A p-block dopant enables energy-efficient hydrogen production from biomass.

Herein, we develop innovative p-block Bi-doped Co3O4 nanoflakes (Bi-Co3O4 NFAs) on nickel foam, which exhibit excellent electrocatalytic activity for both glucose oxidation (GOR) and H2 evolution reactions (HER). The two-electrode GOR-HER electrolyzer using Bi-Co3O4 NFAs as both the cathode and anode shows a remarkable reduced operation voltage of 1.48 V at 10 mA cm-2, superior to the 1.66 V of the OER-HER electrolyzer, demonstrating promising potential for advanced H2 production featuring energy saving and simultaneously produced value-added chemicals.

Phase Engineering of Molybdenum Carbide-Cobalt Heterostructures for Long-Lasting Zn-Air Batteries.

Developing highly active and robust oxygen catalysts is of great significance for the commercialization of Zn-air batteries (ZABs) with long-life stability. Herein, heterostructured catalysts comprising molybdenum carbide and metallic Co are prepared by a simple dicyandiamide-assisted pyrolysis strategy. Importantly, the crystalline phase of molybdenum carbide in the catalysts can be carefully regulated by adjusting the CoMo-imidazole precursor and dicyandiamide ratio. The electronic configuration of Co and Mo centers as well as the phase-dependent oxygen reduction reaction performance of these heterostructures (ß-Mo2C/Co, ß-Mo2C/η-MoC/Co, and η-MoC/Co) was disclosed. A highly active η-MoC/Co cathode enables ZABs with outstanding long-term stability over 850 h with a low voltage decaying rate of 0.06 mV·h-1 and high peak power density of 162 mW·cm-2. This work provides a new idea for the rational design of efficient and stable cathode catalysts for ZABs.

Tunable Heterogeneous FeCo Alloy-Mo0.82N Bifunctional Electrocatalysts for Temperature-Adapted Zn-Air Batteries.

The practical applications of temperature-tolerant Zn-air batteries (ZABs) rely on highly active and stable bifunctional catalysts that accelerate cathodic oxygen reduction (ORR) and oxygen evolution (OER) reactions. Herein, we successfully integrated fascinating transition metal nitrides and FeCo alloys through a simple coordination assembly and pyrolysis process. Importantly, the alloy-to-nitride ratio in the heterogeneous catalyst can be carefully regulated through the subsequent etching process. Moreover, the composition-dependent ORR/OER performance of the FeCo-Mo0.82N catalysts was revealed. Aqueous ZABs using the optimized FeCo-Mo0.82N-60 as a cathode exhibit a high peak power density of 149.7 mW cm-2 and an impressive stability of 600 h with a low charge-discharge voltage gap decay rate of 0.025 mV h-1, which exceeds those of most of recent reports. Furthermore, the FeCo-Mo0.82N-60-based flexible ZABs display a small specific capacity degradation (3%) from 40 to -10 °C, demonstrating excellent temperature tolerance.

Achieving Ultralong-Cycle Zinc-Ion Battery via Synergistically Electronic and Structural Regulation of a MnO2 Nanocrystal-Carbon Hybrid Framework.

Aqueous rechargeable zinc-ion batteries (ZIBs) have attracted burgeoning interests owing to the prospect in large-scale and safe energy storage application. Although manganese oxides are one of the typical cathodes of ZIBs, their practical usage is still hindered by poor service life and rate performance. Here, a MnO2 -carbon hybrid framework is reported, which is obtained in a reaction between the dimethylimidazole ligand from a rational designed MOF array and potassium permanganate, achieving ultralong-cycle-life ZIBs. The unique structural feature of uniform MnO2 nanocrystals which are well-distributed in the carbon matrix leads to a 90.4% capacity retention after 50 000 cycles. In situ characterization and theoretical calculations verify the co-ions intercalation with boosted reaction kinetics. The hybridization between MnO2 and carbon endows the hybrid with enhanced electrons/ions transport kinetics and robust structural stability. This work provides a facile strategy to enhance the battery performance of manganese oxide-based ZIBs.

Promoting Reversible Dissolution/Deposition of MnO2 for High-Energy-Density Zinc Batteries via Enhancing Cut-Off Voltage.

