Mitigating polysulfide shuttling and sluggish redox kinetics is crucial for the practical utilization of lithium-sulfur batteries (LSBs). Using first-principles density functional theory calculations, we investigate a series of N6-coordinated dual-atom catalysts (DACs) to identify efficient and cost-effective catalysts for the sulfur reduction reaction (SRR). Our results demonstrate that, compared with single-atom catalysts (SACs), DACs exhibit improved Li polysulfide adsorption and redox conversion through cooperative metal-sulfur interactions and frontier-orbital-mediated electronic coupling between adjacent metal centers. In particular, (N3)Fe-Ni(N3) and (N3)Fe-Pt(N3) show the most favorable SRR activity, with optimal adsorption energies (-1.0 to -2.3 eV), low free-energy changes (ΔG ≤0.5 eV) for the Li2S2 to Li2S conversion, and facile Li2S decomposition barriers (≤1.0 eV). Additionally, to accelerate catalyst screening, we introduce precise and accelerated configuration evaluation (PACE), a machine-learning-accelerated DFT workflow that integrates machine learning (ML) interatomic potentials with automated configuration evaluation. Furthermore, to rapidly predict the ΔG for unexplored DACs, we developed a regression model using physically interpretable descriptors. Finally, the electronic structure analyses reveal that the superior catalytic behavior arises from the unique nature of frontier orbitals that enables the dual metal centers to function as a "charge-transfer highway," optimal metal-metal covalent bonding that stabilizes reaction intermediates, and desirable d-band positioning that tunes adsorbate binding. This combined mechanistic and ML-DFT strategy offers general design principles based on the electronic and orbital fingerprints for identifying high-performance SRR catalysts for next-generation LSBs.

In this work, we discuss the complexities of Zn2+-ion storage in an organic stacked layered naphthalenediimide (NDI) via systematic experimentation and theoretical calculations. Apart from the possibility of insertion/deinsertion, NDI also provides redox-active docking motifs for Zn2+-ions. Additionally, the anode-associated challenges are mitigated using zinc phthalocyanine (ZnPc) as an organometallic protective layer. Despite achieving a high coulombic efficiency (>99%) at high cycle numbers, capacity degradation is observed during long-term cycling. The observed capacity fade is attributed to the underlying NDI's transformation from a hexagonal to a flower-like morphology. This structural evolution is attributed to the co-insertion of Zn2+ and protons from the electrode/electrolyte interface into the bulk cathode via coordination with carbonyl (─CO) and amine (─NH2) groups. Additionally, the capacity fade is attributed to the sluggish kinetics of Zn2+ stripping/plating. The ZnPc protective layer effectively guides Zn2+ deposition along the (002) crystal plane, suppresses side reactions, and enhances both the capacity retention and cycling stability of the battery. Accounting for Zn2+-ion storage in a redox-active organic host through the elucidation of key roles in phase transitions, ion diffusion dynamics, and zinc electrodeposition/dissolution processes provides a deep-dive conceptual framework for designing novel organic Zn2+-ion hosts for practical AZIBs.

K-rich Fe-fluorophosphate, having only earth-abundant Fe as the transition metal, has been developed in this work and structural, as well as electronic, features have been reported; with the material also been tested as a low-cost, high-performance cathode material for the sustainable K-ion battery chemistry. The preparation involves a room-temperature potassiation process of K-deficient KFePO4F, which is, otherwise, incapable of acting as a true cathode material, viz., as a K-reservoir in K-ion cells. Comprehensive sets of structural, spectroscopic, and electrochemical analyses reveal that just 15 min of potassiation leads to an optimal K-content of close to 2 p.f.u. in K1+xFePO4F, with Fe in +2 oxidation state (as per XPS, ESR, Mossbauer spectroscopy), which also corresponds to the lowest-energy structures, as per DFT-based simulations. DFT also reveals the associated diffraction patterns of this compound, as hitherto not available. However, further potassiation results only in the formation of KF-based surface species (as per NMR, XPS), which are detrimental toward the electrochemical performance. The as-developed, optimized 15 min potassiated K1+xFePO4F delivers a reversible K-storage capacity of similar to 122 mAh/g (based on Fe2+/3+), along with similar to 100% Coulombic efficiency, which are among the best reported for K-ion battery cathodes. Overall, while unraveling the intricacies and phase/structural evolutions during a room-temperature potassiation process toward developing structurally stable Fe-based polyanion materials, this work paves the way for developing high-performance cathodes for the K-ion battery chemistry and beyond.

