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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.

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.

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.

As one of the most promising cathode materials in sodium-ion batteries, manganese-based layered oxides have aroused wide attention due to their high specific capacity and plentiful reserves. However, they are plagued by poor air stability rooting in water/Na

Al has been considered as a promising Li-ion batteries anode. However, the volume expansion always makes the electrode in an unstable structure. Meanwhile, the natural Al2O3 passivation layer may lead to a large voltage dip, which could interrupt the lithiation process and result in a limited capacity. Herein, we report a neat avenue to activate the commercial Al pellet electrode by replacing the Al2O3 layer with Sn at room temperature. Not any acid or tedious process is needed. Benefiting from the elimination of Al2O3 and high electrochemical-activity of Sn, the obtained Al@Sn pellet electrode delivers a reversible capacity of 959.5 mAh g-1 at 0.1 A g-1, which is larger than that (395.7 mAh g-1) of the commercial Al pellet electrode and approaches the calculated theoretical capacity. Notably, the voltage dip is muchly lowered to 0.03 V from 0.1 V. When graphene oxide (GO) was further attached for relieving the volume expansion, the as-prepared Al@Sn@GO pellet electrode presents astonishing Li-ion storage properties both in half and full batteries. This work demonstrates that the cooperation of the Al2O3 elimination and matrix addition is successful in promoting the Li-ion storage properties of Al anode, presenting an attractive vision for the development of practical Al-based anodes.

Aqueous sodium ion batteries have received widespread attention due to their great application potential and high safety. However, the serious capacity fading under low temperature dramatically restricts their practical application. Compared to flammable and toxic organic antifreezing additives, addition of common cheap inorganic inert additives to improve low-temperature performance is of interest scientifically. Herein, low-cost calcium chloride is served as antifreezing additive in 1 m NaClO

Conversion-reaction anode materials always deliver high capacities when used for Li-ion batteries (LIBs). However, the large voltage-hysteresis between the discharge and charge potentials slide down the round-trip efficiency of the electrodes, which restricts their further application on commercial LIBs. Herein, an assumption that lowering the voltage-hysteresis by constructing heterostructure is proposed and further verified by CuS based electrode. As a proof of concept, CuS/MnS heterostructure nanoparticles confined by carbon layers are designed and further crosslinked into a 3D network, constructing CuS/MnS-C heterostructure nanofibers (HNFs). The as-formed heterointerfaces facilitate the charge separation and transfer, and further improve the kinetics. Meanwhile, the confinement and conductive network of the carbon nanofibers improve the structural stability and conductivity of the hybrid electrode. As a result, the voltage-hysteresis values of the CuS anode are lowered to 0.30 and 0.35 V in the well-designed CuS/MnS-C HNFs electrode, much smaller than the original values (0.82 and 0.70 V) in the CuS-C NFs electrode. Moreover, the CuS/MnS-C HNFs electrode exhibits the best excellent rate capability among their counterpart electrodes (493.5 mAh g−1 at 2.0 A g−1 with the coulombic efficiency of about 100%). This work would shed light on the development of practical conversion-reaction anode materials with low voltage-hysteresis.