Abstract: DOI: 10.1002/aenm.201800369 reactions involved.[1] In recent years, tremendous progress has been achieved in the field of heterogeneous electrocatalysis, with rapid development of multifarious electocatalysts toward oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and carbon dioxide reduction reaction (CO2RR). However, electrocatalysts for the reduction of dinitrogen (N2) to ammonia (NH3) at room temperature and atmospheric pressure remain largely underexplored, despite the fact that investigations on catalysts and reaction systems for artificial nitrogen fixation have been continued for more than 100 years.[2–4] Ammonia is primarily used for producing fertilizers to sustain the world’s population.[5] It also serves as a green energy carrier and a potential transportation fuel.[6] Currently, ammonia synthesis is dominated by the industrial Haber–Bosch process using heterogeneous iron-based catalysts at high temperature (300–500 °C) and high pressure (150–300 atm),[7] accounting for more than 1% of the world’s energy supply and generating more than 300 million metric tons of fossil fuel–derived CO2 annually.[8,9] Hence, it is desirable to develop alternative processes that have the potential to overcome the limitations of the Haber–Bosch process including harsh conditions, complex plant infrastructure, centralized distribution, high energy consumption, and negative environmental impacts. In nature, biological N2 fixation occurs under mild conditions via nitrogenase enzymes that contain FeMo, FeV, or FeFe cofactor as catalytic active sites.[10,11] Developed man-made catalysts are therefore stimulated to reduce N2 upon the addition of protons and electrons, which is similar to the nitrogenase catalytic process. Transition metal–dinitrogen complexes such as the molybdenum–, iron–, and cobalt–dinitrogen complexes have been proposed as homogeneous catalysts for the reduction of N2 into NH3 under ambient conditions;[12] however, the stability and recycling issues are challenging.[13] On the other hand, electrochemical and photochemical reduction processes using heterogeneous catalysts benefit from clean and renewable energy sources and are promising for achieving NH3 production directly from N2 and water.[14] The electrochemical reduction of N2 to NH3 can be more efficient than the photochemical counterpart. This is because not all of the photons in the photochemical reduction process can The production of ammonia (NH3) from molecular dinitrogen (N2) under mild conditions is one of the most attractive topics in the field of chemistry. Electrochemical reduction of N2 is promising for achieving clean and sustainable NH3 production with lower energy consumption using renewable energy sources. To date, emerging electrocatalysts for the electrochemical reduction of N2 to NH3 at room temperature and atmospheric pressure remain largely underexplored. The major challenge is to achieve both high catalytic activity and high selectivity. Here, the recent progress on the electrochemical nitrogen reduction reaction (NRR) at ambient temperature and pressure from both theoretical and experimental aspects is summarized, aiming at extracting instructive perceptions for future NRR research activities. The prevailing theories and mechanisms for NRR as well as computational screening of promising materials are presented. State-of-the-art heterogeneous electrocatalysts as well as rational design of the whole electrochemical systems for NRR are involved. Importantly, promising strategies to enhance the activity, selectivity, efficiency, and stability of electrocatalysts toward NRR are proposed. Moreover, ammonia determination methods are compared and problems relating to possible ammonia contamination of the system are mentioned so as to shed fresh light on possible standard protocols for NRR measurements.

Abstract: Zn‐based batteries are safe, low cost, and environmentally friendly, as well as delivering the highest energy density of all aqueous battery systems. However, the application of Zn‐based batteries is being seriously hindered by the uneven electrostripping/electroplating of Zn on the anodes, which always leads to enlarged polarization (capacity fading) or even cell shorting (low cycling stability). How a porous nano‐CaCO3 coating can guide uniform and position‐selected Zn stripping/plating on the nano‐CaCO3‐layer/Zn foil interfaces is reported here. This Zn‐deposition‐guiding ability is mainly ascribed to the porous nature of the nano‐CaCO3‐layer, since similar functionality (even though relatively inferior) is also found in Zn foils coated with porous acetylene black or nano‐SiO2 layers. Furthermore, the potential application of this strategy is demonstrated in Zn|ZnSO4+MnSO4|CNT/MnO2 rechargeable aqueous batteries. Compared with the ones with bare Zn anodes, the battery with a nano‐CaCO3‐coated Zn anode delivers a 42.7% higher discharge capacity (177 vs 124 mAh g−1 at 1 A g−1) after 1000 cycles.

