A Review of In-Situ Techniques for Probing Active Sites and Mechanisms of Electrocatalytic Oxygen Reduction Reactions

Emerging Trends in Two-Dimensional Nanomaterials for Electrocatalytic Nitrate-to-Ammonia Conversion

Electrocatalytic nitrate reduction to ammonia (ENRA) has emerged as a promising strategy due to its dual functionality in wastewater treatment and sustainable ammonia synthesis. Two-dimensional (2D) nanomaterials offer the exposure of highly active sites, tunability of the electronic structure, and enhanced mass transfer capabilities, thereby optimizing the atomic-scale kinetics of the nitrate reduction reaction and improving the ammonia synthesis efficiency. This review provides a comprehensive overview of recent advances in the field of 2D nanomaterials. Initially, fundamental mechanisms are examined. Subsequently, the paper explores the advantages of 2D materials, including metallic variants (e.g., metals, metal oxides, metal hydroxides, metal carbides, metal nitrides, metal borides, and 2D-confined single-atom catalysts) as well as 2D nonmetallic materials, focusing on their roles in nitrate activation and proton-coupled electron transfer processes. Finally, this review provides a prospective development of 2D catalysts, addressing the challenges related to long-term stability under industrial-grade current densities and outlining potential avenues for future research in this area.

Identifying In Situ Activity and Selectivity of Oxygen Reduction Catalysts at the Subparticle Level

Oxygen reduction reaction (ORR) plays a crucial role in both the chemical and energy industries. Despite substantial advancements in theoretical, computational, and experimental studies, identifying both the in situ activity and selectivity in ORR electrocatalysis remains a major challenge. Here, using a suite of correlative operando scanning electrochemical probe and electrochemiluminescence microscopy techniques, we establish a link between the morphological structure and the local ORR activity and selectivity of single Au and Au@Pt platelets at the subparticle level. It is clearly shown that the edge facets of Au and Au@Pt platelets exhibit higher activity for 4e- ORR compared to basal planes, whereas the basal planes of both Au and Au@Pt platelets demonstrate superior 2e- selectivity relative to the edge facets. These findings deepen our understanding of ORR activity and selectivity across different facets at the subparticle level, which offers valuable guidance for the rational design of highly efficient ORR electrocatalysts.

Unveiling an In Situ H2O2 Production: Rechargeable Zinc-H2O2 Battery Powering 26 LEDs

Looking toward ever-growing energy demand, the advancement in energy storage devices and carrying out electrocatalytic reactions in an efficient way is the need of the hour. Herein, we have employed the two birds-one stone approach, viz. fusing energy conversion and storing system enabling 2e- oxygen reduction reaction (ORR) to value-added hydrogen peroxide (H2O2) product and its utilization in the energy storage devices using MnWO4 catalyst, without any external H2O2 source. The designed catalyst exhibited a remarkable H2O2 production of 98% @ 0.37 V versus RHE. The real-time H2O2 production was monitored by in-situ electrochemical Raman and in-situ infrared spectroscopic measurements. The pivotal influence of electrolyte composition, viz. local pH and the formation of carbonate species on H₂O₂ production was meticulously examined through micro-electrochemical studies using gold (Au) microelectrodes. Further, we have explored an aqueous rechargeable Zn-H2O2 battery utilizing MnWO4 as bifunctional electrocatalyst for sustainable H2O2 production simultaneously producing the electricity. The Zn-H2O2 battery exhibited a remarkable cycle life of 136 h and an practical energy efficiency of 43%. The galvanostatic charge-discharge measurement of Zn-H2O2 battery attained a capacity of 25 mAh cm-2 at 3 mA cm-2. The battery also demonstrated ≥90% cycle efficiency. Interestingly, the designed Zn-H2O2 battery (two connected in series) exhibited a stable open circuit voltage (OCV) with a promising power density of 10.5 mW cm-2. As a proof of concept, we have demonstrated Zn-H2O2 batteries by powering 26 blue LEDs for more than 180 h (7 days) without fading in the illumination of LEDs.

