Earth-abundant Materials Research Articles

Chalcogenide perovskites: enticing prospects across a wide range of compositions and optoelectronic properties for stable photodetector devices

Abstract Photodetectors are indispensable components of many modern light sensing and imaging devices, converting photon energy into processable electrical signal through absorption, carrier generation and extraction using semiconducting thin films with appropriate optoelectronic properties. Recently, metal halide perovskites have demonstrated groundbreaking photodetector performance due to their exceptional properties originating from their perovskite structure. However, toxicity and stability remain challenges for their large-scale applications. Inspired by the perovskite structure, intense investigation in search of highly stable, non-toxic and earth abundant materials with superior optoelectronic features has led to the discovery of chalcogenide perovskites (CPs). These are unconventional semiconductors with the formula ABX3, where A and B are cations and X is a chalcogen, which covers the compounds with the corner sharing perovskite structures of type II-IV- VI3 compounds (II = Ba, Sr, Ca, Eu; IV = Zr, Hf; VI = S, Se) and III1-III2-VI3 compounds (III1 and III2 = Lanthanides, Y, Sc; VI = S, Se). The increased coordination and ionicity in these compounds contribute to their excellent charge transport properties and exceptionally high optical absorption coefficient (> 105 cm−1). The present review encompasses theoretical analysis that provides electronic band structures and the orbital contributions that support the excellent optoelectronic properties. Furthermore, the challenging thin film deposition, characterizations, and their application in photodetection focusing on BaZrS3-which is the most studied one, are ascribed. Additionally, we suggest prospects that can bring out the true potential of these materials in photodetection and photovoltaics.

From synthesis to application: a review of BaZrS3 chalcogenide perovskites.

Chalcogenide perovskites are gaining prominence as earth-abundant and non-toxic solar absorber materials, crystallizing in a distorted perovskite structure. Among these, BaZrS3 has attracted the most attention due to its optimal bandgap and its ability to be synthesized at relatively low temperatures. BaZrS3 exhibits a high light absorption coefficient, excellent stability under exposure to air, moisture, and heat, and is composed of earth-abundant elements. These properties collectively position BaZrS3 as a promising candidate for a wide range of applications, although traditional high-temperature synthesis has primarily been a significant challenge. In this review, we provide a critical discussion of the various synthesis methods employed to fabricate BaZrS3, including solid-state synthesis, nanoparticle synthesis, and vacuum-based as well as solution-based approaches to synthesize thin films. We also comprehensively examine the experimentally measured and theoretically calculated optical, optoelectronic, electronic, and defect properties of BaZrS3. Furthermore, this review highlights the functional devices based on BaZrS3, showcasing applications spanning photovoltaics, photodetection, thermoelectrics, photoelectrochemical water splitting, piezoelectricity, and spintronics. Lastly, we propose a future roadmap to maximize the potential of this material. Additionally, this review extends its focus to BaHfS3 and BaTiS3, discussing their synthesis methods, properties, and explored applications, thereby offering a comparative perspective on this emerging family of chalcogenide perovskites.

Nanostructured Fe2O3/Cu x O heterojunction for enhanced solar redox flow battery performance.

Solar redox flow batteries (SRFB) have received much attention as an alternative integrated technology for simultaneous conversion and storage of solar energy. Yet, the photocatalytic efficiency of semiconductor-based single photoelectrodes, such as hematite, remains low due to the trade-off between fast electron hole recombination and insufficient light utilization, as well as inferior reaction kinetics at the solid/liquid interface. Herein, we present an α-Fe2O3/Cu x O p-n junction, coupled with a readily scalable nanostructure, that increases the electrochemically active sites and improves charge separation. Thanks to light-assisted scanning electrochemical microscopy (photo-SECM), we elucidate the morphology-dependent carrier transfer process involved in the photo-oxidation reaction at an α-Fe2O3 photoanode. The optimized nanostructure is then exploited in the α-Fe2O3/Cu x O p-n junction, achieving an outstanding unbiased photocurrent density of 0.46 mA cm-2, solar-to-chemical (STC) efficiency over 0.35% and a stable photocharge-discharge cycling. The average solar-to-output energy efficiency (SOEE) for this unassisted α-Fe2O3-based SRFB system reaches 0.18%, comparable to previously reported DSSC-assisted hematite SRFBs. The use of earth-abundant materials and the compatibility with scalable nanostructuring and heterojunction preparation techniques offer promising opportunities for cost-effective device deployment in real-world applications.

Accelerating the Electrochemical Formation of the δ Phase in Manganese-Rich Rocksalt Cathodes.

