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Fabricating highly efficient and robust oxygen reduction reaction (ORR) electrocatalysts is challenging but desirable for practical Zn-air batteries. As an early transition-metal oxide, zirconium dioxide (ZrO2) has emerged as an interesting catalyst owing to its unique characteristics of high stability, anti-toxicity, good catalytic activity, and small oxygen adsorption enthalpies. However, its intrinsically poor electrical conductivity makes it difficult to serve as an ORR electrocatalyst. Herein, we report ultrafine N-doped ZrO2 nanoparticles embedded in an N-doped porous carbon matrix as an ORR electrocatalyst (N-ZrO2/NC). The N-ZrO2/NC catalyst displays excellent activity and long-term durability with a half-wave potential (E1/2) of 0.84 V and a selectivity for the four-electron reduction of oxygen in 0.1 M KOH. Upon employment in a Zn-air battery, N-ZrO2/NC presented an intriguing power density of 185.9 mW cm−2 and a high specific capacity of 797.9 mA h gZn−1, exceeding those of commercial Pt/C (122.1 mW cm−2 and 782.5 mA h gZn−1). This excellent performance is mainly attributed to the ultrafine ZrO2 nanoparticles, the conductive carbon substrate, and the modified electronic band structure of ZrO2 after N-doping. Density functional theory calculations demonstrated that N-doping can reduce the band-gap of ZrO2 from 3.96 eV to 3.33 eV through the hybridization of the p state of the N atom with the 2p state of the oxygen atom; this provides enhanced electrical conductivity and results in faster electron-transfer kinetics. This work provides a new approach for the design of other enhanced semiconductor and insulator materials.

Hard carbon (HC) is most likely to be a commercialized anode material for sodium-ion batteries (SIBs). However, its low initial coulombic efficiency (ICE) impedes its further large-scale industrialization. Since the ICE is greatly related to the side reactions of the electrolyte on the HC surface, herein, we focus on tailoring the surface chemistry of HC

Aqueous zinc-ion batteries (ZIBs) have attracted great attention as the candidates for large-scale energy storage system, recently, because of their low cost, environment-friendly, high safety, and high theoretical energy densities. Among the numerous cathode materials, layered structure vanadium based polyanionic compounds, such as VOPO4, exhibit high specific capacity for Zn ion storage. However, the low Zn ion diffusion coefficient and limited interlayer spacing make the cathodes low reversible capacity and inferior cycling stability. Herein, K ions were pre-intercalated into the VOPO4 layers via ions exchange adopting VOPO4•2H2O as the precursor. When evaluated as the cathode for ZIBs, an excellent cycle stability of 400 cycles under a current density of 500 mA g−1 was achieved by the obtained KVOPO4 electrode, verifying the positive effect of intercalation engineering. Furtherly, a solid-solution reaction Zn ion storage mechanism was confirmed. This study provides a new insight to explore high performance cathode materials for ZIBs.

Electrochemical water splitting is a sustainable and feasible strategy for hydrogen production but is hampered by the sluggish anodic oxygen evolution reaction (OER). Herein, an effective approach is introduced to significantly decrease the cell voltage by replacing the anodic OER with a urea oxidation reaction (UOR). A Ni2P/NiMoP nanosheet catalyst with a hierarchical architecture is uniformly grown on a nickel foam (NF) substrate through a simple hydrothermal and phosphorization method. The Ni2P/NiMoP achieves impressive HER activity, with a low overpotential of only 22 mV at 10 mA cm–2 and a low Tafel slope of 34.5 mV dec–1. In addition, the oxidation voltage is significantly reduced from 1.49 V to 1.33 V after the introduction of 0.33 M urea. Notably, a two-electrode electrolyzer employing Ni2P/NiMoP as a bifunctional catalyst exhibits a current density of 10 mA cm–2 at a cell voltage of 1.35 V and excellent long-term durability after 80 h.