Abstract: Pumped-Storage of Water: It is the most efficient; it is developed in very large scale capacity storage facilities which require specific sites; nevertheless, in the future due to its long lifetime it will play a significant role for intermediate time storage of a few hours to several days, and even for intermediate scale capacity energy storage. Electrochemical Energy Storage in Batteries: It is now used locally in some places that are not connected to the electricity network and on the smart grids for frequency regulation or small peak production shifts. Examples include sodium sulfur batteries (NaS) which are used in Japan; redox flow batteries under development, and some large scale lithium–ion batteries (LIBs) that are used in specific places. Storage via Hydrogen: The development of hydrogen as a way of using fuel cells is considered and seems very interesting from the pollution point of view at the local scale. From the technical point of view, most of the problems are almost solved. Nevertheless, hydrogen has to be produced and stored; and in this case, the yield is quite low, similar to that of the internal combustion engine. Electricity storage via hydrogen requires water electrolysis, H2 gas storage, and electricity production in fuel cells, all of which leads to a low efficiency and therefore, significant energy loss during electricity storage.

Abstract: Secondary batteries based on metal anodes (e.g., Li, Na, Mg, Zn, and Al) are among the most sought‐after candidates for next‐generation mobile and stationary storage systems because they are able to store a larger amount of energy per unit mass or volume. However, unstable electrodeposition and uncontrolled interfacial reactions occuring in liquid electrolytes cause unsatisfying cell performance and potential safety concerns for the commercial application of these metal anodes. Solid‐state electrolytes (SSEs) having a higher modulus are considered capable of inhibiting difficulties associated with the anodes and may enable building of safe all‐solid‐state metal batteries, yet several challenges, such as insufficient room‐temperature ionic conductivity and poor interfacial stability between the electrode and the electrolyte, hinder the large‐scale development of such batteries. Here, research and development of SSEs including inorganic ceramics, organic solid polymers, and organic–inorganic hybrid/composite materials for metal‐based batteries are reviewed. The comparison of different types of electrolytes is discussed in detail, in the context of electrochemical energy storage applications. Then, the focus of this study is on recent advances in a range of attractive and innovative battery chemistries and technologies that are enabled by SSEs. Finally, the challenges and future perspectives are outlined to foresee the development of SSEs.

Abstract: Lithium (Li) metal is an ideal anode material for high energy density batteries. However, the low Coulombic efficiency (CE) and the formation of dendrites during repeated plating and stripping processes have hindered its applications in rechargeable Li metal batteries. The accurate measurement of Li CE is a critical factor to predict the cycle life of Li metal batteries, but the measurement of Li CE is affected by various factors that often lead to conflicting values reported in the literature. Here, several parameters that affect the measurement of Li CE are investigated and a more accurate method of determining Li CE is proposed. It is also found that the capacity used for cycling greatly affects the stabilization cycles and the average CE. A higher cycling capacity leads to faster stabilization of Li anode and a higher average CE. With a proper operating protocol, the average Li CE can be increased from 99.0% to 99.5% at a high capacity of 6 mA h cm−2 (which is suitable for practical applications) when a high-concentration ether-based electrolyte is used.

Abstract: Supported metal nanoparticles are the most widely investigated heterogeneous catalysts in catalysis community. The size of metal nanostructures is an important parameter in influencing the activity of constructed catalysts. Especially, as coordination unsaturated metal atoms always work as the catalytically active centers, decreasing the particle size of the catalyst can greatly boost the specific activity per metal atom. Single-atom catalysts (SACs), containing single metal atoms anchored on supports, represent the utmost utilization of metallic catalysts and thus maximize the usage efficiency of metal atom. However, with the decreasing of particle size, the surface free energy increases obviously, and tends to aggregate into clusters or particles. Selection of an appropriate support is necessary to interact with isolated atoms strongly, and thus prevents the movement and aggregation of isolated atoms, creating stable, finely dispersed active sites. Furthermore, with uniform single-atom dispersion and well-defined configuration, SACs afford great space for optimizing high selectivity and activity. In this review, a detailed discussion of preparing, characterizing, and catalytically testing within this family is provided, including the theoretical understanding of key aspects of SACs materials. The main advantages of SACs as catalysts and the challenges faced for further improving catalytic performance are also highlighted.