Valorizing Nitrate in Electrochemical Nitrogen Cycling: Copper-Based Catalysts from Reduction to C-N Coupling

Electrochemical nitrate reduction (NO3RR) offers a sustainable approach to mitigating nitrogen pollution while enabling the resourceful conversion of nitrate (NO3 -) into ammonia (NH3), nitrogen gas (N2), and value-added chemicals such as urea. Copper (Cu)-based catalysts, with their versatile catalytic properties and cost-effectiveness, have emerged as pivotal materials in advancing NO3RR. This review systematically summarizes recent progress in Cu-based catalysts for NO3RR, focusing on their catalytic mechanisms, tuning strategies, and applications across diverse product pathways. The intrinsic self-reconstruction behavior and synergistic effects of Cu-based catalysts are elucidated alongside advanced in situ characterization techniques that reveal dynamic structural evolution and intermediate interactions during reactions. We comprehensively discuss the performance of Cu-based catalysts in steering NO3RR toward NH3 or N2 production, emphasizing the role of catalyst design (e.g., single atoms, alloys, oxides, hydroxides) in enhancing selectivity and efficiency. Furthermore, the multifunctionality of Cu catalysts is exemplified through carbon-nitrogen (C-N) coupling reactions, where reactive nitrogen intermediates are valorized into urea. Key challenges and future directions are outlined to guide the rational design of Cu-based systems for efficient electrochemical nitrogen cycling.

Destabilization of Single-Atom Catalysts: Characterization, Mechanisms, and Regeneration Strategies

Numerous in situ characterization studies have focused on revealing the catalytic mechanisms of single-atom catalysts (SACs), providing a theoretical basis for their rational design. Although research is relatively limited, the stability of SACs under long-term operating conditions is equally important and a prerequisite for their real-world energy applications, such as fuel cells and water electrolyzers. Recently, there has been a rise in in situ characterization studies on the destabilization and regeneration of SACs; however, timely and comprehensive summaries that provide the catalysis community with valuable insights and research directions are still lacking. This review summarizes recent advances in the destabilization mechanisms and regeneration strategies of SACs, specifically highlighting various state-of-the-art characterization techniques employed in the studies. The factors that induce destabilization in SACs are identified by discussing the failure of active sites, coordination environments, supports, and reaction conditions under long-term operating scenarios. Next, the primary regeneration strategies for SACs are introduced, including redispersion, surface poison desorption, and exposure of subsurface active sites. Additionally, the advantages and limitations of both in situ and ex situ characterization techniques are discussed. Finally, future research directions are proposed, aimed at constructing structure-stability relationships and guiding the design of more stable SACs.

Built-in electric field guides oxygen evolution electrocatalyst reconstruction

Creating a built-in electric field (BIEF) in catalysts represents an effective strategy to promote electron transfer and induce asymmetric charge distribution, thereby facilitating surface dynamic reconstruction under oxygen evolution reaction (OER) conditions. This review summarizes recent advancements in the field of OER electrocatalysts, with a focus on regulating the work function of components to tailor the BIEFs to guide surface reconstruction processes. It also discusses the importance of surface reconstruction in improving electrocatalytic performance and the influence of BIEFs on the reconstruction of catalysts. By analyzing various strategies for manipulating electric fields for guiding surface reconstruction of OER electrocatalysts, along with numerous representative examples, this review highlights how these techniques can enhance catalytic activity and stability. The findings underscore the potential of engineered BIEFs as a powerful tool in the design of next-generation electrocatalysts, paving the way for more efficient energy conversion technologies.

Three-dimensional porous structured cobalt- and nitrogen-doped carbon nanotube electrocatalyst derived from cobalt-based zeolitic imidazolate framework nanoleaves for high performance zinc-air battery

The development of efficient and cost-effective electrocatalysts to overcome the intrinsic sluggish kinetics of the oxygen reduction reaction (ORR) in zinc-air batteries is crucial. In this study, we introduce a strategy that integrates a template-assisted synthesis with subsequent thermal treatment to fabricate an active and stable cobalt-based nitrogen-doped carbon electrocatalyst, denoted as Co-N-CNT. The strategy adjusts the disordered architecture of the zeolitic imidazolate framework (ZIF) through the synergistic effect of bimetallic species, restricted the growth of zeolitic imidazolate framework nanoleaves (ZIF-L) using salt templates, and directed the transformation from a two-dimensional blade-like morphology to a three-dimensional multi-tiered composite structure. Notably, the Co-N-CNT-800 sample, synthesized at an optimized pyrolysis temperature of 800 °C, exhibits a half-wave potential of 0.89 V and demonstrates stability with sustained cycling over 21 h, which is comparable to the performance of commercial Pt/C electrocatalysts. Moreover, when employed as the cathode in zinc-air batteries, Co-N-CNT-800 not only surpasses Pt/C in terms of power density but also exhibits long-term charge/discharge stability. This findings offer a viable pathway for the design of active and cost-effective ORR electrocatalysts, holding promise for applications in the electrochemical energy storage and conversion systems.

