Constant Current Test Research Articles

Boosting hydrogen production from alkaline water splitting via electrochemical active surface reconstruction of transition metal sulfide electrocatalysts

The degree of surface reconstruction reaction of sulfide catalyst is controlled, 20 s-NMSO could reach a current of 1 A cm−2 at an ultra-low overpotential of 231 mV, and the voltage only increased by 0.06% after 6 days of constant current testing.

Impact of Electrode Reversal Method on Electrode Degradation By High-Potential Environment in Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are key energy conversion devices, that address global energy challenges and climate change and are prized for various applications due to their high efficiency, low operating temperature, fast startup, and low toxic emissions. Enhancing PEMFC durability is crucial for advancing commercialization. Thus, prioritizing research on Catalyst Layer (CL) degradation mechanisms of Membrane Electrode Assembly (MEA) and developing analytical methods to understand extreme degradation conditions are becoming imperative.In PEMFCs’ operational scenarios, various issues deteriorate the membrane electrode assembly (MEA) of PEMFCs, leading to irreversible performance declines. These include Pt dissolution, ionomer degradation, carbon corrosion [1], and occasional membrane mechanical issues. Of these, the electrochemical carbon oxidation reaction is particularly detrimental, causing a significant reduction in electrochemical double layer capacitance (EDLC), the formation of oxygen functional groups in carbon supports, and substantial deterioration in electrochemical surface area (ECSA) [2, 3], ultimately leading to degraded PEMFC performance.On the other hand, reversible performance degradation occurs during fuel cell operation, which specific operational recovery procedures can rectify. Mechanisms contributing to reversible voltage degradation include the platinum oxide formation, adsorption of impurity ions and contaminants on the catalyst surface, water flooding/dehydration, and oxidation of the carbon support surface to create hydrophilic oxygen-containing groups [4]. Understanding reversible degradation mechanisms and recovery strategies is important for efficient operation, improved durability, and prolonged cell lifespan. Typically, the "electrode reversal" method is practical and economical, allowing power output during recovery without additional equipment, thereby minimizing recovery operation runtime.In this study, we examine the impact of the electrode reversal method on PEMFC performance and the deterioration tendency of MEA during carbon corrosion of cathode CL (Figure 1). Accelerated stress tests (AST) were conducted at high potentials exceeding 1.0 V (vs. RHE), specifically investigating the relationship between electrode degradation behaviors, porous carbon structural properties including ionic resistance and EDLC, and overall PEMFC performance.Particularly noteworthy after the electrode reversal recovery method were the discernible variations in degradation behaviors and diverse rates of performance decline observed through electrochemical impedance spectroscopy (EIS) analysis. EIS can be used to isolate the contribution of many processes to performance loss, allowing investigation of the effect of carbon corrosion-induced catalyst layer changes on fuel cell performance [5]. The EIS data underwent evaluation via parametric fitting utilizing the transmission line model (TLM) applied to the EIS spectrum. Furthermore, relaxation time distribution (DRT) analysis was employed to directly analyze internal resistance factors as a diagnostic tool for assessing electrode degradation by enhancing the TLM-based impedance analysis results. During the ASTs, electrochemical measurements (i-V, CV, LSV, and EIS) were performed to estimate the degree of PEMFC degradation, we also conducted ex-situ surface analysis of MEA using SEM, TEM, and XPS to elucidate the specific degradation components. Fig. 1 Electrode Reversal Recovery method during Anode cycling AST of the PEMFC single cell (a) polarization curves (i-V curves); 10 A constant current test (b)-(d): (b) fresh MEA, (c) after 250 cycles, (d) after 500 cycles of Anode cycling AST References [1] Sorrentino, Antonio, Kai Sundmacher, and Tanja Vidakovic-Koch. "Polymer electrolyte fuel cell degradation mechanisms and their diagnosis by frequency response analysis methods: a review." Energies 13.21 (2020): 5825.[2] Macauley, Natalia, et al. "Carbon corrosion in PEM fuel cells and the development of accelerated stress tests." Journal of The Electrochemical Society 165.6 (2018): F3148.[3] Kwon, JunHwa, et al. "Identification of electrode degradation by carbon corrosion in polymer electrolyte membrane fuel cells using the distribution of relaxation time analysis." Electrochimica Acta (2022): 140219.[4] Yang, Wenbin, et al. "Investigation of an electrode reversal method and degradation recovery mechanisms of PEM fuel cell." Electrochimica Acta 449 (2023): 142181.[5] Kwon, JunHwa, et al. "A Comparison Study on the Carbon Corrosion Reaction under Saturated and Low Relative Humidity Conditions via Transmission Line Model-Based Electrochemical Impedance Analysis." Journal of The Electrochemical Society 168.6 (2021): 064515. Figure 1

