Oxygen Gas Evolution Research Articles

Unleashing the impact of Nb-doped, single crystal, cobalt-free P2-type Na0.67Ni0.33Mn0.67O2 on elevating the cycle life of sodium-ion batteries

A synergistic stabilization effect in a Nb-doped P2-type single crystal cobalt-free layered oxide cathode material, offering remarkable cycling stability and high-power performance for Na-ion batteries have unveiled in this study. The introduction of Nb in the transition metal layer not only reduces the electronic band gap but also enhances electronic conductivity and mitigates ionic diffusion energy barriers. The induction of a robust Nb-O bond expedites electron and Na+ transfer, contributing to the stabilization of the host structure is further confirmed through the density functional theory calculations, including electron localization function (ELF) and crystal orbital Hamiltonian population (COHP). To the best of our knowledge, this study is the first to demonstrate a homogeneous distribution of niobium throughout the single crystal, specifically doped at the nickel site within the bulk, without inducing atomic-scale surface reorganization. The presence of single crystals improves various kinetic factors, demonstrating the profound correlation between structural defects and chemical proliferation, thereby reducing the evolution of oxygen gas. The P2-type Nb-doped single crystal cathode (Na0.67Ni0.31Mn0.67Nb0.02O2) exhibits remarkable capacity retention, >95 % after 100 cycles at 0.1 C and >90 % after an extended cycling of 2000 cycles at 1 C. Practical assessments in complete cell setups with a pre-sodiated hard carbon anode further validate the material's viability, showcasing capacity retention of over 93 % after 100 cycles in a coin cell and approximately 89 % in a pouch cell format. This comprehensive study establishes the transformative potential of Nb-doped single crystal cobalt-free P2-type layered oxide cathode materials, marking a significant advancement in sodium-ion battery technology.

Gas Evolution Kinetics in Overlithiated Positive Electrodes and its Impact on Electrode Design.

Increasing lithium contents within the lattice of positive electrode materials is projected in pursuit of high-energy-density batteries. However, it intensifies the release of lattice oxygen and subsequent gas evolution during operations. This poses significant challenges for managing internal pressure of batteries, particularly in terms of the management of gas evolution in composite electrodes-an area that remains largely unexplored. Conventional assumptions postulate that the total gas evolution is estimated by multiplying the total particle count by the quantities of gas products from an individual particle. Contrarily, this investigation on overlithiated materials-a system known to release the lattice oxygen-demonstrates that loading densities and inter-particle spacing in electrodes significantly govern gas evolution rates, leading to distinct extents of gas formation despite of an equivalent quantity of released lattice oxygen. Remarkably, this study discoveres that O2 and CO2 evolution rates are proportional to 1O2 concentration by the factor of second and first-order, respectively. This indicates an exceptionally greater change in the evolution rate of O2 compared to CO2 depending on local 1O2 concentration. These insights pave new routes for more sophisticated approaches to manage gas evolution within high-energy-density batteries.

Numerical investigation of two-phase flow patterns and carbon deposition in a coaxial-type reactor for molten salt electrolysis

The electrodeposition process of carbon in molten lithium carbonate electrolysis and the associated gas-liquid flow hydrodynamics characteristics are for the first time investigated using computational fluid dynamics (CFD). The high-temperature (750 °C) process is challenging for conducting measurements, making CFD a valuable tool for providing insights into the novel coaxial-type cell design. The CFD simulation addresses the electric field distribution, oxygen gas evolution, and electrodeposition of carbon. The effect of gas bubble sizes (1, 0.8, and 0.6 mm) on the electrolysis process was examined at different electrical current densities (0.15 ± 0.01 A cm–2). The CFD results reveal that gas holdup increases by decreasing the bubble size and that the bubble size significantly impacts the current density distribution by affecting the two-phase flow dynamics. The study highlights the potential of CFD for optimization of molten salt processes, while also suggesting the need for further improvements in the model.

