Transition metal (TM) cations exhibit distinct electronic properties, compared to alkali and alkaline earth metal cations. In this work, we aim to explore the electronic coupling between different redox-active TMs guest and conductive MXene host. Specifically, within the confined environment of MXene layers, different inserted TM cations demonstrate varying electronic structures and exert distinct influences on the MXene. Unlike Cu which undergoes unusual reduction upon insertion within MXenes, our Bader charge analysis and X-ray absorption spectroscopy (XAS) results indicate that the oxidation states of inserted Ni, Co, Mn, and Zn ions remain unchanged. Despite the higher degree of Ti oxidation led to higher resistivity of intercalated MXenes, the density of states analysis of Ni and Co highlighted the important contributions of these TM cation guests on the overall electrical conductivity of intercalated-MXenes. Moreover, the TM-intercalated MXenes displayed varying redox contributions to the charge storage, where the redox properties of transition metal can be suppressed. This study highlights the unique influence of each transition metal cation under MXene confinement and lays the groundwork for utilizing transition metal guests in MXenes for various electrochemical applications.

Electrolyte engineering in Zn-metal batteries frequently employs alkaline metal salts to enhance conductivity and reduce overpotential for Zn plating. While these additives improve conductivity, the presence of more mobile alkali cations can negatively affect the Zn2+ transference number. Optimizing this property is crucial for high-rate performance, efficiency, and safety, as high Zn2+ transference number minimizes concentration polarization and dendrite formation during high-current cycling. However, reliably measuring the transference number in non-binary electrolytes presents significant experimental challenges due to dynamic Zn metal interfaces, rendering traditional methods ineffective. Here, we use a modified Hittorf-type method to measure Zn2+ transference numbers in complex electrolytes. Supported by molecular dynamics simulations, this method is applied to obtain transference numbers of Zn2+, K+, and acetate ions in Zn-K acetate electrolytes. By varying the Zn2+ fraction, the impact of co-salts on transport properties is studied and correlated with the Zn solvation environment using X-ray absorption spectroscopy. It is revealed that while ionic conductivity increases with the addition of KOAc co-salt, the Zn2+ transference number dramatically decreases. Electrolytes with higher Zn2+ transference numbers enable longer high-rate cycling, underscoring the importance of optimizing Zn2+ transference for improved performance of Zn-metal anodes.

MXenes are two-dimensional transition metal carbides and nitrides characterized by versatile electronic and electrochemical properties. Herein, we investigate the electronic interactions between various redox-active transition metals (Ni, Co, Mn, and Zn) intercalated into the conductive Ti3C2Tx MXene host. Employing X-ray absorption spectroscopy (XAS) and Bader charge analysis, we reveal that the oxidation states of the intercalated ions remain unchanged upon insertion, whereas Ti atoms within the MXene layers become progressively oxidized with increasing intercalant concentration. Consequently, the electrical resistivity of the intercalated MXenes increases. Ab initio molecular dynamics (AIMD) and density functional theory (DFT) demonstrate distinct spatial arrangements and coordination environments of the intercalated cations, significantly influencing their electronic density of states and interactions with MXene surfaces. Pseudocapacitance measurements in 0.1 M NaOH show distinct behaviors: Co exhibits significant redox activity with less participation from Ti of MXene, while Ni ions show negligible oxidation state changes with predominant Ti redox involvement. Our findings reveal the complex electronic and redox behavior of transition metal-intercalated MXenes, guiding the targeted modification of 2D material properties through careful selection of intercalant species.

Electrochemical energy storage devices are typically based on materials of inorganic nature which require high temperature synthesis and frequently feature scarce and/or toxic elements. Organic-based materials on the other hand can provide an attractive alternative, potentially yielding sustainable, safe, and cost-effective energy storage devices based on abundant elements (e.g. C, N, O, S, and H). However, attempts to incorporate organic and coordination compounds so far have led to sub-par cycling stability and charging rates due to insufficient structural and (electro)chemical stability, low electrical conductivity, and reduced performance at industrially relevant device scales. In recent years metal–organic frameworks (MOFs) have gained attention as having the potential to rival or even supersede traditional energy storage materials. Functional properties such as electronic or ionic conductivity can be incorporated into these materials by judicious design of their constituent inorganic and organic building blocks. However, full realization of the potential of MOFs for electrochemical energy storage requires joint expertise from distinct fields. In particular, bridges must be formed between electrochemists and synthetic and material chemists to establish the unified approach necessary to develop MOF-based energy storage devices exhibiting competitive performance.