Abstract: 2D transition metal carbides and nitrides, known as MXenes, are an emerging class of 2D materials with a wide spectrum of potential applications, in particular in electrochemical energy storage. The hydrophilicity of MXenes combined with their metallic conductivity and surface redox reactions is the key for high-rate pseudocapacitive energy storage in MXene electrodes. However, symmetric MXene supercapacitors have a limited voltage window of around 0.6 V due to possible oxidation at high anodic potentials. In this study, the fact that titanium carbide MXene (Ti3C2Tx) can operate at negative potentials in acidic electrolyte is exploited, to design an all-pseudocapacitive asymmetric device by combining it with a ruthenium oxide (RuO2) positive electrode. This asymmetric device operates at a voltage window of 1.5 V, which is about two times wider than the operating voltage window of symmetric MXene supercapacitors, and is the widest voltage window reported to date for MXene-based supercapacitors. The complementary working potential windows of MXene and RuO2, along with proton-induced pseudocapacitance, significantly enhance the device performance. As a result, the asymmetric devices can deliver an energy density of 37 µW h cm−2 at a power density of 40 mW cm−2, with 86% capacitance retention after 20 000 charge–discharge cycles. These results show that pseudocapacitive negative MXene electrodes can potentially replace carbon-based materials in asymmetric electrochemical capacitors, leading to an increased energy density.

Abstract: Plasmonic metal nanoparticles are a category of plasmonic materials that can efficiently convert light into heat under illumination, which can be applied in the field of solar steam generation. Here, this study designs a novel type of plasmonic material, which is made by uniformly decorating fine metal nanoparticles into the 3D mesoporous matrix of natural wood (plasmonic wood). The plasmonic wood exhibits high light absorption ability (≈99%) over a broad wavelength range from 200 to 2500 nm due to the plasmonic effect of metal nanoparticles and the waveguide effect of microchannels in the wood matrix. The 3D mesoporous wood with numerous low-tortuosity microchannels and nanochannels can transport water up from the bottom of the device effectively due to the capillary effect. As a result, the 3D aligned porous architecture can achieve a high solar conversion efficiency of 85% under ten-sun illumination (10 kW m−2). The plasmonic wood also exhibits superior stability for solar steam generation, without any degradation after being evaluated for 144 h. Its high conversion efficiency and excellent cycling stability demonstrate the potential of newly developed plasmonic wood to solar energy-based water desalination.

Abstract: The low power conversion efficiency (PCE) of tin-based hybrid perovskite solar cells (HPSCs) is mainly attributed to the high background carrier density due to a high density of intrinsic defects such as Sn vacancies and oxidized species (Sn4+) that characterize Sn-based HPSCs. Herein, this study reports on the successful reduction of the background carrier density by more than one order of magnitude by depositing near-single-crystalline formamidinium tin iodide (FASnI3) films with the orthorhombic a-axis in the out-of-plane direction. Using these highly crystalline films, obtained by mixing a very small amount (0.08 m) of layered (2D) Sn perovskite with 0.92 m (3D) FASnI3, for the first time a PCE as high as 9.0% in a planar p–i–n device structure is achieved. These devices display negligible hysteresis and light soaking, as they benefit from very low trap-assisted recombination, low shunt losses, and more efficient charge collection. This represents a 50% improvement in PCE compared to the best reference cell based on a pure FASnI3 film using SnF2 as a reducing agent. Moreover, the 2D/3D-based HPSCs show considerable improved stability due to the enhanced robustness of the perovskite film compared to the reference cell.

Abstract: With the booming development of flexible and wearable electronics, their safety issues and operation stabilities have attracted worldwide attentions. Compared with traditional liquid electrolytes, gel polymer electrolytes (GPEs) are preferred due to their higher safety and adaptability to the design of flexible energy storage devices. This review summarizes the recent progress of GPEs with enhanced physicochemical properties and specified functionalities for the application in electrochemical energy storage. Functional GPEs that are capable to achieve unity lithium-ion transference number and offer additional pseudocapacitance to the overall capacitance are carefully discussed. The smart GPEs with self-protection, thermotolerant, and self-healing abilities are particularly highlighted. To close, the future directions and remaining challenges of the GPEs for application in electrochemical energy storages are summarized to provide clues for the following development.

Abstract: Hydrogen is a promising alternative fuel for efficient energy production and storage, with water splitting considered one of the most clean, environmentally friendly, and sustainable approaches to generate hydrogen. However, to meet industrial demands with electrolysis‐generated hydrogen, the development of a low‐cost and efficient catalyst for the oxygen evolution reaction (OER) is critical, while conventional catalysts are mostly based on precious metals. Many studies have thus focused on exploring new efficient nonprecious‐metal catalytic systems and improving the understandings on the OER mechanism, resulting in the design of catalysts with superior activity compared with that of conventional catalysts. In particular, the use of multimetal rather than single‐metal catalysts is demonstrated to yield remarkable performance improvement, as the metal composition in these catalysts can be tailored to modify the intrinsic properties affecting the OER. Herein, recent progress and accomplishments of multimetal catalytic systems, including several important groups of catalysts: layered hydroxide, spinel, and amorphous metal oxides along with the theoretical principles of activity enhancement in multimetal systems are reviewed. Finally, this is concluded by discussing remaining challenges to achieve further improvements of OER catalyst activities.

