In the realm of sodium-ion batteries (SIBs), Mn-based layered oxide cathodes have garnered considerable attention owing to their anionic redox reactions (ARRs). Compared to other types of popular sodium-ion cathodes, Mn-based layered oxide cathodes with ARRs exhibit outstanding specific capacity and energy density, making them promising for SIB applications. However, these cathodes still face some scientific challenges that need to be addressed. This review systematically summarizes the composition, structure, oxygen-redox mechanism, and performance of various types of Mn-based cathodes with ARRs, as well as the main scientific challenges they face, including sluggish ion diffusion, cationic migration, O2 release, and element dissolution. Currently, to resolve these challenges, efforts mainly focus on six aspects: synthesis methods, structural design, doped modification, electrolyte design, and surface engineering. Finally, this review provides new insights for future direction, encompassing both fundamental research, such as novel cathode types, interface optimization, and interdisciplinary research, and considerations from an industrialization perspective, including scalability, stability, and safety.
Graphene fiber supercapacitors (GFSCs) have garnered significant attention due to their exceptional features, including high power density, rapid charge/discharge rates, prolonged cycling durability, and versatile weaving capabilities. Nevertheless, inherent challenges in graphene fibers (GFs), particularly the restricted ion-accessible specific surface area (SSA) and sluggish ion transport kinetics, hinder the achievement of optimal capacitance and rate performance. Despite existing reviews on GFSCs, a notable gap exists in thoroughly exploring the kinetics governing the energy storage process in GFSCs. This review aims to address this gap by thoroughly analyzing the energy storage mechanism, fabrication methodologies, property manipulation, and wearable applications of GFSCs. Through theoretical analysis of the energy storage process, specific parameters in advanced GF fabrication methodologies are carefully summarized, which can be used to modulate nano/micro-structures, thereby enhancing energy storage kinetics. In particular, enhanced ion storage is realized by creating more ion-accessible SSA and introducing extra-capacitive components, while accelerated ion transport is achieved by shortening the transport channel length and improving the accessibility of electrolyte ions. Building on the established structure–property relationship, several critical strategies for constructing optimal surface and structure profiles of GF electrodes are summarized. Capitalizing on the exceptional flexibility and wearability of GFSCs, the review further underscores their potential as foundational elements for constructing multifunctional e-textiles using conventional textile technologies. In conclusion, this review provides insights into current challenges and suggests potential research directions for GFSCs.
A widely employed energy technology, known as reverse electrodialysis (RED), holds the promise of delivering clean and renewable electricity from water. This technology involves the interaction of two or more bodies of water with varying concentrations of salt ions. The movement of these ions across a membrane generates electricity. However, the efficiency of these systems faces a challenge due to membrane performance degradation over time, often caused by channel blockages. One potential solution to enhance system efficiency is the use of nanofluidic membranes. These specialized membranes offer high ion exchange capacity, abundant ion sources, and customizable channels with varying sizes and properties. Graphene oxide (GO)-based membranes have emerged as particularly promising candidates in this regard, garnering significant attention in recent literature. This work provides a comprehensive overview of the literature surrounding GO membranes and their applications in RED systems. It also highlights recent advancements in the utilization of GO membranes within these systems. Finally, it explores the potential of these membranes to play a pivotal role in electricity generation within RED systems.
The O3-type layered cathode with high Ni content has attracted much attention because of its high capacity and simple synthesis process. However, surface side reaction and O3–P3 phase transitions would occur during Na+ insertion/extraction, resulting in unsatisfying electrochemical performance. Herein, O3-Na[Ni0.6Co0.2Mn0.2]O2 (NNCM622) cathode is modified by a NaTiOx coating layer in a wet chemistry method, which reduces the parasitic reaction and facilitates Na+ migration. Simultaneously, the partially doped Ti improves structural stability by restraining the irreversible multiple-phase transition. As a result, the modified NNCM622 cathode obtains a high specific capacity of 143.4 mAh g–1 and an improved capacity retention of 69% after 300 cycles. Our work offers new prospects for stabilizing the NNCM622 cathode with a feasible coating strategy.