Development of efficient and cost-effective catalysts for the dehydrogenation of Ammonia-Borane (AB) has been a challenge which affects the advancement of the hydrogen economy. Over the last decades, pincer-type transition metal complexes have been known to show promising results in catalyzing many chemical reactions ranging from CO2 reduction to C-H bond activation. In this work we investigate the ability of a high-valent Ni-III-Cl complex (complex 1) for the dehydrogenating AB. Our results show that complex 1 can dehydrogenate two equiv. of AB under reaction conditions slightly higher than room temperature. Although the abstraction of H2 from AB can occur at room temperature, higher temperature is required due to relatively higher free-energy barriers for the formation of molecular H2. However, when the Ni-III center is substituted by a Fe-III center (complex 2), AB dehydrogenation can occur at room temperature for one equiv. of AB with a free-energetic span of 21.07 kcal/mol, but this does not remain the same for the second catalytic cycle for complex 2 and the free-energy energetic span increases to 36.1 kcal/mol. Therefore, for the initial cycle of AB dehydrogenation, the Fe-III complex has better functionality and this work exhibits the impact of metal mono-substitution, specifically Fe in activating AB dehydrogenation at room temperature and further paves the way for simple modelling of transition metal-based complexes as catalysts for such reactions.

Over the past decade, heteroatom-doped metal-free carbon materials (MFCMs) have been recognized as effective oxygen reduction reaction (ORR) catalysts. However, the active centers for the ORR in MFCMs are difficult to precisely confirm and controllably synthesize using conventional methods such as high-temperature pyrolysis or heteroatom doping. To elucidate the active center precisely and the structure-property relationship, we demonstrated a conjugated polymer network (CPN), TTB, comprising triazine, thiophene, and benzothiadiazole for ORR and as a cathode catalyst for a zinc-air battery. Density functional theory calculations revealed that the benzothiadiazole building block acts as an active center, leading to ORR catalytic activity. TTB was thoroughly characterized through different characterization techniques like FTIR, XPS, XRD, FESEM, HRTEM, and BET surface area and pore size analysis. The onset potential of 0.81 V vs reversible hydrogen electrode (RHE), diffusion-limiting current density of 3.0 mA/cm2, and E 1/2 of 0.68 V vs RHE with good electrochemical stability are comparable to the benchmark ORR catalyst (10% Pt/C). TTB was further used as the cathode electrocatalyst for a zinc-air battery, resulting in an open-circuit potential of 1.46 V and a specific capacity of 613 mAh g-1. A rechargeable zinc-air battery was also fabricated with TTB and RuO2 as the cathode electrocatalysts, showing a voltage gap of 0.9 V and good cyclic stability. These findings show that the rational design and precise synthesis of conjugated polymer networks can facilitate the development of new ORR catalysts useful as cathode materials for zinc-air batteries.

The development of efficient, cost-effective, and metal-free catalysts for water electrolysis that can compete with platinum-based systems remains a persistent challenge. Conjugated polymer networks have emerged as promising candidates for metal-free electrocatalytic hydrogen evolution reactions (HERs). In this study, we employ computational chemistry methods to design two triazine-based conjugated polymer networks (TCPNs) and experimentally validate their HER performance. Among these, TCPN2 demonstrates high catalytic activity, achieving a current density of 10 mA cm-2 at a low overpotential (eta) of 211 mV. Density functional theory (DFT) calculations reveal that HER activity in both the TCPNs is contingent on high hydrogen coverage, suggesting that initial activation is required to achieve optimal catalytic states. Experimentally, pristine TCPNs exhibit high overpotentials. However, electrochemical activation through cathodic polarization at -0.40 V (vs RHE) for 5 h drastically enhances their HER performance, aligning with theoretical predictions. This work underscores the critical role of electrochemical activation in optimizing HER activity and establishes a robust computational-experimental framework for the design of metal-free electrocatalysts. The insights presented here advance the rational design of efficient and sustainable alternatives to noble metal-based electrocatalysts.