Mn-rich disordered rocksalt materials with Li-excess (DRX) materials have emerged as a promising class of earth-abundant and energy-dense next-generation cathode materials for lithium-ion batteries. Recently, an electrochemical transformation to a spinel-like "δ" phase has been reported in Mn-rich DRX materials, with improved capacity, rate capability, and cycling stability compared with previous DRX compositions. However, this transformation unfolds slowly over the course of cycling, complicating the development and understanding of these materials. In this work, it is reported that the transformation of Mn-rich DRX materials to the promising δ phase can be promoted to occur much more rapidly by electrochemical pulsing at elevated temperature, rate, and voltage. To extend this concept, micron-sized single-crystal DRX particles are also transformed to the δ phase by the same method, possessing greatly improved cycling stability in the first demonstration of cycling for large, single-crystal DRX particles. To shed light on the formation and specific structure of the δ phase, X-ray diffraction, scanning electron nanodiffraction (SEND) and atomic resolution STEM-HAADF are used to reveal a nanodomain spinel structure with minimal remnantdisorder.

Structural Origins of High Performance in Partially Disordered Li- and Mn-Rich Cathodes

The discovery of Li-excess cation-disordered rocksalt (DRX) cathodes lifts the restriction on a specific Li-TM ordering to enable the exploration of cathode materials in a chemical space of earth abundant materials. Recently, phase transformation in disordered Li- and Mn-rich rock-salts (Li1.05Mn0.85Ti0.1O2) have been shown to form high energy density, capacity retention and rate capability cathode materials (named delta) with partial Spinel-like ordering at short coherence lengths.1 However, atomic scale structural features of the material which determine its high performance such as extent of disordering and Li-transport pathways are not well-understood yet. We first perform symmetry analysis to reveal aspects of the transformation which are central to the nanoscale domain formation in the delta phase and crucial for characterizing its structure. We develop a simple structural order parameter to distinguish the Spinel-like ordering from the disordered rocksalt (DRX) structure, characterizing the extent of disordering, sizes and spatial location of the domains as the transformation proceeds. We perform multi time-scale Kinetic Monte Carlo Simulations for understanding the DRX-to-delta transformation. Our results reveal both thermodynamic and kinetic factors causing the formation of spinel-like nano domains and spatial distribution of Ti and Li-excess in the delta phase of Li1.05Mn0.85Ti0.1O2, providing key insights into its high rate capability. Our simulations reveal principles for designing the structure at nanoscale and electrochemical performance through changes in composition. Cai, Z.; Ouyang, B.; Hau, H.-M.; Chen, T.; Giovine, R.; Koirala, K. P.; Li, L.; Ji, H.; Ha, Y.; Sun, Y.; Huang, J.; Chen, Y.; Wu, V.; Yang, W.; Wang, C.; Clément, R. J.; Lun, Z.; Ceder, G. In Situ Formed Partially Disordered Phases as Earth-Abundant Mn-Rich Cathode Materials. Nat. Energy 2023, 1–10. https://doi.org/10.1038/s41560-023-01375-9.

Accelerating the Electrochemical Formation of the δ Phase in Manganese-Rich Rocksalt Cathodes

Recently, advancements in Mn-based disordered rocksalt (DRX) cathodes have demonstrated not only high energy density but also an electrochemical transformation to a spinel-like phase, now referred to as the δ phase1,2,3. The δ phase possesses a unique domain structure, a flattened voltage profile and improved rate capability. However, two important challenges remain: the necessity to mill the material to reduce particle size after synthesis, and the prolonged cycling required to complete the transformation to spinel-like partial order. To address these challenges, we present the development of an electrochemical formation method that enables rapid and in-situ formation of this partially disordered spinel phase from a DRX cathode, including in micron-sized single crystals.To gain a deeper understanding of this transformation process, we carry out a systematic study to determine whether the transformation to the δ phase can be accelerated through a precycling formation process. By employing this novel electrochemical approach to purposefully stimulate the transformation, we successfully reduce the time required from several weeks to as little as one day for Mn-rich DRX. Extended cycling and synchrotron X-ray diffraction confirm that these materials exhibit both equivalent performance and resulting structure to those obtained through conventional cycling over a much longer duration. Further characterization of this material using HAADF and 4-D STEM reveals the complex local structure of the spinel-like partial ordering. It is hoped that such a practical electrochemical formation method allows for an acceleration of research on these earth-abundant and energy-dense materials. Li, L.; Lun, Z.; Chen, D.; Yue, Y.; Tong, W.; Chen, G.; Ceder, G.; Wang, C. Fluorination-Enhanced Surface Stability of Cation-Disordered Rocksalt Cathodes for Li-Ion Batteries. Adv Funct Mater 2021, 31 (25), 2101888. https://doi.org/10.1002/adfm.202101888.Ahn, J.; Giovine, R.; Wu, V. C.; Koirala, K. P.; Wang, C.; Clément, R. J.; Chen, G. Ultrahigh-Capacity Rocksalt Cathodes Enabled by Cycling-Activated Structural Changes. Adv. Energy Mater. 2023. https://doi.org/10.1002/aenm.202300221.Cai, Z.; Ouyang, B.; Hau, H.-M.; Chen, T.; Giovine, R.; Koirala, K. P.; Li, L.; Ji, H.; Ha, Y.; Sun, Y.; Huang, J.; Chen, Y.; Wu, V.; Yang, W.; Wang, C.; Clément, R. J.; Lun, Z.; Ceder, G. In Situ Formed Partially Disordered Phases as Earth-Abundant Mn-Rich Cathode Materials. Nat. Energy 2023, 1–10. https://doi.org/10.1038/s41560-023-01375-9.