Fabrication of Ruthenium-Based Cathode Material/Solid Electrolyte Composites

Introduction Oxide-based all-solid-state batteries (ASSBs) are considered safe due to their chemical stability and are attracting attention as a power source for electric vehicles (EVs). Because the driving range of EVs is not sufficient compared to conventional gasoline-powered vehicles, ASSBs with higher capacities are required. To overcome the above issue, it is necessary to adopt the electrode material having high energy density such as Li-rich layered oxides, or to increase the amount of active material in the cell. The positive electrode of an ASSB needs to be a composite of electrode material and solid electrolyte to ensure ionic conductive pathways. Therefore, it is necessary to increase the ratio of active material in the composite cathode to improve energy density in the battery. Previously, the ASSB with positive electrode composed of only active material without any conductive additive was reported for Ru containing oxide, Li2Ru0.8S0.2O3.2 [1], having high electronic and ionic conductivity. Therefore, we focused on the Ru containing Li-rich layered oxide, Li2RuO3 and Li2Mn0.4Ru0.6O3. The garnet-type solid electrolyte was selected as an oxide solid electrolyte due to its high ionic conductivity and the reductive tolerance to Li metal having a large capacity of 3860 mAh g–1. The high stiffness of the oxide solid electrolytes leads to a decrease in the contact area and prevents the formation of a superior electrode/electrolyte interface only by mixing and applying pressure, which hinders the operation of ASSBs. To lower the resistance of the interface, the co-firing of cathode material and solid electrolyte is required. However, side reactions associated with co-firing are an issue. Li2TiO3 as a buffer layer was introduced between the cathode material and the solid electrolyte to suppress side reactions. Li2TiO3 has a similar structure to Li2RuO3, which is expected to improve sinterability by a partial substitution. The co-firing of the cathode materials and the garnet-type solid electrolyte and the effect in the suppression of side reactions using buffer layers will be presented. Experimental Li2RuO3 and LMRO were used as cathode materials, Li6.25Ga0.25La3Zr2O12 (LLZ-Ga) as a solid electrolyte, and Li2TiO3 as a buffer layer. The buffer layer was introduced into the cathode surface by solid-phase and liquid-phase methods. LiOH-H2O and TiO2 were mixed and sintered with the cathode material in the solid-phase method. LiOH-H2O and tetra n-butyl titanate monomer were weighed and dissolved in ethanol separately in the liquid-phase method. Each solution and the cathode material were mixed and stirred overnight, then dried at 60 ºC in a rotary evaporator. The resultant powder was pelletized by uniaxial press and then heated at 800 ºC for 5 hours in an oxygen atmosphere. The electrochemical property of the cathode material with the buffer layer was confirmed by a constant-current charge-discharge test using a coin cell. The cathode composite composed of the cathode material (with buffer layer) and the solid electrolyte was fabricated by co-firing at 600-800ºC after the mixing by hand or ball mill. The obtained samples were subjected to phase identification by X-ray diffraction. The reaction process was observed by SEM observation and EDX composition analysis. All-solid-state cells were fabricated by a uniaxial press using the obtained sample as the positive electrode, Li5.5PS4.5Cl1.5 as the solid electrolyte, which has excellent ion conductivity and can easily form a good interface simply by applying pressure, and Li-In alloy as the negative electrode. Constant current charge-discharge tests were performed on the fabricated all-solid-state cells. Results and discussion X-ray diffraction and EDX analysis confirmed that the impurity phase of La2Li(RuO6) formed by co-firing the cathode material and LLZ-Ga. Therefore, the buffer layer was introduced by the solid-phase and liquid-phase methods. In the solid-phase method, Li2TiO3 was not distributed uniformly on the particle surface of the cathode material. In the liquid-phase method, Li2TiO3 covered the cathode surface more uniformly and thinner than that formed in the solid-phase method. Both Li2RuO3 and LMRO retained their original structure, while the lattice parameter of LMRO changed, indicating that LMRO formed the solid solution with Li2TiO3. No inter-diffusion of lanthanum and ruthenium between the cathode material with buffer layer and LLZ-Ga was observed in the EDX analysis. It suggests that the introduction of a buffer layer suppressed the inter-diffusion. The cathode composite co-fired did not exhibit the discharge capacity in the charge-discharge test using the all-solid-state cell. It is attributed to the low conductivity derived from the low sinter ability of the cathode composite.[1] K. Nagao et al., Sci. Adv. 2020; 6 : eaax7236 (2020). Acknowledgements This work was supported by JSPS KAKENHI Grant Number JP22H04615.

Characterization and Electrochemical Performance of Na(Ni,Fe,Mn)O2 for Sodium-Ion Battery Cathodes

Given the escalating demand for sustainable energy storage solutions, sodium-ion batteries (SIBs) have emerged as formidable contenders against lithium-ion batteries (LIBs), capitalizing on the abundant and cost-effective nature of sodium resources. A pivotal determinant in advancing SIB technology lies in the quest for efficient anode materials, which significantly influence the overall performance and stability of the battery system. Among potential candidates, Na(Ni,Fe,Mn)O2, a layered transition metal oxide, holds promise as an anode material for SIBs.To explore this potential, we employed the solid-state reaction method to synthesize and analyze three novel anode materials: NaNiO2, NaNi0.9Fe0.05Mn0.05O2, and NaNi0.8Fe0.1Mn0.1O2. Stoichiometric proportions of Na2O2, NiO, Fe2O3, and Mn2O3 served as the starting materials, supplemented with an additional 15% Na2O2 to ensure thorough decomposition during synthesis.Following synthesis, we conducted a series of analyses to elucidate the structural characteristics of the materials. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to confirm the basic surface morphology, crystal structure, and phase composition. X-ray photoelectron spectroscopy (XPS) analysis provided insights into the elemental composition and chemical states.Further investigation into the nanostructure and electrochemical performance was carried out using transmission electron microscopy (TEM) and in-situ XRD. TEM analysis revealed crystal defects, interface structures, and nanoparticle morphology, while in-situ XRD allowed for real-time observation of crystal structural changes during cycling.Subsequently, the synthesized materials were utilized as active materials to fabricate Half Coincells, with sodium metal serving as the cathode. Electrochemical evaluations, including constant current charge-discharge tests at various current densities and rate performance assessments, were conducted. These evaluations enabled us to assess the specific capacity, rate capability, and cycling stability of each material, facilitating a comparative analysis of their suitability as anode materials for SIBs.In summary, this study employs a comprehensive analytical framework to explore the structural characteristics and electrochemical behavior of Na(Ni,Fe,Mn)O2 for SIB applications. By integrating advanced characterization techniques with electrochemical measurements, we aim to uncover key insights into its potential as a high-performance cathode material, advancing the development of sustainable energy storage technologies.This research was supported by the NRF funded by the MSIT and MEST (grant numbers NRF-2021R1A4A1022198, NRF-2022R1A2B5B01001943, and NRF-2018R1A5A1025594). Figure 1