"Straw in the Clay Soil" Strategy: Anticarbon Corrosive Fluorine-Decorated Graphene Nanoribbons@CNT Composite for Long-Term PEMFC

Carbon corrosion poses a significant challenge in polymer electrolyte membrane fuel cells (PEMFCs), leading to reduced cell performance due to catalyst layer degradation and catalyst detachment from electrodes. A promising approach to address this issue involves incorporating an anticorrosive carbon material into the oxygen reduction reaction (ORR) electrode, even in small quantities (≈3 wt% in electrode). Herein, the successful synthesis of fluorine-doped graphene nanoribbons (F-GNR) incorporated with graphitic carbon nanotubes (F-GNR@CNT), demonstrating robust resistance to carbon corrosion is reported. By controlling the synthesis conditions using an exfoliation method, the properties of the composite are tailored. Electronic structural studies, employing density functional theory (DFT) calculations, to elucidate the roles of fluorine dopants and graphitic carbon nanotubes (CNTs) in mitigating carbon corrosion are conducted. Physicochemical and electrochemical characterization of F-GNR@CNT reveal its effectiveness as a cathode additive at the single-cell scale. The addition of F-GNR@CNT to the Pt/C cathode improves durability by enhancing carbon corrosion resistance and water management, thus mitigating the flooding effect through tailored surface properties. Furthermore, advanced impedance analysis using a transmission line model is performed to gain insights into the internal resistance and capacitive properties of electrode structure.

Structure-Activity Relationships in Oxygen Electrocatalysis

Oxygen electrocatalysis, as the pivotal circle of many green energy technologies, sets off a worldwide research boom in full swing, while its large kinetic obstacles require remarkable catalysts to break through. Here, based on summarizing reaction mechanisms and in situ characterizations, the structure-activity relationships of oxygen electrocatalysts are emphatically overviewed, including the influence of geometric morphology and chemical structures on the electrocatalytic performances. Subsequently, experimental/theoretical research is combined with device applications to comprehensively summarize the cutting-edge oxygen electrocatalysts according to various material categories. Finally, future challenges are forecasted from the perspective of catalyst development and device applications, favoring researchers to promote the industrialization of oxygen electrocatalysis at an early date.

Synergistic Effect of P and Co Dual Doping Endows CuNi with High-Performance Hydrogen Evolution Reaction

The rational design of highly active and durable non-noble electrocatalysts for hydrogen evolution reaction (HER) is significantly important but technically challenging. Herein, a phosphor and cobalt dual doped copper-nickel alloy (P, Co-CuNi) electrocatalyst with high-efficient HER performance is prepared by one-step electrodeposition method and reported for the first time. As a result, P, Co-CuNi only requires an ultralow overpotential of 56 mV to drive the current density of 10 mA cm-2, with remarkable stability for over 360 h, surpassing most previously reported transition metal-based materials. It is discovered that the P doping can simultaneously increase the electrical conductivity and enhance the corrosion resistance, while the introduction of Co can precisely modulate the sub-nanosheets morphology to expose more accessible active sites. Moreover, XPS, UPS, and DFT calculations reveal that the synergistic effect of different dopants can achieve the most optimal electronic structure around Cu and Ni, causing a down-shifted d-band center, which reduces the hydrogen desorption free energy of the rate-determining step (H2O + e- + H* → H2 + OH-) and consequently enhances the intrinsic activity. This work provides a new cognition toward the development of excellent activity and stability HER electrocatalysts and spurs future study for other NiCu-based alloy materials.

Dynamic Active Sites in Electrocatalysis

In-depth understanding of the real-time behaviors of active sites during electrocatalysis is essential for the advancement of sustainable energy conversion. Recently, the concept of dynamic active sites has been recognized as a potent approach for creating self-adaptive electrocatalysts that can address a variety of electrocatalytic reactions, outperforming traditional electrocatalysts with static active sites. Nonetheless, the comprehension of the underlying principles that guide the engineering of dynamic active sites is presently insufficient. In this review, we systematically analyze the fundamentals of dynamic active sites for electrocatalysis and consider important future directions for this emerging field. We reveal that dynamic behaviors and reversibility are two crucial factors that influence electrocatalytic performance. By reviewing recent advances in dynamic active sites, we conclude that implementing dynamic electrocatalysis through variable reaction environments, correlating the model of dynamic evolution with catalytic properties, and developing localized and ultrafast in situ/operando techniques are keys to designing high-performance dynamic electrocatalysts. This review paves the way to the development of the next-generation electrocatalyst and the universal theory for both dynamic and static active sites.