Understanding and optimizing polysulfide adsorption and conversion processes are critical to mitigating shuttle effects and sluggish redox kinetics in lithium-sulfur batteries (LSBs). Here, we introduce a machine-learning-accelerated framework, Precise and Accurate Configuration Evaluation (PACE), that integrates Machine Learning Interatomic Potentials (MLIPs) with Density Functional Theory (DFT) to systematically explore adsorption configurations and energetics of a series of N6-coordinated dual-atom catalysts (DACs). Our results demonstrate that, compared with single-atom catalysts, DACs exhibit improved LiPS adsorption and redox conversion through cooperative metal-sulfur interactions and electronic coupling between adjacent metal centers. Among all DACs, Fe-Ni and Fe-Pt show optimal catalytic performance, due to their optimal adsorption energies (-1.0 to -2.3 eV), low free-energy barriers (<=0.4 eV) for the Li2S2 to Li2S conversion, and facile Li2S decomposition barriers (<=1.0 eV). To accelerate catalyst screening, we further developed a machine learning (ML) regression model trained on DFT-calculated data to predict the Gibbs free energy (ΔG) of Li2Sn adsorption using physically interpretable descriptors. The Gradient Boosting Regression (GBR) model yields an R^2 of 0.85 and an MAE of 0.26 eV, enabling the rapid prediction of ΔG for unexplored DACs. Electronic-structure analyses reveal that the superior performance originates from the optimal d-band alignment and S-S bond polarization induced by the cooperative effect of dual metal centres. This dual ML-DFT framework demonstrates a generalizable, data-driven design strategy for the rational discovery of efficient catalysts for next-generation LSBs.

An efficient electrochemical hydrogen generation catalyst composed of robust ruthenium nanoparticles (Ru NPs) was synthesized through a simple one-pot hydrothermal reaction, where formaldehyde was employed as a reductant and low-molecular-weight poly(vinylpyrrolidone) (PVP) was employed as a stabilizing agent. The as-synthesized nanoparticles were initially characterized by powder X-ray diffraction, which confirmed their hexagonal, close-packed ruthenium phase. Structural analysis was performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which disclosed PVP-stabilized nanoflowers composed of Ru NPs with an average diameter of 5 nm. Further, energy-dispersive X-ray spectroscopy (EDX) confirmed the presence of ruthenium and carbon, and their oxidation states were also studied with X-ray photoelectron spectroscopy (XPS). The as-synthesized PVP-supported Ru NPs exhibited remarkable hydrogen evolution reaction (HER) activity, with overpotentials of 51 and 39 mV at a cathodic current density of -10 mA cm-2 and corresponding Tafel slopes of 23 and 40 mV dec-1 in acidic and alkaline conditions, respectively. Such a high performance of the PVP-protected Ru NPs was further evaluated in a continuous manner by using an electrolyzer flow cell, and our findings were supported by the corresponding density functional theory (DFT) calculations. Calculations of the Gibbs free energy for varied surface coverage on the (002) facet revealed that the individual site activity improved with an increase in surface coverage, enhancing the continuous HER performance. Besides reinforcing the exploitation of eco-friendly raw materials for nanocatalyst development, this work serves as a prelude to our upcoming systematic investigations on the influence of the molecular weight of the PVP polymer on the size of metallic nanoparticles.

Anionic redox chemistry has emerged as a promising strategy to enhance the capacity of sodium-ion battery (SIB) cathode materials by leveraging both cationic and anionic redox processes. While anionic redox offers the potential for higher capacities, its practical implementation is often limited by challenges such as irreversibility, molecular oxygen release, and structural degradation at elevated voltages. In this study, we examine a series of hypothetical prototype cathode materials such as NaAlO2, Na2TiO3, Na2NiO3, and Na2MnO3, using a funnel-based screening approach. Machine learning interatomic potentials are employed to efficiently pre-screen a wide range of structures with different vacancy orderings, enabling the identification of low-energy configurations. These candidate structures are subsequently refined through first-principles calculations based on density functional theory (DFT). To probe the underlying anionic redox mechanisms, we apply both the PBE and SCAN meta-GGA functionals, capturing the behaviour in iono-covalent and strongly covalent Na-ion systems. We define and evaluate key descriptors to quantitatively characterize oxygen redox activity, including changes in the occupancy of metal-d and oxygen-p orbitals, the number of holes generated in these states, and shifts in average net atomic charges. Additionally, we calculate the electronic structure, integrated Crystal Orbital Hamilton Population (COHP) and average operating voltage, using the SCAN functional. This comprehensive investigation offers valuable insights into tuning metal-oxygen bonding to achieve reversible anionic redox, facilitating the rational design of next-generation, high-capacity sodium-ion cathodes.