Development of High-Performance Lithium-Ion Capacitor Using Reduced Nitrogen-Doped Graphene as Capacitor-Type Cathode Material Exhibiting Anomaly Anion Storage Mechanism

1.IntroductionLithium-ion capacitor (LIC) is a capacitor with improved energy density by applying a battery-type active material capable of lithium storage as the anode material. However, a typical cathode of LIC applies a capacitor-type active material that adsorbs anions, limiting its specific capacity as LIC. Therefore, we synthesized and applied reduced nitrogen-doped graphene (N-rGO) as a new cathode active material to achieve high energy density in LIC. The N-rGO cathode exhibits capacitance via an anion intercalation mechanism, a faradaic reaction, and initial charge-discharge characteristics in the N-rGO/Li half-cell showed a high specific capacitance exceeding 160 mAh g-1 in a 2.0 - 4.8 V voltage range and a current density of 150 mA g-1. We also reported that N-rGO cathode exhibits high rate characteristics due to a unique anion storage mechanism in which the capacity increases proportionally to the voltage after the first charge cycle. [1, 2] This suggests that it is suitable as a new cathode material for LIC. This unconventional anion storage mechanism would be ascribed to a change in the N-rGO morphology due to anion intercalation during the initial charging, but there have been still many unresolved points. In this study, we further analyzed the anion storage mechanism in N-rGO cathode and constructed a LIC device using N-rGO, which exhibits an anomaly anion storage mechanism, and examined the possibility of achieving high capacity.2.Experimental sectionN-rGO was synthesized by a hydrothermal reaction of ball-milled graphene oxide (GO) as a N-rGO precursor with urea as a nitrogen source and distilled water as a solvent in an autoclave at 180°C in 12 hours under high pressure conditions. N-rGO and graphite electrodes were prepared by mixing each active material with acetylene black (AB), carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR) in the weight ratio of 90:5:3:2, respectively. The slurry was coated onto Al and Cu current collector, respectively. Cathode half-cells were assembled with the N-rGO cathode, Li-metal as the counter electrode, and 1.0 mol dm-3 LiPF6 / EC : DMC = 1 : 1 (by vol.) as the electrolyte to analyze the anion storage mechanism of N-rGO cathode. Full-cells were assembled with the N-rGO cathode, graphite anode, and 1.0 mol dm-3 LiPF6 / EC : DMC = 1 : 1 (by vol.) as the electrolyte, and its performance as LIC was evaluated.3.Results and discussionIn our previous report, a conventional anion intercalation mechanism undergoes expansion and shrinking of the interlayer distance of carbon as anions are inserted and removed, whereas the N-rGO cathode goes through expanding the interlayer distance of carbon due to anion insertion at the initial charging, and then the expanded interlayer distance is maintained during subsequent charge-discharge cycles. Morphology difference between these materials may have altered the anion storage mechanism. The microstructure within the interlayer was investigated using XANES. Details will be explained in this poster presentation. Constant current charge-discharge tests were conducted to investigate the performance of LIC with this N-rGO as a capacitor-type cathode. With the previous LIC, we pre-doped Li in the graphite anode and constructed a full cell. The specific capacity was almost the same as the N-rGO/Li half cell, but the capacity retention was poor and the capacity was significantly reduced after 10 cycles. We speculated that this was due to a plateau in the charge curve even after the initial charge, and that the morphological change due to sufficient anion insertion had not occurred. Therefore, in addition to pre-doping Li into the graphite anode, we pre-cycled the N-rGO cathode as a single cycle prior to constructing full cell. As a result, the plateau in the charge process almost disappeared, and the specific capacity and high capacity-retention were almost the same as those of the N-rGO/Li half-cell, and long-term cycling was achieved.Reference[1] J. Ishikawa et al., The 64th Battery Symposium Japan, 1F01 (2023).[2] M. Zhang et al., Energy Stor. Mater., 16 (2019) 65-84.

Load Cycling Durability Protocols for Predictive MEA Lifetime Modeling for Long-Life PEMFC Applications