Zn//MnO2 batteries based on the MnO2 /Mn2+ conversion reaction mechanism featuring high energy density, safety, and affordable cost are promising in large-scale energy storage application. Nonetheless, the continuous H+ intercalation at low potential reduces the average output voltage and the energy efficiency, impeding the development of the high-performance zinc battery. In this work, a strategy was proposed of enhancing the cut-off voltage from the perspective of electrochemical parameters, toward high energy efficiency and stable output voltage of the Zn//MnO2 battery. This strategy was beneficial to promoting MnO2 dissolution/deposition through the increase of acidity caused by the constant accumulation of MnO2 and inhibiting H+ (de)intercalation during cycling process, thereby improving the energy efficiency (83.5 %) along with the stable average output voltage (1.88 V) under the cut-off voltage of 1.8 V. This work provides a new pathway to promote aqueous zinc batteries with high energy density and stable output voltage.

Achieving Highly Reversible Zinc Anodes via N, N-Dimethylacetamide Enabled Zn-Ion Solvation Regulation.

Although aqueous zinc-ion batteries (ZIBs) are promising for scalable energy storage application, the actual performance of ZIBs is hampered by the irreversibility. Optimization of electrolyte composition is a relatively practical and facile way to improve coulombic efficiency (CE) and Zn plating/stripping reversibility of ZIBs. N,N-Dimethylacetamide (DMA) has a higher Gutmann donor number (DN) than that of H2 O, abundant polar groups, and economic price. Herein, a mixture electrolyte containing 10 vol% DMA and ZnSO4 , which has an enhanced Zn reversibility almost fourfold higher than that of pure ZnSO4 electrolyte, is demonstrated. The density functional theory (DFT) calculation and spectroscopic analysis reveal DMA has the ability to reconstruct the solvation structure of Zn2+ and capture free water molecules via forming Hbonds. The inhibited dendrite growth on Zn anode is further clarified by an in situ characterization. This work provides a feasible way for the development of long-lifespan ZIBs.

Metal-Organic Framework-Based Materials for Aqueous Zinc-Ion Batteries: Energy Storage Mechanism and Function.

Aqueous rechargeable zinc-ion batteries (ZIBs) featuring competitive performance, low cost and high safety hold great promise for applications in grid-scale energy storage and portable electronic devices. Metal-organic frameworks (MOFs), relying on their large framework structure and abundant active sites, have been identified as promising materials in ZIBs. This review comprehensively presents the current development of MOF-based materials including MOFs and their derivatives in ZIBs, which begins with Zn storage mechanism of MOFs, followed by introduction of various types of MOF-based cathode materials (PB and PBA, Mn-based MOF, V-based MOF, conductive MOF and their derivatives), and the regulation approaches for Zn deposition behavior. The key factors and optimization strategies of MOF-based materials that affect ZIBs performance are emphasized and discussed. Finally, the challenges and further research directions of MOF-based materials for advanced zinc-ion batteries are provided.

Unlocking active metal site of Ti-MOF for boosted heterogeneous catalysis via a facile coordinative reconstruction.

Constructing sophisticated hollow structure and exposing more metal sites in metal-organic frameworks (MOFs) can not only enhance their catalytic performance but also endow them with new functions. Herein, we present a facile coordinative reconstruction strategy to transform Ti-MOF polyhedron into nanosheet-assembled hollow structure with a large amount of exposed metal sites. Importantly, the reconstruction process relies on the esterification reaction between the organic solvent, i.e. ethanol and the carboxylic acid ligand, allowing the conversion of MOF without the addition of any other modulators and/or surfactants. Moreover, the surface and internal structure of the reconstructed MOF can be well tuned via altering the conversion time. Impressively, the reconstructed MOF exhibits ∼5.1-fold rate constant compared to the pristine one in an important desulfurization reaction for clean fuels production, i.e. the oxidation of dibenzothiophene.

Achieving Enhanced Capacitive Deionization by Interfacial Coupling in PEDOT Reinforced Cobalt Hexacyanoferrate Nanoflake Arrays.