The synergistic interaction and strategic manipulation of electronic structures by incorporating metal ions into the host matrix have captivated research efforts for supercapacitors. This study presents an efficient strategy for synthesizing Cu‐ion‐incorporated NiCo2O4 (CNCO) nano/microarchitectures using a hydrothermal method followed by heat treatment. It establishes a clear link between variations in Cu content and their effects on material properties, which influence electrochemical performance. Optimizing the Cu content enhances ion transport and conductivity, while creating active sites for faster charge transfer. The porous framework boosts structural integrity and mass transport, reducing aggregation risks. Enhanced performance stems from synergistic interactions between Cu and the NCO matrix in the CNCO nano/microarchitecture. The experimental findings are further substantiated by computational analyses utilizing density functional theory (DFT) calculations. Impressively, the regulated CNCO electrode material exhibits a remarkable specific capacitance of 1301 F/g at 1 A/g and a rate capability of 81.3% at 20 A/g, significantly outperforming other CNCO variants. The optimized CNCO electrode material contributes to a high‐performance battery‐supercapacitor hybrid system, achieving an energy density of 61.36 Wh/kg at a power density of 1.18 kW/kg, with excellent cyclic stability. This system illuminates green and pink light‐emitting diodes.

In recent years, anionic redox chemistry has garnered significant attention for its application in the development of high-capacity battery materials. However, the incorporation of reversible anionic redox chemistry into cathode materials remains a challenge, primarily due to the release of gaseous molecular oxygen and resulting structural degradation upon cycling. In this study, employing first-principles computational methods and comprehensive analysis, we demonstrate a strategy to adjust the extent of anionic redox in sodium-ion batteries (SIBs) through aliovalent doping. We systematically investigate the electronic structure of a series of metal-doped Na2RuO3 compounds to illustrate this electronic structure tuning approach. Furthermore, we provide a systematic strategy for achieving reversible anionic redox and emphasize that it depends on multiple factors governing the electronic structure of the material, rather than solely relying on the covalent interaction between the transition metal and oxygen. Utilizing the aforementioned strategy, we identify a doped Na-rich material capable of exhibiting reversible cationic and anionic redox. Additionally, we elucidate the reasons for the prevalence of cationic redox over anionic redox in pristine Na2RuO3. Our results not only advance fundamental knowledge but also offer valuable guidance for experimental endeavors aimed at enhancing existing materials and designing innovative cathode materials. References Seo, D.-H., et al., Nature Chemistry, 8(7), (2016), 692-697. Grimaud, A., et al., Nature Materials, 15, (2016), 121-126. Sathiya, M., et al., Nature Materials, 12(9), (2013), 827-835. Dixit, M., et al., The Journal of Physical Chemistry C, 121(41), (2017), 22628-22636.

The low specific capacity of sodium-ion batteries (SIBs) limits their practical use in high-capacity energy storage devices. Recently, cumulative cationic and anionic redox reactions have been identified as promising approaches to achieving high capacity in SIBs. However, the excess oxidation of labile oxygen during anionic redox leads to structural degradation and voltage hysteresis in Na-rich cathode materials. In this work, we employ first-principles density functional theory (DFT) calculations to elucidate the contributions of cationic and anionic redox reactions in a prototype Na-rich cathode material (Na2RuO3) across different voltage windows. Additionally, we utilized machine learning interatomic potentials (MLIPs), CHGNet and MACE-MP-0, to illustrate the phase transitions at varying degrees of deintercalation in Na2RuO3. To understand the redox chemistry of this material, we investigated the electronic structures, the O-2 binding energies, the bond covalency, and the local magnetic moments. Our study demonstrates that the strongly constrained and appropriately normed (SCAN) functional outperforms PBE and PBE + U methods across all voltage ranges within the operating window. Furthermore, our computed electrochemical potentials with the SCAN functional are in agreement with the available experimental data. Additionally, by incorporating a series of Hubbard U values (U = 2, 4, 5 eV), we highlight the importance and accuracy of suitable U parameters depending on the element of interest. Our results indicate that in Na2RuO3, cationic redox is primarily dominant despite it being a Na-rich material. Moreover, we demonstrate that CHGNet and MACE-MP-0 MLIPs can be effectively used to prescreen Na-rich cathode materials with reasonable accuracy for their electrochemical properties.