As the large-scale commercialization of proton exchange membrane fuel cells (PEMFC) for numerous heavy-duty applications draws nearer, there is an increasing emphasis on the delivery of highly robust membrane electrode assemblies (MEAs) capable of achieving upwards of 25,000 hours of on-road durability (1). A particular area of MEA durability focus is that of the proton conducting perfluorosulfonic acid (PFSA) membrane which is subjected to varying degrees of oxidative stress during fuel cell operation. The development of highly durable membranes necessitates the implementation of accelerated testing protocols that can be used to determine the sensitivity of membrane lifetime to a number of operational parameters such as cell temperature and membrane humidification. The objective of sensitivity studies is to develop robust and predictive degradation models using state-of-the-art (SOA) MEAs under the accelerated operational space that can be subsequently applied to the milder operational space of a long-lifetime application. Traditionally, open circuit voltage (OCV) degradation studies have been employed to assess membrane durability. While OCV degradation experiments can be highly accelerating from a chemical degradation perspective, producing high fluoride release and membrane thinning rates, the operating conditions do not sufficiently emulate the dynamic chemical stresses generated under load nor do they provide RH cycling and concomitant mechanical stresses that accompanies load cycling (2). At the other end of the cell load continuum, constant current durability tests have consistently failed to produce high degradation rates, even in the presence of Fe accelerants.In response to the recognized shortcomings of OCV and related accelerated durability tests, we have developed a suite of flexible, single-cell, load-cycling durability tests that more closely emulate stresses experienced in variety of real-world, on-load applications. Test protocols enable the variation numerous operational parameters including temperature, inlet RH, high and low cycling current densities and the ratio of time spent at the high and low current densities. In-situ degradation rates are assessed by monitoring emitted fluoride concentrations at regular intervals. Cerium-mitigated (3), SOA PFSA membranes fabricated with PtCo/HSC cathode electrodes are quite robust even under the harshest load cycling conditions (110 °C/ 30% RH), producing fluoride release rate (FRR) values less than 1x10-8 gF/cm-2h-1. The creation of predictive chemical degradation models requires significant and quantifiable chemical degradation signals to occur across accelerated the reaction space continuum. Therefore, given the high stability of SOA membranes, the degradation rates are further accelerated by the addition of Fe2+ Fenton’s catalysts. The Figure below shows the FRR profiles obtained from a series of four MEAs, differing only in the amount of added Fe2+ prior to the durability test conducted at 95 °C/30% RH with load cycling between 0.02-1.5 A/cm². In addition to Fe sensitivity findings, we will present data regarding sensitivities of degradation rates with respect to temperature, inlet RH, high current density values and time ratios at high and low current densities.(1) D. A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers, A. Kusoglu, Nature Energy, 6, 462–474 (2021)(2) C. S. Gittleman, F. D. Coms, Y.-H. Lai, In Polymer Electrolyte Fuel Cell Degradation, M. Matthew, K. E. Caglan, T. N. Veziroglu, Editors, p. 15, Academic Press, Boston (2012)(3) F. D. Coms, H. Liu, and J. E. Owejan, ECS Transactions, 16, 1735 (2008) Figure 1

Precise Electrochemical Analysis of Carbon-Based Negative Electrode

Lithium-ion batteries (LIBs) are required to have high energy density, high power density, and long life properties. The development of materials for active materials, which are directly involved in the redox reaction of electrodes, is important for improving the performance of storage batteries. Therefore, precise electrochemical properties of active materials should be understood. However, applied electrodes used for general performance evaluation of storage batteries are mainly composed of active material, conductivity additive, and binder, and it is difficult to evaluate only electrochemical properties of the active material. Therefore, we investigated the single-particle electrochemical measurements (SPEM), which enables electrochemical measurement of a single active material particle by using a probe with a Pt wire covered by glass. On the other hand, diluted electrode method[1], which can be relatively easily achieved by replacing some of the active material in to the applied electrode with electrochemically inactive Al2O3. In this study, HCS[2] particles, in which multiple Si nanoparticles are constrained by non-graphitizable carbon (HC) as electrode active materials to physically suppress the volume changes according to the redox reactions, and HC fabricated by similar conditions as the case of HCS, were analyzed and evaluated to compare and investigate electrochemical measurements using SPEM and diluted electrode methods. To prepare the probe for the measurement, the Pt wire (f 20 mm) was inserted into a glass capillary, heated and coated. To ensure sufficient contact between the active material particles and the probe, the tip of the probe was polished. All electrochemical measurements by the SPEM were performed in a glove box with an Ar inert atmosphere. The open cell was used for the measurements consisted of a Li metal foil (counter electrode/reference electrode) on to a stainless steel cup, a glass separator covered with active material particles, and dropped of electrolyte (1.0 mol kg-1 EC-LiFSA). Electrochemical measurements were performed by the fabricated probe into contact with a single active material particle and observed it from above using side with a digital microscope. A dilute applied electrode sheet containing active material , conductivity aid, binder, Al2O3 was prepared. A slurry of HCS and HC, acetylene black (AB), and binder in a mass ratio of 62.5:17.5:20 was applied onto the Cu foil current collector. After drying the prepared electrode sheet in a thermostatic oven for 24 hours, the sheet was punched out at f 16 mm in diameter to prepare a 2032-type coin cell. The diluted electrodes were prepared with varying the weight ratio of x HCS: (1 - x ) Al2O3(x = 1, 0.5, 0.1), and constant current charge-discharge tests were performed, respectively. Fig. 1(a) and (b) show the constant-current charge-discharge profiles of the applied electrodes fabricated with active material percentages of 100 and 10 wt%, respectively. The obtained charge-discharge profiles showed a gradual potential changes around 1.5 - 0.2V. This voltage changes can be attributed to the structural disorder of HC in the HCS. Fig. 2 shows the constant-current charge-discharge profiles using a single HCS particle. The electric capacity in the single particle was calculated from the volume density assuming the particles to be true spheres. The obtained charge-discharge profile exhibits sufficient capacity, suggesting that feasible single-particle measurement of HCS single particles. Moreover, multiple potential changes similar to the charge-discharge behavior of graphite (C6) were observed around 1.5 - 0.2 V. This result might be suggested to the single particle measurement corresponds to the observation of a local area, unlike the applied electrode, where comprehensive information on multiple active materials (104 order grains/cm2) is obtained. A stepwise reaction might be proceed layer by layer, similar to C6. In addition, Fig. 1(b) shows a different charge-discharge profile compared to Fig. 2, suggesting that the environmental conditions at the 10 wt% diluted electrode are not similar to those of the result of single-particle measurement. Of course is further investigation in the active material fraction is necessary. In the presentation, We will report the results of constant-current charge-discharge tests of composite electrodes with active material weight percentages of 100, 50, 10, and 1 wt%, constant-current charge-discharge tests using HCS and HC single particles, and constant-potential tests.[1] T. Sawahashi et. al., RSC Adv., 13, 21667-21672 (2023). [2] U. Tsunoda et. al., Mater. Adv., 4, 4436-4443 (2023). Figure 1

A novel vanadium-copper rechargeable battery for solar energy conversion and storage

To enhance the utilization of abundant yet intermittent sunlight, the integration of solar energy conversion and storage has received increasing attention, and utilizing photoelectrodes to drive non-spontaneous reversible redox reactions provides a promising solution. This study proposes a triple-compartment system combining dual-photoelectrode (TiO2 and pTTh) with vanadium-copper electrolytes for integrated solar energy conversion and storage. The system can convert solar energy into chemical energy under simulated solar illumination (100 mW∙cm−2, AM 1.5G) and controllably release the stored chemical energy in the form of electrical energy. The system achieves a discharge open-circuit voltage of 0.47 V and a short-circuit current density of 1.3 mA∙cm−2. In constant current discharge tests, a discharge capacity of 2 mAh is observed at 0.3 mA∙cm−2.