Capacitive deionization (CDI) as a novel energy and cost-efficient water treatment technology has attracted increasing attention. The recent development of various faradaic electrode materials has greatly enhanced the performance of CDI as compared with traditional carbon electrodes. Prussian blue (PB) has emerged as a promising CDI electrode material due to its open framework for the rapid intercalation/de-intercalation of sodium ions. However, the desalination efficiency, and durability of previously reported PB-based materials are still unsatisfactory. Herein, a self-template strategy is employed to prepare a Poly(3,4-ethylenedioxythiophene) (PEDOT) reinforced cobalt hexacyanoferrate nanoflakes anchored on carbon cloth (denoted as CoHCF@PEDOT). With the high conductivity and structural stability achieved by coupling with a thin PEDOT layer, the as-prepared CoHCF@PEDOT electrode exhibits a high capacity of 126.7 mAh g-1 at 125 mA g-1. The fabricated hybrid CDI cell delivers a high desalination capacity of 146.2 mg g-1 at 100 mA g-1, and good cycling stability. This strategy provides an efficient method for the design of high-performance faradaic electrode materials in CDI applications.

Ultra-Fast and Scalable Saline Immersion Strategy Enabling Uniform Zn Nucleation and Deposition for High-Performance Zn-Ion Batteries.

Although aqueous Zn-ion batteries (ZIBs) with low cost and high safety show great potential in large-scale energy storage system, metallic Zn anode still suffers from unsatisfactory cycle stability due to unregulated growth of Zn dendrites, corrosion, and formation of various side products during electrochemical reaction. Here, an ultrafast and simple method to achieve a stable Zn anode is developed. By simply immersing a Zn plate into an aqueous solution of CuSO4 for only 10-60 s, a uniform and robust protective layer (Zn4 SO4 (OH)6 ·5H2 O/Cu2 O) is formed on commercial Zn plate (Zn/ZCO), which enables uniform electric field distribution and controllable dendrite growth, leading to a long-term cycle life of over 1400 h and high average Coulombic efficiency (CE) of 99.2% at 2.0 mA cm-2 and 2.0 mAh cm-2 . These excellent characteristics of the prepared Zn anode show great potential in practical applications for high-performance aqueous Zn-ion batteries.

Bismuth Nanoparticle-Embedded Porous Carbon Frameworks as a High-Rate Chloride Storage Electrode for Water Desalination.

Capacitive deionization (CDI) is a promising cost-effective and low energy consumption technology for water desalination. However, most of the previous works focus on only one side of the CDI system, i.e., Na+ ion capture, while the other side that stores chloride ions, which is equally important, receives very little attention. This is attributed to the limited Cl- storage materials as well as their sluggish kinetics and poor stability. In this article, we demonstrate that a N-doped porous carbon framework is capable of suppressing the phase-transformation-induced performance decay of bismuth, affording an excellent Cl- storage and showing potential for water desalination. The obtained Bi-carbon composite (Bi/N-PC) shows a capacity of up to 410.4 mAh g-1 at 250 mA g-1 and a high rate performance. As a demonstration for water desalination, a superior desalination capacity of 113.4 mg g-1 is achieved at 100 mA g-1 with excellent durability. Impressively, the CDI system exhibits fast ion capturing with a desalination rate as high as 0.392 mg g-1 s-1, outperforming most of the recently reported Cl- capturing electrodes. This strategy is applicable to other Cl- storage materials for next-generation capacitive deionization.

High-Yield Exfoliation of Ultrathin 2D Ni3 Cr2 P2 S9 and Ni3 Cr2 P2 Se9 Nanosheets.

Multinary layered 2D nanomaterials can exhibit distinct physicochemical properties and innovative applications as compared to binary 2D nanomaterials due to their unique crystal structures. However, it still remains a challenge for the high-yield preparation of high-quality multinary 2D nanosheets. Here, the high-yield and large-scale production of two quaternary metal thiophosphate nanosheets are reported, i.e., Ni3 Cr2 P2 S9 and Ni3 Cr2 P2 Se9 , via the liquid exfoliation of their layered bulk crystals. The exfoliated single-crystalline Ni3 Cr2 P2 S9 nanosheets, with a lateral size ranging from a few hundred nanometers to a few micrometers and thickness of 1.4 ± 0.2 nm, can be easily used to prepare flexible thin films via a simple vacuum filtration process. As a proof-of-concept application, the fabricated thin film is used as a supercapacitor electrode with good specific capacitance. These high-yield, large-scale, solution-processable quaternary metal thiophosphate nanosheets could also be promising in other applications like biosensors, cancer therapies, and flexible electronics.

Boosting Electrocatalytic Activity of 3d-Block Metal (Hydro)oxides by Ligand-Induced Conversion.

