Porous Solid Electrolyte Research Articles

Three-chamber electrochemical reactor for selective lithium extraction from brine

Efficient lithium recovery from geothermal brines is crucial for the battery industry. Current electrochemical separation methods struggle with the simultaneous presence of Na+, K+, Mg2+, and Ca2+ because these cations are similar to Li+, making it challenging to separate effectively. We address these challenges with a three-chamber reactor featuring a polymer porous solid electrolyte in the middle layer. This design improves the transference number of Li+ (tLi+) by 2.1 times compared to the two-chamber reactor and also reduces the chlorine evolution reaction, a common side reaction in electrochemical lithium extraction, to only 6.4% in Faradaic Efficiency. Employing a lithium-ion conductive glass ceramic (LICGC) membrane, the reactor achieved high tLi+ of 97.5% in LiOH production from simulated brine, while the concentrations of Na+ K+, Mg2+, and Ca2+ are below the detection limit. Electrochemical experiments and surface analysis elucidated the cation transport mechanism, highlighting the impact of Na+ on Li+ migration at the LICGC interface.

Electrochemical regeneration of high-purity CO2 from (bi)carbonates in a porous solid electrolyte reactor for efficient carbon capture

Electrochemical regeneration of high-purity CO2 from (bi)carbonates in a porous solid electrolyte reactor for efficient carbon capture

Cobalt-Doped Bismuth Nanosheet Catalyst for Enhanced Electrochemical CO2 Reduction to Electrolyte-Free Formic Acid.

Electrochemical carbon dioxide (CO2) reduction reaction (CO2RR) to valuable liquid fuels, such as formic acid/formate (HCOOH/HCOO-) is a promising strategy for carbon neutrality. Enhancing CO2RR activity while retaining high selectivity is critical for commercialization. To address this, we developed metal-doped bismuth (Bi) nanosheets via a facile hydrolysis method. These doped nanosheets efficiently generated high-purity HCOOH using a porous solid electrolyte (PSE) layer. Among the evaluated metal-doped Bi catalysts, Co-doped Bi demonstrated improved CO2RR performance compared to pristine Bi, achieving ~90 % HCOO- selectivity and boosted activity with a low overpotential of ~1.0 V at a current density of 200 mA cm-2. In a solid electrolyte reactor, Co-doped Bi maintained HCOOH Faradaic efficiency of ~72 % after a 100-hour operation under a current density of 100 mA cm-2, generating 0.1 M HCOOH at 3.2 V. Density functional theory (DFT) results revealed that Co-doped Bi required a lower applied potential for HCOOH generation from CO2, due to stronger binding energy to the key intermediates OCHO* compared to pure Bi. This study shows that metal doping in Bi nanosheets modifies the chemical composition, element distribution, and morphology, improving CO2RR catalytic activity performance by tuning surface adsorption affinity and reactivity.

Highly Stable Organic Molecular Porous Solid Electrolyte with One-Dimensional Ion Migration Channel for Solid-State Lithium-Oxygen Battery.

Solid-state lithium-oxygen (Li-O2 ) batteries have been widely recognized as one of the candidates for the next-generation of energy storage batteries. However, the development of solid-state Li-O2 batteries has been hindered by the lack of solid-state electrolyte (SSE) with high ionic conductivity at room temperature, high Li+ transference number, and the high stability to air. Herein, we developed the organic molecular porous solid cucurbit[7]uril (CB[7]) with one-dimensional (1D) ion migration channels as the SSE for solid-state Li-O2 batteries. Taking advantage of the 1D ion migration channel for Li+ conduction, CB[7] SSE achieved high ionic conductivity (2.45×10-4 S cm-1 at 25 °C). Moreover, the noncovalent interactions facilitated the immobilization of anions, realizing a high Li+ transference number (tLi + = 0.81) and Li+ uniform distribution. The CB[7] SSE also shows a wide electrochemical stability window of 0-4.65V and high thermal stability and chemical stability, as well as realizes stable Li+ plating/stripping (more than 1000h at 0.3mA cm-2 ). As a result, the CB[7] SSE endows solid-state Li-O2 batteries with superior rate capability and long-term discharge/charge stability (up to 500h). This design strategy of CB[7] SSE paves the way for stable and efficient solid-state Li-O2 batteries toward practical applications. This article is protected by copyright. All rights reserved.

