Energy Materials

Ether-based room-temperature sodium–sulfur (RT Na─S) batteries are a promising energy-storage system, yet hindered by the unregulated sulfur redox pathway, severe polysulfide shuttling and rapid capacity fading. Herein, highly unsaturated niobium-oxide sub-nanoclusters (≈0.7 nm) anchored on defective carbon black (NbOx-DCB) as a dynamic sulfur-conversion catalyst are introduced. The delocalized Nb d-electrons in the sub-nanocluster configuration create a mixed Nb4+/Nb5+ valence state that functions as a bidirectional electron reservoir, thereby enabling a distinct d-band-center self-regulation mechanism. The strong d–p orbital coupling enabled by a Nb4+-rich surface effectively captures sodium polysulfides and accelerates sulfur conversion kinetics during discharge, while a Nb5+-rich surface promotes facile solid-polysulfide decomposition during charging. Consequently, the NbOx-DCB/S cathode delivers a reversible capacity of 1184 mAh gS−1 at 0.1 A g−1 after 100 cycles and retains 547 mAh gS−1 after 3000 cycles at 2 A g−1, corresponding to a decay rate of 0.0027% per cycle. The general applicability of this approach is validated by high-performance tungsten and vanadium oxide sub-nanocluster-based sulfur cathodes. These findings highlight sub-nanoscale metal-oxide engineering as a versatile route to high-performance RT Na–S batteries.

The performance of novel electrode materials and the influence of cell geometry or flow rate on capacitive water deionization (CDI) are usually described by global metrics from the analysis of the effluent electrolyte together with the electrochemical response of the system. However, these approaches cannot provide information on local variations of ion concentration and related local efficiency within an operating device. Here, a novel approach of position-resolved operando synchrotron-based X-ray transmission is introduced to determine local ion concentration changes along the flow channel from the inlet (feedwater) to the outlet (effluent water) of a working CDI cell. A specific cell design allows the independent quantification of concentration changes within the bulk electrolyte in the flow channel as well as the two oppositely charged nanoporous electrodes. Results from a 15 mM CsCl feed solution using three flow rates and two carbon materials with hierarchical porosity reveal a complex spatial- and temporal ion distribution in the system. A distinct dependence of local concentration on the flow rate is observed, with generally decreasing local desalination capacity towards the outlet of the cell, particularly for slow flow rates. It is also found that a significantly better overall performance for one of the two materials can be related to dominant counter-ion adsorption within ultramicropores, which ions cannot access in their hydrated state at no applied potential (ionophobicity). Overall, the results demonstrate the unique potential of position-resolved operando X-ray techniques to get mechanistic insight into local ion redistribution in CDI systems, allowing ultimately guiding performance optimization.

The efficient and selective extraction of lithium ions from aqueous media is crucial for resource recovery, yet remains challenging due to the chemical similarity of coexisting alkali ions, such as sodium. In this study, we report a two-step electrochemical strategy that utilizes tailored MXene electrodes for lithium ion extraction with enhanced selectivity and extraction rates. By preintercalating hexadecylamine (HDA) and decyltrimethylammonium (C10), which are long-chain organic molecules, into the Ti3C2Tx MXene structure, we tailored the interlayer environment to favor lithium ions over sodium ions. The HDA-intercalated MXene demonstrated high Li+/Na+ selectivity with a lithium ion uptake of 2.2 mmol/L and a suppressed sodium ion uptake (<0.2 mmol/L). Extended cycling revealed that molecular preintercalation modulates ion transport pathways and influences structural and electrochemical stability. Both HDA-Ti3C2Tx and C10-Ti3C2Tx maintained a lithium ion purity of nearly 100% over 50 cycles.

Electrical double-layer capacitors offer high power density and long cycle life but are limited by moderate energy density. We investigate a strategy to improve their performance using quaternary electrolytes containing two distinct cations and two distinct anions. Our theoretical analysis shows that such electrolytes outperform pure ionic liquids and conventional mixtures sharing a common ion. We validate this approach experimentally using [EMIM][BF4] mixed with lithium salts, characterizing their local structure and electrochemical behavior via NMR, Raman spectroscopy, conductivity measurements, and electrochemical testing. We further demonstrate that the enhancement depends sensitively on electrode microporosity, underscoring the interplay between electrolyte composition and pore structure.

