Earth Abundance Research Articles

Electronic Structure and Phase Stability of Ag and Sn Doped Cu2s: A DFT Study

Cu2S is an important solar absorber material. Despite having excessive Cu vacancy formation tendency and being a degenerate semiconductor, it has gained wide attention due to its non-toxicity, earth abundance, suitable band gap and previously shown nearly 10% efficiency in thin film solar cells. A new theoretical phase of Cu2S, a DFT predicted acanthite like phase, has shown that Ag doping can help to reduce Cu vacancy formation tendency without altering its electronic structure much. Hence, doping Cu2S with suitable cations warrants more studies on its electronic structure and phase stabilities. Here, we are going to present a systematic DFT study for Ag and Sn doped Cu2S acanthite like and low chalcocite phases to explore the electronic structures, optical properties, Cu vacancy formation tendency, and crystal phase stabilities.

Current-Dependent Growth Mechanisms of Sodium Metal Anode in Diglyme-Based Electrolytes

Sodium-ion batteries are economical substitute for lithium-ion batteries due to the earth abundance of sodium element [1, 2]. Similar to lithium metal anodes, while sodium metal anodes hold the promise to improve the energy density of next-generation sodium-ion batteries, the nonuniform electrodeposition of sodium metal that can lead to internal shorts remains a major obstacle toward its practical applications [3]. Here, we systematically investigated the electrodeposition of sodium in diglyme-based electrolytes in our unique capillary cells and realistic split cells. While a similar transition of electrodeposition mode to dendritic growth at Sand’s time was observed for sodium [4], only the smooth surface growths were observed at under-limiting current densities, suggesting a possible much higher cycling efficiency due to much less surface areas to be covered by the solid electrolyte interphase (SEI) layers. By examining the limiting current and Sand’s time obtained from operando experiments with the capillary cells, the diffusion coefficient (1.13×10-6 cm2 s-1) and transference number (0.45) of sodium ions in 1M NaClO4 in diglyme were accurately extracted, which were further verified by post-mortem analyses of linear sweep voltammetry experiments with split cells. The unique two current plateaus, shown in Figure 1, surprisingly can be explained by a single limiting current density in a self-consistent manner. At such plateaus, deposits of sodium metal were discovered to grow along the surface, rather than through the pores, of the ceramic-coated separator and form equiaxed and columnar dendrites with orthogonal branches similar to that found in solidification [5].Our work provides a platform to not only evaluate the current-dependent growth mechanisms of sodium, but also reveal the roles of separators toward designing safe sodium metal batteries.

A Highly Hierarchical Hollow Sodium Sulfide Nanospheres Embedded in Spongy Carbon Composite As Cathode for High-Rate Performance Sodium-Sulfur Batteries

Sodium-sulfur (Na-S) batteries have shown great promise as the next-generation energy storage systems owing to its high specific energy, low cost and high earth abundance of both Na and S. However, the low electronic conductivity and ionic conductivity of the active materials cause slow kinetics of Na-S chemistry and make high-rate performance impossible. Herein, a facile and scalable approach has been employed to synthesize hollow sodium sulfide (Na2S) nanospheres embedded in a highly hierarchical and spongy conductive carbon matrix, forming an intriguing architecture similar to the morphology of frogspawn coral, which has shown great potential as a cathode for high-rate performance Na-S batteries. The shortened Na-ion diffusion pathway benefited from the hollow structures together with the fast electron transfer from the carbon matrix contributes to high electrochemical reactivity, leading to high capacity and superior cycling performance at various current rates. At current densities of 1.4 and 2.1 A/g, high initial discharge capacities of 980 and 790 mAh/g (based on sulfur) can be achieved, respectively, with reversible capacities stabilized at 600 and 400 mAh/g (based on sulfur) after 100 cycles. As a proof of concept, we demonstrate Na-metal free Na-S batteries paired with Sn embedded in carbon as anode, which shows an exciting cycling performance of an initial capacity of 550 mAh/g (based on sulfur) with a capacity retention over 80% for over 50 cycles. Our work could provide guidance on rational materials design towards the success of room-temperature high-rate Na-S batteries.[1] Reference: [1] C. Wang, H. Wang, X. Hu, E. Matios, J. Luo, Y. Zhang, X. Lu, W. Li, Adv. Energy Mater, 2018, 1803251. Figure 1

Study the Activity of a Novel Ni-Based Electrocatalyst for Oxygen Evolution Reaction in Alkaline Media

