Building Fast Ion-Conducting Pathways on 3D Metallic Scaffolds for High-Performance Sodium Metal Anodes.

Building 3D electron-conducting scaffolds has been proven to be an effective way to alleviate severe dendritic growth and infinite volume change of sodium (Na) metal anodes. However, the electroplated Na metal cannot completely fill these scaffolds, especially at high current densities. Herein, we revealed that the uniform Na plating on 3D scaffolds is strongly related with the surface Na+ conductivity. As a proof of concept, we synthesized NiF2 hollow nanobowls grown on nickel foam (NiF2@NF) to realize homogeneous Na plating on the 3D scaffold. The NiF2 can be electrochemically converted to a NaF-enriched SEI layer, which significantly reduces the diffusion barrier for Na+ ions. The NaF-enriched SEI layer generated along the Ni backbones creates 3D interconnected ion-conducting pathways and allows for the rapid Na+ transfer throughout the entire 3D scaffold to enable densely filled and dendrite-free Na metal anodes. As a result, symmetric cells composed of identical Na/NiF2@NF electrodes show durable cycle life with an exceedingly stable voltage profile and small hysteresis, particularly at a high current density of 10 mA cm-2 or a large areal capacity of 10 mAh cm-2. Moreover, the full cell assembled with a Na3V2(PO4)3 cathode exhibits a superior capacity retention of 97.8% at a high current of 5C after 300 cycles.

Precursor-mediated in situ growth of hierarchical N-doped graphene nanofibers confining nickel single atoms for CO2 electroreduction.

Despite the various strategies for achieving metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) with different microenvironments for electrochemical carbon dioxide reduction reaction (CO2RR), the synthesis-structure-performance correlation remains elusive due to the lack of well-controlled synthetic approaches. Here, we employed Ni nanoparticles as starting materials for the direct synthesis of nickel (Ni) SACs in one spot through harvesting the interaction between metallic Ni and N atoms in the precursor during the chemical vapor deposition growth of hierarchical N-doped graphene fibers. By combining with first-principle calculations, we found that the Ni-N configuration is closely correlated to the N contents in the precursor, in which the acetonitrile with a high N/C ratio favors the formation of Ni-N3, while the pyridine with a low N/C ratio is more likely to promote the evolution of Ni-N2. Moreover, we revealed that the presence of N favors the formation of H-terminated edge of sp2 carbon and consequently leads to the formation of graphene fibers consisting of vertically stacked graphene flakes, instead of the traditional growth of carbon nanotubes on Ni nanoparticles. With a high capability in balancing the *COOH formation and *CO desorption, the as-prepared hierarchical N-doped graphene nanofibers with Ni-N3 sites exhibit a superior CO2RR performance compared to that with Ni-N2 and Ni-N4 ones.

Suppression of Gas Crossover and Dendrite Growth in Sodium-Gas Batteries across a Wide Operating Temperature Range.

Enabling highly stable alkali metal anodes in gas atmospheres, such as oxygen and carbon dioxide, is critical for the implementation of emerging metal-gas batteries with high energy density and improved safety. Herein, we demonstrate a three-salt electrolyte system to tackle the problems of gas crossover and uncontrolled metallic dendrite growth for all-climate sodium-gas batteries by the formation of an electrochemically/chemically stable solid electrolyte interphase that is rich in fluoride and sulfate compounds. Consequently, the sodium metal anodes present high reversible capacity (10 mAh cm-2 at 1.5 mA cm-2) and long cycle life (2000 h) in gas atmospheres across a wide operating temperature range. Using the three-salt electrolyte, all-climate sodium-oxygen and sodium-carbon dioxide batteries are demonstrated with a reversible capacity of 1000 mAh g-1 over 100 cycles at ambient temperature and good adaptability to temperatures from -60 to 60 °C.

Stabilizing Sodium Metal Anodes with Surfactant-Based Electrolytes and Unraveling the Atomic Structure of Interfaces by Cryo-TEM.

Sodium (Na) metal batteries are promising as next-generation energy storage systems due to the high specific capacity of the Na metal anode as well as rich natural abundance and low cost of Na resources. Nevertheless, uncontrolled growth of dendritic/mossy Na arising from the unstable solid-electrolyte interphase (SEI) leads to rapid electrode degradation and severe safety issues. In this work, we introduce cetyltrimethylammonium bromide (CTAB) as an electrolyte additive that enables a synergistic effect from both the CTA+ cation and Br- anion in stabilizing the Na metal anode. Notably, cryogenic transmission electron microscopy is utilized to investigate the effect of the additive, revealing the critical morphology and structure of the SEIs and Na electrodes at the nano/atomic scale. Benefiting fromthe additive, a stable Na anode can be realized at an ultrahigh capacity of 30 mAh cm-2 at 10 mA cm-2 over 400 h.