Understanding the Connection between Li-Ion Transport Number and Electrochemical Performance in Fluorinated Ether-Based Electrolytes

As high-performance batteries increase in demand, lithium metal batteries (LMBs) have attracted increasing attention in recent years. Nonetheless, LMBs are limited in their performance due to a low cation transport number (tLi+) of non-aqueous liquid electrolytes, which is the ratio of charge transport of Li-ions to its counterion. This study investigated fluorinated ether-based electrolytes (1,2-(1,1,2,2-tetra fluoroethoxy) ethane, TFEE) with 1,2-dioxolane (DOL) as a co-solvent that were found to have tLi+ of 0.70, which was determined through electrochemical impedance spectroscopy, EIS. This electrolyte mixture gives a low electrolyte coulombic efficiency and poor stability tested in both Li-Cu half and Li – Li4Ti5O12 full cells. The same fluorinated electrolyte with dimethoxy ethane (DME) as a co-solvent showed better coulombic efficiency and stability despite its low tLi+ of 0.18. A significant migration resistance through the porous solid electrolyte interface (SEI) in the case of TFEE-DOL electrolytes is suspected to explain the observed discrepancy, as demonstrated by EIS and X-ray photoelectron spectroscopy. We propose that the properties/process of the Li anode are more crucial for LMBs’ performance than the ionic transport through the bulk electrolyte. Furthermore, the transport number should be determined carefully to avoid any spurious effects associated with SEI properties. Acknowledgments This work has received funding from the European Union Horizon 2020 research and innovation DESTINY program under grant agreement No. 945357. Co-financing from Slovenian Research Agency (ARRS) is fully acknowledged.

Modeling and multiphysics analysis for electrochemical CO2 reduction in solid-electrolyte reactors

Mass transfer and overportential distribution of solid-electrolyte reactors, an electrochemical CO2 conversion equipment, are analyzed by a multiphysics model. It shows that the ohmic loss caused by charge transport in porous solid electrolytes (usually thought to be a major bottleneck of solid-electrolyte reactors) begins to show its significantly negative effect on reactor performance till current densities reach 400 mA/cm2, much higher than that required for relevant commercial operation (∼200 mA/cm2). Thus, we suggest much attention should still be put on how to decrease thermodynamics (∼1.46 V) and activation losses (>1.4 V) of reactors, rather than developing elaborate structures and materials of porous solid electrolytes to decrease ohmic losses.

Strongly Coupled Ag/Sn–SnO2 Nanosheets Toward CO2 Electroreduction to Pure HCOOH Solutions at Ampere-Level Current

HighlightsThe strongly coupled Ag/Sn–SnO2 nanosheets (NSs) were prepared via a versatile electrochemical template strategy, and the generated electron-enriched Sn sites promote the formation of *OCHO and alleviate the energy barriers of *OCHO to *HCOOH.Ag/Sn–SnO2 NSs afford a superior activity toward CO2 electroreduction with current densities up to 2000 mA cm‒2 and near-unity selectivity for formate production.Ag/Sn–SnO2 NSs as the cathode in a membrane electrode assembly with porous solid electrolyte reactor enable the direct production of ~ 0.12 M pure HCOOH solution for 200 h.

Electrochemical removal of gaseous benzene using a flow-through reactor with efficient and ultra-stable titanium suboxide/titanium-foam anode at ambient temperature

Catalytic oxidation technology is currently considered as a feasible approach to degrade and mineralize volatile organic compounds (VOCs). However, it is still challenging to realize efficient removal of VOCs through catalytic oxidation at room temperature. In our study, a novel flow-through electrocatalytic reactor was designed, composed of porous solid-electrolyte, gas-permeable titanium sub-oxides/titanium-foam (TiSO/Ti-foam) as anode and platinum coated titanium foam (Pt/Ti-foam) as cathode. This device could oxidize nearly 100% of benzene (10 ppm) to carbon dioxide at a current density of 1.2 mA/cm2 under room temperature. More importantly, the device maintained excellent stability over 1000 h. Mechanism of benzene mineralization was discussed. Hydroxyl radicals generated on the TiSO/Ti-foam anode played a crucial role in the oxidation of benzene. This study provides a promising prototype of the electrochemical air purifier, and may find its application in domestic and industrial air pollution control.

