Mesoporous carbon spheres with programmable interiors as efficient nanoreactors for H2O2 electrosynthesis

Tuning the Formation Kinetics of *OOH Intermediate with Hollow Bowl-Like Carbon by Pulsed Electroreduction for Enhanced H2O2 Production

The electrochemical synthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e- ORR) is a promising alternative to the conventional anthraquinone method. However, due to local alkalinization near the catalyst surface, the restricted oxygen replenishment and insufficient activated water molecule supply limit the formation of the key *OOH intermediate. Herein, a pulsed electrocatalysis approach based on a structurally optimized S/N/O tridoped hollow carbon bowl catalyst has been proposed to overcome this challenge. In an H-type electrolytic cell, the pulsed method achieves a superior H2O2 yield rate of 55.6 mg h-1 mgcat.-1, approximately 1.6 times higher than the conventional potentiostatic method (34.2 mg h-1 mgcat.-1), while maintaining the Faradaic efficiency above 94.6%. In situ characterizations, finite element simulations, and density functional theory analyses unveil that the application of pulsed potentials mitigates the local OH- concentration, enhances the water activation and proton generation, and facilitates oxygen production within the hollow bowl-like carbon structure. These effects synergistically accelerate the formation kinetics of the *OOH intermediate by the efficient generation of *O2 and *H2O intermediates, leading to superior H2O2 yields. This work develops a strategy to tune catalytic environments for diverse catalytic applications.

Integrated Two-in-one Strategy for Efficient Neutral Hydrogen Peroxide Electrosynthesis via Phosphorous Doping in 2D Mesoporous Carbon Carriers

Herein, we demonstrate a two-in-one strategy for efficient neutral electrosynthesis of H2O2 via two-electron oxygen reduction reaction (2e- ORR), achieved by synergistically fine-modulating both the local microenvironment and electronic structure of indium (In) single atom (SA) sites. Through a series of finite elemental simulations and experimental analysis, we highlight the significant impact of phosphorous (P) doping on an optimized 2D mesoporous carbon carrier, which fosters a favorable microenvironment by improving the mass transfer and O2 enrichment, subsequently leading to an increased local pH levels. Consequently, an outstanding 2e- ORR performance is observed in neutral electrolytes, achieving over 95 % selectivity for H2O2 across a broad voltage range of 0.1 to 0.5 V vs RHE. In a flow cell, the production rate of H2O2 exceeds 22.54 mol gcat -1 h-1 while maintaining high stability at industrial-level current densities. These results are comparable to, if not better than, those achieved under alkaline conditions. Further analysis, both experimental and theoretical, indicates that the P dopant occupies the second coordination sphere of the In SA, which shows optimized OOH* binding strength for an enhanced 2e- ORR kinetic.

Advanced development of finite element analysis for electrochemical catalytic reactions

The development of robust simulation techniques is crucial for elucidating electrochemical catalytic mechanisms and can even provide guidance for the tailored design and regulation of highly efficient catalysts. Finite element analysis (FEA), as a powerful numerical simulation tool, can effectively simulate and analyze the sophisticated processes involved in electrochemical catalytic reactions and unveil the underlying microscopic mechanisms. By employing FEA, researchers can gain better insights into reaction kinetics and transport processes, optimize electrode design, and predict electrochemical performance under various reaction conditions. Consequently, the application of FEA in electrochemical catalytic reactions has emerged as a critical area of current research and a summary of the advanced development of FEA for electrochemical catalytic reactions is urgently required. This review focuses on exploring the applications of FEA in investigating the crystal structure effect, tip effect, multi-shell effect, porous structure effect, and mass transfer phenomena in electrochemical reactions. Particularly emphasized are its applications in the fields of CO2 reduction, oxygen evolution reaction, and nitrogen reduction reaction. Finally, the challenges encountered by this research field are discussed, along with future directions for further advancement. We aim to provide comprehensive theoretical and practical guidance on FEA methods for researchers in the field of electrochemical catalysis, thereby fostering the advancement and wider implementation of FEA within this domain.