Electrocatalytic water splitting into hydrogen and oxygen has a great potential to produce hydrogen as a carbon neutral source of energy. However, the sluggish kinetics of oxygen evolution reaction (OER) leads to an inefficient process prohibiting industrial application [1]. Therefore, highly efficient OER electrocatalysts are needed to reduce the energy barrier and enhance the efficiency of water electrolysis cell [2]. IrO2 and RuO2 are the most efficient electrocatalysts for OER, however their commercial industrial applications are limited due to their high cost and low earth abundance. To address this issue, several non-noble metal based OER electrocatalysts including transition metal oxide/hydroxides, perovskite, and molecular electrocatalysts have been developed [3]. Among them, Ni-based materials attract substantial attention owing to their low cost, high corrosion stability, and remarkable catalytic activity in alkaline media. The present work aims to evaluate and compare the electrochemical activity of a novel Ni-based electrocatalyst prepared from two different plating baths toward OER. Electrochemical measurements including cyclic voltammetry (CV), quasi-steady state polarization (QSSP), electrochemical impedance spectroscopy (EIS), and chronopotentiometry (CP) were carried out to study and compare the activity, charge transfer resistance and stability of different electrocatalysts developed in this study toward OER in alkaline media.

One‐Step Synthesis of 2‐Ethylhexylamine Pillared Vanadium Disulfide Nanoflowers with Ultralarge Interlayer Spacing for High‐Performance Magnesium Storage

AbstractRechargeable magnesium batteries (RMBs) are attractive candidates for large‐scale energy storage owing to the high theoretical specific capacity, rich earth abundance, and good safety characteristics. However, the development of desirable cathode materials for RMBs is constrained by the high polarity and slow intercalation kinetics of Mg2+ ions. Herein, it is demonstrated that 2‐ethylhexylamine pillared vanadium disulfide nanoflowers (expanded VS2) with enlarged interlayer distances exhibit greatly boosted electrochemical performance as a cathode material in RMBs. Through a one‐step solution‐phase synthesis and in situ 2‐ethylhexylamine intercalation process, VS2 nanoflowers with ultralarge interlayer spacing are prepared. A series of ex situ characterizations verify that the cathode of expanded VS2 nanoflowers undergoes a reversible intercalation reaction mechanism, followed by a conversion reaction mechanism. Electrochemical kinetics analysis reveal a relatively fast Mg‐ion diffusivity of expanded VS2 nanoflowers in the order of 10−11–10−12 cm2 s−1, and the pseudocapacitive contribution is up to 64% for the total capacity at 1 mV s−1. The expanded VS2 nanoflowers show highly reversible discharge capacity (245 mAh g−1 at 100 mA g−1), good rate capability (103 mAh g−1 at 2000 mA g−1), and stable cycling performance (90 mAh g−1 after 600 cycles at 1000 mA g−1).

Low cost ionic liquid electrolytes for rechargeable aluminum/graphite batteries

Rechargeable aluminum batteries are promising large-scale energy storage candidates due to the high natural earth abundance and high theoretical volumetric capacity of Al metal. However, they face many problems, including a limited lifetime, rate performance, and high electrolyte cost. Herein, we have designed a high-performance Al rechargeable battery using a graphite cathode and an economical AlCl3/Et3NHCl ionic liquid electrolyte. Based on the high conductivity of the AlCl3/Et3NHCl electrolyte, the battery achieved a reversible capacity of 96 mAh g−1 at 100 mA g−1, which is even higher than that of the battery using an AlCl3/urea electrolyte (89 mAh g−1). Furthermore, almost no capacity attenuation was observed, with AlCl3/Et3NHCl electrolyte having a capacity of 64 mAh g−1 after 1000 cycles, at 1000 mA g−1, while the AlCl3/urea electrolyte had a capacity of only 24 mAh g−1. Therefore, the aluminum/ graphite battery using AlCl3/Et3NHCl ionic liquid electrolyte with a high specific capacity and good long-term cycling stability is a promising candidate for future high-performance, large-scale energy storage devices.

Capturing Reversible Cation Migration in Layered Structure Materials for Na‐Ion Batteries

AbstractNa‐ion batteries are promising for large‐scale energy storage due to the low cost and earth abundance of the sodium resource. Despite tremendous efforts being made to improve the battery performance, some fundamental mechanism issues still are not sufficiently understood. One such issue in the most popularized layered structure materials is the potential cation migration into sodium layers, which would highly affect the energy efficiency thus hindering its widespread use in the future. Here a systematic study of the cation migration in layered structure materials is presented and its relationship with voltage hysteresis is disclosed. Using the high‐angle annular dark field‐scanning transmission electron microscopy and in operando X‐ray diffraction as implements, for the first time, the reversible migration of the transition metal between transition metal layers and sodium layers is captured. The research inspires a novel insight into the cation migration related layered materials, which should be considered for future battery design toward conventional use.