Antibacterial sponge for rapid noncompressible hemostatic treatment: spatiotemporal studies using a noninvasive model.

Hemorrhage is one of the leading causes of preventable death. While minor injuries can be treated mainly by conventional methods, deep and irregular wounds with profuse bleeding present significant challenges, some of which can be life-threatening and fatal. This underscores the need to develop easily applicable FDA-approved hemostatic treatments that can effectively stanch blood loss at the point of care before professional medical care. A silicone-based bandage system (SilFoam), a non-compressible, self-expanding, antibacterial hemostatic treatment, is reported here. Its two-component system reacts in situ upon mixing to form a stretchable sponge that acts as a 'tamponade' by expanding within seconds with the evolution of oxygen gas from the interaction of the reactive components present in the formulation. This generates autogenous pressure on the wound that can effectively arrest heavy bleeding within minutes. Possessing optimal adhesive properties, the expanded sponge can be easily removed, rendering it optimal for hemostatic wound dressing. With recent advances in biotechnological research, there is a growing awareness of the potential issues associated with in vivo trials, spanning ethical, psychological, economic, and physiological concerns like burnout and fatigue. Bearing this in mind, a unique manikin system simulating a deep abdominal wound has been employed to investigate SilFoam's hemostatic efficacy with different blood-flow rates using a non-invasive model that aims to provide an easy, fast, and economical route to test hemostatic treatments before in vivo studies. This is the first time an Ag2O-based oxygen-induced foaming system has been reported as a hemostatic agent.

Surface Design Engineering of LiTaO3 Coating on Li-Excess Li2NiO2 Cathode Additive for Lithium-Ion Batteries

The latest research has mainly focused on enhancement in the energy density of lithium-ion batteries (LIBs) to satisfy the rigorous industrial demands. As the most common approach for improving the energy density of LIBs, the utilization of high capacity anode materials, such as silicon suboxide (SiOx), has been highlighted, instead of graphite. SiOx anodes are known to have a high specific capacity and low operating voltage (< 0.5 V vs. Li/Li+). However, the severe initial capacity loss induced by the formation of solid electrolyte interphase (SEI) limits their commercial use in LIBs. To compensate for the initial loss of available Li+, the application of Li-excess cathode additives has been considered as the most practical strategy for supplying surplus Li+ during the initial charge process. In this respect, Li2NiO2 is a suitable cathode additive because it offers a high initial charge capacity (≥ 320 mAh g-1) and a compatible operating voltage with commercial cathode materials. Surface protection of Li2NiO2 is still required, however, due to its vulnerability to moisture (H2O) and carbon dioxide (CO2) in the ambient atmosphere. Moreover, Li2NiO2 becomes more structurally unstable during cycle due to oxygen (O2) gas evolution, leading to the formation of microcracks. To overcome these obstacles, we suggest a functional LiTaO3 coating layer onto the surface of Li2NiO2 for structural stabilization. In practice, the LiTaO3 coating layer can effectively suppress the production of impurities (i.e., LiOH and Li2CO3) at the surface of Li2NiO2 after air exposure. Furthermore, the gas evolution and microcracks can be minimized by enhancing the structural stability of Li2NiO2 during cycling. These synergetic effects of the LiTaO3 coating layer can provide clear insights for the development of Li-excess cathode additives for achieving advanced LIBs.

Confinement Accelerates Water Oxidation Catalysis: Evidence from In Situ Studies.