Stable sodium-sulfur electrochemistry enabled by phosphorus-based complexation.

A series of sodium phosphorothioate complexes are shown to have electrochemical properties attractive for sodium-sulfur battery applications across a wide operating temperature range. As cathode materials, they resolve a long-standing issue of cyclic liquid-solid phase transition that causes sluggish reaction kinetics and poor cycling stability in conventional, room-temperature sodium-sulfur batteries. The cathode chemistry yields 80% cyclic retention after 400 cycles at room temperature and a superior low-temperature performance down to -60 °C. Coupled experimental characterization and density functional theory calculations revealed the complex structures and electrochemical reaction mechanisms. The desirable electrochemical properties are attributed to the ability of the complexes to prevent the formation of solid precipitates over a fairly wide range of voltage.

SnO2 Quantum Dots Enabled Site-Directed Sodium Deposition for Stable Sodium Metal Batteries.

Dendrite growth has been severely impeding the implementation of sodium (Na) metal batteries, which is regarded as one of the most promising candidates for next-generation high-energy batteries. Herein, SnO2 quantum dots (QDs) are homogeneously dispersed and fully covered on a 3D carbon cloth scaffold (SnO2-CC) with high affinity to molten Na, given that SnO2 spontaneously initiates alloying reactions with Na and provides low nucleation barrier for Na deposition. Molten Na can be rapidly infused into the SnO2-CC scaffold as a free-standing anode material. Because of the affinity between SnO2 and Na ion, SnO2 QDs can effectively guide Na nucleation and attains site-directed dendrite-free Na deposition when combined with the 3D CC scaffold. This electrochemically stable anode enables almost 400 cycles at ultrahigh current density of 20 mA cm-2 in Na symmetric battery and delivers superior cycling performance and reversible rate capability in Na-Na3V2(PO4)3 full batteries.

Deeply Cycled Sodium Metal Anodes at Low Temperature and in Lean Electrolyte Conditions.

Enabling high-performing alkali metal anodes at low temperature and in lean electrolyte conditions is critical for the advancement of next-generation batteries with high energy density and improved safety. We present an ether-ionic liquid composite electrolyte to tackle the problem of dendrite growth of metallic sodium anode at low temperatures ranging from 0 to -40 °C. This composite electrolyte enables a stable sodium metal anode to be deeply cycled at 2 mA cm-2 with an ultrahigh reversible capacity of 50 mAh cm-2 for 500 hours at -20 °C in lean electrolyte (1.0 µL mAh-1 ) conditions. Using the composite electrolyte, full cells with Na3 V2 (PO4 )3 as cathode and sodium metal as anode present a high capacity retention of 90.7 % after 1,000 cycles at 2C at -20 °C. The sodium-carbon dioxide batteries also exhibit a reversible capacity of 1,000 mAh g-1 over 50 cycles across a range of temperatures from -20 to 25 °C.

Tunable MXene-Derived 1D/2D Hybrid Nanoarchitectures as a Stable Matrix for Dendrite-Free and Ultrahigh Capacity Sodium Metal Anode.

Although sodium (Na) is one of the most promising alternatives to lithium as an anode material for next-generation batteries, uncontrollable Na dendrite growth still remains the main challenge for Na metal batteries. Herein, a novel 1D/2D Na3Ti5O12-MXene hybrid nanoarchitecture consisting of Na3Ti5O12 nanowires grown between the MXene nanosheets is synthesized by a facile approach using cetyltrimethylammonium bromide (CTAB)-pretreated Ti3C2 MXene. Used as a matrix for the Na metal anode, the Na3Ti5O12 nanowires, formed benefiting from the CTAB stabilization, have chemical interaction with Na and thus provide abundant Na nucleation sites. These 1D nanostructures, together with the unique confinement effect from the 2D nanosheets, effectively guide and control the Na deposition within the interconnected nanochannels, preventing the "hot spot" formation for dendrite growth. A stable cycling performance can be achieved at a high current density up to 10 mA cm-2 along with an ultrahigh capacity up to 20 mAh cm-2.

Combining theories and experiments to understand the sodium nucleation behavior towards safe sodium metal batteries.