Advances and challenges in MXene-based electrocatalysts: unlocking the potential for sustainable energy conversion

MXenes, a novel class of two-dimensional materials, have garnered significant attention for their promising electrocatalytic properties in various energy conversion applications such as water splitting, fuel cells, metal-air batteries, and nitrogen reduction reactions. Their excellent electrical conductivity, high specific surface area, and versatile surface chemistry enable exceptional catalytic performance. This review highlights recent advancements in the design and application strategies of MXenes as electrocatalysts, focusing on key reactions including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and nitrogen reduction reaction (NRR). We discuss the tunability of MXenes' layered structures and surface properties through surface modification, MXene lattice substitution, defect and morphology engineering, and heterostructure construction. Despite the considerable progress, MXenes face challenges such as restacking during catalysis, stability issues, and difficulties in large-scale production. Addressing these challenges through innovative engineering approaches and advancing industrial synthesis techniques is crucial for the broader application of MXene-based materials. Our review underscores the potential of MXenes in transforming electrocatalytic processes and highlights future research directions to optimize their catalytic efficiency and stability.

Coupling Cu Coordination Polymers with CdS Forming an S-Scheme Heterojunction for Rapid Charge Separation and High Photocatalytic Activity

Energy and the environment are significant impacting factors for the future development of humankind. In order to improve the corrosion resistance of CdS and decrease the recombination of photogenerated carriers, a novel Cu-CPs@CdS heterojunction with high efficiency mesopores was constructed by a simple hydrothermal method. The effective interfacial contact formation between nano-CdS and Cu-CPs promotes the transfer of photogenerated carriers while exhibiting a high spatial separation rate of charges. The photocatalytic performance of the heterojunction was evaluated by the photocatalytic degradation of organic pollutants and photocatalytic hydrogen generation. The photocatalytic degradation of ciprofloxacin (CIP) could reach 90.34%, and the hydrogen generation was high as 9227.82 μmol·g-1 under simulated sunlight irradiation. The boosted photocatalytic activity of Cu-CPs@CdS results from (i) the formation of coordination bonds, which not only enhanced the stability of heterojunctions but also provided a path for photogenerated carrier migration, (ii) integrating Cu-CPs, which provided more active sites, and (iii) the matched energy band structure between CdS and Cu-CPs that promoted speedy S-scheme interfacial charge-transfer pathways, culminating in efficient photogenerated charge separation and transfer. This research offered a fresh tactic to restrict photocorrosion and enhance the production of photocatalytic H2 over CdS-based catalysts.

Recent development and applications of differential electrochemical mass spectrometry in emerging energy conversion and storage solutions

Electrochemical energy conversion and storage are playing an increasingly important role in shaping the sustainable future. Differential electrochemical mass spectrometry (DEMS) offers an operando and cost-effective tool to monitor the evolution of gaseous/volatile intermediates and products during these processes. It can deliver potential-, time-, mass- and space-resolved signals which facilitate the understanding of reaction kinetics. In this review, we show the latest developments and applications of DEMS in various energy-related electrochemical reactions from three distinct perspectives. (I) What is DEMS addresses the working principles and key components of DEMS, highlighting the new and distinct instrumental configurations for different applications. (II) How to use DEMS tackles practical matters including the electrochemical test protocols, quantification of both potential and mass signals, and error analysis. (III) Where to apply DEMS is the focus of this review, dealing with concrete examples and unique values of DEMS studies in both energy conversion applications (CO2 reduction, water electrolysis, carbon corrosion, N-related catalysis, electrosynthesis, fuel cells, photo-electrocatalysis and beyond) and energy storage applications (Li-ion batteries and beyond, metal-air batteries, supercapacitors and flow batteries). The recent development of DEMS-hyphenated techniques and the outlook of the DEMS technique are discussed at the end. As DEMS celebrates its 40th anniversary in 2024, we hope this review can offer electrochemistry researchers a comprehensive understanding of the latest developments of DEMS and will inspire them to tackle emerging scientific questions using DEMS.