Solubility of Iridium and Ruthenium Organometallic Photoredox Catalysts.

Despite the exponential growth of the field of photocatalysis, for reasons that are not entirely clear, these precious photocatalysts are often used in the literature at loadings that exceed their maximum solubility. On an industrial scale, the quantity of any precious metal catalyst can be a substantial financial burden or a sourcing issue, not to mention concerns as to the ecological and earth abundance of these catalysts. We believe that inattention to solubility has made these reactions appear less efficient than they actually are, because much of the photocatalyst remains undissolved. Therefore, the maximum solubilities of iridium and ruthenium centered photocatalysts have been systematically identified in industrially relevant solvents. Further, a literature photocatalytic reaction which our results suggested was beyond the maximum solubility has been revisited, with interesting results.

Rational design of sulfur-containing composites for high-performance lithium–sulfur batteries

Sulfur has received considerable attention as a cathode material for lithium—sulfur (Li—S) batteries due to its high theoretical energy density (2567 W h kg−1), high earth abundance, and environmental benignity. However, the insulating nature of sulfur and the shuttle effect of soluble lithium polysulfides result in serious technical issues, such as low utilization rate of sulfur, reduced columbic efficiency, and poor cycling stability, which compromise the high theoretical performance of Li—S batteries. In the past years, various attempts have been made to achieve high specific capacity and reliable cycling stability of Li—S batteries. Incorporation of sulfur into functional host materials has been demonstrated to be effective to improve the electrochemical performance of sulfur-based cathodes via enhancing the electron and Li ion conductivities, immobilizing sulfur/lithium polysulfides in cathodes, and accommodating the volume changes in sulfur-based cathodes. Therefore, the rational design of sulfur-containing composites needs to be emphasized as key strategies to develop high-performance cathodes for Li—S batteries. In this perspective, after reviewing the achievements obtained in the design of sulfur-containing composites as cathodes for Li—S batteries, we propose the new issues that should be overcome to facilitate the practical application of Li—S batteries.

Size effect enhanced thermoelectric properties of nanoscale Cu2-xSe

As a promising thermoelectric material, copper selenides have attracted the interest of researchers owing to their low cost, abundance in earth, environmental friendliness, and low thermal conductivity. In this study, copper selenide (Cu2-xSe) powders with controllable sizes from nanoscale to mesoscale were obtained by a facile one-pot solvothermal method. After treatment with spark plasma sintering, the nanoscale Cu2-xSe pellets exhibited excellent thermoelectric properties such as sharply reduced thermal conductivity and enhanced Seebeck coefficient as well as a suppressed electrical conductivity. The figure of merit (ZT) of the nanoscale Cu2-xSe reached up to ∼1.51 at 873 K, which is about 2.67 times higher than that of the meso-Cu2-xSe. This study confirms that thermoelectric properties can be enhanced by the size effect.

A novel rechargeable potassium–sulfur battery based on liquid alloy anode

Considering high earth abundance and low cost of potassium resource, potassium ion batteries are very promising candidates for energy storage devices due to its similar electrochemical performance to lithium ion batteries and more negative potential than sodium anode. K–Na alloy extending from 41.8 to 90.8 wt% potassium is liquid at ambient temperature. It was used as anode for a rechargeable potassium–sulfur battery in this work because of its high capacity and dendrite-free when charging and discharging. Sulfurized polyacrylonitrile (SPAN) nanocomposites were synthesized and adopted as cathode in the novel battery within good performance. The novel battery presented better cycling stability than K–SPAN battery. We obtained a highly reversible capacity of 513 mAh g−1 and excellent cycling performance of 490 mAh g−1 retention after 100 cycles at a current density of 35 mA g−1, in addition the coulombic efficiency approximately approached to 100% in successive cycles.

Chemical Approaches to Carbon-Based Metal-Free Catalysts.

Highly active and durable catalysts play a key role in clean energy technologies. However, the high cost, low reserves, and poor stability of noble-metal-based catalysts have hindered the large-scale development of renewable energy. Owing to their low cost, earth abundance, high activity, and excellent stability, carbon-based metal-free catalysts (CMFCs) are promising alternatives to precious-metal-based catalysts. Although many synthetic methods based on solution, surface/interface, solid state, and noncovalent chemistries have been developed for producing numerous CMFCs with diverse structures and functionalities, there is still a lack of effective approaches to precisely control the structures of active sites. Therefore, novel chemical approaches are needed for the development of highly active and durable CMFCs that are capable of replacing precious-metal catalysts for large-scale applications. Herein, a comprehensive and critical review on chemical approaches to CMFCs is given by summarizing important advancements, current challenges, and future perspectives in this emerging field. Through such a critical review, our understanding of CMFCs and the associated synthetic processes will be significantly increased.