The 3d-transition-metal (hydro)oxides belong to a group of highly efficient, scalable and inexpensive electrocatalysts for widespread energy-related applications that feature easily tailorable crystal and electronic structures. We propose a general strategy to further boost their electrocatalytic activities by introducing organic ligands into the framework, considering that most 3d-metal (hydro)oxides usually exhibit quite strong binding with reaction intermediates and thus compromised activity due to the scaling relations. Involving weakly bonded ligands downshifts the d-band center, which narrows the band gap, and optimizes the adsorption of these intermediates. For example, the activity of the oxygen evolution reaction (OER) can be greatly promoted by ≈5.7 times over a NiCo layered double hydroxide (LDH) after a terephthalic acid (TPA)-induced conversion process, arising from the reduced energy barrier of the deprotonation of OH* to O*. Impressively, the proposed ligand-induced conversion strategy is applicable to a series of 3d-block metal (hydro)oxides, including NiFe2 O4 , NiCo2 O4 , and NiZn LDH, providing a general structural upgrading scheme for existing high-performance electrocatalytic systems.

MnO2 -Based Materials for Environmental Applications.

Manganese dioxide (MnO2 ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO2 single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO2 -based composites via the construction of homojunctions and MnO2 /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO2 -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO2 -based materials for comprehensive environmental applications is provided.

Bioinspired interfacial engineering of a CoSe2 decorated carbon framework cathode towards temperature-tolerant and flexible Zn-air batteries.

A high-performance air electrode is essential for the successful application of flexible Zn-air batteries in wearable devices. However, endowing the electrode-electrolyte interface with high stability and fast electron/ion transportation is still a great challenge. Herein, we report a bioinspired interfacial engineering strategy to construct a cactus-like hybrid electrode comprising CoSe2 nanoparticles embedded in an N-doped carbon nanosheet arrays penetrated with carbon nanotubes (CoSe2-NCNT NSA). Associated with the synergistic effect of highly active CoSe2 nanoparticles and N-doped carbon moieties and a stable 3D interconnected CNT network, the obtained self-standing electrode exhibits satisfactory catalytic activities towards oxygen evolution/reduction and hydrogen evolution, as well as an enhanced electrode-electrolyte interaction/interface area, and thus delivers superior performance for flexible Zn-air batteries. Remarkably, the fabricated flexible Zn-air battery with this CoSe2-NCNT NSA cathode achieves a high peak power density (51.1 mW cm-2), considerable mechanical flexibility, and excellent durability in a wide temperature range of 0 to 40 °C. Furthermore, the assembled Zn-air batteries can efficiently power a water-splitting device that adopts the CoSe2-NCNT NSA as both the anode and cathode, demonstrating promising potential in energy conversion and portable electronic applications.

High mass loading flower-like MnO2 on NiCo2O4 deposited graphene/nickel foam as high-performance electrodes for asymmetric supercapacitors.

The implementation of high mass loading MnO2 on electrochemical electrodes of supercapacitors is currently challenging due to the poor electrical conductivity and elongated electron/ion transport distance. In this paper, a NiCo2O4/MnO2 heterostructure was built on the surface of three-dimensional graphene/nickel foam (GNF) by a hydrothermal method. The petal structured NiCo2O4 loaded on graphene played a wonderful role as a supporting framework, which provided more space for the growth of high mass loading MnO2 microflowers, thereby increasing the utilization rate of the active material MnO2. The GNF@NiCo2O4/MnO2 composite was used as a positive electrode and achieved a high areal capacitance of 1630.5 mF cm-2 at 2 mA cm-2 in the neutral Na2SO4 solution. The asymmetric supercapacitor assembled with the GNF@NiCo2O4/MnO2 positive electrode and activated carbon negative electrode possessed a wide voltage window (2.1 V) and splendid energy density (45.9 Wh kg-1), which was attributed to the satisfactory electroactive area, low resistance, quick mass diffusion and ion transport caused by high mass loading MnO2.

Enabling Superior Sodium Capture for Efficient Water Desalination by a Tubular Polyaniline Decorated with Prussian Blue Nanocrystals.