Abstract: The layered nickel-rich cathode materials are considered as promising cathode materials for lithium-ion batteries (LIBs) due to their high reversible capacity and low cost. However, several significant challenges, such as the unstable powder properties and limited electrode density, hindered the practical application of the nickel-rich cathode materials with the nickel content over 80%. Herein, important stability issues and in-depth understanding of the nickel-rich cathode materials on the basis of the industrial electrode fabrication condition for the commercialization of the nickel-rich cathode materials are reviewed. A variety of factors threatening the battery safety such as the powder properties, thermal/structural stability are systemically investigated from a material point of view. Furthermore, recent efforts for enhancing the electrochemical stability of the nickel-rich cathode materials are summarized. More importantly, critical key parameters that should be considered for the high energy LIBs at an electrode level are intensively addressed for the first time. Current electrode fabrication condition has a difficulty in increasing the energy density of the battery. Finally, light is shed on the perspectives for the future research direction of the nickel-rich cathode materials with its technical challenges in current state by the practical aspect.

Abstract: Thermoelectric (TE) materials have the capability of converting heat into electricity, which can improve fuel efficiency, as well as providing robust alternative energy supply in multiple applications by collecting wasted heat, and therefore, assisting in finding new energy solutions. In order to construct high performance TE devices, superior TE materials have to be targeted via various strategies. The development of high performance TE devices can broaden the market of TE application and eventually boost the enthusiasm of TE material research. This review focuses on major novel strategies to achieve high-performance TE materials and their applications. Manipulating the carrier concentration and band structures of materials are effective in optimizing the electrical transport properties, while nanostructure engineering and defect engineering can greatly reduce the thermal conductivity approaching the amorphous limit. Currently, TE devices are utilized to generate power in remote missions, solar-thermal systems, implantable or/wearable devices, the automotive industry, and many other fields; they are also serving as temperature sensors and controllers or even gas sensors. The future tendency is to synergistically optimize and integrate all the effective factors to further improve the TE performance, so that highly efficient TE materials and devices can be more beneficial to daily lives.

Abstract: Transition metal sulfides, as an important class of inorganics, can be used as excellent electrode materials for various types of electrochemical energy storage, such as lithium‐ion batteries, sodium‐ion batteries, supercapacitors, and others. Recent works have identified that mixing graphene or graphene derivatives with transition metal sulfides can result in novel composites with better electrochemical performance. This review summarizes the latest advances in transition metal sulfide composites with graphene or graphene derivatives. The synthetic strategies and morphologies of these composites are introduced. The authors then discuss their applications in lithium‐ion batteries, sodium‐ion batteries, and supercapacitors. Finally, the authors give their personal viewpoints about the challenges and opportunities for the future development about this direction.

Abstract: DOI: 10.1002/aenm.201702884 during desalination process and block the channels for vapor escape, resulting in the reduction of energy transfer efficiency, pure water yield, and unstable performance. Therefore, long-term stability becomes critical issues that need to be addressed. Recently, Janus membrane is emerging as a novel class of materials comprised of a two-layer structure with opposing properties and different functions.[26,27] Since the first study of Janus particle by Cho and Lee in 1985,[28] various Janus such as micelles,[29] rods,[30] and sheets[31] have been fabricated, with wide applications in oil/water separation,[32] switchable ion transport,[33] interfacial mass transfer,[34] and fog collection.[35] Here we demonstrate that a flexible Janus absorber fabricated by convenient electrospinning process can enable stable and efficient solar desalination. Taking advantage of the unique structures of Janus absorbers, two functions of solar steam generation, solar absorption and water pumping, are decoupled into different layers, with upper hydrophobic carbon black nanoparticles (CB) coating polymethylmethacrylate (PMMA) layer for light absorption and water evaporation, and bottom hydrophilic polyacrylonitrile (PAN) layer for pumping water. Therefore, salt may only be deposited in the hydrophilic PAN layer and quickly be dissolved because of continuous water pumping. Under 1-sun illumination, the Janus absorber demonstrates efficient solar steam generation (72%) and stable water output (1.3 kg m−2 h−1, over 16 d, with 45 min each day), not achieved in most of previous absorbers. With unique structure design achieved by scalable process, our flexible Janus absorber provides an efficient, stable, and portable solar steam generator for direct solar desalination. Figure 1 presents the illustration of solar steam generation (Figure 1a), and structures of Janus absorber (Figure 1b) in sea water. Porous absorbers naturally float on the water surface, absorbing solar energy to generate steam, without heating the bulk water. CB coating PMMA (CB/PMMA) layer stays above the water surface due to its hydrophobic property while PAN layer is immersed in water for efficient water supply. During the solar steam generation process, the CB/PMMA layer harvests solar energy and converts light to heat, generating vapor from the interfacial region of CB/PMMA and PAN. Thus, the With recent progress in interfacial solar steam generation, direct solar desalination is considered a promising technology for providing a clean water solution through a cost effective and environmental-friendly pathway. As a high and stable water production rate is the key to enable widespread applications, salt deposition becomes a critical issue that needs to be addressed. Herein, the authors demonstrate that a flexible Janus absorber fabricated by sequential electrospinning can enable stable and efficient solar desalination. Taking advantage of the unique structure of Janus, two functions of steam generation, solar absorption and water pumping, are decoupled into different layers, with an upper hydrophobic carbon black nanoparticles (CB) coating poly methylmethacrylate (PMMA) layer for light absorption, and a lower hydrophilic polyacrylonitrile (PAN) layer for pumping water. Therefore, salt can only be deposited in the hydrophilic PAN layer and quickly be dissolved because of continuous water pumping. Janus absorber demonstrates high efficiency (72%) and stable water output (1.3 kg m–2 h–1, over 16 days) under 1-sun, not achieved in most previous absorbers. With a unique structure design achieved by scalable process, this flexible Janus absorber provides an efficient, stable and portable solar steam generator for direct solar desalination.