Basic insight into the structural evolution of electrocatalysts under operating conditions is of substantial importance for designing water oxidation catalysts. The first-row transition metal-based catalysts present state-of-the-art oxygen evolution reaction (OER) performance under alkaline conditions. Apparently, confinement has become an exciting strategy to boost the performance of these catalysts. The van der Waals (vdW) gaps of transition metal dichalcogenides are acknowledged to serve as a suitable platform to confine the first-row transition metal catalysts. This study focuses on confining Ni(OH)2 nanoparticle in the vdW gaps of 2D exfoliated SnS2 (Ex-SnS2 ) to accelerate water oxidation and to guarantee long term durability in alkaline solutions. The trends in oxidation states of Ni are probed during OER catalysis. The in situ studies confirm that the confined system produces a favorable environment for accelerated oxygen gas evolution, whereas the un-confined system proceeds with a relatively slower kinetics. The outstanding OER activity and excellent stability, with an overpotential of 300mV at 100mAcm-2 and Tafel slope as low as 93mVdec-1 results from the confinement effect. This study sheds light on the OER mechanism of confined catalysis and opens up a way to develop efficient and low-cost electrocatalysts.

Stabilizing the surface of Li2NiO2 cathode additive by coating amorphous niobium oxy-carbide for lithium-ion batteries

The formation of solid electrolyte interphase at the first cycle has raised technical issues of capacity loss in anode materials for lithium-ion batteries. As one solution, using Li-excess Li2NiO2 as a cathode additive aims to compensate for the initial Li+ consumption by anode materials using some of the high irreversible capacity. However, Li2NiO2 is insufficient for satisfying atmospheric stability, which induces spontaneous side reactions (e.g. Li2CO3 and LiOH), resulting in an increase of interfacial resistance for Li+ migration. In addition, the small but significant evolution of oxygen (O2) gas during the charge process over 3.8 V vs. Li/Li+ brings an extra caution for safety concerns. There is no doubt that structural stabilization of Li2NiO2 is a prerequisite for practical use in lithium-ion batteries. In this study, we propose a surface coating of amorphous niobium oxycarbide (NbOxCy) onto Li2NiO2 particles to improve their atmospheric stability, together with suppression of O2 gas evolution. Owing to its distinctive physicochemical properties, NbOxCy is beneficial for enhancing vulnerability to moisture as well as scavenging any residual O2 gas. In practice, the adoption of NbOxCy-coated Li2NiO2 improved electrochemical performance in full cells and was verified as a strategic solution to two fundamental challenges.

Surface coating engineering of Li-excess cathode additive of lithium-ion batteries for initial charge compensation

Silicon based anodes are known to have a high specific capacity and low operating voltage (less than 0.5 V vs. Li/Li+). Even so, the solid electrolyte interphase (SEI) formation induces the severe capacity loss at the first cycle, known as a critical factor in reducing the energy density of lithium-ion batteries (LIBs). To improve the energy density by compensating the initial Li+ loss, the utilization of Li-excess cathode additives has been considered as the most practical strategy for supplying surplus Li+ during the initial charge. Li2NiO2 is an ideal cathode additive thanks to its large charge capacity (≥320 mAh g−1) and low Coulombic efficiency (∼35%) at the first cycle. Surface protection of Li2NiO2 is still required, however, due to its vulnerability to moisture (H2O) and carbon dioxide (CO2) in the ambient atmosphere. In addition, Li2NiO2 becomes more structurally unstable due to oxygen (O2) gas evolution, leading to the formation of microcracks. Herein, we introduce a functional LiTaO3 coating layer onto the surface of Li2NiO2 for structural stabilization. The LiTaO3 coating layer can effectively suppress the formation of impurities (i.e., LiOH and Li2CO3) after air exposure. Furthermore, the gas evolution and mechanical cracking can be minimized by enhancing the structural integrity of Li2NiO2 during cycling.

Pressure-Driven Fabrication of Zn-Doped Co3C@Carbon Nano-Onions for Robust Oxygen Evolution Reaction