Rechargeable sodium (Na) based batteries have gained tremendous research interest because of the high natural abundance and low cost of Na resources, as well as electrochemical similarities with lithium (Li) based batteries. However, despite the great potential as a candidate for next-generation grid-scale energy storage, the implementation of the Na metal anode has been primarily hindered by dendritic and "dead" Na formation that leads to low Coulombic efficiency, short lifespan and even safety concerns. Na dendrite formation mainly originates from the uncontrolled Na deposition behavior in the absence of nucleation site regulation. Hence, the Na nucleation and initial stage of growth are critically important for the final morphology of Na metal. Here, this tutorial review aims to provide a comprehensive understanding of the importance of the nucleation behavior towards dendrite-free Na metal anodes. Firstly, we start with an introduction about the advantages of Na metal batteries over the Li counterpart and the challenges faced by Na metal anodes. The differences between metallic Li and Na are summarized according to advanced in situ characterization techniques. Next, we elucidate the key factors that influence the Na nucleation and growth behaviors based on the existing theoretical models. Then, we review the state-of-the-art approaches that have been applied to effectively regulate Na nucleation for dendrite-free Na deposition. Lastly, we conclude the review with perspectives on realizing safe Na metal batteries with high energy density.

Designing an All-Solid-State Sodium-Carbon Dioxide Battery Enabled by Nitrogen-Doped Nanocarbon.

All-solid-state sodium-carbon dioxide (Na-CO2) battery is an emerging technology that effectively utilizes the greenhouse gas, CO2, for energy storage with the virtues of minimized electrolyte leakage and suppressed Na dendrite growth for the Na metal anode. However, the sluggish reduction/evolution reactions of CO2 on the solid electrolyte/CO2 cathode interface have caused premature battery failure. Herein, nitrogen (N)-doped nanocarbon derived from metal-organic frameworks is designed as a cathode catalyst to solve this challenge. The porous and highly conductive N-doped nanocarbon possesses superior uptake and binding capability with CO2, which significantly accelerates the CO2 electroreduction and promotes the formation of thin sheetlike discharged products (200 nm in thickness) that can be easily decomposed upon charging. Accordingly, reduced discharge/charge overpotential, high discharge capacity (>10 000 mAh g-1), long cycle life, and high energy density (180 Wh kg-1 in pouch cells) are achieved at 50 °C.

Rapid and Scalable Synthesis of Cuprous Halide-Derived Copper Nano-Architectures for Selective Electrochemical Reduction of Carbon Dioxide.

Electrochemical reduction of carbon dioxide (CO2) into value-added chemicals and fuels provides a promising pathway for environmental and energy sustainability. Copper (Cu) demonstrates a unique ability to catalyze the electrochemical conversion of CO2 into valuable multicarbon products. However, developing a rapid, scalable and cost-effective method to synthesize efficient and stable Cu catalysts with high selectivity toward multicarbon products at a low overpotential is still hard to achieve and highly desirable. In this work, we present a facile wet chemistry approach to yield well-defined cuprous halide (CuX, X = Cl, Br or I) microcrystals with different degrees of truncations at edges/vertices, which can be ascribed to the oxidative etching mechanism of halide ions. More importantly, the as-obtained cuprous halides can be electrochemically transformed into varied Cu nanoarchitectures, thus exhibiting distinct CO2 reduction behaviors. The CuI-derived Cu nanofibers composed of self-assembled nanoparticles are reported for the first time, which favor the formation of C2+3 products at a low overpotential with a particular selectivity toward ethane. In comparison, the Cu nanocubes evolved from CuCl are highly selective toward C1 products. For CuBr-derived Cu nanodendrites, C1 products are subject to form at a low overpotential, while C2+3 products gradually become dominant with a favorable formation of ethylene when the potential turns more negative. This work explicitly reveals the critical morphology effect of halide-derived Cu nanostructures on the CO2 product selectivity, and also provides an ideal platform to investigate the structure-property relationship for CO2 electroreduction.

Graphene Regulated Ceramic Electrolyte for Solid-State Sodium Metal Battery with Superior Electrochemical Stability.