Abstract: DOI: 10.1002/aenm.201702463 other secondary batteries.[6–8] However, LIBs are too expensive to scale up for the processing cost resulted from the limited lithium resources, and SIBs are subjected to complicated issues of safety as well as environmental issues.[9–12] So, it is an urgent challenge for exploring new energy storage systems. As an alternative, rechargeable aqueous Zn-ion batteries (ZIBs) have received incremental attention owing to the following advantages, including low cost, safety, and environmentally friendly.[13] Meanwhile, using aqueous electrolyte to replace the organic electrolyte is of great significance for reducing the cost and environmental pollution.[14] However, it is difficult to find suitable cathode material as the host for the intercalation of Zn2+ owing to the high polarization of Zn2+ as well as the narrow applicable voltage range, which is limited by the water splitting in the aqueous battery system.[15] Typically, polymorphs of MnO2 (α-, γ-phase) are highly attractive as the cathode material because of the tunnel structure suiting for the intercalation of Zn2+ and a matched potential within the stable range of water. Some results, based on the reversible intercalation of Zn2+, have been reported in recent years, and they show either limited specific capacity or poor cycling performance.[16–19] Recently, the MnO2 nanofiber electrode, reported by Liu and co-workers, shows high capacity and excellent cycling performance.[20] However, the rate performance is not high enough due to the sluggish reaction dynamics of conversion reaction. Prussian blue analogues, including of zinc hexacyanoferrate and copper hexacyanoferrate, are another class of cathode materials, which show limited specific capacity as well as poor cyclic stability.[21–23] Until very recently, vanadiumbased materials are explored for reversible Zn2+ intercalation.[24] Nazar and co-workers reported a bilayered Zn0.25V2O5·nH2O cathode, which shows a high-capacity and long-life performance.[25] However, the development of ZIBs is in the primary stage, some new cathode materials should also be explored to enhance the energy density as well as cycle life for ZIBs. Over the past decades, layered vanadium oxides have been applied as electrode materials for LIBs or SIBs due to their low cost and high capacities.[26,27] Generally, the bulk vanadium oxides suffer from a rapid capacity fading resulting from low electronic conductivity, poor structural stability during the ion de/intercalation.[28] Recent studies show that interlayer metal ions (MxVnOm, M = metal ion) can act as pillars to increase the Aqueous Zn-ion batteries (ZIBs) have received incremental attention because of their cost-effectiveness and the materials abundance. They are a promising choice for large-scale energy storage applications. However, developing suitable cathode materials for ZIBs remains a great challenge. In this work, pioneering work on the designing and construction of aqueous Zn//Na0.33V2O5 batteries is reported. The Na0.33V2O5 (NVO) electrode delivers a high capacity of 367.1 mA h g−1 at 0.1 A g−1, and exhibits long-term cyclic stability with a capacity retention over 93% for 1000 cycles. The improvement of electrical conductivity, resulting from the intercalation of sodium ions between the [V4O12]n layers, is demonstrated by single nanowire device. Furthermore, the reversible intercalation reaction mechanism is confirmed by X-ray diffraction, Raman, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy analysis. The outstanding performance can be attributed to the stable layered structure and high conductivity of NVO. This work also indicates that layered structural materials show great potential as the cathode of ZIBs, and the indigenous ions can act as pillars to stabilize the layered structure, thereby ensuring an enhanced cycling stability. Zinc Ion Batteries