Synergy of Cu/C3N4 Interface and Cu Nanoparticles Dual Catalytic Regions in Electrolysis of CO to Acetic Acid

AbstractElectrochemical reduction reaction of carbon monoxide (CORR) offers a promising way to manufacture acetic acid directly from gaseous CO and water at mild condition. Herein, we discovered that the graphitic carbon nitride (g‐C3N4) supported Cu nanoparticles (Cu−CN) with the appropriate size showed a high acetate faradaic efficiency of 62.8 % with a partial current density of 188 mA cm−2 in CORR. In situ experimental and density functional theory calculation studies revealed that the Cu/C3N4 interface and metallic Cu surface synergistically promoted CORR into acetic acid. The generation of pivotal intermediate −*CHO is advantage around the Cu/C3N4 interface and migrated *CHO facilitates acetic acid generation on metallic Cu surface with promoted *CHO coverage. Moreover, continuous production of acetic acid aqueous solution was achieved in a porous solid electrolyte reactor, indicating the great potential of Cu−CN catalyst in the industrial application.

Synergy of Cu/C3 N4 Interface and Cu Nanoparticles Dual Catalytic Regions in Electrolysis of CO to Acetic Acid.

Electrochemical reduction reaction of carbon monoxide (CORR) offers a promising way to manufacture acetic acid directly from gaseous CO and water at mild condition. Herein, we discovered that the graphitic carbon nitride (g-C3 N4 ) supported Cu nanoparticles (Cu-CN) with the appropriate size showed a high acetate faradaic efficiency of 62.8 % with a partial current density of 188 mA cm-2 in CORR. In situ experimental and density functional theory calculation studies revealed that the Cu/C3 N4 interface and metallic Cu surface synergistically promoted CORR into acetic acid. The generation of pivotal intermediate -*CHO is advantage around the Cu/C3 N4 interface and migrated *CHO facilitates acetic acid generation on metallic Cu surface with promoted *CHO coverage. Moreover, continuous production of acetic acid aqueous solution was achieved in a porous solid electrolyte reactor, indicating the great potential of Cu-CN catalyst in the industrial application.

Interplay between Elastic and Electrochemical Properties during Active Material Transitions and Aging of a Lithium‐Ion Battery

AbstractThe interplay between the internal mechanical properties and external mechanical conditions of a battery cell, e. g., Young's modulus and thickness change, has a crucial impact on the cell performance and lifetime, and thus, needs to be fully understood. In this work, 12 Ah lithium‐ion battery pouch cells were studied during cycling and aging by non‐invasive operando ultrasonic and dilation measurements. The effective Young's modulus increases and the thickness varies the most within a single cycle during the graphite transition from stage 1L to 4, at the beginning of the 2 to 1 stage transition and at the phase transition of the nickel‐rich NCM from H2 to H3. After 1000 cycles of aging, the overall effective Young's modulus of the lithium‐ion battery decreases by ∼11 %–12 % and the cell thickness increases irreversibly by ∼3 %–4 %, which is mostly related to a thicker and possibly softer, more porous solid electrolyte interphase layer.