Recent advances in catalyst design, performance, and challenges of metal-heteroatom-co-doped biochar as peroxymonosulfate activator for environmental remediation

The escalation of global water pollution due to emerging pollutants has gained significant attention. To address this issue, catalytic peroxymonosulfate (PMS) activation technology has emerged as a promising treatment approach for effectively decontaminating a wide range of pollutants. Recently, modified biochar has become an increasingly attractive as PMS activator. Metal-heteroatom-co-doped biochar (MH-BC) has emerged as a promising catalyst that can provide enhanced performance over heteroatom-doped and metal-doped biochar due to the synergism between metal and heteroatom in promoting PMS activation. Therefore, this review aims to discuss the fabrication pathways (i.e., internal vs external doping and pre-vs post-modification) and key parameters (i.e., source of precursors, synthesis methods, and synthesis conditions) affecting the performance of MH-BC as PMS activator. Subsequently, an overview of all the possible PMS activation pathways by MH-BC is provided. Subsequently, Also, the detection, identification, and quantification of several reactive species (such as, •OH, SO4•-, O2•-, 1O2, and high valent oxo species) generated in the catalytic PMS system by MH-BC are also evaluated. Lastly, the underlying challenges associated with poor stability, the lack of understanding regarding the interaction between metal and heteroatom during PMS activation and quantification of radicals in multi-ROS system are also deliberated.

Catalytically Active Carbon for Oxygen Reduction Reaction in Energy Conversion: Recent Advances and Future Perspectives

The shortage and unevenness of fossil energy sources are affecting the development and progress of human civilization. The technology of efficiently converting material resources into energy for utilization and storage is attracting the attention of researchers. Environmentally friendly biomass materials are a treasure to drive the development of new-generation energy sources. Electrochemical theory is used to efficiently convert the chemical energy of chemical substances into electrical energy. In recent years, significant progress has been made in the development of green and economical electrocatalysts for oxygen reduction reaction (ORR). Although many reviews have been reported around the application of biomass-derived catalytically active carbon (CAC) catalysts in ORR, these reviews have only selected a single/partial topic (including synthesis and preparation of catalysts from different sources, structural optimization, or performance enhancement methods based on CAC catalysts, and application of biomass-derived CACs) for discussion. There is no review that systematically addresses the latest progress in the synthesis, performance enhancement, and applications related to biomass-derived CAC-based oxygen reduction electrocatalysts synchronously. This review fills the gap by providing a timely and comprehensive review and summary from the following sections: the exposition of the basic catalytic principles of ORR, the summary of the chemical composition and structural properties of various types of biomass, the analysis of traditional and the latest popular biomass-derived CAC synthesis methods and optimization strategies, and the summary of the practical applications of biomass-derived CAC-based oxidative reduction electrocatalysts. This review provides a comprehensive summary of the latest advances to provide research directions and design ideas for the development of catalyst synthesis/optimization and contributes to the industrialization of biomass-derived CAC electrocatalysis and electric energy storage.

Covalent Organic Frameworks Based Electrocatalysts for Two-Electron Oxygen Reduction Reaction: Design Principles, Recent Advances, and Perspective

Hydrogen peroxide (H2O2) is an environmentally friendly oxidant with a wide range of applications, and the two-electron pathway (2e-) of the oxygen reduction reaction (ORR) for H2O2 production has attracted much attention due to its eco-friendly nature and operational simplicity in contrast to the conventional anthraquinone process. The challenge is to design electrocatalysts with high activity and selectivity and to understand their structure-activity relationship and catalytic mechanism in the ORR process. Covalent organic frameworks (COFs) provide an efficient template for the construction of highly efficient electrocatalysts due to their designable structure, excellent stability, and controllable porosity. This review firstly outlines the design principles of COFs, including the selection of metallic and nonmetallic active sites, the modulation of the electronic structure of the active sites, and the dimensionality modulation of the COFs, to provide guidance for improving the production performance of H2O2. Subsequently, representative results are summarized in terms of both metallic and metal-free sites to follow the latest progress. Moreover, the challenges and perspectives of 2e- ORR electrocatalysts based on COFs are discussed.