Abstract: Mixed metal sulfides (MMSs) have attracted increased attention as promising electrode materials for electrochemical energy storage and conversion systems including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), hybrid supercapacitors (HSCs), metal–air batteries (MABs), and water splitting. Compared with monometal sulfides, MMSs exhibit greatly enhanced electrochemical performance, which is largely originated from their higher electronic conductivity and richer redox reactions. In this review, recent progresses in the rational design and synthesis of diverse MMS-based micro/nanostructures with controlled morphologies, sizes, and compositions for LIBs, SIBs, HSCs, MABs, and water splitting are summarized. In particular, nanostructuring, synthesis of nanocomposites with carbonaceous materials and fabrication of 3D MMS-based electrodes are demonstrated to be three effective approaches for improving the electrochemical performance of MMS-based electrode materials. Furthermore, some potential challenges as well as prospects are discussed to further advance the development of MMS-based electrode materials for next-generation electrochemical energy storage and conversion systems.

Abstract: The increasing demand for replacing conventional fossil fuels with clean energy or economical and sustainable energy storage drives better battery research today. Sodium-ion batteries (SIBs) are considered as a promising alternative for grid-scale storage applications due to their similar “rocking-chair” sodium storage mechanism to lithium-ion batteries, the natural abundance, and the low cost of Na resources. Searching for appropriate electrode materials with acceptable electrochemical performance is the key point for development of SIBs. Layered transition metal oxides represent one of the most fascinating electrode materials owing to their superior specific capacity, environmental benignity, and facile synthesis. However, three major challenges (irreversible phase transition, storage instability, and insufficient battery performance) are known for cathodes in SIBs. Herein, a comprehensive review on the latest advances and progresses in the exploration of layered oxides for SIBs is presented, and a detailed and deep understanding of the relationship of phase transition, air stability, and electrochemical performance in layered oxide cathodes is provided in terms of refining the structure–function–property relationship to design improved battery materials. Layered oxides will be a competitive and attractive choice as cathodes for SIBs in next-generation energy storage devices.

Abstract: Sodium-ion batteries (SIBs) are considered to be a low-cost complement or competitor to Li-ion batteries for large-scale electric energy storage applications; however, their development has been less successful due to the lack of suitable host materials to enable reversible Na+ insertion reactions. Prussian blue analogs (PBAs) appear to be attractive candidates for SIB cathodes because of their open channel structure, compositional and electrochemical tunability. In this paper, the authors present a comprehensive review on the recent advances in the development of PBA frameworks as SIB cathodes with particular attention to the structure-performance correlation of the PBA materials, and discuss the possible strategies to address the problems present in the SIB applications of PBAs. Also, the development of the PBA frameworks for the insertion cathodes of other monovalent and multivalent ions is briefly introduced, with the aim of providing a new insight into the design and development of new host materials for the next-generation advanced batteries.

Abstract: Flexible and semitransparent organic solar cells (OSCs) have been regarded as the most promising photovoltaic devices for the application of OSCs in wearable energy resources and building-integrated photovoltaics. Therefore, the flexible and semitransparent OSCs have developed rapidly in recent years through the synergistic efforts in developing novel flexible bottom or top transparent electrodes, designing and synthesizing high performance photoactive layer and low temperature processed electrode buffer layer materials, and device architecture engineering. To date, the highest power conversion efficiencies have reached over 10% of the flexible OSCs and 7.7% with average visible transmittance of 37% for the semitransparent OSCs. Here, a comprehensive overview of recent research progresses and perspectives on the related materials and devices of the flexible and semitransparent OSCs is provided.

Abstract: Author(s): Kim, H; Kim, JC; Bianchini, M; Seo, DH; Rodriguez-Garcia, J; Ceder, G | Abstract: The development of rechargeable batteries using K ions as charge carriers has recently attracted considerable attention in the search for cost-effective and large-scale energy storage systems. In light of this trend, various materials for positive and negative electrodes are proposed and evaluated for application in K-ion batteries. Here, a comprehensive review of ongoing materials research on nonaqueous K-ion batteries is offered. Information on the status of new materials discovery and insights to help understand the K-storage mechanisms are provided. In addition, strategies to enhance the electrochemical properties of K-ion batteries and computational approaches to better understand their thermodynamic properties are included. Finally, K-ion batteries are compared to competing Li and Na systems and pragmatic opportunities and future research directions are discussed.

