Nowadays, increasing emissions of hazardous chemicals cause serious environmental pollution. The advanced oxidation processes (AOPs), which produce numbers of reactive oxygen species (ROS), are one of the most widely used technologies for degrading refractory pollutants in aqueous phase. Among these, Fenton reaction including both homogeneous and heterogeneous processes, has received increasing attention for water treatment. In this review, various nanomaterials with different size such as nanocrystals, nanoparticles (e.g., iron-based minerals, bimetallic oxides, zero-valent iron, quantum dots) and metal-based single atom catalysts (SACs) applied in homogeneous and heterogeneous Fenton reactions, as well as the corresponding catalytic mechanisms will be systematically summarized. Several factors including the morphology, chemical composition, geometric/electronic structures influence the catalytical behavior simultaneously. Here, the recent research advancement including the advantages and further challenges in homogeneous and heterogeneous Fenton system will be introduced in detail. Furthermore, developments for different nanomaterials, from nanocrystals, nanoparticles (minerals, bimetallic oxides represented by Fe-based catalysts, and nanosized zero valent iron materials) to SACs will be discussed. Some representative catalysts for Fenton reaction and their applications will be presented. In addition, commonly-used supports (e.g., graphene oxide, g-C₃N₄, and carbon nanotubes) and metal-organic frameworks (MOFs)/derivatives and metal-support interaction for improving Fenton-like performance will be introduced. Finally, different types of catalysts for Fenton reaction are compared and their practical application and operational costs are summarized.

Heterogeneous Fenton-like reaction shows great potential for eliminating organic substances (e.g. emerging organic contaminants (EOCs)) in water, which has been widely explored in recent decades. However, the catalytic mechanisms reported in current studies are extremely complicated because multiple mechanisms coexist and contribute to the removal efficiencies. Most importantly, heterogeneous systems show selective oxidation properties, which are crucial for improving the efficiencies in the catalytic elimination of organic substances. Thus, this critical review summarizes and compares the diverse existing mechanisms (non-radical and radical pathways) in heterogeneous catalytic processes based on recent studies. The typical oxidation mechanisms during selective advanced oxidation of EOCs were systematically discussed based on the following sections, including the selective adsorption and generation of reactive oxygen species (ROS) in photo/electron-Fenton and Fenton-like systems. Moreover, the non-radical pathways are discussed in depth by the singlet oxygen, high-valent metal-oxo, electron transfer process, etc. Moreover, the direct oxidative transfer process for the removal of EOCs was introduced in recent studies. Finally, the cost, feasibility as well as the sustainability of heterogeneous Fenton-like catalysts are summarized. This review offers useful guidance for developing suitable strategies to develop materials for decomposing the organic substrates.

Precisely designing atomic metal-nitrogen-carbon (M-N-C) catalysts with asymmetric diatomic configurations and studying their structure–activity relationships for oxygen reduction reaction (ORR) are important for zinc-air batteries (ZABs). Herein, a dual-atomic-site catalyst (DASC) with CoN₃S-MnN₂S₂ configuration was prepared for the cathodes of ZABs. Compared with Co-N-C (Mn-free) and CoMn-N-C (S-free doping), CoMn-N/S-C exhibits excellent half-wave potential (0.883 V) and turnover frequency (1.54 e·s⁻¹·site⁻¹), surpassing most of the reported state-of-the-art Pt-free ORR catalysts. The CoMn-N/S-C-based ZABs achieve extremely high specific capacity (959 mAh·g⁻¹) and good stability (350 h@5 mA·cm⁻²). Density functional theory (DFT) calculation shows that the introduction of Mn and S can break the electron configuration symmetry of the original Co 3d orbital, lower the d-band center of the Co site, and optimize the desorption behavior of *OH intermediate, thereby increasing the ORR activity.