The electrochemical reduction of CO2 (eCO2R) is governed by complex interactions at the electrode-electrolyte interface. Recent studies show that electrolyte species in the electrical double layer can strongly affect the CO2 reduction activity and selectivity. While the role of cations in eCO2R is relatively well understood, recent studies show that anions and molecular additives can be equally influential. Here, we discuss how these species can facilitate eCO2R intermediate stabilization and suppress the hydrogen evolution reaction, enhancing the activity and selectivity of eCO2R.

Water-in-salt electrolytes (WISEs) offer extended voltage stability, enabling the use of high-voltage materials in aqueous energy storage systems. The solid-electrolyte interphase (SEI) formed in some WISEs plays a key role in enabling this enhanced stability by passivating the electrode surface. However, non-SEI-forming WISEs also exhibit similar stability window, despite the lack of an SEI, though the mechanism behind remains insufficiently understood. In this work, we investigate the origins of the hydrogen evolution reaction (HER) suppression across a range of electrolyte concentrations of the non-SEI-forming electrolytes: from dilute solutions to WISE, using electrochemical techniques, molecular dynamics (MD) simulations, and density functional theory (DFT) calculations. We disentangle the contributions of water activity, local pH changes induced by HER in non-buffering neutral electrolytes, and kinetic and mass transport effects. We establish a correlation between HER activity and active surface coverage by water molecules: in WISEs sluggish HER kinetics is observed, as indicated by a sevenfold decrease in exchange current density. Additionally, we reveal that in WISE HER is significantly limited by the sluggish water transport in the double layer, further contributing to the extended experimental voltage stability window.

Controlling solid electrolyte interphase (SEI) in batteries is crucial for their efficient cycling. Herein, we demonstrate an approach to enable robust battery performance that does not rely on high fractions of fluorinated species in electrolytes, thus substantially decreasing the environmental footprint and cost of high-energy batteries. In this approach, we use very low fractions of readily reducible fluorinated cations in electrolyte (~0.1 wt.%) and employ electrostatic attraction to generate a substantial population of these cations at the anode surface. As a result, we can form a robust fluorine-rich SEI that allows for dendrite-free deposition of dense Li and stable cycling of Li metal full cells with high-voltage cathodes. Our approach represents a general strategy for delivering desired chemical species to battery anodes through electrostatic attraction while using minute amounts of additive.

MXenes are 2D transition metal carbides, nitrides, and/or carbonitrides that can be intercalated with cations through chemical or electrochemical pathways. While the insertion of alkali and alkaline earth cations into Ti3C2Tx MXenes is well studied, understanding of the intercalation of redox-active transition metal ions into MXenes and its impact on their electronic and electrochemical properties is lacking. In this work, we investigate the intercalation of Cu ions into Ti3C2Tx MXene and its effect on its electronic and electrochemical properties. Using X-ray absorption spectroscopy (XAS) and ab initio molecular dynamics (AIMD), we observe an unusual phenomenon whereby Cu2+ ions undergo partial reduction upon intercalation from the solution into the MXene. Furthermore, using in situ XAS, we reveal changes in the oxidation states of intercalated Cu ions and Ti atoms during charging. We show that the pseudocapacitive response of Cu-MXene originates from the redox of both the Cu intercalant and Ti3C2Tx host. Despite highly reducing potentials, Cu ions inside the MXene show an excellent stability against full reduction upon charging. Our findings demonstrate how electronic coupling between Cu ions and Ti3C2Tx modifies electrochemical and electronic properties of the latter, providing the framework for the rational design and utilization of transition metal intercalants for tuning the properties of MXenes for various electrochemical systems.