Despite being an essential half-reaction for splitting water, the oxygen evolution reaction (OER) is rarely used in the industry because it is slow and requires expensive catalysts. Here, in the present study, the nanosheet of Co3C and carbon nano-onions (CNOs) have been prepared using an annealing process under high pressure, and Zn-doped Co3C was additionally prepared to investigate the impact of doping on Co3C nanosheet as an OER electrocatalyst. The synthesized electrocatalyst is portrayed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmet–Teller (BET), and Fourier transform infrared (FTIR). The standing nanoflakes are shaped on the nanosheets of Co3C in the wake of the doping effect. The mesoporous nanoflakes Zn-Co3C@CNO have shown striking OER activity requiring 1.45 V vs RHE as the beginning potential for the OER and required a 276 mV overpotential (η) at 10 mA cm–2. Indeed, even the higher current densities of 50 and 78 mA cm–2 were achieved individually at lower η of 301 and 345 mV, respectively. The prepared electrocatalyst has shown unusual activity fit for continuous oxygen gas evolution for more than 50 h. Such excellent OER performance can be credited to doping Zn particles into the lattice structure of Co3C, along with nanoflakes like standing construction are shaped on the nanosheet of Co3C and microporosity of arranged terminals are considered as efficient for higher OER activity.

The Boundary between Two Modes of Gas Evolution: Oscillatory (H2 and O2) and Conventional Redox (O2 Only), in the Hydrocarbon/H2O2/Cu(II)/CH3CN System

During the oxidation of hydrocarbons using hydrogen peroxide solutions, the evolution of gaseous oxygen is a side and undesirable process, in which the consumption of the oxidizer is not associated with the formation of target products. Therefore, no attention is paid to the systematic study of the chemical composition of the gas and the mechanisms of its formation. Filling this gap, the authors discovered a number of new, previously unidentified, interesting facts concerning both gas evolution and the oxidation of hydrocarbons. In a 33% H2O2/Cu2Cl4·2DMG/CH3CN system, where DMG is dimethylglyoxime (Butane-2,3-dione dioxime), and is at 50 °C, evidence of significant evolution of gaseous hydrogen, along with the evolution of gaseous oxygen was found. In the authors’ opinion, which requires additional verification, the ratio of gaseous hydrogen and oxygen in the discussed catalytic system can reach up to 1:1. The conditions in which only gaseous oxygen is formed are selected. Using a number of oxidizable hydrocarbons with the first adiabatic ionization potentials (AIPs) of a wide range of values, it was found that the first stage of such a process of evolving only gaseous oxygen was the single electron transfer from hydrogen peroxide molecules to trinuclear copper clusters with the formation, respectively, of hydrogen peroxide radical cations H2O2•+ and radical anions Cu3Cl5•− (AIP = 5 eV). When the conditions for the implementation of such a single electron transfer mechanism are exhausted, the channel of decomposition of hydrogen peroxide molecules into gaseous hydrogen and oxygen is switched on, which is accompanied by the transition of the system to an oscillatory mode of gas evolution. In some cases, the formation of additional amounts of gaseous products is provided by the catalytically activated decomposition of water molecules into hydrogen and oxygen after the complete consumption of hydrogen peroxide molecules in the reaction of gaseous oxygen evolution. The adiabatic electron affinity of various forms of copper molecules involved in chemical processes is calculated by the density functional theory method.

Metastable Cubic Structure Exceeds Capacity Limit of Antifluorite Li5FeO4 Cathode Using Small Polarized Oxygen Redox

AbstractCost‐effective Fe‐based cathode materials have attracted significant attention. Recently, antifluorite‐type Li5FeO4 has been investigated as a high‐capacity cathode material owing to its high lithium content and solid‐state oxygen redox reactions. However, its reversible capacity is restricted to transition‐metal redox reactions because of its irreversible structural transformation and oxygen evolution. This study demonstrates the reversible oxygen redox reaction in metastable cubic antifluorite Li5FeO4 obtained by mechanochemical treatment. It exhibits a reversible capacity of more than 300 mAh g‐1, corresponding to an approximately 1.7‐electron reaction, without oxygen gas evolution. Combined analyses of X‐ray absorption spectroscopy (XAS) and theoretical calculations reveal that both Fe3+/Fe4+ and O2‐/O22‐ redox reactions proceed under semi‐coherent structural transformations between antifluorite and rocksalt, which differs from the known orthorhombic Li5FeO4 phase. Although the cyclability of oxygen redox is poor, its solid solution with Co2+ enhances cyclability by suppressing oxygen evolution. Tuning the structural symmetry and transition‐metal content can overcome the reversible capacity limit of antifluorite cathode materials, which is useful for the development of high‐energy cathode materials by the effective utilization of solid‐state oxygen redox reactions.

