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Powered by optical energy, photocatalytic reduction for fuel production promises to be an ideal long-term solution to a number of key energy challenges. Photocatalysts with enhanced light absorption, fast electron/hole separation rates, and exposed activity sites are essential to improve photocatalytic efficiency. Semiconductors are constrained by their own intrinsic properties and have limited performance in photocatalysis, but defect engineering provides an opportunity to modulate the physical and chemical properties of semiconductors. Defect engineering has been shown to be effective in regulating electron distribution and accelerating photocatalytic kinetics during photocatalysis. This review introduces the definition and categorization of defects, then explains the main effects of defect engineering on photoabsorption, carrier separation/migration, and surface reduction reactions. We then review the milestones in the design of defect-engineered photocatalysts for key chemical reactions, including hydrogen evolution, CO₂ reduction, and N₂ reduction, and tabulate their respective effects on catalytic performance. Finally, we provide insights and perspectives on the challenges and potential of defect engineering for photoreduction reactions.

The complex multistep electrochemical reactions of lithium polysulfides and the solid–liquid–solid phase transformation involved in the S₈ to Li₂S reactions lead to slow redox kinetics in lithium–sulfur batteries (Li–S batteries). However, some targeted researches have proposed strategies requiring the introduction of significant additional inactive components, which can seriously affect the energy density. Whereas polymer binders, proven to be effective in suppressing shuttle effects and constraining electrode volume expansion, also have promising potential in enhancing Li–S batteries redox kinetics. Herein, a novel aqueous polymer binder is prepared by convenient amidation reaction of fully biomaterials, utilizing its inherent rich amide groups for chemisorption and redox mediating ability of thiol groups to achieve adsorption redox-mediated synergism for efficient conversion of polysulfides. Li–S batteries based on N-Acetyl-L-Cysteine-Chitosan (NACCTS) binder exhibit high initial discharge specific capacity (1260.1 ​mAh ​g⁻¹ at 0.2 ​C) and excellent cycling performance over 400 cycles (capacity decay rate of 0.018% per cycle). In addition, the batteries exhibit great areal capacity and stable capacity retention of 83.6% over 80 cycles even under high sulfur loading of 8.4 ​mg ​cm⁻². This work offers a novel perspective on the redox-mediated functional design and provides an environmentally friendly biomaterials-based aqueous binder for practical Li–S battery.

Stimuli-responsive coordination polymers (CPs) are among one of the most prolific research areas in developing the next-generation functional materials. Their capability of being accurately excited by particular external changes with pre-determined and observable/characterizable behaviors correspond, are the so called “stimuli” and “responsive”. Abundant types of CP compounds, especially metal-organic frameworks (MOFs), are of rocketing interest owing to their compositional diversity, structural tunability, and in essence their highly engineerable functionality. This present review is aimed to sketch several common types of stimulation and the corresponding responses for CPs, accompanied with the broad logic and mechanisms underneath. And further from the aspect of material revolution, some representative progresses together with the latest advances of CP-based materials in various fields are covered in attempt to display a broader picture towards the possible prospects of this topic.

With the proposal of a “smart battery,” real-time sensing by rechargeable batteries has become progressively more important in both fundamental research and practical applications. However, many traditional sensing technologies suffer from low sensitivity, large size, and electromagnetic interference problems, rendering them unusable in the harsh and complicated electrochemical environments of batteries. The optical sensor is an alternative approach to realize multiple-parameter, multiple-point measurements simultaneously. Thus, it has garnered significant attention. Through analyzing these measured parameters, the state of interest can be decoded to monitor a battery's health. This review summarizes current progress in optical sensing techniques for batteries with respect to various sensing parameters, discussing the current limitations of optical fiber sensors as well as directions for their future development.

Devising a desirable nano-heterostructured photoelectrode based on the charge transfer kinetics mechanism is a pivotal strategy for implementing efficient photoelectrocatalytic (PEC) technology, since the charge separation and utilization efficiency of a photoelectrode is critical to its PEC performance. Herein, we fabricate a F–Co₃O₄@Bi₂WO₆ core–shell hetero-array photoanode by coupling Bi₂WO₆ nanosheets with F–Co₃O₄ nanowires using a simple solvothermal solution method. The three-dimensional hierarchical heterostructure has a homogeneous chemical interface, helping it to promote an S-scheme-based carrier transport kinetics and maintain excellent cycling stability. Charge density difference calculations verify the electron migration trend from F–Co₃O₄ to Bi₂WO₆ upon hybridization and the formation of an internal electric field in the heterojunction, consistent with the S-scheme mechanism, which is identified by in situ irradiation X-ray photoelectron spectroscopy and by ultraviolet photoelectron spectroscopy. The optimized F–Co₃O₄@Bi₂WO₆-2 photoelectrode achieves high carrier utilization efficiency and exhibits superior PEC degradation performance for various organic pollutants, including reactive brilliant blue KN-R, rhodamine B, sulfamethoxazole, and bisphenol A. This work not only reveals that F–Co₃O₄@Bi₂WO₆-2 is effective for PEC water remediation but also provides a strategy to enhance carrier transport kinetics by designing binary oxides.