Electrochemical energy storage is vital as we transition towards sustainable energy sources. Energy storage systems must meet performance criteria related to energy and power density, safety, and cost. Battery metrics optimization depends on the end-application of the energy storage device. Selection of energy storage device components, such as electrode materials and electrolytes, directly affects performance metrics. The local chemical environment of these components can impact the transport of ions, charge transfer reactions, and stability. As such, understanding the role of local chemical environments is vital in developing next-generation energy storage technologies. This talk will discuss the importance of local chemical environments in sustainable energy technologies. We will explore how optimizing the chemical properties of electrode materials and electrolytes can improve energy storage system performance metrics, and how this can lead to more sustainable and environmentally friendly energy solutions.

As electronic technology advances, the need in safe and long-lasting energy storage devices that occupy minimum volume arises. Short charging times of several seconds to minutes, with energy densities comparable to those of batteries, can be achieved in pseudocapacitors. These are sub-class of supercapacitors, where capacitance is mediated by fast redox reactions and can enable at least an order of magnitude more energy to be stored than in typical electrical double layer capacitors. Transition metal oxides (e.g. RuO 2 , MnO 2 ) and conducting polymers (e.g. polyaniline) serve as typical examples. However, these materials are often high in cost and/or suffer from low cycling stability. As a result, the search for new pseudocapacitive materials constitutes an important direction today. In my talk, I will discuss various strategies to improve the performance metrics of pseudocapacitors, specifically focusing on enhancing capacitance and charging rates. I will primarily discuss the electrochemical behavior of layered materials, such as 2D transition metal carbides (MXenes) and 2D pi-conjugated conductive metal-organic frameworks, with a strong emphasis on understanding the mechanisms of charge storage and the various factors influencing electrochemical performance. Additionally, I will explore the role of cation intercalation in layered MXenes as a means to finely tune their electrochemical responses.

Electric vehicles provide the ability to substantially reduce or eliminate greenhouse gas emissions from transportation. Such vehicles utilize a fundamentally different powertrain technology compared to conventional vehicles based on the internal combustion of liquid fuels. In this series of articles, we discuss material challenges related to three key subsystems related to the powertrain of electric vehicles: batteries, power electronics, and permanent magnets. Given that electric vehicles currently occupy ~20% of the market share and are projected to rapidly rise, a cross-cutting challenge among these systems is the sustainability and resilience of the global supply chain of critical minerals to enable this adoption of electric vehicles.

Synchrotron X-ray absorption spectroscopy (XAS) serves as a robust and powerful technique for probing the oxidation state and coordination surrounding of specific elements. In particular, operando XAS has been employed to elucidate charge storage mechanisms by monitoring changes in the oxidation state through the absorption edge energy of metals in electrodes such as MnO 2 and RuO 2 during charging/discharging [1] [2] . Herein, we utilized in-situ XAS technique to uncover the charge storge mechanisms of transition metal (TM)-intercalated MXenes (Ti 3 C 2 T x ). We specifically probed the K-edges of intercalated TM and Ti MXene to reveal their oxidation states changes, shedding light on their respective contributions to capacitance. Aiming to gain further insights into the confined environment between MXene layers, we also employed ab-initio molecular dynamics (AIMD) to further interpret and validate the coordination environment obtained through in-situ extended X-ray absorption fine structure (EXAFS). This investigation lays the groundwork for tailoring the electronic and electrochemical properties of MXenes by the intercalation of various transition metal cations across diverse electrochemical systems. [1] J.-K. Chang, M.-T. Lee, W.-T. Tsai, Journal of Power Sources 2007 , 166 , 590-594. [2] Y. Mo, M. R. Antonio, D. A. Scherson, The Journal of Physical Chemistry B 2000 , 104 , 9777-9779.