Electrolytic water splitting (EWS) is an attractive and promising technique for the production of hydrogen energy. Nevertheless, the sluggish kinetic rate of hydrogen/oxygen evolution reactions leads to a high overpotential and low energy efficiency. Up to date, Pt/Ir-based nanocatalysts have become the state-of-the-art EWS catalysts, but disadvantages such as high cost and low earth abundance greatly limit their applications in EWS devices. As an attractive candidate for the Pt/Ir catalysts, series of Ru-based nanomaterials have aroused much attention for their low price, Pt-like hydrogen bond strength, and high EWS activity. In particular, Ru-doped functional porous materials have been becoming one of the most representative EWS catalysts, which can not only achieve the dispersion and adjustment for active Ru sites, but also simultaneously solve the problems of mass transfer and catalytic conversion in EWS. In this review, the design and preparation strategies of Ru-doped functional porous materials toward EWS in recent years are summarized, including Ru-doped metal organic frameworks (MOFs), Ru-doped porous organic polymers (POPs), and their derivatives. Meanwhile, detailed structure–activity relationships induced by the tuned geometric/electronic structures of Ru-doped functional porous materials are further depicted in this review. Last but not least, the challenges and perspectives of Ru-doped functional porous materials catalysts are reasonably proposed to provide fresh ideas for the design of Ru-based EWS catalysts.

The effective management of oxygen transport resistance (OTR) within the cathode catalyst layer (CCL) is crucial for achieving a high catalyst performance at low platinum (Pt) loading. Over the past two decades, significant advancements have been made in the development of various high active platinum-based catalysts, aiming at enhancing oxygen mass transport and the oxygen reduction reaction (ORR). However, experimental investigations of transport processes in porous media are often computational costs and restrained by limitations in in-situ measurement capabilities, as well as spatial and temporal resolution. Fortunately, numerical simulation provides a valuable alternative for unveiling the intricate relationship between local transport properties and overall cell performance that remain unresolved or uncoupled through experimental approach. In this review, we elucidate the primary experimental and numerical efforts undertaken to improve OTR. We consolidate the available literature on OTR values and perform a quantitative comparison of the effectiveness of different strategies in mitigating OTR. Furthermore, we analyze the intrinsic limitations and challenges associated with current experimental and numerical methods. Finally, we outline future prospect for advancements in both experimental techniques and modelling methods.

Single atom (SA)-embedded nitrogen-doped carbon has shown great potential in environmental remediation. Nowadays, engineered nanomaterials (ENMs) have attracted great research interests in recent years. Metal-organic framework (MOF) derived SAs show the advantages of tunable topology and averaged separated active sites. SAs bridge the gap between homogeneous and heterogeneous catalysts. The reaction efficiency can be significantly improved by designing the MOFs derived from carbon and SAs. In this review, the research advanced in MOFs-derived carbon and SAs in advanced oxidation process (AOP) in water were summarized. Major strategies to fabricate the SAs derived from MOFs were discussed, including the mixed/single metal strategy, metal-containing linker strategy, pore confinement strategy, thermal diffusion strategy, and pyrolysis MOFs with bulk metals. Advanced characterization technologies have been introduced, including electron microscopy and spectroscopic methods. To explain the catalytic mechanism for various applications, the relationship between the performance and the atomic configuration was systematically discussed. Recent applications of the MOFs derived from carbon and SAs have been summarized. A series of the latest work on effectively removing pollutants by SAs are also listed. Based on the fundamental knowledge and recent practical application of MOFs-derived carbon and SAs, some perspectives on the further directions were presented. This review offers guidance for applying novel engineered nanomaterials in the water treatment field.

Aqueous zinc-ion batteries (ZIBs) have attracted increasing attention due to their low cost and high safety. MoS₂ is a promising cathode material for aqueous ZIBs due to its favorable Zn²⁺ accommodation ability. However, the structural strain and large volume changes during intercalation/deintercalation lead to exfoliation of active materials from substrate and cause irreversible capacity fading. In this work, a highly stable cathode was developed by designing a hierarchical carbon nanosheet-confined defective MoS_x material (CNS@MoS_x). This cathode material exhibits an excellent cycling stability with high capacity retention of 88.3% and ~ 100% Coulombic efficiency after 400 cycles at 1.2 A·g⁻¹, much superior compared to bare MoS₂. Density functional theory (DFT) calculations combined with experiments illustrate that the promising electrochemical properties of CNS@MoS_x are due to the unique porous conductive structure of CNS with abundant active sites to anchor MoS_x via strong chemical bonding, enabling MoS_x to be firmly confined on the substrate. Moreover, this unique hierarchical complex structure ensures the fast migration of Zn²⁺ within MoS_x interlayer.