A Bis(2-fluoroethyl) Carbonate as a New Electrolyte Additive for Enhancing the Long-Term Cycle Performance of Li-Metal Batteries

To meet the demand for high energy density, Li metal is considered a next-generation anode material owing to its high theoretical specific capacity and low electrode potential. However, conventional LiPF6-based electrolytes form a thick and porous solid electrolyte interphase (SEI) on Li metal, resulting in poor cycle performance. One of attempts to resolve these is to optimize the electrolyte composition because the Li metal reacts most actively with electrolyte. Here, bis(2-fluoroethyl) carbonate (B-FC), as a new fluorine-based linear carbonate, was added to a LiTFSI–LiBOB-based dual-salt electrolyte. To confirm the effect of B-FC on the electrochemical properties, Li || Li symmetric cells and LiNi0.6Co0.2Mn0.2O2 (NMC622) || Li metal full cells with or without B-FC were evaluated. The addition of B-FC forms LiF-rich SEI and significantly reduced Li dendrite growth, leading to the thin dead Li layer formation. Furthermore, high-voltage performances of NMC622 || Li metal full cells with B-FC were effectively improved compared to the pure DSL (capacity retention of 73.1% vs 62.4% after 300 cycles and a capacity of 117 mAh g−1 vs 87 mAh g−1 at 21 mA cm−2). Consequently, herein, we demonstrated that the dual-salts with B-FC can stabilize the SEI even under the 4.5 V cut-off condition.

Insights into Cationic Transference Number Values and Solid Electrolyte Interphase Growth in Liquid/Solid Electrolytes for Potassium Metal Batteries.

Liquid/solid battery electrolytes make separators dispensable and enable a high cationic transference number with liquid-like room temperature ionic conductivity. This work gives insights into electrochemical behavior (galvanostatic polarization and time-dependent impedance spectroscopy) of liquid/solid electrolytes containing potassium salts in battery cells enclosing potassium metal anodes. Very high potassium transference numbers (t K = 0.88) are observed in carbonate-based electrolytes, linked with long-term mechanical instability of the solid electrolyte interphase on the potassium anode. In the case of glyme-based electrolytes, electrochemical behavior indicates the existence of the highly porous solid electrolyte interphase and additional surface porosity of the potassium electrode.

On-site H2O2 electro-generation process combined with ultraviolet: A promising approach for odorous compounds purification in drinking water system

The on-site generation of hydrogen peroxide (H2O2) attracts much attention for advanced oxidation processes (AOPs) in water treatment. In this work, we reported a novel on-site H2O2 generation reactor combined with ultraviolet (UV) for taste and odor (T&O) compounds removal in drinking water purification systems. The reactor is equipped with a gas diffusion electrode (GDE) accompanied by a proton-conducting solid electrolyte. In this reactor, GDE is used to improve the oxygen transfer efficiency. The porous solid electrolyte is selected for the proton and electron conduction instead of an electrolyte solution, which is crucial for producing pure H2O2 solution. The production rate and concentration of H2O2 can be controlled through adjusting the applied current efficiency and the flow rate of deionized water in a solid chamber. Meanwhile, this system exhibits long-term stability during a continuous operation for 96 h. For the application of the system, the single-cell was assembled into cell stacks, which improved the H2O2 concentration from 780.9 to 2301.3 mg·L−1, along with the energy consumption reduced from 23.81 to 6.67 kWh·kg−1 under the applied current density of 30 mA·cm−2. To evaluate the water purification performance of this system, the oxidation degradation of 2,4,6-trichloroanisoles (TCA) was conducted using the on-site H2O2 generation process under both static and dynamic flow conditions combined with UV light. The degradation rate of TCA was >95% with its initial concentration of 1 μg·L−1 under the hydraulic retention time from 10 to 40 min−1 and H2O2 dosage from 10 to 100 mg·L−1. Meanwhile, almost no residual H2O2 was detected after the degradation process. This study proposed a promising device for drinking water purification.

Highly active and selective oxygen reduction to H2O2 on boron-doped carbon for high production rates

Oxygen reduction reaction towards hydrogen peroxide (H2O2) provides a green alternative route for H2O2 production, but it lacks efficient catalysts to achieve high selectivity and activity simultaneously under industrial-relevant production rates. Here we report a boron-doped carbon (B-C) catalyst which can overcome this activity-selectivity dilemma. Compared to the state-of-the-art oxidized carbon catalyst, B-C catalyst presents enhanced activity (saving more than 210 mV overpotential) under industrial-relevant currents (up to 300 mA cm−2) while maintaining high H2O2 selectivity (85–90%). Density-functional theory calculations reveal that the boron dopant site is responsible for high H2O2 activity and selectivity due to low thermodynamic and kinetic barriers. Employed in our porous solid electrolyte reactor, the B-C catalyst demonstrates a direct and continuous generation of pure H2O2 solutions with high selectivity (up to 95%) and high H2O2 partial currents (up to ~400 mA cm−2), illustrating the catalyst’s great potential for practical applications in the future.