Bimetallic sulfides display good electroconductibility and more redox active sites for sodium ion storage, which are expected to realize fast charging/discharging of sodium ion hybrid capacitors (SIHCs) integration. Herein, Sb was introduced into SnS2 on graphene (ATS/GNS) to enhance the kinetics of Na+ storage. The introduction of Sb at Sn site in SnS2 leads to a residual delocalized s electron and forms a half-filled and delocalized intermediate band, which can effectively improve electroconductivity. ATS possesses a high adsorption energy (-3.13 eV) and low diffusion energy barrier (0.26 eV) of Na+ by density functional theory calculations. ATS/GNS with remarkable stability possesses a reversible capacity of 507 mAh g−1 at 1 A g−1 after 3000 cycles. The ATS/GNS//N, S doped porous carbon SIHC delivers high energy/power densities (115 Wh kg−1/351 W kg−1 and 41 Wh kg−1/18750 W kg−1), and an excellent capacity retention of 70% after 10000 cycles at 5 A g−1. This work may present a feasible approach to design high-rate and long-term stability of sodium-based devices.

Main-group (s- and p-block) metals are generally regarded as catalytically inactive due to the delocalized s/p-band. Herein, we successfully synthesized a p-block antimony single-atom catalyst (Sb SAC) with the Sb-N4 configuration for efficient catalysis of the oxygen reduction reaction (ORR). The obtained Sb SAC exhibits superior ORR activity with a half-wave potential of 0.86 V and excellent stability, which outperforms most transition-metal (TM, d-block) based SACs and commercial Pt/C. In addition, it presents an excellent power density of 184.6 mW cm-2 and a high specific capacity (803.5 mAh g-1 ) in Zn-air battery. Both experiment and theoretical calculation manifest that the active catalytic sites are positively charged Sb-N4 single-metal sites, which have closed d shells. Density of states (DOS) results unveil the p orbital of the atomically dispersed Sb cation in Sb SAC can easily interact with O2 -p orbital to form hybrid states, facilitating the charge transfer and generating appropriate adsorption strength for oxygen intermediates, lowering the energy barrier and modulating the rate-determining step. This work sheds light on the atomic-level preparing p-block Sb metal catalyst for highly active ORR, and further provides valuable guidelines for the rational design of other main-group-metal SACs.

Aqueous Zn-storage behaviors of MoS2 -based cathodes mainly rely on the ion-(de)intercalation at edge sites but are limited by the inactive basal plane. Herein, an in-situ molecular engineering strategy in terms of structure defects manufacturing and O-doping is proposed for MoS2 (designated as D-MoS2 -O) to unlock the inert basal plane, expand the interlayer spacing (from 6.2 to 9.6 A), and produce abundant 1T-phase. The tailored D-MoS2 -O with excellent hydrophilicity and high conductivity allows the 3D Zn2+ transport along both the ab plane and c-axis, thus achieving the exceptional high rate capability. Zn2+ diffusion through the basal plane is verified by DFT computations. As a proof of concept, the wearable quasi-solid-state rechargeable Zn battery employing the D-MoS2 -O cathode operates stably even under severe bending conditions, showing great application prospects. This work opens a new window for designing high-performance layered cathode materials for aqueous Zn-ion batteries.

The electrochemical oxidation of small molecules to generate value-added products has gained enormous interest in recent years because of the advantages of benign operation conditions, high conversion efficiency and selectivity, the absence of external oxidizing agents, and eco-friendliness. Coupling the electrochemical oxidation of small molecules to replace oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode in an electrolyzer would simultaneously realize the generation of high-value chemicals or pollutant degradation and the highly efficient production of hydrogen. This Minireview presents an introduction on small-molecule choice and design strategies of electrocatalysts as well as recent breakthroughs achieved in the highly efficient production of hydrogen. Finally, challenges and future orientations are highlighted.