Hydrogen energy from electrocatalysis driven by sustainable energy has emerged as a solution against the background of carbon neutrality. Proton exchange membrane (PEM)-based electrocatalytic systems represent a promising technology for hydrogen production, which is equipped to combine efficiently with intermittent electricity from renewable energy sources. In this review, PEM-based electrocatalytic systems for H2 production are summarized systematically from low to high operating temperature systems. When the operating temperature is below 130°C, the representative device is a PEM water electrolyzer; its core components and respective functions, research status, and design strategies of key materials especially in electrocatalysts are presented and discussed. However, strong acidity, highly oxidative operating conditions, and the sluggish kinetics of the anode reaction of PEM water electrolyzers have limited their further development and shifted our attention to higher operating temperature PEM systems. Increasing the temperature of PEM-based electrocatalytic systems can cause an increase in current density, accelerate reaction kinetics and gas transport and reduce the ohmic value, activation losses, ΔGH*, and power consumption. Moreover, further increasing the operating temperature (120–300°C) of PEM-based devices endows various hydrogen carriers (e.g., methanol, ethanol, and ammonia) with electrolysis, offering a new opportunity to produce hydrogen using PEM-based electrocatalytic systems. Finally, several future directions and prospects for developing PEM-based electrocatalytic systems for H2 production are proposed through devoting more efforts to the key components of devices and reduction of costs.
In recent years, renewable energy sources, which aim to replace rapidly depleting fossil fuels, face challenges due to limited energy storage and conversion technologies. To enhance energy storage and conversion efficiency, extensive research has been conducted in the academic community on numerous potential materials. Among these materials, metal fluorides have attracted significant attention due to their ionic metal–fluorine bonds and tunable electronic structures, attributed to the highest electronegativity of fluorine in their chemical composition. This makes them promising candidates for future electrochemical applications in various fields. However, metal fluorides encounter various challenges in different application directions. Therefore, we comprehensively review the applications of metal fluorides in the field of energy storage and conversion, aiming to deepen our understanding of their exhibited characteristics in different electrochemical processes. In this paper, we summarize the difficulties and improvement methods encountered in different types of battery applications and several typical electrode optimization strategies in the field of supercapacitors. In the field of water electrolysis, we focus on surface reconstruction and the critical role of fluorine, demonstrating the catalytic performance of metal fluorides from the perspectives of reconstruction mechanism and process analysis. Finally, we provide a summary and outlook for this field, aiming to offer guidance for future breakthroughs in the energy storage and conversion applications of metal fluorides.
Zn-CO2 batteries (ZCBs) are promising for CO2 conversion and electric energy release. However, the ZCBs couple the electrochemical CO2 reduction (ECO2R) with the oxygen evolution reaction and competitive hydrogen evolution reaction, which normally causes ultrahigh charge voltage and CO2 conversion efficiency attenuation, thereby resulting in ∼90% total power consumption. Herein, isolated FeN3 sites encapsulated in hierarchical porous carbon nanoboxes (Fe-HPCN, derived from the thermal activation process of ferrocene and polydopamine-coated cubic ZIF-8) were proposed for hydrazine-assisted rechargeable ZCBs based on ECO2R (discharging process: CO2 + 2H+ → CO + H2O) and hydrazine oxidation reaction (HzOR, charging process: N2H4 + 4OH– → N2 + 4H2O + 4e–). The isolated FeN3 endows the HzOR with a lower overpotential and boosts the ECO2R with a 96% CO Faraday efficiency (FECO). Benefitting from the bifunctional ECO2R and HzOR catalytic activities, the homemade hydrazine-assisted rechargeable ZCBs assembled with the Fe-HPCN air cathode exhibited an ultralow charge voltage (decreasing by ∼1.84 V), excellent CO selectivity (FECO close to 100%), and high 89% energy efficiency. In situ infrared spectroscopy confirmed that Fe-HPCN can generate rate-determining *N2 and *CO intermediates during HzOR and ECO2R. This paper proposes FeN3 centers for bifunctional ECO2R/HzOR performance and further presents the pioneering achievements of ECO2R and HzOR for hydrazine-assisted rechargeable ZCBs.