Although Ammonia-borane (AB) has considerably high hydrogen content, it faces significant challenges as an on-board hydrogen storageHydrogen storage material due to its sluggish dehydrogenation kinetics. It is essential to find an efficient and cost-effective catalytic system for AB dehydrogenationAmmonia Borane Dehydrogenation catalyst. Herein, we design an iron-based catalyst, Fe-Bis(pyridyl)borate complex (Fe-CATPh–OH) which is a cost-effective counterpart of a promising but expensive Ru-Bis(pyridyl)borate complex (CAT). This new Fe-system has three aceto-iso-nitrile ligands instead of acetonitrile ligands with a Ph–OH group substituted at its µ–O–B position. Also, the proton at the µ–OH group has been replaced by a –CH3 group to avoid its derivatization. The free-energy energetic span for AB dehydrogenationAmmonia Borane Dehydrogenation by Fe-CATPh–OH 32.13 kcal/mol suggests that this catalyst is likely to operate effectively at around 90 °C. This work demonstrates a protocol to tune the existing catalyst without significantly affecting their functionality under experimental conditions.

The capacity of sodium-ion batteries (SIBs) can be enhanced by incorporating anionic redox into Na-rich cathode materials. However, excessive participation of oxygen in the redox process during the cycling often leads to several undesired issues including oxygen release. In this study, using first-principles computational methods through a systematic investigation and detailed analysis, we demonstrate an electronic structure tuning strategy through the aliovalent doping method to tune the amount of anionic redox in SIBs. Furthermore, we provide a method for achieving reversible anionic redox and emphasize that reversible anionic redox is not solely dependent on the covalent interaction between the transition metal and oxygen but is influenced by multiple factors that govern the electronic structure of the material. Using the aforementioned strategy, we identify an Al-doped Na-rich material, Na2Ru0.5Al0.5O3, which exhibits reversible cationic and anionic redox. Additionally, we rationalize the dominance of cationic redox in pristine Na2RuO3.

Over the last few decades, lithium-ion batteries (LIBs) have dominated the market of energy storage devices due to their wide range of applications ranging from grid–scale energy storage systems to electric vehicles (EVs). However, the increasing demand for sustainable energy sources and scarcity of lithium draws attention to other alternatives, such as Sodium-ion batteries (SIBs). SIBs are potential candidates for sustainable energy storage devices due to their high natural abundance and low cost of Na-based materials. However, the low specific capacity of standard cathodes and the poor cycle life of Na-rich cathodes still limit the practical application of SIBs for high-energy applications. This review summarizes the challenges and recent progress in the development of Na-rich layered cathode materials. We highlight some of the critical parameters that modulate the anionic redox in high-capacity Na-ion batteries. This review provides the present state of understanding and is expected to be helpful for the future design and development of improved Na-based cathode materials for high-energy applications.

Designing an efficient and cost-effective catalyst for ammonia borane (AB) dehydrogenation remains a persistent challenge in advancing a hydrogen-based economy. Transition metal complexes, known for their C-H bond activation capabilities, have emerged as promising candidates for AB dehydrogenation. In this study, we investigated two recently synthesized C-H activation catalysts, 1 (CoIV-dinitrate complex) and 2 (NiIV-nitrate complex), and demonstrated their efficacy for AB dehydrogenation. Using density functional theory calculations and a detailed analysis, we elucidated the AB dehydrogenation mechanism of these complexes. Our results revealed that both complexes 1 and 2 can efficiently dehydrogenate AB at room temperature, although the abstraction of molecular H2 from these complexes requires slightly elevated temperatures. We utilized H2 binding free energy calculations to identify potentially active sites and observed that complex 2 can release two equivalents of H2 at a temperature slightly higher than room temperature. Furthermore, we investigated AB dehydrogenation kinetics and thermodynamics in iron (Fe)-substituted systems, complexes 3 and 4. Our results showed that the strategic alteration of the central metal atom, replacing Ni in complex 2 with Fe in complex 4, resulted in enhanced kinetics and thermodynamics for AB dehydrogenation in the initial cycle. These results underscore the potential of high-valent first-row transition metal complexes for facilitating AB dehydrogenation at room temperature. Additionally, our study highlights the beneficial impact of incorporating iron into such mononuclear systems, enhancing their catalytic activity.

