Ni-rich layered oxide cathode materials are promising candidates for high-specific-energy battery systems owing to their high reversible capacity. However, their widespread application is still severely impeded by severe capacity loss upon long-term cycling. It has been proven that the cyclic stability of Ni-rich cathode materials is closely related to their microstructure and morphology. Despite this, the influence of the microstructure of primary particles on the fatigue mechanism of Ni-rich cathode materials during prolonged cycling has not been fully understood. Here, two Ni-rich layered spherical agglomerate oxides consisting of the primary particle with different length/width ratios are successfully synthesized. It is found that the long-term structural stability of both materials strongly depends on the microstructure of primary crystallites, although there is no significant difference between the electrochemical and crystalline characteristics during the initial cycle. A higher primary particle length/width ratio could effectively inhibit the accumulation of microcracks and chemical degradation during long-term cycling, thereby promoting the electrochemical performance of the cathode materials (80% capacity retention after 200 cycles at 1 C compared to the 55% of the counterpart with a lower primary particle length/width ratio). This study highlights the structure-activity relationship between the primary particle microstructure and fatigue mechanisms during long-term cycling, thereby advancing the development of Ni-rich cathode materials.

Sodium-ion batteries (SIBs) are emerging as a possible substitute for lithium-ion batteries (LIBs) in low-cost and large-scale electrochemical energy storage systems owing to the lack of lithium resources. The properties of SIBs are correlated to the electrode materials, while the performance of electrode materials is significantly affected by the morphologies. In recent years, several kinds of anode materials involving carbon-based anodes, titanium-based anodes, conversion anodes, alloy-based anodes, and organic anodes have been systematically researched to develop high-performance SIBs. Nanostructures have huge specific surface areas and short ion diffusion pathways. However, the excessive solid electrolyte interface film and worse thermodynamic stability hinder the application of nanomaterials in SIBs. Thus, the strategies for constructing three-dimensional (3D) architectures have been developed to compensate for the flaws of nanomaterials. This review summarizes recent achievements in 3D architectures, including hollow structures, core-shell structures, yolk-shell structures, porous structures, and self-assembled nano/micro-structures, and discusses the relationship between the 3D architectures and sodium storage properties. Notably, the intention of constructing 3D architectures is to improve materials performance by integrating the benefits of various structures and components. The development of 3D architecture construction strategies will be essential to future SIB applications.

The inherent technical challenges of metal-air batteries (MABs), arising from the sluggish redox electrochemical reactions on the air electrode, significantly affect their efficiency and life cycle. Two-dimensional (2D) nanomaterials with near-atomic thickness have potential as bifunctional catalysts in MABs because of their distinct structures, exceptional physical properties, and tunable surface chemistries. In this study, the chemistry of representative 2D materials was elucidated, and the comprehensive analysis of the primary modification techniques, including geometric structure manipulation, defect engineering, crystal facet selection, heteroatom doping, single-atom catalyst construction, and composite material synthesis, was conducted. The correlation between material structure and activity is illustrated by examples, with the aim of leading the development of advanced catalysts in MABs. We also focus on the future of MABs from the perspective of bifunctional catalysts, definite mechanisms, and standard measurement. We expect this work to serve as a guide for the design of air electrode materials that can be used in MABs.

Niobium-tungsten oxides with tungsten bronze and confined ReO₃ crystal structures are prospective anode candidates for lithium-ion batteries since the multi-electron transfer per niobium/tungsten offers large specific capacities. To combine the merits of the two structures, porous Nb₄W₇O₃₁ microspheres constructed by nanorods are synthesized based on a facile solvothermal method. This new material contains different tungsten bronze structures and 4 × 4 ReO₃-type blocks confined by tungsten bronze matrices, generating plenty of pentagonal and quadrangular tunnels for Li⁺ storage, as confirmed by spherical-aberration-corrected scanning transmission electron microscopy. Such structural mixing enables three-dimensionally uniform and small lattice expansion/shrinkage during lithiation/delithiation, leading to good structural and cyclic stability (95.2% capacity retention over 1,500 cycles at 10C). The large interlayer spacing (~3.95 Å), coupled with the abundant pentagonal/quadrangular tunnels, results in ultra-high Li⁺ diffusion coefficients (1.24 × 10^-11 cm² s^-1 during lithiation and 1.09 × 10^-10 cm² s^-1 during delithiation) and high rate capability (10C vs. 0.1C capacity retention percentage of 47.6%). Nb₄W₇O₃₁ further exhibits a large reversible capacity (252 mAh g^-1 at 0.1C), high first-cycle Coulombic efficiency (88.4% at 0.1C), and safe operating potential (~1.66 V vs. Li/Li⁺). This comprehensive study demonstrates that the porous Nb₄W₇O₃₁ microspheres are very promising anode materials for future use in high-performance Li⁺ storage.