The growing need for flexible and wearable electronics, such as smartwatches and foldable displays, highlights the shortcomings of traditional energy storage methods. In response, scientists are developing compact, flexible, and foldable energy devices to overcome these challenges. MXenes—a family of two-dimensional nanomaterials—are a promising solution because of their unique properties, including a large surface area, excellent electrical conductivity, numerous functional groups, and distinctive layered structures. These attributes make MXenes attractive options for flexible energy storage. This paper reviews recent advances in using flexible MXene-based materials for flexible Li–S batteries, metal-ion batteries (Zn and Na), and supercapacitors. The development of MXene-based composites is explored, with a detailed electrochemical performance analysis of various flexible devices. The review addresses significant challenges and outlines strategic objectives for advancing robust and flexible MXene-based energy storage devices.
The progress from intelligent interactions requires electronic skin (E-skin) to shift from single-functional perception to multisensory capabilities. However, the intuitive and interference-free reading of multiple sensory signals without involving complex algorithms is a critical challenge. Herein, we propose a flexible multisensory E-skin by developing a highly homogeneous dispersion of BaTiO3 nanoparticles in polydimethylsiloxane dielectric layer. The E-skin is sensitive to externally applied pressure as well as temperature and can distinguish dual synergetic stimuli by the time decoupling effect. The pressure and temperature perception was achieved in an individual device, which greatly reduced the structural complexity compared with multifunctional integrated devices. The sensitivity of E-skin for pressure detection is as high as 0.0724 kPa–1 and the detection range reaches as wide as 15.625–10 MPa. The sensitivity to temperature detection is as high as –1.34°C–1 and the detection range reaches 20–200°C. More importantly, by equipping with a multilayer neural network, the evolution from tactile perception to advanced intelligent tactile cognition is demonstrated.
Exploration of efficient and stable photocatalysts to mimic natural leaves for the conversion of atmospheric CO2 into hydrocarbons utilizing solar light is very important but remains a major challenge. Herein, we report the design of four novel metal–salen-incorporated conjugated microporous polymers as robust artificial leaves for photoreduction of atmospheric CO2 with gaseous water. Owing to the rich nitrogen and oxygen moieties in the polymeric frameworks, they show a maximum CO2 adsorption capacity of 46.1 cm3 g–1 and adsorption selectivity for CO2/N2 of up to 82 at 273 K. Under air atmosphere and simulated solar light (100 mW cm–2), TEPT-Zn shows an excellent CO yield of 304.96 µmol h–1 g–1 with a selectivity of approximately 100%, which represents one of the best results in terms of organic photocatalysts for gas-phase CO2 photoreduction so far. Furthermore, only small degradation in the CO yield is observed even after 120-h continuous illumination. More importantly, a good CO yield of 152.52 µmol g–1 was achieved by directly exposing the photocatalytic reaction of TEPT-Zn in an outdoor environment for 3 h (25–28°C, 52.3 ± 7.9 mW cm–2). This work provides an avenue for the continued development of advanced polymers toward gas-phase photoconversion of CO2 from air.
Organic thermoelectric generators (TEGs) are flexible and lightweight, but they often have high electrical resistance, poor output power, and low mechanical durability, because of which their thermoelectric performance is poor. We used a facile and rapid solvent evaporation process to prepare a robust carbon nanotube/Bi0.45Sb1.55Te3 (CNT/BST) foam with a high thermoelectric figure of merit (zT). The BST sub-micronparticles effectively create an electrically conductive network within the three-dimensional porous CNT foam to greatly improve the electrical conductivity and the Seebeck coefficient and reinforce the mechanical strength of the composite against applied stresses. The CNT/BST foam had a zT value of 7.8 × 10–3 at 300 K, which was 5.7 times higher than that of pristine CNT foam. We used the CNT/BST foam to fabricate a flexible TEG with an internal resistance of 12.3 Ω and an output power of 15.7 µW at a temperature difference of 21.8 K. The flexible TEG showed excellent stability and durability even after 10,000 bending cycles. Finally, we demonstrate the shapeability of the CNT/BST foam by fabricating a concave TEG with conformal contact on the surface of a cylindrical glass tube, which suggests its practical applicability as a thermal sensor.