Second-Shell N Dopants Regulate Acidic O2 Reduction Pathways on Isolated Pt Sites

Pt is a well-known benchmark catalyst in the acidic oxygen reduction reaction (ORR) that drives electrochemical O2-to-H2O conversion with maximum chemical energy-to-electricity efficiency. Once dispersing bulk Pt into isolated single atoms, however, the preferential ORR pathway remains a long-standing controversy due to their complex local coordination environment and diverse site density over substrates. Herein, using a set of carbon nanotube supported Pt-N-C single-atom catalysts, we demonstrate how the neighboring N dopants regulate the electronic structure of the Pt central atom and thus steer the ORR selectivity; that is, the O2-to-H2O2 conversion selectivity can be tailored from 10% to 85% at 0.3 V versus reversible hydrogen electrode. Moreover, via a comprehensive X-ray-radiated spectroscopy and shell-isolated nanoparticle-enhanced Raman spectroscopy analysis coupled with theoretical modeling, we reveal that a dominant pyridinic- and pyrrolic-N coordination within the first shell of Pt-N-C motifs favors the 4e- ORR, whereas the introduction of a second-shell graphitic-N dopant weakens *OOH binding on neighboring Pt sites and gives rise to a dominant 2e- ORR. These findings underscore the importance of the chemical environment effect for steering the electrochemical performance of single-atom catalysts.

Surface reconstruction in amorphous CoFe-based hydroxides/crystalline phosphide heterostructure for accelerated saline water electrolysis

Developing electrocatalysts with high activity and robust performance for large-scale seawater electrolysis to produce hydrogen holds immense significance. Herein, a highly active bifunctional electrode composed of amorphous cobalt-iron layered double hydroxides (CoFeLDH) and crystalline nickel phosphide (Ni2P) (denoted as CoFeLDH@Ni2P), is employed to boost hydrogen production through seawater electrolysis. The strong interface coupling effectively modifies the electronic structure at active sites, thereby accelerating the catalytic reaction kinetics. Impressively, in situ Raman and post-stability analyses demonstrate a unique reconstruction behavior on the CoFeLDH@Ni2P electrode. Bimetal co-incorporated NiOOH (CoFe-NiOOH) and Ni(OH)2 species are formed during the oxygen evolution reaction (OER), while CoFeLDH@Ni2P can transform into Ni(OH)2 species during the hydrogen evolution reaction (HER) process. Furthermore, the highly negatively charged surface selectively rejects Cl- ions by formed PO43-, endowing CoFeLDH@Ni2P with excellent tolerance and promising durability in saline electrolytes. Consequently, the CoFeLDH@Ni2P electrode exhibits an overpotential of 106 mV for HER at 10 mA cm-2 and 308 mV for OER to achieve 100 mA cm-2 in 1.0 M KOH solution. Additionally, the CoFeLDH@Ni2P(+,-) electrolyzer requires a low cell voltage of 1.56 V to deliver 10 mA cm-2 in 1.0 M KOH + Seasalt. This work presents an appealing strategy for the rational design of advanced electrocatalysts with amorphous-crystalline interfaces, which reveals the source of the activity of transition-metal phosphating compounds in saline water electrolysis.

A review of neuroimaging-based data-driven approach for Alzheimer's disease heterogeneity analysis

Alzheimer's disease (AD) is a complex form of dementia and due to its high phenotypic variability, its diagnosis and monitoring can be quite challenging. Biomarkers play a crucial role in AD diagnosis and monitoring, but interpreting these biomarkers can be problematic due to their spatial and temporal heterogeneity. Therefore, researchers are increasingly turning to imaging-based biomarkers that employ data-driven computational approaches to examine the heterogeneity of AD. In this comprehensive review article, we aim to provide health professionals with a comprehensive view of past applications of data-driven computational approaches in studying AD heterogeneity and planning future research directions. We first define and offer basic insights into different categories of heterogeneity analysis, including spatial heterogeneity, temporal heterogeneity, and spatial-temporal heterogeneity. Then, we scrutinize 22 articles relating to spatial heterogeneity, 14 articles relating to temporal heterogeneity, and five articles relating to spatial-temporal heterogeneity, highlighting the strengths and limitations of these strategies. Furthermore, we discuss the importance of understanding spatial heterogeneity in AD subtypes and their clinical manifestations, biomarkers for abnormal orderings and AD stages, the recent advancements in spatial-temporal heterogeneity analysis for AD, and the emerging role of omics data integration in advancing personalized diagnosis and treatment for AD patients. By emphasizing the significance of understanding AD heterogeneity, we hope to stimulate further research in this field to facilitate the development of personalized interventions for AD patients.