Synergistic heterostructural interface of CoP and WC for high-performance wide pH-universal hydrogen evolution electrocatalysis

The development of cost-effective catalysts with high activity and stability over a wide pH range is urgent, but there are great challenges in the selection and design of catalyst materials. In this work, cobalt phosphide nanoparticles were modified onto tungsten carbide nanowire arrays (CoP@WC/CC) on carbon cloth substrate by a two-step method. The construction of CoP@WC heterostructure results in the downward shift of the d-band center, which optimizes the adsorption energy of catalyst and reaction intermediates. Meanwhile, the synergistic effect of CoP and WC contributes to the alkaline HER kinetic process. In addition, binder-free self-supporting nanoarray have excellent electrical conductivity, large specific surface area and strong structure, which is conducive to charge/matter exchange and catalyst stability. The results show that CoP@WC/CC can effectively drive HER over a wide pH range and exhibit better catalytic performance than the single component control sample. In 0.5 M H2SO4 and 1 M KOH, CoP@WC/CC can drive the current density of 10 mA cm−2 with only 52 and 70 mV, while showing excellent stability without obvious performance degradation during 100 h of constant current test. A proton exchange membrane water electrolysis (PEMWE) using CoP@WC/CC catalyst operates stably for 200,000 s at 30 mA cm−2. This study provides a new reference for the design and development of high efficiency, low cost and wide pH-universal hydrogen evolution electrocatalysts.

Polymer Composite Electrolytes Membrane Consisted of Polyacrylonitrile Nanofibers Containing Lithium Salts: Improved Ion Conductive Characteristics and All‐Solid‐State Battery Performance

AbstractPolymer electrolyte membranes with superior lithium‐ion (Li+) conductivity and sufficient electrochemical stability are desired for all‐solid‐state lithium‐ion batteries (ASS‐LIBs). This paper reports novel polymer composite membranes consisting of polyacrylonitrile (PAN) nanofibers (Nfs) containing lithium salts. It is first revealed that the lithium salt addition increases polar surface groups on the PAN nanofibers. Subsequently, the lithium salts‐containing PAN nanofiber (PAN/Li Nf) composite membrane affects the matrix poly(ethylene oxide) (PEO)/lithium bis(trifluoromethyl sulfonylimide) (LiTFSI) electrolyte to increase the numbers of Li+ with high mobility. Consequently, the PAN/Li Nf composite membrane shows relatively good ion conductivity (σ = 9.0 × 10−5 S cm−1) and a considerably large Li+ transference number (tLi+ = 0.41) at 60 °C, compared to the PEO/LiTFSI membrane without nanofibers. The 6Li solid‐state NMR study supports that the PAN/Li Nf bearing abundant polar nitrile groups at their surface enhances Li+ diffusion in the PEO‐based electrolyte membranes. The galvanostatic constant current cycling tests reveal that the PAN/Li Nf composite membrane possesses good electrochemical and mechanical stabilities. The ASS‐LIB consisting of the PAN/Li Nf composite membrane shows significantly improved charge and discharge cycling performances, promising future all‐solid‐state batteries.

Highly efficient NiCo/VN electrocatalyst co-facilitated by interfacial engineering and support effect for large-current-density alkaline water/seawater hydrogen evolution reaction

Developing efficient and continuously stable water electrolysis catalysts to cope with harsh industrial conditions remains a huge challenge in the alkaline seawater electrolysis hydrogen production process. Transition metal nitrides are potential catalysts for seawater electrolysis, but they are still being modified to further improve catalytic performance. Here, a nanosheet-like NiCo/VN heterostructure electrocatalyst was prepared. The heterogeneous interface formed between and VN and NiCo alloy and the strong metal-support interaction regulate the electronic structure and optimizes the adsorption and desorption of intermediates. Moreover, the introduction of the NiCo alloy greatly facilitates the water dissociation step. Therefore, the prepared NiCo/VN catalyst exhibits excellent alkaline HER performance, with a low overpotential of 38 mV and 318 mV at a current density of 10 mA cm−2 and 1000 mA cm−2, shows high durability in 50 h of constant current tests at current densities of 10, 100, and 1000 mA cm−2 in alkaline seawater. This work proposes an effective strategy for preparing multiphase electrocatalysts, and the mechanism research fully confirms that it can promote the dissociation of water and the adsorption and desorption of intermediates.