Investigation of Lithium Transport in 3D Porous Solid-State Li-Ion Electrolytes

All-solid-state batteries (ASSB) are candidates for the next generation of high power- and energy storage systems. To reach their full potential, limiting factors like high interfacial resistances or decomposition of the electrolyte require further understanding and optimization. Porous 3D electrolyte networks, like the oxidic trilayer structures prepared by the authors, provide a much higher specific contact area between the electrolyte and the active materials [1]. The fabrication via a tape casting process allows for control of the porosity and sample thickness and is scalable to industrial production levels [2]. It was demonstrated that such a system allows for much higher current densities compared to a planar setup. Nevertheless, the critical influences of grain and grain boundaries on the cell performance and the lithium transport in these porous oxidic systems are still under investigation and not fully resolved.In this contribution, we investigate the lithium transport in porous garnet-type 3D electrolyte network consisting of Li7La2.75Ca0.25Zr1.75Nb0.25O12. The focus of our study is on the influence of grain and grain boundary effects. Our multi-scale approach consists of 3D microstructure-resolved simulations, which are supplemented by a thermodynamically consistent modeling framework [3,4]. The modeling framework enables us to provide additional microscopic interface- and bulk properties such as space charge layer effects, which are transferred as theory-based input parameters to our 3D microstructure-resolved simulations.The 3D simulations are performed directly on virtual microstructures reconstructed from FIB-SEM tomography measurements. In our study, we investigate samples with different porosity, thereby, our approach inherently incorporates the morphological features of the porous solid electrolyte. Moreover, we perform impedance simulations on the porous polycrystalline 3D electrolyte network. The simulations reproduce the experimental data and allow us to identify features in the corresponding impedance spectra. This approach enables us to analyze the correlation between grain size and garnet porosity on the cell impedance.In the final step, we virtually fill the porous electrolyte networks with metallic lithium corresponding to different state of charges during operation. Based on the impedance analysis, we evaluate the area specific resistance in our simulations and validate the results against experimental data. The current density distribution analysis allows identifying flux hot spots, which can serve as an indicator for dendrite growth [5]. The comparison between simulations and experiments demonstrates the importance of interfacial processes at the grain boundaries and gives directions for optimizing future oxide-based ASSBs. Acknowledgment This work was conducted as part of the US-German joint collaboration on "Interfaces and Interphases In Rechargeable Li-metal based Batteries” supported by the US Department of Energy (DOE) and German Federal Ministry of Education and Research (BMBF). Financial support was provided by BMBF under grant number 03XP0223E and DOE under grant number DEEE0008858. Reference s : [1] T. Hamann et al., Adv. Funct. Mater. 30 (2020) 1910362. [2] T. Hitz et al., Materials Today 22 (2019) 50-57. [3] A. Latz and J. Zausch, J. Power Sources 196 (2011) 3296-3302. [4] S. Braun et al., J. Phys. Chem. C 119 (2015) 22281-22288. [5] C.Tsai et al., ACS Appl. Mater. Interfaces 8 (2016) 10617-10626.

Emerging Porous Solid Electrolytes for Hydroxide Ion Transport

AbstractAnion exchange membrane fuel cells (AEMFCs) offer several advantages over proton exchange membrane fuel cells, such as the use of a non‐precious metal catalyst, but these cells suffer from various issues related to OH–‐conducting electrolytes, including low conductivity and the formation of K2CO3 salt. These issues need to be resolved for the widespread use of AEMFCs. Recently, many studies have focused on developing excellent ion‐conductive electrolytes using porous materials based on metal–organic and covalent organic frameworks. However, most of this research is biased toward proton‐conducting electrolytes; to the best of the authors’ knowledge, reviews addressing OH–‐conducting electrolytes using porous materials have not been reported thus far. This review discusses OH–‐conducting porous crystalline materials and their membranes in terms of different synthetic strategies, conduction mechanisms, and experimental modalities for the design and development of future anion conductive electrolytes in fuel cells.