Five-membered pyrroline nitroxides with high-potential is fascinating as catholyte for aqueous organic redox flow batteries (AORFBs), however, it suffers from a primary deficiency of insufficient stability due to ring-opening side reaction. Herein we report a spatial structure regulation strategy by host-guest chemistry, encapsulating 3-carbamoyl-2,2,5,5-tetramethylpyrroline-1-oxyl (CPL) into hydrosoluble cyclodextrins (CDs) with an inclusion structure of N–O· head towards cavity bottom, to boost the solubility and cyclability of pyrroline nitroxides significantly. The armor-clad CPL (CPL⊂HP-β-CD) catholyte in 0.05–0.5 ​M presents a battery capacity fade rate as low as 0.002 ​%/cycle (0.233 ​%/day) compared to the sole CPL in 0.05 ​M (0.039 ​%/cycle or 5.23 ​%/day) over 500 cycles in assembled AORFBs. The optimized reclining spatial structure with N–O· head towards CD cavity bottom effectively inhibits the attack of Lewis base species on the hydrogen abstraction site in pyrroline ring, and thus avoids the ring-opening side reaction of pyrroline nitroxides.

Sodium-ion batteries (SIBs) are regarded as the most promising technology for large-scale energy storage systems. However, the practical application of SIBs is still hindered by the lack of applicable cathode materials. Herein, a novel phase-pure polyanionic Na₈Fe₅(SO₄)₉ is designed and employed as a cathode material for SIBs for the first time. The Na₈Fe₅(SO₄)₉ has an alluaudite-type sulfate framework and small Na⁺ ion diffusion barriers. As expected, the as-synthesized Na₈Fe₅(SO₄)₉@rGO exhibits a high working potential of 3.8 ​V (versus Na/Na⁺), a superior reversible capacity of 100.2 mAh g⁻¹ at 0.2 ​C, excellent rate performance (∼80 mAh g⁻¹ at 10 ​C, ∼63 mAh g⁻¹ at 50 ​C), and an ultra-long cycling life (91.9% capacity retention after 10,000 cycles at 10 ​C, 81% capacity retention after 20,000 cycles at 50 ​C). We use various techniques and computational methods to comprehensively investigate the electrochemical reaction mechanisms of Na₈Fe₅(SO₄)₉@rGO.

Integrating lithium metal anodes with polymer electrolytes is a promising technology for the next generation high-energy-density rechargeable batteries. As the progress is often hindered by the dendrite growth upon cycling, quantifying three-dimensional (3D) microstructures of dendrites in polymer electrolytes is essential to better understanding of dendrite formation for the development of mitigation strategies. Techniques for 3D quantification and visualization of dendrites, especially those with low Li contents, are rather limited. This study reports quantitative measurements of the spatial distribution of Li dendrites grown in solid polymer electrolytes using 3D tomographic neutron depth profiling (NDP) with improved spatial resolution, compositional range, and data presentation. Data reveal heterogeneous distribution of Li over length scales from tens nanometers to centimeters. While most dendrites grow from the plating toward the stripping electrode with dwindling Li quantities, dendrites apparently grown from the Li-stripping electrode are also observed. The discovery is only possibly due to the unique combination of the high specificity and high sensitivity of the neutron activation analysis of Li isotope.

This review describes recent advances in wettability adjustment to improve the main green energy conversion and storage systems, i.e., photocatalysis and electrocatalysis. Because both are redox reactions involving electron behavior, they follow a similar pattern in the surface reaction step, which is related to wettability adjustment. Thus, we consider photocatalysis and electrocatalysis together in terms of mass transfer adjustment based on commonalities, aiming to understand the fundamentals more deeply and bring greater mutual inspiration to photocatalysis and electrocatalysis. The theoretical basis is first laid out, and then various strategies are introduced. Subsequently, according to the different requirements of mass transfer, we classify the photocatalytic and electrocatalytic reactions into gas consumption reactions preferring hydrophobic surfaces, and gas evolution reactions preferring hydrophilic surfaces. Pollutant degradation reactions involving different water-soluble substrates are also mentioned. Further, we introduce the specific optimization effect of wettability regulation on the reaction, and the mechanism behind the effect. This comprehensive and insightful review will provide a strategic guide to the reasonable design and development of wettability-optimized photocatalytic and electrocatalytic systems.