Abstract: Crumpled nitrogen‐doped MXene nanosheets with strong physical and chemical coadsorption of polysulfides are synthesized by a novel one‐step approach and then utilized as a new sulfur host for lithium–sulfur batteries. The nitrogen‐doping strategy enables introduction of heteroatoms into MXene nanosheets and simultaneously induces a well‐defined porous structure, high surface area, and large pore volume. The as‐prepared nitrogen‐doped MXene nanosheets have a strong capability of physical and chemical dual‐adsorption for polysulfides and achieve a high areal sulfur loading of 5.1 mg cm–2. Lithium–sulfur batteries, based on crumpled nitrogen‐doped MXene nanosheets/sulfur composites, demonstrate outstanding electrochemical performances, including a high reversible capacity (1144 mA h g–1 at 0.2C rate) and an extended cycling stability (610 mA h g–1 at 2C after 1000 cycles).

Abstract: Binary NiFe layer double hydroxide (LDH) serves as a benchmark non‐noble metal electrocatalyst for the oxygen evolution reaction, however, it still needs a relatively high overpotential to achieve the threshold current density. Herein the catalyst's electronic structure is tuned by doping vanadium ions into the NiFe LDHs laminate forming ternary NiFeV LDHs to reduce the onset potential, achieving unprecedentedly efficient electrocatalysis for water oxidation. Only 1.42 V (vs reversible hydrogen electrode (RHE), ≈195 mV overpotential) is required to achieve catalytic current density of 20 mA cm−2 with a small Tafel slope of 42 mV dec−1 in 1 m KOH solution, which manifests the best of NiFe‐based catalysts reported till now. Electrochemical analysis and density functional theory +U simulation indicate that the high catalytic activity of NiFeV LDHs mainly attributes to the vanadium doping which can modify the electronic structure and narrow the bandgap thereby bring enhanced conductivity, facile electron transfer, and abundant active sites.

Abstract: Direct electrochemical production of hydrogen peroxide (H2O2) through two‐electron oxygen electrochemistry, for example, the oxygen reduction in fuel cells or water oxidation in water electrolyzers, could provide an attractive alternative to locally produce this chemical on demand. The efficiency of these processes depends greatly on the availability of cost‐effective catalysts with high selectivity, activity, and stability. In recent years, various novel nanostructured materials have been reported to selectively produce H2O2. Through combined experimental and theoretical approaches, underlying mechanisms in the electrochemical synthesis of H2O2 via oxygen electrochemistry have been unveiled. Considering the remarkable progress in this area, the authors summarize recent developments regarding the direct production of H2O2 through two‐electron electrochemical oxygen reactions. The fundamental aspects of electrochemical oxygen reactions are first introduced. Various types of catalysts that can effectively produce H2O2 via two‐electron oxygen electrochemistry are then presented. In parallel, the unique structure‐, component‐, and composition‐dependent electrochemical performance together with the underlying catalytic mechanisms are discussed. Finally, a brief conclusion about the recent progress achieved in electrochemical generation of H2O2 and an outlook on future research challenges are given.

Abstract: Sodium-ion batteries (SIBs) have been considered as the most promising candidate for large-scale energy storage system owing to the economic efficiency resulting from abundant sodium resources, superior safety, and similar chemical properties to the commercial lithium-ion battery Despite the long period of academic research, how to realize sodium-ion battery commercialization for market applications is still a great challenge Thus, from the perspective of future practical application, this review will identify the factors that are restricting commercialization, and evaluate the existing active materials and sodium-ion-based full-cell system The design and development trends that are needed for SIBs to meet the requirements of practical applications in large-scale energy storage will also be discussed in detail

Abstract: The development of efficient and robust earth‐abundant electrocatalysts for the oxygen evolution reaction (OER) is an ongoing challenge. Here, a novel and stable trimetallic NiFeCr layered double hydroxide (LDH) electrocatalyst for improving OER kinetics is rationally designed and synthesized. Electrochemical testing of a series of trimetallic NiFeCr LDH materials at similar catalyst loading and electrochemical surface area shows that the molar ratio Ni:Fe:Cr = 6:2:1 exhibits the best intrinsic OER catalytic activity compared to other NiFeCr LDH compositions. Furthermore, these nanostructures are directly grown on conductive carbon paper for a high surface area 3D electrode that can achieve a catalytic current density of 25 mA cm−2 at an overpotential as low as 225 mV and a small Tafel slope of 69 mV dec−1 in alkaline electrolyte. The optimized NiFeCr catalyst is stable under OER conditions and X‐ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and elemental analysis confirm the stability of trimetallic NiFeCr LDH after electrochemical testing. Due to the synergistic interactions among the metal centers, trimetallic NiFeCr LDH is significantly more active than NiFe LDH and among the most active OER catalysts to date. This work also presents general strategies to design more efficient metal oxide/hydroxide OER electrocatalysts.