Electrolytic MnO₂-Zn batteries possess high energy density due to the high reduction potential and capacity of the cathode Mn²⁺/MnO₂. However, the low reversibility of the Mn²⁺/MnO₂ conversion results in a limited lifespan. In this study, we propose the utilization of VOSO₄ as a redox mediator in the MnO₂-Zn battery to facilitate the dissolution of MnO₂. Through various techniques such as electrochemical measurements, ex-situ UV-visible spectroscopy, X-ray diffraction, and scanning electron microscopes, we validate the interaction between VO²⁺ and MnO₂, which effectively mitigates the accumulation of MnO₂. The introduction of the redox mediator results in exceptional redox reversibility and outstanding cycling stability of the MnO₂/VOSO₄-Zn battery at high areal capacities, with 900 cycles at 5 mAh cm^-2 and 500 cycles at 10 mAh cm^-2. Notably, even in the flow battery device, the battery exhibits a stable cycling performance over 300 cycles at 20 mAh cm^-2. These research findings shed light on the potential large-scale application of electrolytic MnO₂-Zn batteries.

This review provides an overview of recent advancements in vapor-fed photoelectrochemical (PEC) systems specifically designed for utilizing water vapor as a hydrogen resource. The PEC system under water vapor feeding utilizes a proton exchange membrane as a solid polymer electrolyte. Additionally, it utilizes gas-diffusion photoelectrodes composed of a fibrous conductive substrate with macroporous structures. Herein, the porous photoelectrodes are composed of n-type oxides for oxygen evolution reactions and used with a Pt electrocatalyst cathode for hydrogen evolution reactions. The topics covered include the conceptual framework of vapor-fed PEC hydrogen production, strategic design of gas-phase PEC reaction interfaces, and development of porous photoanodes such as titanium dioxide (TiO₂), strontium titanate (SrTiO₃), tungsten trioxide (WO₃), and bismuth vanadate (BiVO₄). A significant enhancement in the PEC efficiency was achieved through the application of a thin proton-conducting ionomer film on these porous photoelectrodes for surface functionalization. The rational design of proton exchange membrane-based PEC cells will play a pivotal role in realizing renewable-energy-driven hydrogen production from atmospheric humidity in the air.

As a clean and efficient energy conversion device, solid oxide fuel cells have been garnering attention due to their environmentally friendly and fuel adaptability. Consequently, they have become one of the current research directions of new energy. The cathode, as the electrochemical reaction site of an oxidation atmosphere in solid oxide fuel cells, plays a key role in determining the output performance. In recent years, the development of double perovskite cathode materials with mixed ionic and electronic conductors has made significant progress in intermediate-temperature (600-800 °C) fuel cells. These materials have the potential to deliver higher power densities and improved stability, making them promising candidates for future fuel cell applications. The Fe-based double perovskite structure cathode material has gained extensive attention due to its adjustable crystal structure and performance, as it has A(A’) or B(B’) positions in its AA’BB’O₆ structure. This material has several advantages, such as high oxygen catalytic activity, low thermal expansion coefficient, and compatibility with the thermal expansion of the electrolyte. An increasing number of researchers have been exploring the performance reaction mechanism of double perovskite by modifying and adjusting its material microstructure, crystal structure, and electronic structure. In this paper, the research progress of LnBaFe₂O₅ and Sr₂Fe_2-xMo_xO₆ double perovskite cathode materials is reviewed to highlight the effects of various modification methods developed on electrochemical performance of these materials. Furthermore, the potential future research directions of double perovskite cathode materials are prospected.

An essential component of a working electrode is the conductive additive: whether it is used in very low amounts or constitutes the conductive matrix, its electrochemical response is not negligible. Commercially diffused carbon black species (i.e., Super P, Super C65, and Super C45) still lack an in-depth electrochemical characterisation in the emerging field of potassium-ion battery systems, which are on the way towards large-scale stationary storage application. Thus, this work aims to provide strong tools to discriminate their active role in such secondary cells. First, the effect of their pseudo-amorphous structure on the storage mechanism of potassium ions, which tend mainly to adsorb on their surface rather than intercalate within graphene layers, leading to a pseudocapacitive response, is discussed. Then, Dunn’s and Trasatti’s methods are considered to identify the potential ranges in which surface-dominated reactions occur, quantifying their weight at the same time. This observation is surely linked with surface properties and exposed functional groups; thus, X-ray photoelectron spectroscopy is exploited to correlate electrochemical features with both pristine and cycled surfaces of the carbon black species.