Transition metal borides (TMBs) are a new class of promising electrocatalysts for hydrogen generation by water splitting. However, the synthesis of robust all-in-one electrodes is challenging for practical applications. Herein, a facile solid-state boronization strategy is reported to synthesize a series of self-supported TMBs thin films (TMB-TFs) with large area and high catalytic activity. Among them, MoB thin film (MoB-TF) exhibits the highest activity toward electrocatalytic hydrogen evolution reaction (HER), displaying a low overpotential (η10 = 191 and 219 mV at 10 mA cm–2) and a small Tafel slope (60.25 and 61.91 mV dec–1) in 0.5 M H2SO4 and 1.0 M KOH, respectively. Moreover, it outperforms the commercial Pt/C at the high current density region, demonstrating potential applications in industrially electrochemical water splitting. Theoretical study reveals that both surfaces terminated by TM and B atoms can serve as the active sites and the H* binding strength of TMBs is correlated with the p band center of B atoms. This work provides a new pathway for the potential application of TMBs in large-scale hydrogen production.
Electrocatalytic reduction of nitrate pollutants to produce ammonia offers an effective approach to realizing the artificial nitrogen cycle and replacing the energy-intensive Haber-Bosch process. Nitrite is an important intermediate product in the reduction of nitrate to ammonia. Therefore, the mechanism of converting nitrite into ammonia warrants further investigation. Molecular cobalt catalysts are regarded as promising for nitrite reduction reactions (NO2–RR). However, designing and controlling the coordination environment of molecular catalysts is crucial for studying the mechanism of NO2–RR and catalyst design. Herein, we develop a molecular platform of cobalt porphyrin with three coordination microenvironments (Co-N3X1, X = N, O, S). Electrochemical experiments demonstrate that cobalt porphyrin with O coordination (CoOTPP) exhibits the lowest onset potential and the highest activity for NO2–RR in ammonia production. Under neutral, non-buffered conditions over a wide potential range (–1.0 to –1.5 V versus AgCl/Ag), the Faradaic efficiency of nearly 90% for ammonia was achieved and reached 94.5% at –1.4 V versus AgCl/Ag, with an ammonia yield of 6,498 µg h–1 and a turnover number of 22,869 at –1.5 V versus AgCl/Ag. In situ characterization and density functional theory calculations reveal that modulating the coordination environment alters the electron transfer mode of the cobalt active center and the charge redistribution caused by the break of the ligand field. Therefore, this results in enhanced electrochemical activity for NO2–RR in ammonia production. This study provides valuable guidance for designing adjustments to the coordination environment of molecular catalysts to enhance catalytic activity.
The single-atom M-N-C (M typically being Co or Fe) is a prominent material with exceptional reactivity in areas of catalysis for sustainable energy. However, the formation of metal nanoparticles in M-N-C materials is coupled with high-temperature calcination conditions, limiting the density of M-Nx active sites and thus restricting the catalytic performance of such catalysts. Herein, we describe an effective decoupling strategy to construct high-density M-Nx active sites by generating polyfurfuryl alcohol in the MOF precursor, effectively preventing the formation of metal nanoparticles even with up to 6.377% cobalt loading. This catalyst showed a high H2 production rate of 778 mL gcat–1 h–1 when used in the dehydrogenation reaction of formic acid. In addition to the high density of the active site, a curved carbon surface in the structure is also thought to be the reason for the high performance of the catalyst.
Switchable radiative cooling/heating holds great promise for mitigating the global energy and environmental crisis. Here, we reported a cost-effective, high-strength Janus film through surface optical engineering waste paper with one side decorated by a hydrophobic polymeric cooling coating consisting of micro/nanopore/particle hierarchical structure and the other side coated with hydrophilic MXene nanosheets for heating. The cooling surface demonstrates high solar reflectivity (96.3%) and infrared emissivity (95.5%), resulting in daytime/nighttime sub-ambient radiative cooling of 6°C/8°C with the theoretical cooling power of 100.6 and 138.5 W m–2, respectively. The heating surface exhibits high solar absorptivity (83.7%) and low infrared emissivity (15.2%), resulting in excellent radiative heating capacity for vehicle charging pile (∼6.2°C) and solar heating performance. Impressively, the mechanical strength of Janus film increased greatly by 563% compared with that of pristine waste paper, which is helpful for its practical applications in various scenarios for switchable radiative thermal management through mechanical flipping. Energy-saving simulation results reveal that significant total energy savings of up to 32.4 MJ m–2 can be achieved annually (corresponding to the 12.4% saving ratio), showing the immense importance of reducing carbon footprint and promoting carbon neutrality.