The overall performance of dual-ion batteries (DIBs) is strongly linked to anions storage properties of cathodes. Whereas high energy/power densities and stabilities for DIBs are limited by cathodes. To overcome these barriers, we have designed a novel fluoridized-polyaniline-H

Na superionic conductor (NASICON)-type Na

Hydrogen, as a clean energy carrier, is of great potential to be an alternative fuel in the future. Proton exchange membrane (PEM) water electrolysis is hailed as the most desired technology for high purity hydrogen production and self-consistent with volatility of renewable energies, has ignited much attention in the past decades based on the high current density, greater energy efficiency, small mass-volume characteristic, easy handling and maintenance. To date, substantial efforts have been devoted to the development of advanced electrocatalysts to improve electrolytic efficiency and reduce the cost of PEM electrolyser. In this review, we firstly compare the alkaline water electrolysis (AWE), solid oxide electrolysis (SOE), and PEM water electrolysis and highlight the advantages of PEM water electrolysis. Furthermore, we summarize the recent progress in PEM water electrolysis including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalysts in the acidic electrolyte. We also introduce other PEM cell components (including membrane electrode assembly, current collector, and bipolar plate). Finally, the current challenges and an outlook for the future development of PEM water electrolysis technology for application in future hydrogen production are provided.

The lower energy density and safety issues of liquid sodium-ion batteries have been unable to satisfy the ever-increasing demands for large-scale energy storage system. As a low-cost alternative, s...

Sodium-ion batteries (SIBs) have been considered as an ideal choice for the next generation large-scale energy storage applications owing to the rich sodium resources and the analogous working principle to that of lithium-ion batteries (LIBs). Nevertheless, the larger size and heavier mass of Na+ ion than those of Li+ ion often lead to sluggish reaction kinetics and inferior cycling life in SIBs compared to the LIB counterparts. The pursuit of promising electrode materials that can accommodate the rapid and stable Na-ion insertion/extraction is the key to promoting the development of SIBs toward a commercial prosperity. One-dimensional (1D) nanomaterials demonstrate great prospects in boosting the rate and cycling performances because of their large active surface areas, high endurance for deformation stress, short ions diffusion channels, and oriented electrons transfer paths. Electrospinning, as a versatile synthetic technology, features the advantages of controllable preparation, easy operation, and mass production, has been widely applied to fabricate the 1D nanostructured electrode materials for SIBs. In this review, we comprehensively summarize the recent advances in the sodium-storage cathode and anode materials prepared by electrospinning, discuss the effects of modulating the spinning parameters on the materials’ micro/nano-structures, and elucidate the structure-performance correlations of the tailored electrodes. Finally, the future directions to harvest more breakthroughs in electrospun Na-storage materials are pointed out.

Layered transition-metal oxides have been extensively pursued as promising cathodes for sodium-ion batteries (SIBs) by virtue of their two-dimensional Na-diffusion channels and high theoretical capacities. Nevertheless, irreversible phase transitions, structural instability, and moisture sensitivity place obstacles in their way to approach higher performance. Aiming at tackling these challenging issues, an in-depth understanding of the structural evolutions, morphology changes, composition and valence variations, as well as the electrode/electrolyte interface reactions upon battery cycling is of vital importance. Current state-of-the-art characterization techniques can gain valuable insights into the elusive reaction mechanisms, yield an overall picture of the battery configurations, and provide a guideline for the design of new electrode materials. Herein, the latest progresses on the applications of advanced analytical techniques to probe the Na-storage layered oxide cathodes are comprehensively summarized. In-situ or operando techniques are highlighted in this review to directly link the real-time structure, morphology, composition information with the electrochemical response, and the electrochemical measurements are also mentioned in selected examples. Special attention is paid to the detection principle of each technique and what valuable information can be obtained. Finally, the future developments of layered oxides towards high-performance SIB cathode materials with the help of advanced diagnostic methods are well prospected.