Recent Advances in the Design and Application of Asymmetric Carbon-Based Materials

Asymmetric carbon-based materials (ACBMs) have received significant attention in scientific research due to their unique structures and properties. Through the introduction of heterogeneous atoms and the construction of asymmetric ordered/disordered structures, ACBMs are optimized in terms of electrical conductivity, pore structure, and chemical composition and exhibit multiple properties such as hydrophilicity, hydrophobicity, optical characteristics, and magnetic behavior. Here, the recent research progress of ACBMs is reviewed, focusing on the potential of these materials for electrochemical, catalysis, and biomedical applications and their unique advantages over conventional symmetric carbon-based materials. Meanwhile, a variety of construction strategies of asymmetric structures, including template method, nanoemulsion assembly method, and self-assembly method, are described in detail. In addition, the contradictions between material synthesis and application are pointed out, such as the limitations of synthesis methods and morphology modulation means, as well as the trade-off between property improvement and production costs. Finally, the future development path of ACBMs is envisioned, emphasizing the importance of the close integration of theory and practice, and looking forward to promoting the research and development of a new generation of high-performance materials through the in-depth understanding of the design principles and action mechanisms of ACBMs.

Regulating the Local Reaction Microenvironment at Chromium Metal-Organic Frameworks for Efficient H2O2 Electrosynthesis in Neutral Electrolytes

The electrochemical synthesis of hydrogen peroxide represents a promising alternative to the traditional anthraquinone process, aiming for zero pollution. However, achieving efficient electrochemical synthesis of hydrogen peroxide in neutral electrolytes is challenging due to the sluggish kinetics of the two-electron oxygen reduction reaction. To address this issue, a unique metal-organic framework (MOF) featuring Cr metal sites coordinated with tetrabromoterephthalic acid (Cr-TBA) is synthesized. This specially designed MOF exhibits a distinctive paper-clip-like structure and remarkably enhanced Lewis acidity. Experimental results demonstrate that the obtained structure can facilitate the attraction of OH- ions in solution, promoting their accumulation on the catalyst surface. This enhancement leads to excellent performances of Cr-TBA in neutral electrolytes, achieving Faradaic efficiencies of 96-98% and a production rate of 13.4 mol gcat -1 h-1 at the current density of 150 mA cm-2. Operando spectroscopy and density functional theory calculations indicate that this modified microenvironment effectively facilitates the conversion of the *OOH intermediates to H2O2 on the catalyst surface.

Metalloenzyme-Inspired Cluster Fabrication within Mesoporous Channels Featuring Optimized Catalytic Microenvironments for Efficient Neutral pH H2O2 Electrosynthesis

In nature, some metalloenzymes facilitate highly efficient catalytic transformations of small molecules, primarily attributed to the effective coupling between their metal cluster active sites and the surrounding microenvironment. Inspired by this, a thermotropic redispersion strategy to incorporate bismuth nanoclusters (Bi NCs) into mesoporous channels, mimicking metalloenzyme-like catalysis to enhance the two-electron oxygen reduction reaction (2e- ORR) for efficient neutral pH H2O2 electrosynthesis, is developed. This model electrocatalyst exhibits exceptional 2e- ORR performance with >95% H2O2 selectivity across 0.2-0.6 V vs RHE in neutral electrolyte. Notably, the system produces up to 7.2 wt% neutral H2O2 solution at an industrially relevant current density of ≈320 mA cm-2, with 90% Faradaic efficiency for H2O2 over 120 h in a flow cell, demonstrating significant practical potential. Mechanistic insights reveal that the introduction of Bi NCs enhances the adsorption of the *OOH intermediate, facilitating a highly active 2e- ORR process. Moreover, the mesoporous channels of the carbon support create a favorable catalytic microenvironment for O2 aeration and local alkalinity, further boosting H2O2 productivity. This catalyst design mimics metalloenzymes by optimal integration of the active site with the surrounding microenvironment, offering valuable insights for the rational design of nature-inspired small-molecule catalysts.