Durability Assessment of Roll-to-Roll Coated PEM Water Electrolysis Anodes

Widespread adoption of green hydrogen relies on the high-throughput production of key electrolyzer components in a manner yielding acceptable stack manufacturing costs. Roll-to-roll liquid coating methods, such as slot die and gravure coating, are particularly relevant means to produce key components (e.g., membranes and electrodes) at high throughput. In the case of proton exchange membrane water electrolysis (PEMWE), thrifting of expensive iridium-based catalysts poses additional challenges to the implementation of such high-throughput coating methods for iridium-based anode manufacture.Herein, we investigate key challenges around roll-to-roll manufacture of low-loaded (<0.2 mgIr/cm2) iridium-based electrodes for PEMWE. In particular, we highlight fundamental limitations in coating the thin layers required to manufacture low-loaded electrodes, for which the improper choice of coating conditions may lead to macro- and micro-scale heterogeneity. By addressing causes of this heterogeneity, homogeneous slot-die coated iridium oxide anodes of varying iridium loading are produced on decal substrates. Catalyst coated membranes (CCMs) are subsequently produced from these anodes via hot-pressed decal transfer, and 1,000 hour constant current tests are conducted with intermediate diagnostics (polarization curves and impedance spectroscopy). Key effects of loading and homogeneity on electrode durability are highlighted, and future directions are discussed.This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office and Advanced Manufacturing Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

Enhancing Efficiency and Durability of PEM Water Electrolysis with Low Iridium Loading through Nanofiber-Modified Porous Transport Electrodes

Hydrogen plays a significant role in the transition of the global energy system towards achieving net-zero emissions. According to the “Hydrogen for Net-Zero” report by Hydrogen Council and McKinsey & Company, the demand for clean hydrogen could reach 140 metric tons (MT) by 2030, with a further increase to 660 MT by 2050. For future high-volume production of green hydrogen, Proton Exchange Membrane Water Electrolysis (PEMWE) is a crucial technology due to its advantages of high-purity hydrogen, large operational current densities, and great energy conversion efficiency [1]. However, the use of precious metal-based catalysts for the sluggish oxygen evolution reaction (OER) on the anode side hinders the high-volume manufacturability of PEMWE. To ensure cost-effectiveness in large-scale PEMWE deployment for hydrogen production, developing strategies to reduce Iridium loading to 0.1 - 0.2 mg Ir/cm2 without compromising overall performance is essential. The challenge of reducing Ir loading also involves improving or maintaining the electrical contact between the catalyst layers and the substrate [2-3].Smoltek Hydrogen has made significant strides in achieving low iridium loading through our innovative Porous Transport Electrode (PTE) concept. This approach involves modifying a Porous Transport Layer (PTL) by growing vertically aligned Carbon Nanofibers (CNFs) using our in-house patented technology, efficiently increasing surface area [4]. Following this modification, a protective layer of corrosion-resistant and conductive material (e.g., Platinum) is applied to the CNFs. Subsequently, an OER catalyst layer is deposited utilizing a three-electrode cathodic electrodeposition method (Fig. 1a and 1b). The electrodeposited Ir catalyst exhibits strong adhesion to the CNF PTEs, resulting in a high electrical conductivity [5].In this work, we successfully reduced Ir loadings to 0.1 mg/cm2 in the PTE, demonstrating excellent mass activity in the half-cell tests (Fig. 1c). In the PEMWE tests, the polarization curves of electrodes with low Ir loading exhibited superior performance compared to cells with significantly higher Ir loading (Fig. 1d). The next step of our research involves conducting constant current durability tests for over 600 hours on PEMWE operation using low Ir loaded PTEs. The aim is to minimize degradation and overcome mass transport limitations, particularly at higher current densities.These unique PTEs developed by Smoltek Hydrogen, with CNF technology, maximize the electrode surface area and pave a new way to increase the utilization ratio of catalyst surface at a low loading amount, which makes it a competitive anode material in today’s PEMWE market. References https://www.iea.org/reports/hydrogen-2156#dashboardMöckl et al. J. Electrochem. Soc., 2022, 169, 064505.Bernt et al. Chem. Ing. Tech., 2020, 92, 31-39.https://www.smoltek.com/applications/electrolyzers/Krivina et al. Adv.Mater., 2022, 34, 2203033.https://publications.jrc.ec.europa.eu/repository/handle/JRC104045 Figure 1

Fabrication of Na+-Conducting Ionic Liquids Na[((FSO2)2n) x ((CF3SO2)(FSO2)N)1-X ], and Its Physical and Electrochemical Properties