Nickel-iron layered double hydroxides (NiFe LDHs) have been identified as one of the best promising electrocatalysts-candidates for oxygen evolution reaction (OER). However, the catalytic activity effected by interlayer water molecules is ignored and rarely reported. Herein, Ni(OH)2, NiFe LDHs vertically aligned Ni foam are designed for OER. As a contrast, the corresponding electrocatalysts with the removal of the interlayer water molecules (Ni(OH)2-AT, NiFe LDHs-AT) are developed to probe into the influence of the interlayer water molecules towards OER. As expected, NiFe LDH nanoplates exhibit excellent catalytic performance and durability for water electrolysis in alkaline conditions with lower overpotential and smaller Tafel slope compared to those of NiFe LDHs-AT, which are influenced mainly by stability of crystal structure due to the existence of interlayer water molecules. The discovery opens up a similar pathway by controlling the amount of water molecules to boost catalytic performance for studying other electrocatalysts with heteroatom dopant.

Electrochemical water splitting is a fascinating technology for sustainable hydrogen production, and electrocatalysts are essential to accelerate the sluggish hydrogen and oxygen evolution reactions (HER and OER). Transition-metal-based electrocatalysts have attracted enormous interests due to the abundant resources, low cost, and comparable catalytic performance to noble metals. Among these studies, fibrous materials possess distinct advantages, such as unique structure, high active surface area, and fast electron transport. Herein, the most recent progress of nanofiber electrocatalysts on synthesis and application in HER and OER is summarized, with emphasis on iron-, cobalt-, and nickel-based materials. Moreover, the challenge and prospects of fibrous-structured electrocatalysts on water splitting is provided.

Coupling metal oxides with heterostructured catalysts have been regarded as a promising strategy for promoting the hydrogen evolution reaction (HER). However, it remains a great challenge for optimal H adsorption and fast reaction kinetics. Herein, we fabricated few-layered MoN–MnO heterostructure catalysts implanted with interfacial-O configuration as synergistic sites. The unique structure promotes charge redistribution in the coupled boundary, which regulates the adsorption strength of H and synergistically interacts with nitrides for optimal H adsorption. Combined with a few-layered (5 layers, 3.5 nm) curved structure, the MoN–MnO electrode exhibits surpassed-Pt activity for HER under alkaline and neutral conditions. First-principles calculations indicate that the interfacial configuration is superactive and favorable for H adsorption. This work contributes to the understanding of heterostructured catalysts for promoting activity, and presents a new strategy to design interfacial engineering catalysts.

The intrinsically sluggish kinetics of the anodic oxygen evolution reaction (OER) is deemed to be the bottleneck for highly efficient electrocatalytic hydrogen production, and the by-product is less value-added oxygen. Herein, we report rational construction of Mo doped Co4N nanoarrays (Mo-Co4N) with an open skeleton structure as a robust bifunctional electrocatalyst for concurrent electrolytic high-purity hydrogen and value-added formate productions in the cathodic and anodic process. Benefitting from Mo doping, the unique structure characteristics of more exposed active sites, and optimized electronic synergy, Mo-Co4N exhibits intriguing hydrogen evolution reaction (HER) activity with an exceptionally small overpotential of 45 mV at 10 mA cm−2 and a low Tafel slope of 42 mV dec−1. Meanwhile, when the anodic partial methanol oxidation reaction (MOR) is used to replace the OER, the oxidation potential is significantly reduced to 1.356 V at 10 mA cm−2. In particular, a two-electrode electrolyzer employing Mo-Co4N as a bifunctional catalyst only requires an ultralow cell voltage of 1.427 V to achieve a current density of 10 mA cm−2, featuring low energy consumption in comparison to traditional overall water splitting. Furthermore, high Faraday efficiencies approaching 100% for hydrogen evolution and value-added formate production are achieved, as well as excellent 60 h long-term durability.