Employing solid ceramic electrolyte in sodium (Na) metal batteries enables safe and cost-effective energy storage solution toward the advent of sustainable energy. Nevertheless, the development of solid-state Na batteries is hindered by the large interfacial charge transfer resistance between electrodes and solid electrolyte. Here, a novel and scalable design approach is utilized to significantly reduce the interfacial resistance through the direct growth of graphene-like interlayer on Na+ superionic conductor (NASICON) ceramic electrolyte, resulting in a 10-fold decrease of interfacial resistance. Benefiting from the graphene regulated NASICON, extremely stable Na plating/stripping cycling performance using solid electrolyte at a current density up to 1 mA/cm2 with a cycling capacity of 1 mAh/cm2 for 500 cycles (1000 h) is demonstrated for the first time. The surface of Na electrode after 1000 h of cycling remained smooth because of uniform Na+ flux across graphene-coated-NASICON/Na interface enabled by the abundant graphene defects network for efficient Na+ transport. Solid-state room temperature battery consists of graphene-regulated NASICON electrolyte, Na3V2(PO4)3 cathode and Na anode delivered a reversible initial capacity of 108 mAh/g at 1C current density for 300 cycles with 85% capacity retention, far superior than the battery with pristine NASICON. This work can be a valuable contribution toward a safe and stable solid-state Na metal battery system, and provide insights for solid-state lithium metal batteries as well.

Facile Stabilization of the Sodium Metal Anode with Additives: Unexpected Key Role of Sodium Polysulfide and Adverse Effect of Sodium Nitrate.

Sodium metal is an attractive anode for next-generation energy storage systems owing to its high specific capacity, low cost, and high abundance. Nevertheless, uncontrolled Na dendrite growth caused by the formation of unstable solid electrolyte interphase (SEI) leads to poor cycling performance and severe safety concerns. Sodium polysulfide (Na2 S6 ) alone is revealed to serve as a positive additive or pre-passivation agent in ether electrolyte to improve the long-term stability and reversibility of the Na anode, while Na2 S6 -NaNO3 as co-additive has an adverse effect, contrary to the prior findings in the lithium anode system. A superior cycling behavior of Na anode is first demonstrated at a current density up to 10 mA cm-2 and a capacity up to 5 mAh cm-2 over 100 cycles. As a proof of concept, a high-capacity Na-S battery was prepared by pre-passivating the Na anode with Na2 S6 . This study gives insights into understanding the differences between Li and Na systems.

Critical Role of Ultrathin Graphene Films with Tunable Thickness in Enabling Highly Stable Sodium Metal Anodes.

Sodium (Na) metal has shown great promise as an anode material for the next-generation energy storage systems because of its high theoretical capacity, low cost, and high earth abundance. However, the extremely high reactivity of Na metal with organic electrolyte leads to the formation of unstable solid electrolyte interphase (SEI) and growth of Na dendrites upon repeated electrochemical stripping/plating, causing poor cycling performance, and serious safety issues. Herein, we present highly stable and dendrite-free Na metal anodes over a wide current range and long-term cycling via directly applying free-standing graphene films with tunable thickness on Na metal surface. We systematically investigate the dependence of Na anode stability on the thickness of the graphene film at different current densities and capacities. Our findings reveal that only a few nanometer (∼2-3 nm) differences in the graphene thickness can have decisive influence on the stability and rate capability of Na anodes. To achieve the optimal performance, the thickness of the graphene film covered on Na surface needs to be meticulously selected based on the applied current density. We demonstrate that with a multilayer graphene film (∼5 nm in thickness) as a protective layer, stable Na cycling behavior was first achieved in carbonate electrolyte without any additives over 100 cycles at a current density as high as 2 mA/cm2 with a high capacity of 3 mAh/cm2. We believe our work could be a viable route toward high-energy Na battery systems, and can provide valuable insights into the lithium batteries as well.

Ecosystem Services Mapping for Sustainable Agricultural Water Management in California's Central Valley.

Accurate information on agricultural water needs and withdrawals at appropriate spatial and temporal scales remains a key limitation to joint water and land management decision-making. We use InVEST ecosystem service mapping to estimate water yield and water consumption as functions of land use in Fresno County, a key farming region in California's Central Valley. Our calculations show that in recent years (2010-2015), the total annual water yield for the county has varied dramatically from ∼0.97 to 5.37 km3 (all ±17%; 1 MAF ≈ 1.233 km3), while total annual water consumption has changed over a smaller range, from ∼3.37 to ∼3.98 km3 (±20%). Almost all of the county's water consumption (∼96% of total use) takes place in Fresno's croplands, with discrepancy between local annual surface water yields and crop needs met by surface water allocations from outside the county and, to a much greater extent, private groundwater irrigation. Our estimates thus bound the amount of groundwater needed to supplement consumption each year (∼1.76 km3 on average). These results, combined with trends away from field crops and toward orchards and vineyards, suggest that Fresno's land and water management have become increasingly disconnected in recent years, with the harvested area being less available as an adaptive margin to hydrological stress.