To achieve low-carbon society in near future, it’s imperative to research and develop high-performance and low-cost batteries. Therefore, sodium-ion batteries (SIBs) are attracting attention owing to their possibility to be composed of elements with no resource scarcity and low cost.To solve the challenge of low energy density in SIBs, it is essential to focus on developing electrodes of the 4V to 5V class. Simultaneously, electrolytes with wide electrochemical window are crucial from in terms of electrolyte decomposition at high operating voltages. Molten salt electrolytes exhibit relatively high ionic conductivity and electrochemical stability. On the other hands, there is an issue that the electrolyte must be heated to a high temperature to maintain molten state of the electrolytes. In this study, with the goal of expanding the melting temperature range of molten salt electrolytes, we precisely mixed relatively low-melting sodium salts Na(FSO2)2N (NaFSA) and Na(CF3SO2)(FSO2)N (NaFTA) and found a composition with a melting point below 100 ℃. As a result, we successfully fabricated novel single-sodium cationic salt ionic liquid. In this presentation, we will report on its bulk properties and electrochemical characteristics. All mixed sodium salts were mixed NaFSA and NaFTA in each molar ratio and stirred during gradually cooling after uniformly melting at 170 ℃ in Ar-filled grove box. The thermal properties of the mixed sodium salts were evaluated by differential scanning calorimetry (DSC). The samples were stored at room temperature for 2~3 days to reach equilibrium state, and then sealed in a high-pressure SUS pan. Ionic conductivity (σ) of the mixed sodium salts were also measured from 60 ℃ to 135 ℃ at each temperature. Symmetrical cells were constructed by put the mixed sodium salt between two SUS or sodium metal electrodes. Ionic conductivity of mixed sodium salts was evaluated by electrochemical impedance spectroscopy (EIS) with SUS electrodes symmetric cells. Na+ transference number was measured by potentiostatic polarization and EIS with sodium metal symmetric cells at 90℃. The binary phase diagram of NaFSA and NaFTA were shown in Fig.1. In the NaFTA-rich composition range (0.1 < x < 0.4), the phase diagram resembles a simple eutectic phase diagram, while, in the NaFTA-rich composition range (0.5 < x < 0.9), the mixed sodium salts exhibited pseudo-single-phase behavior, and the lowest liquid-phase transition temperature (T L) was observed at 90℃ of Na[(FSA)0.8(FTA)0.2].(1) Additionally, in this composition range, glass transition points (T g) were also confirmed, indicating the supercooled behavior.The Arrhenius plot of the ionic conductivity (σ) for Na[(FSA)0.8(FTA)0.2] was shown in Fig.2. At the T L around 90℃, σ was observed to 0.69 mS cm-1. This is attributed to the strong interactions between Na+ and anion in the absence of solvents, causing high viscosity and decreasing mobility. Below the T L, there was no remarkable decrease in σ and Nyquist plots remained non-divergent to 55℃, allowing for the attribution of σ. Moreover, below the T L, the glass transition and crystallization of Na[(FSA)0.8(FTA)0.2] were not observed. The temperature dependence of σ was analyzed by the Vogel-Fulcher-Tamman (VFT) equation.(2) In addition, the σ(T g) at the observed T g from DSC were calculated by VFT equation. Also, the decoupling index (R τ), representing the ratio of ionic conductive relaxation time (τ σ) to structural relaxation time (τ s), were calculated.(3) The value of logR τ value for Na[(FSA)0.8(FTA)0.2] was -0.62 and the low value indicates that τ s is coupled with τ σ.To investigate the Na+ conduction behavior in Na[(FSA)0.8(FTA)0.2], chronoamperograms with an applied potential of 500 mV to the sodium metal symmetric cells were shown in Fig.3(a). Fig.3(b) shows Nyquist plots before and after direct current polarization. The steady current was observed after 8h. Furthermore, there was slightly changes of Nyquist plots before and after direct current (DC) polarization, stable interface between sodium metal and Na[(FSA)0.8(FTA)0.2] was also confirmed. The Na+ transference Number (t Na+) in the Na[(FSA)0.8(FTA)0.2] was estimated to be 0.86. Tatara et al. reported the t Na+ of 0.18 in the 1M NaPF6/PC+0.5vol% FEC.(4) Since molten salts consisting of only cations and anions should not be occurred concentration polarization, it exhibited a considerably higher t Na+ in Na[(FSA)0.8(FTA)0.2] compared to the t Na+ in dilute non-aqueous sodium electrolyte. In the presentation, we will discuss the cycle characteristics obtained by constant current charge-discharge tests of both half-cell and full-cell configurations using generic positive and negative electrode materials.(1) K. Kubota et al., J. Chem. Eng. Data, 55, No. 9, 2010, 3142–3146.(2) H. Vogel., Phys. Z. 1921, 22, 645.(3) C. A. Angell, Annu. Rev. Phys. Chem. 1992, 43, 693.(4) R. Tatara et al., Electrochemistry, 89(6), 2021, 590–596. Figure 1

Dual photoelectrode-drived Fe–Br rechargeable flow battery for solar energy conversion and storage: A cost-effective approach

The integrated design of solar energy conversion and storage systems has attracted increasing attention, and non-spontaneous redox reactions driven by dual photoelectrodes provide a potential solution to this issue. This study presents a solar rechargeable flow battery (SRFB) that combines dual photoelectrodes (BiVO4 or Mo–BiVO4 as photoanode, polyterthiophene (pTTh) as photocathode) with cost-effective redox pairs (Fe3+/Fe2+ and Br3−/Br−). The system charges under simulated solar illumination (100 mW∙cm−2, AM 1.5G) and releases stored energy controllably as electrical energy. Research indicates the Mo–BiVO4 photoanode and pTTh photocathode achieve an open-circuit voltage of 0.34 V and a short-circuit current density of 0.38 mA cm−2. Using a specially designed Fe3+/Fe2+-Br3−/Br− (Fe–Br) SRFB device made via 3D printing, a charging photocurrent of approximately 1.9 mA cm−2 is attained. In constant current discharge tests, an initial discharge voltage of 0.23 V is observed at 0.1 mA∙cm−2 within the 10 discharge cycles, demonstrating system stability and offering a viable solution for low-cost, large-scale solar energy storage and conversion.

Phosphorus doped Li2FeSiO4 thin films prepared by magnetron sputtering as high-performance thin-film cathode materials

Polycrystalline Li2FeSiO4 (LFS) and Li2FePxSi1-xO4 (LFSP) thin film cathode materials tested in quasi-solid thin-film Li-ion cells have been synthesized using radio frequency magnetron sputtering in combination with rapid thermal annealing. The thin films were characterized for their phase and morphology using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The charge transport properties and electrochemical performance of the films were evaluated through constant current charge-discharge tests, cyclic voltammetry, rate performance testing, electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT). The research findings revealed that after the sputtering growth process, during rapid annealing at 850 °C, the as prepared amorphous Li2FeSiO4 thin film showed selective crystalline growth, while crystallized grains on the surface of Li2FeSi0.95P0.05O4 thin films exhibited a fusion like and relatively regular distribution. The electronic conductivity and ionic conductivity of Li2FeSi0.95P0.05O4 thin films were measured at 6.60 × 10−7 S·cm−1 and 4.87 × 10−7 S·cm−1, respectively. The Li2FeSi0.95P0.05O4 thin film displayed an initial discharge specific capacity of 224.05 mAh g−1 at a rate of 0.1 C, with a capacity retention of 73.5 % after 100 cycles in half-cell structure. The assembled Li2FeSi0.95P0.05O4/Li1.3Al0.3Ti1.7(PO4)3/Li quasi-solid-state battery presented an initial discharge specific capacity of 195.62 mAh g−1 at 0.1 C, with a capacity retention of 55.03 % after 100 cycles. This study offers a valuable reference for the fabrication and doping modification of poly-anion-type Li2FeSiO4 cathode thin film materials, thus aiding the progress of next-generation thin-film quasi-solid-state lithium-ion batteries.