This study investigates the role of microporous carbons and carbonate-based electrolytes in addressing challenges related to polysulfides dissolution and electrolyte compatibility in lithium–sulfur (Li–S) batteries. By employing microporous carbons and varying the sulfur content, we investigate the formation of the cathode-electrolyte interphase (CEI) during the first discharge process. We propose an electrochemical nucleophilic mechanism for the formation of the CEI involving polysulfides and solvent molecules in the confined small pores of the cathode. This interphase, primarily composed of LiF, effectively seals the carbon pores, preventing further solvent intrusion and stabilizing the system. Furthermore, it allows the use of wider pores without compromising the system. Our findings reveal that an increased sulfur content within the micropores enhances cycling stability, contradicting trends observed in ether-based systems. These insights highlight the potential of designing Li–S systems with optimized pore structures and electrolyte compositions to achieve greater stability and capacity retention, marking a significant step forward in the development of practical Li–S batteries.

There is a need for new electrochemical energy storage materials that can handle high cycling rates (high power) for rapid charging without compromising high energy density, such as high-power Li-ion batteries (LIBs) and Li-ion capacitors (LICs). Electrically conductive and redox-active two-dimensional (2D) materials, such as transition metal carbides and borides, are promising candidates for these applications. Tailoring in-plane chemically ordered MAB phases (i-MAB) has facilitated the synthesis of their 2D derivatives (i-MBenes), which possess ordered vacancies at the metal sites. The first reported i-MBene paper is Mo4/3B2Tx, which is derived from the parent i-MAB phase (Mo2/3Y1/3)2AlB2 by the selective etching of Al and Y. In this study, we report on the synthesis of 2D Mo4/3B2Tx aerogel and its electrochemical performance as an electrode material for LIBs. Our aerogel exhibits remarkable stability during life-cycling testing at high applied specific currents, maintaining a specific capacity of 260 mAh g−1 even after completing 500 cycles under a high specific current of 2 A g−1. At a moderate specific current of 100 mA g−1, it delivers an energy density of 363 Wh kg−1, while at a high specific current of 2 A g−1, it achieves a specific power of 1300 W kg−1. Complementary density functional theory calculations further reveal that Li preferentially occupies hexagonal Mo sites in Mo4/3B2Tx, supporting the observed stable lithiation behavior and excellent high-rate capability. These results suggest that 2D Mo4/3B2Tx aerogel is a promising candidate for high-power LIBs and LICs.

Herein, we report the charge storage and plastic properties of the redox-active, bimetallic metal phosphonate framework of [Cu(2,2′-bpy)VO(O3PC6H5)2]. The flexible crystals of [Cu(2,2′-bpy)VO(O3PC6H5)2] combine high energy storage with mechanical flexibility on the same platform, which is an unusual and significant property that is not observed in traditional rigid layered electrode materials. In contrast to RuO2, graphene, or MXenes, which prefer concentrated acidic or basic electrolytes to operate effectively as electrodes, [Cu(2,2′-bpy)VO(O3PC6H5)2] operates between pH values of 4 and 10 while reaching a specific capacitance of about 140 F/g in H3PO4 at pH 4 and in NaOH at pH 10 at 1 mV/s. It also demonstrates high chemical and electrochemical stability between pH 2 and 12 and in lithium hexafluorophosphate for extended periods. The use of [Cu(2,2′-bpy)VO(O3PC6H5)2] as electrodes eliminates the need for harsh chemical environments, generating more sustainable and environmentally friendly energy storage solutions, and [Cu(2,2′-bpy)VO(O3PC6H5)2] can be synthesized in water at mild temperatures. The combination of chemical stability, mechanical flexibility of [Cu(2,2′-bpy)VO(O3PC6H5)2], and compatibility with mild electrolytes makes [Cu(2,2′-bpy)VO(O3PC6H5)2] a more sustainable alternative to conventional metal oxides, MXenes, and carbon-based electrodes in next-generation supercapacitors and battery technologies.