CsCu5S3: Promising Thermoelectric Material with Enhanced Phase Transition Temperature.

Cu2S, featuring low cost, nontoxicity, and earth abundance, has been recently recognized as a high efficiency thermoelectric (TE) material. However, before reaching the maximum of the figure of merit ( ZT), Cu2S undergoes three phase transformations starting at 370 K, which give rise to severe problems, such as possible decomposition and low reliability. Herein, we discover CsCu5S3 with phase transformation at 823 K, which is significantly higher than the 370 K value of Cu2S. Single crystal diffraction data reveal that its two phases are constructed by the same Cu4S4 columnar building unit via propagating either at the opposite sides into a layered o-CsCu5S3, or at the four apexes into a 3D t-CsCu5S3, respectively. Interestingly, the o-to- t transformation is quick, but the reverse one is relatively slow. Theoretical studies reveal that the Cu4S4 column exhibits not only the most condensed atomic aggregation ( Dcolumn) but also the lightest effective mass ( m*), along which higher σ is realized. More interestingly, both phases exhibit remarkable ZT enhancements, 0.46 at 800 K for o-CsCu5S3, and 0.56 at 875 K for t-CsCu5S3, which are 170% and 175% that of Cu2S at the same temperature.

Fabrication of Si/graphene/Si Double Heterostructures by Semiconductor Wafer Bonding towards Future Applications in Optoelectronics.

A Si/graphene/Si planar double heterostructure has been fabricated by means of semiconductor wafer bonding. The interfacial mechanical stability and interlayer electrical connection have been verified for the structure. To the best of our knowledge, this is the first realization of a monolayer-cored double heterostructure. In addition, a double heterostructure with bilayer graphene has been prepared for bandgap generation and tuning by application of a bias voltage. These structures move towards the realization of versatile graphene optoelectronics, such as an electrically pumped graphene laser. Our Si/graphene/Si double heterostructure is positioned to form a new basis for next-generation nanophotonic devices with high photon and carrier confinements, earth abundance (C, Si), environmental safety (C, Si), and excellent optical and electrical controllability by silicon clads.

Interfacially Induced Cascading Failure in Graphite-Silicon Composite Anodes.

Silicon (Si) has been well recognized as a promising candidate to replace graphite because of its earth abundance and high‐capacity storage, but its large volume changes upon lithiation/delithiation and the consequential material fracturing, loss of electrical contact, and over‐consumption of the electrolyte prevent its full application. As a countermeasure for rapid capacity decay, a composite electrode of graphite and Si has been adopted by accommodating Si nanoparticles in a graphite matrix. Such an approach, which involves two materials that interact electrochemically with lithium in the electrode, necessitates an analytical methodology to determine the individual electrochemical behavior of each active material. In this work, a methodology comprising differential plots and integral calculus is established to analyze the complicated interplay among the two active batteries and investigate the failure mechanism underlying capacity fade in the blend electrode. To address performance deficiencies identified by this methodology, an aluminum alkoxide (alucone) surface‐modification strategy is demonstrated to stabilize the structure and electrochemical performance of the graphite‐Si composite electrode. The integrated approach established in this work is of great importance to the design and diagnostics of a multi‐component composite electrode, which is expected to be high interest to other next‐generation battery system.

CuO photoelectrodes synthesized by the sol–gel method for water splitting

CuO is an attractive photocatalytic material for water splitting due to its high earth abundance and low cost. In this paper, we report the deposition of CuO thin films by sol–gel dip-coating process. Sol deposition has attractive advantages including low-cost solution processing and uniform film formation over large areas with a fairly good control of the film stoichiometry and thickness. Pure CuO phase was obtained for calcination temperatures higher than 360 °C in air. The CuO photocurrents for hydrogen evolution depend on the crystallinity and the microstructure of the film. Values of −0.94 mA cm−2 at pH = 8 and 0 V vs. RHE were achieved for CuO photoelectrodes annealed at 400 °C under air. More interestingly, the stability of the photoelectrode was enhanced upon the sol–gel deposition of a TiO2 protective layer. In this all sol–gel CuO/TiO2 photocathode, a photocurrent of −0.5 mA cm−2 is achieved at pH = 7 and 0 V vs. RHE with a stability of ~100% over 600 s.