Visualizing 4D Pore-Scale Gas Transport in Operating PEM Electrolyzers Using X-Ray Computed Tomography

Mass transport losses in polymer electrolyte membrane (PEM) electrolyzers are predominantly caused by the accumulation of oxygen gas within the pores of the porous transport layer (PTL), hindering reactant water delivery to reaction sites (1). To enhance mass transport and optimize electrolyzer performance, a comprehensive understanding of the mechanisms driving oxygen gas transport in the PTL is required. Numerous studies have utilized various imaging techniques - including optical, neutron, and X-ray radiography to elucidate the evolution and transport of oxygen gas in the multiphase flow regime during PEM electrolyzer operation (2). However, these techniques only capture two-dimensional (2D) images, resolving average gas distributions rather than a holistic pore-scale quantification. Few studies have used three-dimensional (3D) imaging to resolve the dynamic microscale distributions of oxygen gas in the PTL. Understanding the impact of key parameters affecting 3D oxygen gas transport, such as PTL morphology, will allow for tailored pore-scale material optimization for enhanced gas transport and improved performance of PEM electrolyzers.This study presents a non-destructive operando imaging approach using X-ray computed tomography (CT), enabling the visualization of transient 3D oxygen gas evolution and transport in the PTL of a PEM electrolyzer. Using state-of-the-art synchrotron X-rays, high temporal and spatial resolutions were achieved to capture the pore-scale formation and growth of oxygen gas pathways within the PTL at various operating conditions. Electrochemical performance of an in-house designed electrolyzer cell was also characterized while acquiring tomographic images to investigate the impact of observed transport mechanisms on performance. The methodology presented in this work showcases the capability of using X-ray CT to visualize the complex interfacial multiphase flow in PTLs. Findings from this study will provide valuable insight towards pore-scale material optimization of clean energy porous materials aimed at curtailing the costs of green hydrogen production.

Amine and Carbon-pretreated nickel–molybdenum disulfide as bifunctional electrocatalysts for hydrogen and oxygen gas evolution

We report the synthesis and characterization of a variety of nickel molybdenum disulfide (NiMoS2) materials as efficient bifunctional electrocatalysts for both the hydrogen evolution and oxygen evolution reactions (HER and OER, respectively). These catalysts were obtained from pretreated ammonium tetrathiomolybdate (ATM) using ethylenediamine (EDA), diethylenetriamine (DETA), or carbon nanotubes (CNT), which were further reacted with Ni(NO3)2. All the materials were characterized by scanning electron microscopy (SEM) and powder X-ray diffraction (pXRD), and all materials were evaluated as both HER and OER electrocatalysts. The NiMoS2 synthesized from DETA-pretreatment exhibits the best HER catalytic performance with the lowest overpotential of 0.151 V, while the CNT-modified NiMoS2 shows the lowest OER overpotential of 0.310 V. All the pretreated NiMoS2 electrocatalysts show significantly improved catalytic activity compared to the one prepared directly from pristine ATM precursor.

Morphological comparison and growth mechanism of TiO2 nanotubes in HBF4 and NH4F electrolytes

At present, the growth mechanism of TiO2 nanotubes in different electrolytes is still controversial. Field assisted dissolution (FAD) theory believes that fluoride ion is the main factor affecting the growth of TiO2 nanotubes. In this paper, we conducted a comparative experiment in HBF4 and NH4F electrolytes which containing the same fluoride ion molarity. By comparing the growth morphology of TiO2 nanotubes in two electrolytes, orderly nanotube arrays were obtained in NH4F electrolyte. However, only dense films and nanotube embryos were formed in HBF4 electrolyte. Obviously, FAD theory cannot explain these phenomena. Ionic current and electronic current theories and oxygen bubble model are reasonable for these phenomena. In the NH4F electrolyte, there are high electronic current and intense oxygen evolution, so the nanotube embryos cannot be seen. The low electronic current in the HBF4 electrolyte and the slow evolution of oxygen gas lead to the discovery of the nanotube embryos. This phenomenon also confirms that the formation process of TiO2 nanotubes is that anodic oxides grow upward around the oxygen bubble to form the nanotube walls.