Component-controlled synthesis of PdxSny nanocrystals on carbon nanotubes as advanced electrocatalysts for oxygen reduction reaction

Pd-based bimetallic or multimetallic nanocrystals are considered to be potential electrocatalysts for cathodic oxygen reduction reaction (ORR) in fuel cells. Although much advance has been made, the synthesis of component-controlled Pd-Sn alloy nanocrystals or corresponding nanohybrids is still challenging, and the electrocatalytic ORR properties are not fully explored. Herein, component-controlled synthesis of PdxSny nanocrystals (including Pd3Sn, Pd2Sn, Pd3Sn2, and PdSn) has been realized, which are in situ grown or deposited on pre-treated multi-walled carbon nanotubes (CNTs) to form well-coupled nanohybrids (NHs) by a facile one-pot non-hydrolytic system thermolysis method. In alkaline media, all the resultant PdxSny/CNTs NHs are effective at catalyzing ORR. Among them, the Pd3Sn/CNTs NHs exhibit the best catalytic activity with the half-wave potential of 0.85 V (vs. RHE), good cyclic stability, and excellent methanol-tolerant capability due to the suited Pd-Sn alloy component and its strong interaction or efficient electronic coupling with CNTs. This work is conducive to the advancement of Pd-based nanoalloy catalysts by combining component engineering and a hybridization strategy and promoting their application in clean energy devices.

Modified separators boost polysulfides adsorption-catalysis in lithium-sulfur batteries from Ni@Co hetero-nanocrystals into CNT-porous carbon dual frameworks

In this manuscript, nickel/cobalt bimetallic nanocrystals confining into three-dimensional interpenetrating dual-carbon conductive structure (NiCo@C/CNTs) were successfully manufactured by annealing its core-shell structure (Ni-ZIF-67@ZIF-8) precursor under the high temperature. The results presented that the bimetallic nickel and cobalt nanocrystals with superior catalytic activity could quickly convert solid Li2S/Li2S2into soluble LiPSs and effectively decrease the energy barrier. While the hierarchical CNT-porous carbon dual frameworks can provide quick electron/ion transport because of their large specific surface area and the exposure of enough active sites. When used as the separator modifier for lithium sulfur batteries, the battery properties were significantly improved with high specific capacity, outstanding rate capability, and long-term cycle stability. Specifically, its initial specific capacity can achieve to 1038.51 mAh g-1 at 0.5C. At the high rate of 3C, it still delivers satisfactory discharge capacity of 555 mAhg-1 and the capacity decay rate is only 0.065% per cycle after 1000 cycles at 1C. Furthermore, even exposed to heavy sulfur loading (3.61 mg/cm2), they still maintain promising cycle stability. Therefore, such kinds of MOFs derivative with powerful chemical immobilization and catalytic conversion for polysulfides provides a novel guidance for the modification separator and the potential application in the field of high-performance Li-S batteries.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Metalation of functionalized benzoquinoline-linked COFs for electrocatalytic oxygen reduction and lithium-sulfur batteries

It is worthwhile to explore and develop multifunctional composites with unique advantages for energy conversion and utilization. Post-synthetic modification (PSM) strategies can endow novel properties to already excellent covalent organic frameworks (COFs). In this study, we prepared a range of COF-based composites via a multi-step PSM strategy. COF-Ph-OH was acquired by demethylation between anhydrous BBr3 and - OMe, and then, M@COF-Ph-OH was further obtained by forming the N - M - O structure. COF-Ph-OH exhibited a 2e--dominated oxygen reduction reaction (ORR) pathway with high H2O2 selectivity, while M@COF-Ph-OH exhibited a 4e--dominated ORR pathway with low H2O2 selectivity, which was due to the introduction of a metal salt with a d electron structure that facilitated the acquisition of electrons and changed the adsorption energy of the reaction intermediate (*OOH). It was proven that the d electron structure was effective at regulating the reaction pathway of the electrocatalytic ORR. Moreover, Co@COF-Ph-OH showed better 4e- ORR properties than Fe@COF-Ph-OH and Ni@COF-Ph-OH. In addition, compared with the other sulfur-impregnated COF-based composites examined in this study, S-Co@COF-Ph-OH had a larger initial capacity, a weaker impedance, and a stronger cycling durability in Li-S batteries, which was attributed to the unique porous structure ensuring high sulfur utilization, the loaded cobalt accelerating LiPS electrostatic adsorption and promoting LiPS catalytic conversion, and the benzoquinoline ring structure being ultra-stable. This work offers not only a rational and feasible strategy for the synthesis of multifunctional COF-based composites, but also promotes their application in electrochemistry.