Proton-Conducting Solid Oxide Electrolysis Cells with Scandia-Doped Barium Zirconate Electrolytes

Proton-conducting solid oxide electrolysis cells (P-SOECs) leverage their low activation energy for proton-conduction to achieve high water electrolysis performance in the intermediate temperature regime (400-600°C). In this sought after temperature zone critical challenges that face high-temperature systems (>700°C) such as balance-of-plant costs, degradation, and oxidation may be alleviated while still retaining favorable reaction kinetics with earth-abundant materials. The electrolyte in P-SOECs plays a vital role in full cell performance and efficiency. P-SOEC electrolytes must have high ionic conductivity, low electronic conductivity, and exceptional durability in high steam atmospheres. Yttrium-doped barium zirconate (BZY) and yttrium/ytterbium co-doped barium cerate zirconate (BZCYYb) are the most widely used P-SOEC electrolyte materials to date. However, practical applications for these materials are in question due to the low protonic conductivity of BZY, poor durability of BZCYYb in high steam environments, and the depressed faradaic efficiencies achieved by P-SOECs utilizing these electrolytes. In this work we show that scandium-doped barium zirconate (BZSc) is a promising electrolyte material to produce P-SOECs with a combination of high performance, efficiency, and durability. Relevant electrolysis current densities were attained below 500°C and long-term durability is demonstrated. Cell architecture and operating conditions are optimized to maximize faradaic efficiency. Our results indicate that high proton concentrations in the electrolyte achieved through high dopant levels can boost performance in barium zirconate-based P-SOECs while preserving unrivalled durability. This work demonstrates the potential for BZSc as an effective P-SOEC electrolyte and we anticipate future studies to further characterize BZSc. Furthermore, this work opens the door for more research into proton conducting materials with dopant levels exceeding 20 mol%.

(Invited) Optimizing CO2 Reduction in Aprotic Media: Insights Via Kinetic Modeling of Bimetallic CuxZn1-X Electrocatalysts

Bimetallic CuxZn1-x electrocatalysts, as an earth-abundant material, have emerged as promising candidates for improving the efficiency and selectivity of CO2 reduction in aqueous electrolytes.[1] However, the use of aqueous electrolytes has several drawbacks, including limited CO2 transport due to its low solubility in the electrolyte solution and, most importantly, the competing hydrogen evolution reaction (HER).[2] These challenges can be effectively circumvented by using aprotic organic electrolytes instead, which offer higher CO2 solubility and minimize HER.[3] Aprotic electrolytes (e.g., acetonitrile) show distinct differences in the reaction pathway, yielding either CO or oxalate. Studies under these conditions are scarce, and fundamental knowledge of the performance-limiting processes at the electrode-electrolyte interface is lacking. This knowledge gap hinders further development and process design for efficient CO2R in aprotic media.In this contribution, we present a comprehensive analysis of CO2R on Cu and CuxZn1-x electrocatalysts in acetonitrile. By combining standard electrochemical methods such as cyclic voltammetry, polarization curve, and electrochemical impedance spectroscopy, with mathematical modeling that couples microkinetics with continuum transport, we elucidate reaction and transport phenomena and reveal the underlying performance limitations. Based on this approach, we provide insights into the local reaction environment and discuss in detail the rates, surface coverages of adsorbed species, and local concentration profiles at the electrode. We investigate Cu and α-brass at different CuxZn1-x ratios as planar as well as nanoparticle coated electrodes. For Cu, we find that adsorbed CO2 is being consumed faster than it replenishes, suggesting that CO2 adsorption is the bottleneck in aprotic electrolytes,[4] as opposed to CO2 transport as in alkaline solution[5]. With increasing Zn content of the α-brass, higher CO2R performance is achieved. According to our simulations this can be attributed to i) higher utilization of the electrocatalyst and ii) improved CO2 adsorption capability compared to pure Cu.The gained insights allow for a better understanding of the effects of the catalyst composition on the performance and highlight the importance of CO2 adsorption on the performance of CO2 electroreduction in organic electrolytes. This enables knowledge-based optimization of the electrocatalysts and tailoring of reaction conditions. Overall, our results provide valuable insights into the poorly understood organic electrolytes for CO2R as a viable alternative to aqueous electrolytes and pave the way for the analysis of more complex reaction systems such as electro-organic syntheses or CO2R with protic additives.