Key Strategies to Advance the Photoelectrochemical Water Splitting Performance of α‐Fe2O3 Photoanode

AbstractThe last few decades’ extensive research on the photoelectrochemical (PEC) water splitting has projected it as a promising approach to meet the steadily growing demand for cleaner and renewable energy in a sustainable and economically viable fashion. Among many potential photocatalysts, hematite (α‐Fe2O3) emerges as a highly promising photoanode material with favorable characteristics including visible light absorption (a suitable band gap energy), earth abundance, chemical stability, and low cost. A pronounced disadvantage of α‐Fe2O3 is its low photovoltage together with an extremely short hole diffusion length and a low electrical conductivity, which limit its PEC water oxidation performance. To make α‐Fe2O3 as a viable photocatalyst for PEC water splitting, one needs to rectify these unfavorable characteristics of α‐Fe2O3 by elaborated multiple modifications. In this review article, we introduce various modification strategies of hematite with emphasis on surface modifications to achieve low onset potential as well as high photocurrent approaching the theoretical value for solar water splitting.

Geochemistry and Petrogenesis of Mesoproterozoic Dykes of the Irkutsk Promontory, Southern Part of the Siberian Craton

We present new geochemical and Nd isotopic data on two Mesoproterozoic Listvyanka (1350 ± 6 Ma) and Goloustnaya (1338 ± 3 Ma) mafic dyke swarms located in the Irkutsk Promontory of the southern part of the Siberian craton. Listvyanka dykes are sub-vertical with NNE trend, while Goloustnaya dykes are characterized by prevailing W trend. Listvyanka and Goloustnaya dykes are composed of medium to coarse grained dolerites. All dolerites correspond to sub-alkaline tholeiitic basalts according to their major-element compositions with lower to moderate mg#, varying from 36 to 54. The trace and rare earth element abundances in Listvyanka and Goloustnaya dolerites are generally close to basalts of the oceanic island basalts (OIB) type. The Listvyanka dolerites demonstrate slightly positive εNd(t) values varying from +1.1 to +1.5, while the Goloustnaya dolerites are characterized by lower εNd(t) values ranging from −0.9 to +0.1. Geochemical and isotopic affinities of the Listvyanka dolerites suggest their enrichment by a mantle plume related source. For the Goloustnaya dolerites, we assume also some additional lithospheric input to their mantle plume-related source. The emplacement of both studied dolerites took place in intracontinental extensional setting, caused by a single rising mantle plume. Listvyanka and Goloustnaya dolerites are coeval to several mafic magmatic events in northern Laurentia and likely represent part of the Mesoproterozoic plumbing system of a Siberian–Laurentian Large Igneous Province.

Noble-Metal-Free Electrocatalysts for Oxygen Evolution.

Oxygen evolution reaction (OER) plays a vital role in many energy conversion and storage processes including electrochemical water splitting for the production of hydrogen and carbon dioxide reduction to value-added chemicals. IrO2 and RuO2 , known as the state-of-the-art OER electrocatalysts, are severely limited by the high cost and low earth abundance of these noble metals. Developing noble-metal-free OER electrocatalysts with high performance has been in great demand. In this review, recent advances in the design and synthesis of noble-metal-free OER electrocatalysts including Ni, Co, Fe, Mn-based hydroxides/oxyhydroxides, oxides, chalcogenides, nitrides, phosphides, and metal-free compounds in alkaline, neutral as well as acidic electrolytes are summarized. Perspectives are also provided on the fabrication, evaluation of OER electrocatalysts and correlations between the structures of the electrocatalysts and their OER activities.

Highly oriented CuSbS2 thin films by rapid thermal processing of pre-annealed Sb2S3-Cu layers for PV applications

Copper antimony sulfide (CuSbS2) is an emerging absorber material in solar cells due to its nearly ideal optoelectronic properties, earth abundancy and environmentally benign composed elements. In the present work, highly oriented CuSbS2 thin films have been prepared by annealing layered structures of chemical bath deposited Sb2S3 and thermal evaporated Cu, followed by rapid thermal processing (RTP). A systematic study was performed by varying the processing time. Crystalline structure, morphology, elemental composition, chemical state, optical and electrical properties of the films formed at different conditions were analyzed using various techniques. X-Ray diffraction analysis showed that the post RTP treatment resulted CuSbS2 thin films with preferential orientation along (301) planes perpendicular to the substrate surface, on glass as well as Mo coated glass substrates. Optical properties showed that CuSbS2 has a direct bandgap of 1.6 eV supported by photo-current sensitivity at different wavelengths, which is nearly the ideal bandgap for an absorber layer in solar cell.