Developing an efficient, interface-rich, and free-standing non-noble-metal electrocatalyst is vital for the flexible zinc-air batteries (ZABs). Herein, a three-dimensional (3D) heterogeneous carbon-based flexible membrane was assembled by Co@carbon nanosheets/carbon nanotubes and hollow carbon nanofiber (Co@NS/CNT-CNF) as an efficient oxygen reduction reaction (ORR) catalyst with a positive half-wave potential of 0.846 V and a small Tafel slope of 79 mV·dec⁻¹. Meanwhile, the Co@NS/CNT-CNF electrode also exhibits excellent open-circuit voltage, peak power density, and long-time cycling stability in liquid-state ZABs (1.605 V, 163 mW·cm⁻², and 400 h) and flexible ZABs under flat/bending condition (1.47 V, 102 mW·cm⁻², and 80 h). Such heterogeneous flexible membrane architecture not only optimizes the electrolyte infiltration, but also provides capacious possibility for O₂ and electrolyte transfer. Meanwhile, work-function analyses coupled with density functional theory (DFT) results demonstrate that the electron transfer capability and metal–support interaction can be well optimized in the obtained Co@NS/CNT-CNF catalyst.

Metal-organic frameworks (MOFs), which are constructed by metal ions or clusters with organic ligands, have shown great potential in gas storage and separation, luminescence, catalysis, drug delivery, sensing, and so on. More than 20,000 MOFs have been reported by adjusting the composition and reaction conditions, and most of them were synthesized by hydrothermal or solvothermal methods. The conventional solvothermal methods are favorable for the slow crystallization of MOFs to obtain single crystals or highly crystalline powders, which are suitable for the structure analysis. However, their harsh synthesis conditions, long reaction time, and difficulty in continuous synthesis limit their scale-up in industrial production and application. Meanwhile, shaping or processing is also required to bring MOF crystals and powders into the market. Therefore, this review demonstrates the crystallization mechanisms of MOFs to understand how the synthetic parameters affect the final products. Additionally, a variety of promising synthetic routes which can be used for large scale synthesis were reviewed in details. Lastly, the prospects of MOF shaping and processing are provided to promote their industrial application.

Cobalt hydroxide nanosheet is among the most popular oxygen evolution reaction (OER) catalyst yet still suffers from sluggish catalytic kinetics, limited activity, and poor stability. Here, an efficient in situ electrochemical reconstructed CoFe-hydroxides derived OER electrocatalyst was reported. The introduction of Fe promoted the transformation of Co²⁺ into Co³⁺ in CoFe-hydroxides nanosheet, along with the formation of abundant amorphous/crystalline interfaces. Thanks for the retained nanosheet microstructure, high valence Co³⁺ and Fe³⁺ species, and the amorphous/crystalline heterostructure interfaces, the as-designed electrochemical reconstructed CoFeOOH nanosheet/Ni foam (CoFeOOHNS/NF) electrode delivers 100 mA·cm⁻² in alkaline at an overpotential of 275 mV and can stably electrocatalyze water oxidation for at least 35 h at 100 mA·cm⁻². Meanwhile, the alkaline full water splitting electrolyzer achieves a current density of 10 mA·cm⁻² only at 1.522 V for CoFeOOHNS/NF‖Pt/C/NF, which is much lower than that of Ru/C/NF‖Pt/C/NF (1.655 V@10 mA·cm⁻²). This work paves the way for in-situ synergetic modification engineering of electrochemical active components.