(Invited) Strategies for Enabling Stable Cycling in High-Capacity Li-Ion Cathodes

While significant advancements have been made with the prevailing layered oxide cathodes, there remains a need for the development of next-generation cathodes for high-energy Li-ion batteries to support the electrification needs of modern society. Li excess disordered rocksalt (DRX) cathodes present a promising avenue for achieving even higher capacities. However, this family of cathodes often faces a challenge in maintaining both high capacity and stable long-term cycling. Due to their structural flexibility, a wide range of compositional variations has been explored, including adjusting the Li/TM ratios, transition metal species, and anions. Through a deeper investigation into DRX chemistry, we have identified that the capacity and energy decay issues are influenced by the combination of transition metals and their respective redox chemistries. This presentation highlights our recent research efforts aimed at developing strategies to ensure stable, long-term cycling in high-capacity DRX cathodes using cost-effective and earth-abundant materials.

Hydrophilic Separator Stables CO2-to-C2H4 Conversion at Low Cell Voltage with Non-Noble Metal Anode

Electrochemical carbon dioxide (CO2) reduction (ECR) is a promising approach for enabling the conversion of greenhouse gas CO2 into valuable products with electricity from renewable sources to achieve net-zero CO2 emission. ECR simultaneously reduces carbon emissions and dependence on fossil-based fuels and chemicals. Membrane electrode assemblies (MEAs), which often comprise an anion exchange membrane (AEM) and a precious iridium oxide (IrOx)-based anode, have been extensively studied in the last few years. However, challenges such as salt precipitation on cathodic gas diffusion electrodes (GDEs), high cell voltage and the need to use noble metal anodes have hindered ECR's practical applications. Herein, we introduce a new design of MEA cells using a low-cost hydrophilic film separator and a Nickel (Ni) foam instead of AEM and IrOx, respectively. Hydrophilic separator material with high water permeability lowers the full-cell voltage and eliminates the salt accumulation on the GDE in both alkaline and neutral-pH conditions. Using copper-sputtered polytetrafluoroethylene (Cu/PTFE) as cathodes, we demonstrated a stable conversion of CO2 to ethylene (C2H4) at current densities over 100 mA/cm2. In neutral-pH anolyte, the average C2H4 FE was sustained at around 50% for more than 200 hours with a cell voltage of 3.1 V at the current density of 110 mA/cm2. Under alkaline conditions, this system showed 500 hours of stability of CO2-to-C2H4 conversion: the C2H4 FE was maintained above 60% with the cell voltage of only 2.2 V at 110 mA/cm2 current density. Our research provides a solution for achieving stable ECR operation at a relatively high current density using Earth-abundant materials. This work opens opportunities for energy-efficient and stable CO2 conversion without needing expensive and rare elements, which are crucial for practical applications.

High-Performance Aqueous Zinc-Ion Batteries Using Centrifugal Jet-Spun Non-Woven Chitin Fiber Separator

Although lithium-ion batteries (LIBs) are key prevailing energy storage devices, alternative battery technologies based on earth-abundant materials are being sought as a viable energy storage systems that could possibly replace LIBs. Among several alternatives is aqueous zinc-ion batteries (AZIBs), which are more eco-friendly, cost-effective, and even safer. Despite their potential advantages, the development of appropriate separators for ZIBs has been elusive, and the issue of zinc metal dendrites on the negative electrode remains a critical challenge.In this work, we introduces a novel approach to prepare a non-woven spun fiber mat made of chitin, an abundant natural polymer, which could function as a separator for AZIBs. In particular, we use centrifugal jet-spinning (CJS) to fabricate the chitin separator. The use of chitin as a separator offers several advantages over existing ZIB separators, such as high stability, improved capacity, environmental friendliness, and cost-effectiveness. We demonstrate that the chitin separator can be applied in AZIB cells based on symmetric and full cell models, which showed stable cell operation for long-term cycling. Figure 1