In recent years, high-energy-density sodium ion batteries (SIBs) have attracted enormous attention as a potential replacement for LIBs due to the chemical similarity between Li and Na, high natural abundance, and low cost of Na. Despite the promise of high energy, SIBs with layered cathode materials face several challenges including irreversible capacity loss, voltage hysteresis, voltage decay, irreversible TM migrations that lead to fast capacity fading, and structural degradation. However, their electrochemical performance can be improved by introducing reversible anionic redox along with conventional cationic redox. This Perspective systematically summarizes different factors that trigger the irreversible anionic redox in Na-based cathode materials. Additionally, this Perspective highlights the mechanistic understanding and key challenges for reversible anionic redox and proposes plausible solutions to overcome these limitations. The overview of various existing experimental and theoretical approaches presented here could provide a futuristic pathway to design Na-based cathode materials for high-energy-density SIBs.

In recent years, the high availability of methane in the shale gas reserves has raised significant interest in its conversion to high-value chemicals but this process is still not commercially viable. Metal oxides, due to their surface heterogeneity and the presence of Lewis acidic and basic site pairs are known to facilitate the activation of C-H bonds of methane. In this work, we investigate the C-H bond activation of methane on pristine and doped γ-Al2 O3 clusters using density functional theory (DFT) calculations. Our results demonstrate that the polar pathway is energetically preferred over the radical pathway on these systems. We found that the metal dopants (boron and gallium) not only alter the catalytic activity of dopant sites but this effect is more pronounced on some of the adjacent sites (non-local). Among the selected dopants, gallium greatly improves the catalytic activity on most of the site pairs (including most active and least active) of pristine γ-Al2 O3 . Additionally, we identified a correlation between H2 binding energies and the C-H activation free energies on Ga-doped γ-Al2 O3 .

Amino acids and proteins are ubiquitous in all biological processes. Therefore, fluctuations in their levels pro-foundly impact the general well-being of any human being. Structural similarities between amino acids hamper their direct detection by fluorophores. Thus, it becomes crucial to employ an ancillary approach to accomplish this goal. In this work, the selective fluorescence response of Ni2+ towards a probe PyPP was used as a precursor for selective histidine sensing. The probe showed selectivity towards Ni2} by fluorescence quenching, and it could be revived only in the presence of histidine. The limit of detection (LOD) for Ni2+ was 4 x10(-6) M, whereas LOD for histidine was 1.08 x 10(-6 )M. The Ni2+ mediated selectivity could also be extended to histidine-rich proteins bovine serum albumin (BSA) and human serum albumin (HSA). The devised system was also applied to a macrophage cell line (RAW 264.7) to indicate the presence of Ni2+/histidine/HSA-BSA via confocal fluo-rescence microscopy, and quantitative response could be studied with flow cytometry.

Developing suitable materials that can differentiate between chemically similar substances such as aliphatic and aromatic amines is challenging. Aliphatic and aromatic amines vary considerably in size and electronic properties despite possessing the same functional group. This makes the entire separation process more tedious. Metal-organic frameworks known for their inherent permanent porosity can be designed using appropriate building blocks that can lead to multifunctional materials. Here we utilize two Co-based multifunctional MOFs for discriminative sensing of amines and on-site detection of ammonia. Both the MOF materials display unique fluorescence behavior where aliphatic amines lead to "turn-off", and aromatic amines show "turn-on" fluorescence intensities of the two MOFs. Real-time sensing experiments with MOF-based mixed matrix membranes show an instant color change when ammonia is liberated from a chemical reaction. Density functional theory calculations unravel that the aliphatic and aromatic amines interact with the MOF structures in different ways that lead to "turn-off" and "turn-on" fluorescence behavior, respectively.