The application of electrochemical energy storage materials to capacitive deionization (CDI), a low-cost and energy-efficient technology for brackish water desalination, has recently been proven effective in solving problems of traditional CDI electrodes, i.e., low desalination capacity and incompatibility in high salinity water. However, Faradaic electrode materials suffer from slow salt removal rate and short lifetime, which restrict their practical usage. Herein, a simple strategy is demonstrated for a novel tubular-structured electrode, i.e., polyaniline (PANI)-tube-decorated with Prussian blue (PB) nanocrystals (PB/PANI composite). This composite successfully combines characteristics of two traditional Faradaic materials, and achieves high performance for CDI. Benefiting from unique structure and rationally designed composition, the obtained PB/PANI exhibits superior performance with a large desalination capacity (133.3 mg g-1 at 100 mA g-1 ), and ultrahigh salt-removal rate (0.49 mg g-1 s-1 at 2 A g-1 ). The synergistic effect, interfacial enhancement, and desalination mechanism of PB/PANI are also revealed through in situ characterization and theoretical calculations. Particularly, a concept for recovery of the energy applied to CDI process is demonstrated. This work provides a facile strategy for design of PB-based composites, which motivates the development of advanced materials toward high-performance CDI applications.

Exploration of Energy Storage Materials for Water Desalination via Next-Generation Capacitive Deionization.

Clean energy and environmental protection are critical to the sustainable development of human society. The numerous emerged electrode materials for energy storage devices offer opportunities for the development of capacitive deionization (CDI), which is considered as a promising water treatment technology with advantages of low cost, high energy efficiency, and wide application. Conventional CDI based on porous carbon electrode has low salt removal capacity which limits its application in high salinity brine. Recently, the faradaic electrode materials inspired by the researches of sodium-batteries appear to be attractive candidates for next-generation CDI which capture ions by the intercalation or redox reactions in the bulk of electrode. In this mini review, we summarize the recent advances in the development of various faradaic materials as CDI electrodes with the discussion of possible strategies to address the problems present.

Stereoassembled V2O5@FeOOH Hollow Architectures with Lithiation Volumetric Strain Self-Reconstruction for Lithium-Ion Storage.

Vanadium oxides have recently attracted widespread attention due to their unique advantages and have demonstrated promising chemical and physical properties for energy storage. This work develops a mild and efficient method to stereoassemble hollow V2O5@FeOOH heterostructured nanoflowers with thin nanosheets. These dual-phased architectures possess multiple lithiation voltage plateau and well-defined heterointerfaces facilitating efficient charge transfer, mass diffusion, and self-reconstruction with volumetric strain. As a proof of concept, the resulting V2O5@FeOOH hollow nanoflowers as an anode material for lithium-ion batteries (LIBs) realize high-specific capacities, long lifespans, and superior rate capabilities, e.g., maintaining a specific capacity as high as 985 mAh g-1 at 200 mA g-1 with good cyclability.

Non-3d Metal Modulation of a 2D Ni-Co Heterostructure Array as Multifunctional Electrocatalyst for Portable Overall Water Splitting.

Portable water splitting devices driven by rechargeable metal-air batteries or solar cells are promising, however, their scalable usages are still hindered by lack of suitable multifunctional electrocatalysts. Here, a highly efficient multifunctional electrocatalyst is demonstrated, i.e., 2D nanosheet array of Mo-doped NiCo2 O4 /Co5.47 N heterostructure deposited on nickel foam (Mo-NiCo2 O4 /Co5.47 N/NF). The successful doping of non-3d high-valence metal into a heterostructured nanosheet array, which is directly grown on a conductive substrate endows the resultant catalyst with balanced electronic structure, highly exposed active sites, and binder-free electrode architecture. As a result, the Mo-NiCo2 O4 /Co5.47 N/NF exhibits remarkable catalytic activity toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), affording high current densities of 50 mA cm-2 at low overpotentials of 310 mV for OER, and 170 mV for HER, respectively. Moreover, a low voltage of 1.56 V is achieved for the Mo-NiCo2 O4 /Co5.47 N/NF-based water splitting cell to reach 10 mA cm-2 . More importantly, a portable overall water splitting device is demonstrated through the integration of a water-splitting cell and two Zn-air batteries (open-circuit voltage of 1.43 V), which are all fabricated based on Mo-NiCo2 O4 /Co5.47 N/NF, demonstrating a low-cost way to generate fuel energy. This work offers an effective strategy to develop high-performance metal-doped heterostructured electrode.