MXenes, are a family of two-dimensional (2D) transition metal carbides, nitrides and/ or carbonitrides. [1] The intercalation of different metal cations and organic molecules into MXene for tuning MXenes’ electronic and electrochemical properties have been widely reported. [2] [3] [4] However, transition metals (TMs) which have distinct electrochemical behaviors [5] [6] have not been explored in the literature of MXenes’ intercalation. Therefore, we herein compared the intercalation effects of different TM cations on Ti 3 C 2 T x , for offering a general insight on the influences of multi-valent, redox-active TMs on MXenes. In particular, the changes on the physiochemical and electrochemical properties of MXenes were investigated using different in-situ and ex-situ methods, for a better understanding on the interfacial interactions of TM cations and MXenes in the confined environment of MXenes’ multilayer structures. This work serves as a foundation for the fine-tuning of MXenes’ properties by utilizing a variety of TM cations intercalation for different electrochemical systems. [1] B. Anasori, M. R. Lukatskaya, Y. Gogotsi, Nature Reviews Materials 2017 , 2 , 16098. [2] M. R. Lukatskaya, O. Mashtalir, E. Ren Chang, Y. Dall’Agnese, P. Rozier, L. Taberna Pierre, M. Naguib, P. Simon, M.W. Barsoum, Y. Gogotsi, Science 2013 , 341 , 1502-1505. [3] J. Li, H. Wang, X. Xiao, Energy & Environmental Materials 2020 , 3 , 306-322 [4] M. Ghidiu, S. Kota, J. Halim, A. W. Sherwood, N. Nedfors, J. Rosen, V. N. Mochalin, M. W. Barsoum, Chemistry of Materials 2017 , 29 , 1099-1106. [5] D. Göhl, H. Rueß, M. Pander, A. R. Zeradjanin, K. J. J. Mayrhofer, J. M. Schneider, A. Erbe, M. Ledendecker, Journal of The Electrochemical Society 2020 , 167 , 021501. [6] M. Esmaeilirad, A. Baskin, A. Kondori, A. Sanz-Matias, J. Qian, B. Song, M. Tamadoni Saray, K. Kucuk, A. R. Belmonte, P. N. M. Delgado, J. Park, R. Azari, C. U. Segre, R. Shahbazian-Yassar, D. Prendergast, M. Asadi, Nature Communications 2021 , 12 , 5067.

Conventional Li-ion electrolytes consist of carbonate solvents and Li-ion salts that were made for carbonaceous negative electrodes. When the electrolytes are used with metallic lithium anodes, carbonate electrolytes lead to low charge-discharge cycle stability due to adverse reactive species at the anode surface. 1-4 This reactive species are called the solid electrolyte interface (SEI). 1 SEI instabilities/inhomogeneities result in its continuous thickening and formation of electronically non-active dead lithium. 2 SEI composition and structure are affected by both solvent and electrolyte chemistry in bulk solution and, more importantly, at the electrode-electrolyte interface. 4 Current research studies suggest that X-rich (where X is a halogen) SEI yields superior performance compared to halogen-free SEI. 1,5 Electrolytes that have large volume fractions of halogenated species have statistically higher probability to be reduced at the electrode surface and yield X-rich SEI layers. 6 Therefore, the use of halogenated solvent and/or high concentrated (> 1 M) lithium salt with halogenated anions has been actively explored for LiMBs. However, the high cost of Li salts and high viscosity of the electrolyte at high salt concentration make the concentrated electrolytes unrealistic for commercial battery applications. In search of a cost-effective solution for high performance LiMBs, halogenated electrolyte additives could serve as an ideal approach since only a small amount of the additive would be potentially required to induce similar X-rich interface that can be seen in the case of the halogenated ether electrolyte. In this meeting abstract, we present a new concept that leverages favorable electrostatic interactions with the electrolyte additive to drive the formation of robust SEI layers even at low additive content. Specifically, custom-designed additives can be electrostatically attracted to the negatively charged electrode, creating a high population of halogenated species at the anode surface even at a dilute Li salt concentration. Effective SEI formation with a low-concentration additive circumvents the challenges associated with the current state-of-the-art approach of using halogenated species at high concentration (i.e., unfavorably high solution viscosity and high cost). Reference 1 Louli, A. J. et al. Diagnosing and correcting anode-free cell failure via electrolyte and morphological analysis. Nature Energy 5 , 693-702, (2020). 2 Chen, K.-H. et al. Dead lithium: mass transport effects on voltage, capacity, and failure of lithium metal anodes. Journal of Materials Chemistry A 5 , 11671-11681, (2017). 3 Lin, D. et al. Three-dimensional stable lithium metal anode with nanoscale lithium islands embedded in ionically conductive solid matrix. Proc Natl Acad Sci U S A 114 , 4613-4618, (2017). 4 Lin, D., Liu, Y. & Cui, Y. Reviving the lithium metal anode for high-energy batteries. Nat Nanotechnol 12 , 194-206, (2017). 5 Yu, Z. et al. Molecular design for electrolyte solvents enabling energy-dense and long-cycling lithium metal batteries. Nature Energy 5 , 526-533, (2020). 6 Yamada, Y., Wang, J., Ko, S., Watanabe, E. & Yamada, A. Advances and issues in developing salt-concentrated battery electrolytes. Nature Energy 4 , 269-280, (2019).