Title : The Flexible Solar Cells Using Earth Abundant Materials

The development of flexible solar cells utilizing non-toxic, earth-abundant materials is of paramount importance in driving market competitiveness and fostering the adoption of innovative business models such as Building Integrated Photovoltaics. While CZTS-based (Cu2ZnSnS4, Cu2ZnSnSe4, Cu2ZnSn(S,Se)4) solar cells offer promising cost advantages due to their low-cost available absorber materials, their progress has been impeded by challenges like narrow phase stability and secondary phase defects.To address these challenges, researchers have been actively exploring the potential of metal-doping effects, employing elements such as Ag, Li, Na, K, and Rb to enhance the performance and stability of CZTS-based solar cells. Understanding the reaction mechanisms involved in dopant incorporation is crucial for optimizing fabrication processes and ultimately improving solar cell efficiency.In this study, CZTSSe solar cell devices were designed, comprising an Mo back contact, CZTSSe absorber, CdS buffer layer, ZnO layer, Al-doped ZnO layer, and an Al collection grid. The doping effects of Ag (applied on a rigid SLG substrate with Na impurity) and Na (applied on a flexible substrate without Na impurity) at different dopant layer positions of the Sn/Cu/Zn precursor structure were investigated.Without a dopant layer, the precursors revealed the formation of Cu-Zn and Cu-Sn alloys despite the deposition sequence of Zn, Cu, Sn at room temperature. Upon pre-annealing at 300 °C, the formation of the ZnSSe layer was observed from the Cu-Zn alloy, followed by the formation of Cu2Se and SnSe at temperatures exceeding 400 °C [1]. In the Sn/Cu/dopant layer/Zn precursor structure, the reaction pathways of CZTSSe were found to be influenced by the presence of dopant layers, which acted as barriers, blocking Zn and Cu/Sn diffusion, and altering the initial reaction mechanism during the annealing process.It was observed that the application of Sn/Cu/Zn/dopant layer or Sn/dopant layer/Cu/Zn precursor significantly enhanced the characteristics of the solar cell devices. By mitigating defect levels and reducing the Voc deficit, dopants led to an improvement in power conversion efficiency [2]. This enhancement can be attributed to the associated decrease in defects, which are considered recombination centers within the CZTSSe absorber layer and can be effectively passivated by dopants.Overall, the CZTSSe solar cells exhibited promising efficiencies of 12.6% and 12.3% on rigid and flexible substrates, respectively.[1] Kim, S.-Y., Son, D. H., Kim, Y. I., Kim, S. H., Kim, S. M., Ahn, K. S., Sung, S. J., Hwang, D. K., Yang, K. J., Kang, J. -K., Kim, D.-H., Nano Energy 59 (2019) 399-411[2] K.-J.Yang, S.Kim, S.-Y.Kim, D.-H.Son, J.Lee, Y.-I.Kim, S.-J.Sung, D.H.Kim, T.Enkhbat, J.H.Kim, J.Kim, W.Jo, J.-K. Kang, Advanced Functional Materials 31 (2021) 2102238Acknowledgment: This work was supported in part by the program of Phased development of carbon-neutral technologies (2022M3J1A1085371) through NRF (National Research Foundation of Korea) and in part by DGSIT R&D Program of the Ministry of Science and ICT of Korea (Grant numbers 23-ET-08 and 23-CoE-ET-01).

Controlled Phase Transformation Toward Stable Cycling of Layered Oxides for Sodium Ion Batteries

The demands for sustainable energy systems underscores the importance in developing sodium-ion batteries (NIBs) with earth abundant raw materials, enhanced energy density, prolonged lifespan, and reduced cost. Among potential candidates for such advancements, intercalation-type layered transition metal oxide (LTMO) positive electrode materials are attractive due to their notable high theoretical specific capacity and tunable chemistry. However, LTMO electrodes are often subjected to anisotropic changes during cycling. Repeated anisotropic changes cause host structure strain, eventually leading to material degradation. Regulating the electrostatic interactions is generally perceived to be a viable approach for structure stabilization in layered oxides during cycling, but conventional synthesis approaches have been unable to tame the effect. Here, we demonstrate negligible anisotropic changes in layered P2-type Na0.67Ni0.33Mn0.67O2 through regulation of electrostatic repulsion realized by modulation of transition metal ions occupancy. The electrode exhibits a capacity retention of 83.3% in 100 cycles between 2 - 4.3 V, which is significantly better than the 36.9% retention of the pristine sample. Our study emphasizes the highly correlated nature of the redox mechanism that deserves the attention and is critical for high-energy batteries.

Pathways Toward High-Energy Li-Sulfur Batteries, Identified Via Multi-Reaction Chemical Modeling

Lithium-sulfur (Li-S) batteries, which promise high gravimetric capacity and use Earth-abundant raw materials, could accelerate global energy decarbonization. Currently, Li-S performance is limited by non-conductive cathode phases (solid sulfur S8(s), lithium disulfide Li2S(s)), PS shuttling and precipitation at the anode, and sluggish Li+ transport. Mitigation often aims to control the reaction pathways or prevent PS shuttle, but a better understanding of the underlying phenomena is needed to guide development.Here we present a 1D model of a Li-Sulfur battery with physically derived geometric parameters and thermodynamically consistent electrochemical kinetics. The approach enables straightforward comparison of proposed Li-S mechanisms and provides insights into the influence of polysulfide intermediates on battery discharge. Comparing predictions from multiple mechanisms demonstrates the need for both lithiated and non-lithiated polysulfide species and highlights the challenge of developing parameter estimates for complex electrochemical mechanisms. The model is also used to explore cathode design strategies. Discharge performance and polysulfide concentrations for electrolyte/sulfur ratios in the range 2–4 μL mg−1 identifies trade-offs that limit battery energy and power density and highlights the risk of polysulfide precipitation. New cathode and electrolyte approaches must limit polysulfide concentrations in the electrolyte, both to unlock better rate capabilities in Li-S technology and to prevent capacity fade due to polysulfide precipitation. Moreover, the tools developed and presented here present a pathway to flexibly incorporate atomistically-derived reduction-oxidation thermos-kinetics and polysulfide transport properties to unlock predictive models for design and control of high-performance Li-S batteries.