Direct and continuous generation of pure acetic acid solutions via electrocatalytic carbon monoxide reduction

Electrochemical CO2 or CO reduction to high-value C2+ liquid fuels is desirable, but its practical application is challenged by impurities from cogenerated liquid products and solutes in liquid electrolytes, which necessitates cost- and energy-intensive downstream separation processes. By coupling rational designs in a Cu catalyst and porous solid electrolyte (PSE) reactor, here we demonstrate a direct and continuous generation of pure acetic acid solutions via electrochemical CO reduction. With optimized edge-to-surface ratio, the Cu nanocube catalyst presents an unprecedented acetate performance in neutral pH with other liquid products greatly suppressed, delivering a maximal acetate Faradaic efficiency of 43%, partial current of 200 mA⋅cm-2, ultrahigh relative purity of up to 98 wt%, and excellent stability of over 150 h continuous operation. Density functional theory simulations reveal the role of stepped sites along the cube edge in promoting the acetate pathway. Additionally, a PSE layer, other than a conventional liquid electrolyte, was designed to separate cathode and anode for efficient ion conductions, while not introducing any impurity ions into generated liquid fuels. Pure acetic acid solutions, with concentrations up to 2 wt% (0.33 M), can be continuously produced by employing the acetate-selective Cu catalyst in our PSE reactor.

Electrochemical CO2 reduction to high-concentration pure formic acid solutions in an all-solid-state reactor

Electrochemical CO2 reduction reaction (CO2RR) to liquid fuels is currently challenged by low product concentrations, as well as their mixture with traditional liquid electrolytes, such as KHCO3 solution. Here we report an all-solid-state electrochemical CO2RR system for continuous generation of high-purity and high-concentration formic acid vapors and solutions. The cathode and anode were separated by a porous solid electrolyte (PSE) layer, where electrochemically generated formate and proton were recombined to form molecular formic acid. The generated formic acid can be efficiently removed in the form of vapors via inert gas stream flowing through the PSE layer. Coupling with a high activity (formate partial current densities ~450 mA cm−2), selectivity (maximal Faradaic efficiency ~97%), and stability (100 hours) grain boundary-enriched bismuth catalyst, we demonstrated ultra-high concentrations of pure formic acid solutions (up to nearly 100 wt.%) condensed from generated vapors via flexible tuning of the carrier gas stream.

Highly conducting Sc and Y co-doped ZrO2 thin film solid electrolyte on a porous Ni/YSZ electrode prepared via simple drop-coating method

Dense and crack-free thin film solid electrolyte of scandium and yttrium co-doped zirconia (Sc0.08Y0.08Zr0.84O1.92) or 4S4YSZ has been successfully deposited on a NiO-YSZ porous electrode substrate via simple drop-coating deposition method. The 4S4YSZ precursor powder was synthesized using sol-gel method and the NiO-YSZ substrate, with 1:1 wt% composition, was prepared via modified glycine-nitrate combustion method. The NiO-YSZ substrates were pre-sintered at different temperatures, 1000 °C and 1300 °C, to investigate the effect on the thin film deposition and its microstructure. XRD results showed that both 4S4YSZ and NiO-YSZ exhibited a cubic crystal structure with no observable impurity peaks. SEM-EDS revealed a dense morphology of 4S4YSZ thin film with thickness of about 7μm after sintering while maintaining a desirable porous NiO-YSZ microstructure of the electrode substrate for the 1000 °C pre-sintered substrate as compared to a still porous solid electrolyte for the higher substrate pre-sintering temperature at 1300 °C. And from the conductivity measurements using EIS, the 4S4YSZ thin film revealed a notable high total conductivity of about 1.2x10-1 Scm-1 at 700 °C with 0.73 eV activation energy. Reduction of NiO/YSZ to Ni/YSZ further increases the porosity of the electrode substrate while maintaining a dense solid electrolyte thin film.