Electrochemical CO2 reduction reaction (eCO2RR) offers a pathway to produce valuable chemical fuels from CO2. However, its efficiency in aqueous electrolytes is hindered by the concurrent H2 evolution reaction (HER), which takes place at similar potentials. While the influence of cations on this process has been extensively studied, the influence of anions remains largely unexplored. In this work, we study how eCO2RR selectivity and activity on a gold catalyst are affected by a wide range of inorganic and carboxylate anions. We utilize in situ differential electrochemical mass spectrometry (DEMS) for real-time product monitoring, coupled with molecular dynamics (MD) simulations. We show, that anions significantly impact eCO2RR kinetics and eCO2RR selectivity. MD simulations reveal a new descriptor – free energy of anion physisorption – where weakly adsorbing anions enable favorable CO2 reduction kinetics. By leveraging these fundamental insights, we identify propionate as the most promising anion, achieving nearly 100% Faradaic efficiency while showing high CO production rates that are comparable to those in bicarbonate. These insights underscore the vital role of anion selection in achieving highly efficient eCO2RR in aqueous electrolytes.

Nanoparticle radioenhancement offers a promising strategy for augmenting radiotherapy by locally increasing radiation damage to tumor tissue. While past research has predominantly focused on nanomaterials with high atomic numbers, such as Au and HfO2, recent work has revealed that their radioenhancement efficacy decreases considerably when using clinically relevant megavoltage X-rays as opposed to the orthovoltage X-rays typically employed in research settings. Here, radiocatalytically active Ti-based nanomaterials for clinical X-ray therapy settings are designed. A range of candidate materials, including TiO2 (optionally decorated with Ag or Pt nanoseeds), Ti-containing metal-organic frameworks (MOFs), and 2D Ti-based carbides known as Ti3C2Tx MXenes, is investigated. It is demonstrated that these titanium-based candidates remain consistently performant across a wide energy spectrum, from orthovoltage to megavoltage. This sustained performance is attributed to the catalytic generation of reactive oxygen species, moving beyond the simple physical dose enhancements associated with photoelectric effects. Beyond titania, emergent materials like titanium-based MOFs and MXenes exhibit encouraging results, achieving dose-enhancement factors of up to three in human soft tissue sarcoma cells. Notably, these enhancements are absent in healthy human fibroblast cells under similar conditions of particle uptake, underscoring the selective impact of titanium-based materials in augmenting radiotherapy across the clinically relevant spectral range.

This approach utilizes electrostatic attraction of very low fractions (~0.1 wt%) of readily reducible fluorinated cations in electrolyte to form a robust fluorine-rich SEI and enable stable Li-metal batteries.

Rechargeable aqueous Zn metal batteries are promising systems for grid storage because of their high energy density, low cost, and non-flammability. However, Zn metal anodes have major limitations due to dendrite formation and concurrent water splitting during charge-discharge cycling. Both processes negatively affect coulombic efficiency (CE) and long-term cycling stability. Water-in-salt (WIS) electrolytes were previously proposed to address these challenges, yielding improvements in the cycling stability of Zn metal anodes. While WIS electrolytes help increase CE, they require high amounts of salt (often toxic) and have dramatically increased viscosity, which in turn limit their transport properties, charge-discharge rates, and usability in advanced Zn batteries. In this manuscript, we propose a strategy for simultaneously achieving high CE (>99.99%), high rate, low cost and reduced environmental footprint. Specifically, we show that by using coordinating anions like acetate a WIS-like Zn coordination environment can be achieved even in relatively dilute conditions, enabling prolonged cycling of Zn metal anodes. Such electrolytes have an order of magnitude higher conductivity and lower viscosity than traditional WIS electrolytes, thus enabling lower overpotentials and higher rate of Zn plating/stripping.