double layer capacitance of the cell. As a result, the maximum energy density of 28.3 Wh kg −1 is obtained from the hybrid EC at 0.5 A g −1 without sacrificing its power density, which is around 4 times larger than that of the electrical double layer capacitor constructed by FCNT electrodes and 1 M Na 2 SO 4 electrolyte. Moreover, the discharge capacity retained 86.3% of its initial performance after 10000 cycles of galvanostatic charge and discharge test (10 A/g), suggesting its long life cycle even at high current loading.