Diffusion-Equation-Based Electrical Modeling for High-Power Lithium Titanium Oxide Batteries

Lithium titanium oxide (LTO) batteries offer superior performance compared to graphite-based anodes in terms of rapid charge/discharge capability and chemical stability, making them promising candidates for fast-charging and power-assist vehicle applications. However, commonly used battery models often struggle to accurately describe the current–voltage characteristics of LTO batteries, particularly before the charge/discharge cutoff conditions. In this work, a novel electrical model based on the solid-phase diffusion equation is proposed to capture the unique electrochemical phenomena arising from the diffusion mismatch between the positive and negative electrodes in high-power LTO batteries. The robustness of the proposed model is evaluated under various loading conditions, including constant current and dynamic current tests, and the results are compared against experimental data. The experimental results for LTO batteries exhibit remarkable alignment with the model estimation, demonstrating a maximum voltage error below 3%.

Hydrothermal synthesis of αILiVOPO4 as a cathode material for Li-ion batteries

This paper presents the synthesis of a novel cathode material, αI-LiVOPO4, featuring a porous multilayered lamellar structure, achieved through the hydrothermal method. Initially, αI-LiVOPO4·2 H2O was synthesized by maintaining a reaction kettle at 160 °C for 40 h. Subsequently, the parent compound underwent dehydration at various temperatures for 2 h to yield αI-LiVOPO4. The dehydration process was investigated through thermogravimetric analysis. Analysis via powder X-ray diffraction confirmed the crystallization of the product into the αI-LiVOPO4 phase. TEM and EDS analyses revealed an irregular porous structure with uniform distribution of elements. The electrochemical performance of αI-LiVOPO4 was evaluated through constant current charge-discharge tests within a voltage range of 3–4.5 V. Results demonstrated an initial capacity of 106.9 mAh·g–1 at 0.05 C, with a capacity retention of 100.9 mAh·g–1 after the 50th cycle. Additionally, cyclic voltammetry indicated favorable cycling performance and minimal polarization at elevated voltages.

Experimental Approach for Reliability Analysis of Medium-Power Zener Diodes under DC Switching Surge Degradation

This study investigated the reliability of Zener diodes subjected to a gradually increasing DC switching surge amplitude with delay internals between surges to avoid thermal degradation from different manufacturers with similar specifications. The analysis involved applying occasional 3 ms direct current (DC) switching surges with a gradual increasing surge voltage, followed by a constant current test to verify device functionality for three different selected manufacturer 5.1 V Zener diodes. This experimental approach was used to identify the maximum surge current that each Zener diode could handle before failing to clamp the surge voltage at the specified Zener reference voltage. Statistical analysis revealed significant differences in the maximum average surge current between different manufacturers. The maximum average surge current findings just before failure were 1.98 A, 3.18 A, and 3.33 A, respectively, and associated 95% confidence interval ranges can be used as a reliable metric to compare Zener diode population reliability against occasional DC switching surges. The findings revealed variations in the DC switching surge current handling capabilities between Zener diodes from different manufacturers with similar electrical specifications. The statistically measured maximum average surge current just before device failure can be considered an effective metric to compare the reliability of Zener diodes against DC switching surge degradation.

Unravelling the O-doping effect on chemical/electrochemical stability of Li5.5PS4.5Cl1.5 for all-solid-state lithium batteries

Chlorine-rich Li-argyrodite sulfide solid electrolytes Li5.5PS4.5Cl1.5 are applied in all-solid-state batteries (ASSBs) due to the promising ionic transport and structural stability. However, the poor air/moisture stability and incompatibility to Li metal impede their practical applications. Herein, we synthesized a Li5.5PS4.5Cl1.5-based argyrodite exhibiting improved moisture stability and electrochemical performance to metallic Li, as well as high-voltage cathodes through O doping. The prepared oxygen-doped Li5.5PS4.5Cl1.5 samples (Li5.5PS4.425O0.075Cl1.5) possess significantly enhanced air stability and lower migration barrier in comparison with pristine Li5.5PS4.5Cl1.5. Moreover, Li5.5PS4.425O0.075Cl1.5 exhibits lower polarization voltage and better compatibility with lithium metal in the constant current charge-discharge tests of Li-Li symmetrical cell. This is attributed to the Cl-O coexistence coating interface that observed in the interface of Li/Li5.5PS4.425O0.075Cl1.5. To fully leverage the ultrafast ionic conductivity of Li5.5PS4.5Cl1.5, we construct ASSBs using optimized Li5.5PS4.425O0.075Cl1.5 as buffer layer between pristine LiNi0.6Mn0.2Co0.2O2 cathode materials and Li5.5PS4.5Cl1.5, leading to higher discharge capacities and elevated capacity retention. Based on above results, we further introduce LiNbO3-coated LiCoO2 as cathode, combined with Li5.5PS4.425O0.075Cl1.5 as an isolating layer between Li anode and Li5.5PS4.5Cl1.5 to suppress the growth of Li dendrite and achieve superior cyclability at wide voltage windows. Consequently, the all-solid-state lithium batteries exhibit promising application in a wide temperature range. This work provides a compelling strategy for achieving improved Chlorine-rich Li-argyrodite solid electrolytes with excellent air stability, high ionic conductivity and Li dendrite suppression capability, hence enabling all-solid-state batteries with high energy density and superior cyclability.