Engineering Fe-N4 Electronic Structure with Adjacent Co-N2C2 and Co Nanoclusters on Carbon Nanotubes for Efficient Oxygen Electrocatalysis

Regulating the local configuration of atomically dispersed transition-metal atom catalysts is the key to oxygen electrocatalysis performance enhancement. Unlike the previously reported single-atom or dual-atom configurations, we designed a new type of binary-atom catalyst, through engineering Fe-N4 electronic structure with adjacent Co-N2C2 and nitrogen-coordinated Co nanoclusters, as oxygen electrocatalysts. The resultant optimized electronic structure of the Fe-N4 active center favors the binding capability of intermediates and enhances oxygen reduction reaction (ORR) activity in both alkaline and acid conditions. In addition, anchoring M-N-C atomic sites on highly graphitized carbon supports guarantees of efficient charge- and mass-transports, and escorts the high bifunctional catalytic activity of the entire catalyst. Further, through the combination of electrochemical studies and in-situ X-ray absorption spectroscopy analyses, the ORR degradation mechanisms under highly oxidative conditions during oxygen evolution reaction processes were revealed. This work developed a new binary-atom catalyst and systematically investigates the effect of highly oxidative environments on ORR electrochemical behavior. It demonstrates the strategy for facilitating oxygen electrocatalytic activity and stability of the atomically dispersed M-N-C catalysts.

Biaxially-Strained Phthalocyanine at Polyoxometalate@Carbon Nanotube Heterostructure Boosts Oxygen Reduction Catalysis

Iron phthalocyanine (FePc) with unique FeN4 site has attracted increasing interests as a promising non-precious catalyst. However, the plane symmetric structure endows FePc with undesired catalytic performance toward the oxygen reduction reaction (ORR). Here, we report a novel one-dimensional heterostructured ORR catalyst by coupling FePc at polyoxometalate-encapsulated carbon nanotubes (FePc-{PW12 }@NTs) using host-guest chemistry. The encapsulation of polyoxometalates can induce a local tensile strain of single-walled NTs to strengthen the interactions with FePc. Both the strain and curvature effects of {PW12 }@NT scaffold tune the geometric structure and electronic localization of FeN4 centers to enhance the ORR catalytic performance. As expected, such a heterostructured FePc-{PW12 }@NT electrocatalyst exhibits prominent durability, methanol tolerance, and ORR activity with a high half-wave potential of 0.90 V and a low Tafel slope of 30.9 mV dec-1 in alkaline medium. Besides, the assembled zinc-air battery demonstrates an ultrahigh power density of 280 mW cm-2 , excellent charge/discharge ability and long-term stability over 500 h, outperforming that of the commercial Pt/C+IrO2 cathode. This study offers a new strategy to design novel heterostructured catalysts and opens a new avenue to regulate the electrocatalytic performance of phthalocyanine molecules.

PtNi-W/C with Atomically Dispersed Tungsten Sites Toward Boosted ORR in Proton Exchange Membrane Fuel Cell Devices

The performance of proton exchange membrane fuel cells is heavily dependent on the microstructure of electrode catalyst especially at low catalyst loadings. This work shows a hybrid electrocatalyst consisting of PtNi-W alloy nanocrystals loaded on carbon surface with atomically dispersed W sites by a two-step straightforward method. Single-atomic W can be found on the carbon surface, which can form protonic acid sites and establish an extended proton transport network at the catalyst surface. When implemented in membrane electrode assembly as cathode at ultra-low loading of 0.05 mgPt cm-2, the peak power density of the cell is enhanced by 64.4% compared to that with the commercial Pt/C catalyst. The theoretical calculation suggests that the single-atomic W possesses a favorable energetics toward the formation of *OOH whereby the intermediates can be efficiently converted and further reduced to water, revealing a interfacial cascade catalysis facilitated by the single-atomic W. This work highlights a novel functional hybrid electrocatalyst design from the atomic level that enables to solve the bottle-neck issues at device level.