Data-Driven Design for Electrolyte Additives Supporting High-Performance Lithium-Ion Batteries

We presented here two cases of data-driven electrolyte additive design, using two cathodes as examples. In scenario 1, LiNi0.5Mn1.5O4 (LNMO), a spinel-structured material with an average lithiation/de-lithiation potential at ca. 4.6-4.7 V, was used as an example for the extreme high working potentials and the resultant strains on electrolytes. In this study, we first selected and tested a diverse collection of 28 single and dual additives for the LNMO//Gr system using descriptors representative of chemical functionality.(1) Subsequently, we trained and employed machine learning (ML) models to suggest 6 binary compositions out of 125 based on predicted final area specific impedance (ASI), impedance rise (ΔASI), and final specific capacity(Q). Notably, this approach led to the discovery of a new dual additive which outperforms the initial dataset.In Scenario 2, the AI-guided workflow undergoes further enhancement for accelerated additive optimization employing new data featuring an earth-abundant cathode material of 0.3Li2MnO3·0.7LiMn0.5Ni0.5O2. This phase of the study introduces a more robust machine learning (ML) model for performance prediction, utilizing Figure of Merit Energy (FOME) and Figure of Merit Power (FOMP) as predictive metrics. Following three , Bayesian optimization iterations, 15 out of 78,000 binary and tertiary additive combinations was suggested for experiments, and several novel addtive compositions exhibiting unexpectedly high performance were subsequently identified. The optimal formulation surpasses the current standard by achieving a performance enhancement of 15-19%, as confirmed through experimental testing conducted in coin cells.Overall, our findings not only underscores the efficacy of ML in identifying new additives combinations, but also introduces an accelerated material discovery workflow that directly integrates data-drive methods with battery testing experiments.(1) ACS Omega 2018, 3, 7, 7868–7874

Two-Dimensional Covalent Organic Framework Photoanode for High Capacity Solar Battery

To mitigate our reliance on fossil fuels and facilitate energy transition, efficient conversion and storage of ubiquitous solar energy is a key strategy. Despite significant research progress in photovoltaics, energy storage in decentralized batteries requires the decoupling of energy conversion and storage, which causes major energy loss and higher cost. Seamless integration of a photoconversion system and an energy storage system in a single device can effectively store the excess energy. Materials that can demonstrate light harvesting, effective charge carrier separation for long-term charge storage, and on-demand charge retrieval as electrical energy, would be the most suitable choice. Such properties have been demonstrated in graphene-, carbon-nitride-, polyoxometalate-, and metal organic frameworks- based materials; however, the charge storage capacity remains uncompetitive. Driven by the need for earth-abundant and sustainable materials for solar energy storage, covalent organic frameworks (COFs) have emerged as a new generation of molecularly defined semiconductors with tunable optoelectronic properties. Herein, the rational integration of an electron reservoir in a polyimide two-dimensional COF unlocks the unique combination of light harvesting and electrical energy storage. When used as an aqueous solar battery anode, the COF demonstrated a capacity of ~40 mAh g-1 operating as a pseudocapacitor, which stores charge as long-lived radical anions for days. With photo-electrochemical measurements in conjunction with detailed spectroscopic studies and theoretical support, we attempt to unravel the mechanism of long-term charge stabilization. Furthermore, on-demand release of long-lived electrons with a suitable co-catalyst unlocks the prospects of dark photocatalysis, which will be investigated in the future.

Dynamic Stabilization of Nickel-Based Oxygen Evolution Anodes by Phosphate Additive Functioning in the Presence of Chloride Ions