Polymer Complexes for Electrocatalytic Oxygen Evolution

Electrocatalytic water oxidation for oxygen gas evolution has been widely studied from the perspective of sustainable technology. However, the use of organic polymers as catalyst layers for this reaction remains un-developed. We discuss, here, the prerequisites, characteristics, and advantages of π-conjugated polymers as electrochemical catalysts to modify anodic current collectors for water oxidation, including some examples by citing the previous works in literature. In section 3, we present our latest results, the use of an organic pol-ymer complex of poly(ethylenedioxythiophene) and phytic acid supported by a hydrophilic poly(hydroxy-ethyl methacrylate) platform, which efficiently generates oxygen gas through anodic water oxidation.

Inexpensive Amorphous FeIII Oxo‐/Hydroxide as Highly Active and Ultradurable Electrocatalyst for Water Electrolysis

AbstractDeveloping highly active, cost‐effective, and robust electrocatalysts for the oxygen evolution reaction (OER) still remains a crucial challenge for enhancing the conversion of sustainable energy resources. The performances of existing electrocatalysts is restricted by low electronic conductivity and the limited amount of active sites. Herein, newly synthesized FeIIIOH nanoparticles (NPs) are shown to be efficient and durable electrocatalysts for the OER reaction. FeIIIOH NP‐coated nickel foam (FeIIIOH NPs/NF) operates at an overpotential of 300 mV (@10 mA cm−2) with excellent stability even after 30 h and shows higher stability relative to a cell voltage of 1.55 V in alkaline media, which is substantially lower than the commercial electrocatalyst IrO2 (1.61 V). The FeIIIOH NPs/NF overpotential of 300 mV at 10 mA cm−2 is 89 and 127 mV lower than IrO2/NF (389 mV) and NF (427 mV), respectively. The Tafel slope of FeIIIOH NPs/NF (104 mV dec−1) is lower than IrO2/NF (164 mV dec−1) and NF (199 mV dec−1). The calculated turnover frequency (TOF) of FeIIIOH NPs (0.0128 s−1) is approximately five times higher than that of the IrO2 catalyst (0.0089 s−1) at 1.60 V. This reflects that the FeIIIOH NP catalyst is intrinsically active, giving outstanding OER performances and showing satisfactory kinetics to overcome the sluggish water oxidation rate. Solar water electrolysis shows continuous evolution of oxygen and hydrogen gas at the anode and cathode, respectively, at 1.55 V. The amount of hydrogen generated during solar water electrolysis was calculated as 3.22 mmol h−1 cm−2, which is close to the coulombic efficiency at 1.55 V. This demonstration develops the hope for superior exploration of FeIIIOH NPs/NF toward the expansion of real and large‐scale hydrogen production with the lowest price.

Electrolysis of iron with oxygen gas evolution from molten sodium borate electrolytes

ABSTRACT Molten oxide electrolysis can be used to reduce the carbon dioxide emissions from ironmaking. In this paper, we electrochemically decompose iron oxide (Fe2O3) into iron (Fe) and oxygen (O2) using boron trioxide and sodium oxide (B2O3–Na2O) as the molten oxide electrolyte at 1000°C that is less than the temperature of other molten oxide electrolysis. The formation of Fe at the cathode and O2 at the anode is identified by analysing products from both electrodes. The results suggest that the cathodic current efficiency of electrolysis at 2 V is about 54.7%, energy consumption is about 5.27 kW h kg–1 of Fe at 2 V electrolysis, and purity of the reduced Fe was more than 97 mol.%. With respect to the process temperature and product yield, B2O3–Na2O molten oxide has potential as a supporting electrolyte to reduce Fe2O3 to Fe without consuming any carbon.