Abstract: The demand for electrochemical energy storage technologies is rapidly increasing due to the proliferation of renewable energy sources and the emerging markets of grid- scale battery applications. The properties of batteries and electrochemical energy storage (EES) technologies ideal for most of these applications, yet, faced with resource constraints, the ability of current lithium-ion batteries (LIB) to match this overwhelming demand is uncertain. Sodium-ion batteries (SIB) are a novel class of batteries with similar performance characteristics to LIB. Since they are composed of earth abundant elements, cheaper and utility scale battery modules can be assembled. As a result of the learning curve in LIB technology, a phenomenal progression in material development has been realised in the SIB concept. In this SIB review, various innovative strategies used in material development, as well as the electrochemical properties of possible anode, cathode and electrolyte combinations are unravelled. Attractive performance characteristics are herein evidenced, based on comparative gravimetric and volumetric energy densities to state-of-the-art LIB. Furthermore, opportunities and challenges towards commercialization are herein discussed. Combined with more industrial adaptations, the commercial prospects of SIB look promising and this challenging new technology is set to play a major role in grid-scale EES applications.

Abstract: DOI: 10.1002/aenm.201702149 most of the designed solar thermal absorbers involve either costly materials such as plasmonic noble metal nanostructures or extensive fabrication processes— critical-point or freeze drying, with a poor perspective of manufacturing cost and scalability.[7–14] Moreover, the light-to-heat conversion is commonly demonstrated with membranes, paper, thin film-based material systems, which need to be in continual and direct contact with the bulk water.[15–19] Hence, immense heat losses persist in the nonevaporative part of the bulk fluid driven by thermal diffusion.[10,20] Meanwhile, carbon-based solar absorber materials are gaining attention in view of its intrinsic broadband light absorption, excellent photothermal conduction, and low thermal emission, which is promising for efficient solar-driven vaporization.[15,21,22] Furthermore, carbon materials display good photostability in a wide wavelength range, biodegradability, and low toxicity attributes that are essential for future technological translation.[23–26] Different forms of carbon, i.e., carbon nanotubes, graphenebased aerogel, exfoliated graphite layer, etc., have been successfully developed as solar absorber materials.[19,27,28] However, the carbon nanostructures are often susceptible to aggregation in aqueous solution and are structurally fragile due to dynamic fluid flow and volume variations stress. This has restricted the materials lifetime associated to mechanical deterioration for repetitive usage. Till date, there is no report on the design of low-cost, mechanically robust, and self-contained, a truly heat localized solar-vaporization sponge that can operate efficiently in isolation, completely cut off from the bulk water supply. Herein, we make use of an ultralight weight nitrogenenriched carbon sponge (CS), a 3D elastic cellular solid to soak up water and perform efficient in situ photothermic vaporization. The CSs possess a favorable inbuilt structural hierarchy with mesoporous fibers that are seamlessly interconnected to form elastic macroporous open cells. We exploit the sponge capillary action to wick and confine the liquid within the vicinity of perpetually hot spots so as to deliberately isolate from the bulk water body. By doing so, the bulk water heat losses are eliminated and markedly enhanced in situ photothermic vaporization can be realized. Notably, the hierarchical cellular Solar vaporization has received tremendous attention for its potential in desalination, sterilization, distillation, etc. However, a few major roadblocks toward practical application are the high cost, process intensive, fragility of solar absorber materials, and low efficiency. Herein an inexpensive cellular carbon sponge that has a broadband light absorption and inbuilt structural features to perform solitary heat localization for in situ photothermic vaporization is reported. The defining advantages of elastic cellular porous sponge are that it self-confines water to the perpetually hot spots and accommodates cyclical dynamic fluid flow-volume variable stress for practical usage. By isolating from bulk water, the solar-to-vapor conversion efficiency is increased by 2.5-fold, surpassing that of conventional bulk heating. Notably, complementary solar steam generation-induced electricity can be harvested during the solar vaporization so as to capitalize on waste heat. Such solar distillation and waste heat-to-electricity generation functions may provide potential opportunities for on-site electricity and fresh water production for remote areas/emergency needs.