The technology of seawater splitting driven by renewable energy potentially produces green and inexpensive hydrogen by simplifying the complex process lines and saves scarce sources of safe and fresh water. Chloride ions (Cl−), a dominant impurity in seawater, is reported to corrode the earth-abundant Ni-based oxygen evolution anode materials in both non-extreme and alkaline pH mediums, resulting in the short operation time.[1,2] Thus, engineering of the reaction field mainly consisting of the electrodes and electrolytes is a recent issue to achieve the prolonged operation time. In this study, we used one of the most active electrodes of NiFeOx/Ni foam (NF) and newly introduced the phosphate ions into the potassium borate electrolyte (K-borate) at pH 9.2. Added phosphate dynamically and selectively formed passivation layer with Ni, preventing corrosion from Cl− and leaching of Ni, which led to longer operation time.[3] Firstly, the redox behavior of NiFe hydroxides (NiFeOx)/NF was investigated using the cyclic voltammetry (CV) in 1.0 mol kg−1 K-borate buffer solution with 0.5 mol kg−1 KCl at pH 9.2 (Figure 1). The electrode was corroded with the formation of green solid Ni(OH)x. In contrast, when the phosphate at 1.0 mol kg−1 was added to the system, the corrosion current was not observed. In addition, the chronopotentiometry testing was conducted at the commercially relevant current density of 500 mA cm−2 at 353 K in K-borate and K-borate/phosphate electrolytes, both of which contained KCl. The rapid corrosion within 10 min happened only in K-borate electrolytes. However, the potential was stable at 1.68 V vs. RHE in phosphate-containing electrolytes for 10 h. These results highlight the advantages of mixing the phosphate into the borate electrolytes. A previous study proposed that the adsorbed phosphate works as a charge repulsion layer in alkaline mediums[2] In the following sections, the role of phosphate is clarified by using spectroscopic and electrochemical analysis.CVs were recorded in both K-borate and K-borate/phosphate electrolytes. In the latter electrolyte, the reduction peak of Ni shifted to more positive than that in pure K-borate. This potential shift was also observed in a single K-phosphate electrolyte. Ex-situ X-ray photoelectron spectroscopy (XPS) testing over the sample tested in phosphate-containing electrolyte shows a lower area ratio of Ni3+/Ni2+ than that tested in K-borate. In addition, operando X-ray absorption near edge structure (XANES) spectra depict the lower Ni absorption edge in the presence of phosphate additive than that in the K-borate electrolyte. In contrast, the spectra of Fe K-edge did not shift under various conditions. These electrochemical and spectroscopic analysis insist on the selective interaction between Ni2+ and phosphate additive. The stability testing was conducted at 50 mA cm−2 and 298 K. The potential increased as time passed in 24 h in K-borate electrolyte, but it was not the case for the phosphate-containing electrolyte. The dissolution amount of Ni in K-borate was 3 times higher than that in the presence of phosphate after the testing, suggesting that the stabilization of Ni2+ by phosphate led to a longer operation. The potential profile and dissolution amount of Ni in the presence of Cl− was similar to without Cl− condition in K-borate/phosphate electrolyte, highlighting that the stabilized Ni was highly tolerant toward the Cl−.The charge repulsion effect is discussed by using the redox probes of other halide ions (Br− and I−). The CVs were recorded in K-borate and K-borate/phosphate with 0.5 mol kg−1 KBr and KI. In K-borate electrolyte, the corrosion current was observed, which disappears by phosphate addition. In contrast, the Faradaic efficiency of O2 (FEO2) at 50 mA cm−2 was close to zero in the presence of both Br− and I−. The two oxidation potentials are 1.31 and 1.59 VRHE which are lower than the onset potential of OER, which would trigger the halide ion oxidation. Given that halide ions were found to react on the surface, the charge repulsion layer did not form on the surface at the present pH level. This is contrary to the previous reports in alkaline mediums, highlighting the uniqueness of non-extreme pH conditions where the phosphate works as a stabilizer toward NiFeOx/NF.This study shows that a concerted design of the electrocatalyst and electrolyte can introduce unique functions.Reference[1] H. Komiya, T. Shinagawa, K. Takanabe, ChemSusChem 2022, 15, e202201088.[2] M. Yu, J. Li, F. Liu, J. Liu, W. Xu, H. Hu, X. Chen, W. Wang, F. Cheng, J. Energy Chem. 2022, 72, 361–369.[3] H. Komiya, K. Obata, T. Honma, K. Takanabe, J. Mater. Chem. A 2024, 12, 3513–3522. Figure 1

Localized High-Concentration Electrolytes for High-Voltage Disordered Rocksalt Cathode Materials

With the pursuit of high energy-density battery systems, cathode materials with high specific capacity and high working voltage are of high interest. Among the transition metal oxide cathode materials, lithium (Li)-rich cation disordered rock salt (DRX) cathode materials are promising candidates for next-generation high-energy-density Li batteries because they offer high specific capacities and cost benefits. Particularly, the manganese (Mn)-based DRXs show more promise due to the utilization of earth abundant material and good thermal stability of Mn. However, these cathodes often face big challenges when cycled in the state-of-the-art LiPF6/carbonate-based electrolytes at voltages up to 4.8 V. These include severe side reactions between the cathode and the electrolyte, transition metal dissolution and structural instability of the cathode particles, all of which result in fast capacity fading. In this work, we developed advanced localized high-concentration electrolytes (LHCEs) to mitigate these problems and enable stable cycling of a DRX cathode material, Li1.2Mn0.6Ti0.2O2 (LMTO). The LHCEs demonstrate high voltage stability of 4.9 V vs. Li/Li+ and capability of forming an ultrathin and stable cathode-electrolyte interphase. Consequently, Li||LMTO half cells with the optimal LHCE exhibit increased capacity, enhanced cycling stability and superior rate capability when compared to the cells with the conventional electrolyte. This work sheds the light of electrolyte development to enable practical DRX cathode-based high-energy Li batteries.