High Pressure Effect on Structural and Electrochemical Properties of Anionic Redox-Based Lithium Transition Metal Oxides

Summary The richness of anionic redox chemistry in the solid state offers new opportunities and a possible paradigm shift in energy storage. The excess capacity that goes beyond conventional theoretical values is attributed to the anionic redox in Li-rich transition metal oxide cathodes for Li-ion batteries. Their electrochemical behavior is thermodynamically determined by structural evolution. To better understand the electrochemical dependence on structural factors, we have induced structural modifications in pristine and electrochemically activated Li1.144Ni0.136Co0.136Mn0.544O2 through high-pressure treatment. A unique cyclical change of structural reordering is observed in the anionic redox-activated material during operando pressure sweep, characterized by a periodic evolution of superlattice peak intensity in synchrotron X-ray diffraction patterns. During the structural reordering period, the bulk compressibility of the material decreases, even becoming negative. These insights elucidate the structural flexibility and metastability of anionic redox-based materials, which can undergo large compressions and structural modifications while delivering good electrochemical properties.

Electrochemically driven degradation of chemical solution deposited ferroelectric thin-films in humid ambient

The ambient humidity significantly accelerates the degradation of lead zirconate titanate (PZT) films in microelectromechanical systems; the cause of such degradation is under debate. Here, it is shown that the degradation of chemical solution derived PZT thin-films in humid conditions is driven by the system's electrochemical activity toward water electrolysis. The layer stacks with Pt-based electrodes exhibited a faster degradation rate owing to their higher electrocatalytic activity compared to Au. A degradation model is proposed based on the electrolysis of liquid or gaseous H2O, involving the evolution of oxygen and hydrogen gas at the top and bottom electrodes. Degradation proceeds above the threshold voltage for a given electrode system and is driven by the evolution and pressure build-up of gaseous species at the PZT/electrode interfaces. The pressure build-up causes film cracking, delamination of the film and electrodes, electrothermal breakdown events, and eventually time-dependent dielectric breakdown. Significantly larger post-breakdown crater sizes in humid than in dry conditions suggests that larger cracks through which dielectric breakdown through humidified air can occur. Overall, these effects are shown to cause sample failure up to six orders of magnitude of time earlier than for operation in dry conditions. Thus, in order to improve the resilience of thin-film systems in humid conditions, it is imperative to protect the electrochemically active electrode components of the device.

Revealing the Local pH Value Changes of Acidic Aqueous Zinc Ion Batteries with a Manganese Dioxide Electrode during Cycling

The research on aqueous zinc ion batteries (AZIB) is getting more attention as the energy transition continues to develop and the need for inexpensive and safe stationary storage batteries is growing. As the detailed reaction mechanisms are not conclusively revealed, we want to take an alternative approach to investigate the importance of pH value changes during cycling. By adding a pH-indicator to the electrolyte (2 M ZnSO4 + 0.1 M MnSO4), the local pH-value change during operation is visualized in operando. The overall pH value was found to increase during cycling whereas a major temporary pH drop in close proximity of the manganese dioxide electrode surface occurs. Additionally, this pH value change was quantified locally by in operando measurements with a pH micro electrode. Different electrolyte compositions with additives (sodium dodecyl sulfate (SDS), sulfuric acid (H2SO4)) and operation voltages were tested. The pH-potential-diagrams of manganese and zinc reveal pH value and potential limits, leading to active material dissolution at lower pH values and oxygen gas evolution at higher potentials >1.7 V. The procedure of combining a pH indicator, pH microelectrode measurements and pH-potential diagrams can be seen as an appropriate method to determine the recommendable working window of aqueous batteries.