Solid state Na-CO2 batteries are a kind of promising energy storage system, which can use excess CO2 for electrochemical energy storage. They not only have high theoretical energy densities, but also feature a high safety level of solid-state batteries and low cost owing to abundant sodium metal resources. Although many efforts have been made, the practical application of Na-CO2 battery technology is still hampered by some crucial challenges, including short cycle life, high charging potential, poor rate performance and lower specific full discharge capacity. This paper systematically reviews the recent research advances in Na-CO2 batteries in terms of understanding the mechanism of CO2 reduction, carbonate formation and decomposition reaction, design strategies of cathode electrocatalysts, solid electrolytes and their interface design. In addition, the application of advanced in situ characterization techniques and theoretical calculation of metal–CO2 batteries are briefly introduced, and the combination of theory and experiment in the research of battery materials is discussed as well. Finally, the opportunities and key challenges of solid-state Na-CO2 electrochemical systems in the carbon-neutral era are presented.

NaAlH4 is one of the most promising hydrogen storage materials due to its high energy density. However, the sluggish kinetic hindered it stepping into practical application. In this work, a bottom-up strategy was employed to confine NaAlH4 between graphene nanosheets with a millefeuille-liked multi-layer morphology. The NaAlH4 particles were uniformly arranged between graphene layers, with a high loading up to 90%, and performed improved dehydrogenation kinetic. The dehydrogenation peak temperature 55.7 °C decreased comparing with commercial NaAlH4. The generality of this nano-structuring strategy were confirmed by the successful synthesis of TiO2–NaAlH4 co-confined composites as well as the further enhanced kinetic.

The interfacial instability between Ni-rich layered oxide cathodes and sulfide electrolytes is a serious problem, leading to poor electrochemical properties of all-solid-state lithium batteries (ASSLB). The chemical/electrochemical side reactions are considered to be the origin of the interfacial deterioration. However, the influence of chemical and electrochemical side reactions on the interfacial deterioration is rarely studied specifically. In this work, the deterioration mechanism of the interface between LiNi0.85-xCo0.15AlxO2 and Li10GeP2S12 is investigated in detail by combining in/ex-situ Raman spectra and Electrochemical Impedance Spectroscopy (EIS). It can be determined that chemical side reaction between LiNi0.8Co0.15Al0.05O2 and Li10GeP2S12 will occur immediately once contacted, and the interfacial deterioration becomes more serious after charge-discharge process under the dual effects of chemical and electrochemical side reactions. Moreover, our research reveals that the interfacial stability and the cycle performance of ASSLB can be greatly enhanced by increasing Al-substitution for Ni in LiNi0.85-xCo0.15AlxO2. In particular, the capacity retention of LiNi0.6Co0.15Al0.25O2 cathode after 200 cycles can reach 81.9%, much higher than that of LiNi0.8Co0.15Al0.05O2 cathode (12.5%@200 cycles). This work gives an insight to study the interfacial issues between Ni-rich layered oxide cathode and sulfide electrolyte for ASSLBs.

P2-type layered oxides suffer from an ordered Na+ /vacancy arrangement and P2→O2/OP4 phase transitions, leading them to exhibit multiple voltage plateaus upon Na+ extraction/insertion. The deficient sodium in the P2-type cathode easily induces the bad structural stability at deep desodiation states and limited reversible capacity during Na+ de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2-type layered oxides. To address these challenges, a novel high sodium content (0.85) and plateau-free P2-type cathode-Na0.85 Li0.12 Ni0.22 Mn0.66 O2 (P2-NLNMO) was developed. The complete solid-solution reaction over a wide voltage range ensures both fast Na+ mobility (10-11 to 10-10 cm2 s-1 ) and small volume variation (1.7 %). The high sodium content P2-NLNMO exhibits a higher reversible capacity of 123.4 mA h g-1 , superior rate capability of 79.3 mA h g-1 at 20 C, and 85.4 % capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid-solution reaction are critical to realizing high-performance P2-type cathodes for sodium-ion batteries.