(Invited) Enhancing the Performance of Lithium-Ion Cathodes

Significant attention has recently been given to increasing the energy density of commercial LiNi1-x-yMnxCoyO2 (NMC) lithium-ion cathodes with an added constraint of greatly mitigating the use of cobalt. These two goals can be achieved in a seemingly straightforward manner by simply increasing Ni contents, and several Ni-rich compositions have found commercial success. Nonetheless, the increasing demand for lithium-ion batteries has brought about the realization that a more diverse portfolio, with respect to cathode materials, will be critical to ensure supply chain security, lower costs, and wide-spread adoption of energy storage technologies. More specifically, substantially increasing the use of earth-abundant materials is now viewed as a necessary path forward to ensure sustainability. Earth-abundant elements are attractive options in terms of sustainable technological development as they have the potential for positive impact with respect to increasing the availability of raw materials, ultimately lowering costs, and increasing accessibility of dependent technologies such as electric vehicles. Regardless of the class of cathode under consideration for a given application, a common theme among all lithium-ion cathode materials is their need for modification in order to meet the stringent demands of application. Of note, all cathode materials generally require surface stabilization to help enable acceptable performance in terms of metrics such as cycle-life and impedance. This is particularly true in the drive to develop solid-state batteries. In addition, small compositional changes in the way of bulk and surface dopants can also have a major impact on long-term performance. This presentation will discuss work ongoing at Argonne National Laboratory related to the modification of lithium-ion cathodes. Commercially relevant materials, as well as novel materials currently in development at Argonne, will be explored. Atomic layer deposition will be highlighted as a unique tool to not only enable enhanced battery cell performance, but also as an opportunity to discover new materials in the rapidly expanding market of lithium batteries.

In Operando Raman Spectroscopy – a Powerful Tool for Understanding the Chemistry and Electrochemistry of Aqueous Redox Flow Batteries

Of the many emerging technologies for low-cost, grid-scale energy storage, redox flow batteries have been an area of active investigation for decades. More recently, a focus on lower cost alternatives to the foundational Vanadium-based redox flow batteries has been a major focus of the flow battery research community. Specifically, there is great interest in redox active species based on Earth-abundant materials suitable for aqueous systems such that the overall cost per kWh of energy storage can be minimized to enable economical and reliable grid storage to utilize energy generated from intermittent, renewable sources.The use of aqueous electrolytes, ideally at mild pH, in conjunction with inexpensive and highly soluble active material presents an exciting challenge for grid-scale flow batteries. Many new aqueous-soluble, redox active compounds have garnered interest, including water-soluble organic redox species and low-cost transition-metal complexes based on Fe or other earth-abundant metals. Recently, our group has devoted significant attention to new anolytes based on Fe(II)/Fe(III) complexes with various types of low-cost and easily synthesizable phosphonate ligands. Specifically, the nature and fine-tuning of phosphonate ligands allows a high degree of control over the redox potential, rate capability and kinetics, and stability of Fe-based complexes for flow battery anolytes. The wide variety of potential ligands with different functional moieties sometimes produces complicated electrochemical behavior, which has motivated us to apply in operando analysis to inform interpretation of electrochemical and battery cycling results.This presentation focuses on one such analytical tool, namely Raman spectroscopy, applied in operando to several flow batteries based on various Fe-phosphonate anolyte complexes to understand the effects of various substituents and functional groups on the Fe(II)/Fe(III) redox behavior, potential, kinetics, and even structural transformations of these complexes during battery cycling. Examples based on recently reported nitrilotri(methylphosphonic acid) (NTMPA) and related phosphonic acid ligands and their resultant Fe-complex-based anolytes will be presented showing that online vibrational spectroscopy can provide clarity on the effects of varied functional groups on both the molecular structure of redox-active Fe-complexes and the effects of ligand binding on kinetics. This experimental tool beneficially compliments and confirms results from density functional theory to elucidate the structure of these Fe-complexes. Further, the multivariate spectral response provided by in operando Raman spectroscopy allows the state of charge of the cell to be monitored readily. Overall, we aim to highlight the utility of Raman spectroscopy in probing the chemical transformations that occur during electrochemical measurements and battery testing in real time, with potential benefits to a much wider variety of promising redox flow battery systems and the flow battery community at large. Figure 1