The demand for lithium production has seen a significant rise, with the growing electric vehicle and stationary battery markets requiring further development of sustainable and scalable extraction methods. Direct lithium extraction technologies have been developed to address potential shortages, with adsorption emerging as a key method due to its efficiency and low environmental impact. Given that Al(OH)3 is already utilized as an adsorbent in various industrial applications, the practical importance of Al-based alternative systems for lithium ion extraction is increasing, yet lithium ion recovery requires harsh chemicals. In this study, we report a novel lithium extraction method combining chemical adsorption and electrochemical release using a synthesized aluminum layered double hydroxide (Al-LDH) material, developed under mild reaction conditions. The performance of the Al-LDH electrode was evaluated against a commercial Al(OH)3 adsorbent. Comprehensive characterization using techniques such as X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy revealed detailed insights into the crystalline structure, particle size distribution, and surface morphology of the materials. The Al-LDH electrode exhibited a lithium ion adsorption capacity, achieving an average chemical uptake of lithium ions of 57.6 mg/g. In contrast, lithium-ion uptake capacity for Al(OH)3 was 1.0 mg/g over 15 cycles. Notably, this method operates under pH-neutral conditions, eliminating the need for harsh acidic or basic eluents. As a result, it prevents structural degradation and minimizes secondary pollution for potential future applications of lithium-ion recovery. The material’s layered structure selectively allowed lithium ion intake while blocking sodium ions, demonstrating its high selectivity and utility in lithium ion recovery processes. The integration of pH-neutral regeneration and high selectivity shows that Al-LDH electrodes as viable candidates for next-generation, green lithium extraction technologies.

Supercapacitors are efficient and versatile energy storage devices, offering remarkable power density, fast charge/discharge rates, and exceptional cycle life. As research continues to push the boundaries of their performance, electrode fabrication techniques are critical aspects influencing the overall capabilities of supercapacitors. Herein, we aim to shed light on the advantages offered by dry electrode processing for advanced supercapacitors. Notably, our study explores the performance of these electrodes in three different types of electrolytes: organic, ionic liquids, and quasi-solid states. By examining the impact of dry electrode processing on various electrode and electrolyte systems, we show valuable insights into the versatility and efficacy of this technique. The supercapacitors employing dry electrodes demonstrated significant improvements compared with conventional wet electrodes, with a lifespan extension of +45% in organic, +192% in ionic liquids, and +84% in quasi-solid electrolytes. Moreover, the increased electrode densities achievable through the dry approach directly translate to improved volumetric outputs, enhancing energy storage capacities within compact form factors. Notably, dry electrode-prepared supercapacitors outperformed their wet electrode counterparts, exhibiting a higher energy density of 6.1 Wh cm−3 compared with 4.7 Wh cm−3 at a high power density of 195 W cm−3, marking a substantial 28% energy improvement in the quasi-solid electrolyte.

Currently, over 60% of the world's population lives in cities. Urban living has many advantages but there are also challenges regarding the need for smart urbanization. The next generation of tunable 2D nanomaterials, called MXenes, is the critical enabling technology that can bring the current urban thinking to the next level, called a smart city. The smart city is a novel concept based on a framework of self-sufficient technologies that are interactive and responsive to citizens’ needs. In this perspective, MXene-enabled technologies for sustainable urban development are discussed. They can advance self-sufficient, adaptive, and responsive buildings that can minimize resource consumption, solving the deficiency of essential resources such as clean energy, water, and air. MXenes are at the cutting edge of technological limitations associated with the Internet of Things (IoT) and telemedicine, combining diverse properties and offering multitasking. It is foreseen that MXenes can have a bright future in contributing to the smart city concept. Therefore, the roadmap is presented for demonstrating the practical feasibility of MXenes in the smart city. Altogether, this study promotes the role of MXenes in advancing the well-being of citizens by raising the quality of urban living to the next level.