Sulfide solid electrolytes are regarded as a pivotal component for all-solid-state lithium batteries (ASSLBs) due to their inherent advantages, such as high ionic conductivity and favorable mechanical properties. However, persistent challenges related to electrochemical stability and interfacial compatibility have remained significant hurdles in their practical application. To address these issues, we propose an anion-cation co-doping strategy for the optimization of Li₇P₃S₁₁ (LPS) through chemical bonding and structural modifications. The co‐doping effects on the structural and electrochemical properties of SiO₂-, GeO₂-, and SnO₂-doped sulfide electrolytes were systematically investigated. Cations are found to preferentially substitute the P⁵⁺ of the P₂S₇^4- unit within the LPS matrix, thereby expanding the Li⁺ diffusion pathways and introducing lithium defects to facilitate ion conduction. Concurrently, oxygen ions partially substitute sulfur ions, leading to improved electrochemical stability and enhanced interfacial performance of the sulfide electrolyte. The synergistic effects resulting from the incorporation of oxides yield several advantages, including superior ionic conductivity, enhanced interfacial stability, and effective suppression of lithium dendrite formation. Consequently, the application of oxide-doped sulfide solid electrolytes in ASSLBs yields promising electrochemical performances. The cells with doped-electrolytes exhibit higher initial coulombic efficiency, superior rate capability, and cycling stability when compared to the pristine LPS. Overall, this research highlights the potential of oxide-doped sulfide solid electrolytes in the development of advanced ASSLBs.

Hydrogen, characterized by its carbon-neutral attributes and high energy density, is gaining momentum as a promising energy source. Platinum group metal (PGM) catalysts have emerged as pivotal components in water electrolysis and fuel cell technologies. However, their constrained availability and high cost impede the advancement of energy conversion systems. To address these challenges, various strategies have been explored within the realm of PGM catalysts. Particularly noteworthy are catalysts that exhibit an overlayer structure, offering exceptional catalyst utilization efficiency, bimetallic synergies, and strain-induced enhancements. Self-terminated electrodeposition (SED) stands out as a technique that enables precise atomic layer electrodeposition within an aqueous electrolyte environment. It allows meticulous control of metal loading quantities and surface coverage while operating at low temperatures and without the need for vacuum conditions. Catalysts with tailored properties achieved through SED exhibit distinct electrochemical reactivity compared to bulk catalysts, showcasing exceptional electrocatalytic activity, particularly in terms of mass and specific activity. This comprehensive review provides insights into the SED phenomenon, elucidates methodologies for fabricating PGM electrocatalysts using SED, and highlights their applications in water electrolysis and fuel cells.

Accelerants can enhance methane production in biomass energy systems. Single-component accelerants cannot satisfy the demands of anaerobic co-digestion (AcoD) to maximize overall performance. In this work, nitrogen-doped bio-based carbon derived from coconut shells, containing bimetallic Ni/Fe nanoparticles, FeNi₃ alloys, and compounds (Fe₂O₃, FeN, and Fe₃O₄), was constructed as hybrid accelerants (Ni-N-C, Fe-N-C, and Fe/Ni-N-C) to boost CH₄ production and CO₂ reduction. The cumulative biogas yield (553.65, 509.65, and 587.76 mL/g volatile solids), methane content (63.58%, 57.90%, and 67.39%), and total chemical oxygen demand degradation rate (60.15%, 54.92%, and 65.38%) of AcoD with Ni-N-C (2.625 g/L), Fe-N-C (3.500 g/L), and Fe/Ni-N-C (2.625 g/L) were higher than control (346.32 mL/g volatile solids, 40.13%, and 32.03%), respectively. These digestates with Ni-N-C, Fe-N-C, and Fe/Ni-N-C showed excellent stability (mass loss: 22.97%-32.75%) and total nutrient content (4.43%-4.61%). Based on the synergistic effects of the different components of the hybrid accelerant, an understanding of the enhanced methanogenesis of AcoD was illustrated.

In the last few decades, there has been remarkable progress in the development of solid oxide fuel cells (SOFCs) based on both traditional solid electrolyte materials and novel semiconductor membranes. However, limited attention has been given to the transition of SOFCs from oxide ion-based electrolyte membranes to semiconductor membrane devices, considering the overall perspective of materials, technology, and scientific principles. Traditional knowledge strictly dictates that semiconductors should not be used as the membrane unless these materials possess negligible electronic conduction. This is because semiconductor membrane materials typically exhibit significantly higher electrical conductivity, surpassing the inherent ionic conductivity. Interestingly, by using semiconductors as the membrane, numerous novel materials have been demonstrated in the literature, which seems difficult to understand from traditional SOFC knowledge. Therefore, there is an emerging need to summarize and explore new understanding and knowledge of materials, technology, and science of SOFCs and Semiconductor Membrane Fuel Cells and their transition. In this review, we attempted to summarize the gap between the current state of SOFCs and the advancements in new materials, technologies, scientific principles, and mechanisms driving the development of such devices.