Atomically Dispersed Co/Mo Sites Anchored on Mesoporous Carbon Hollow Spheres for Highly Selective Oxygen Reduction to Hydrogen Peroxide in Acidic Media

Two-electron oxygen reduction reaction (2e- ORR) in acidic media is a promising route for the decentralized and on-site hydrogen peroxide (H2O2) generation. Nevertheless, strong interaction between active sites and *OOH intermediates usually induces the O─O bond cleavage to convert 2e- pathway into the sluggish 4e- ORR. Therefore, it is highly necessary to optimize the electronic structure of 2e- ORR electrocatalysts for the regulation of adsorption energy. Herein, we propose the utilization of atomically dispersed Co/Mo sites anchored on mesoporous carbon hollow spheres (Co/Mo-MCHS) via a template-engaged strategy for highly selective ORR to H2O2 in acid. Benefitting from the electron-donating effect of Mo atoms, an enriched electron density around the Co center for Co/Mo-MCHS is observed, resulting in optimal adsorption of the key *OOH intermediates to approach the apex of 2e- ORR volcano plot. Moreover, the introduction of Mo species simultaneously suppresses the electroreduction of as-obtained H2O2 on Co sites. As a consequence, Co/Mo-MCHS delivers a high H2O2 selectivity of 90-95% in acid. The flow cell based on the Co/Mo-MCHS catalyst achieves a remarkable H2O2 yield of 2102 mg for 150 h. Moreover, this strategy can be extended to other early transition metal elements with similar electronic modifier effects.

Recent Progress in Oxygen Reduction Reaction Toward Hydrogen Peroxide Electrosynthesis and Cooperative Coupling of Anodic Reactions

Electrosynthesis of hydrogen peroxide (H2O2) via two-electron oxygen reduction reaction (2e- ORR) is a promising alternative to the anthraquinone oxidation process. To improve the overall energy efficiency and economic viability of this catalytic process, one pathway is to develop advanced catalysts to decrease the overpotential at the cathode, and the other is to couple 2e- ORR with certain anodic reactions to decrease the full cell voltage while producing valuable chemicals on both electrodes. The catalytic performance of a 2e- ORR catalyst depends not only on the material itself but also on the environmental factors. Developing promising electrocatalysts with high 2e- ORR selectivity and activity is a prerequisite for efficient H2O2 electrosynthesis, while coupling appropriate anodic reactions with 2e- ORR would further enhance the overall reaction efficiency. Considering this, here a comprehensive review is presented on the latest progress of the state-of-the-art catalysts of 2e- ORR in different media, the microenvironmental modulation mechanisms beyond catalyst design, as well as electrocatalytic system coupling 2e- ORR with various anodic oxidation reactions. This review also presents new insights regarding the existing challenges and opportunities within this rapidly advancing field, along with viewpoints on the future development of H2O2 electrosynthesis and the construction of green energy roadmaps.

Sulfur-doping tunes p-d orbital coupling over asymmetric Zn-Sn dual-atom for boosting CO2 electroreduction to formate

The interaction of p-d orbitals at bimetallic sites plays a crucial role in determining the catalytic reactivity, which facilitates the modulation of charges and enhances the efficiency of CO2 electroreduction process. Here, we show a ligand co-etching approach to create asymmetric Zn-Sn dual-atom sites (DASs) within metal-organic framework (MOF)-derived yolk-shell carbon frameworks (named Zn1Sn1/SNC). The DASs comprise one Sn center (p-block) partially doped with sulfur and one Zn center (d-block) with N coordination, facilitating the coupling of p-d orbitals between the Zn-Sn dimer. The N-Zn-Sn-S/N arrangement displays an asymmetric distribution of charges and atoms, leading to a stable adsorption configuration of HCOO* intermediates. In H-type cell, Zn1Sn1/SNC exhibits an impressive formate Faraday efficiency of 94.6% at -0.84 V. In flow cell, the asymmetric electronic architecture of Zn1Sn1/SNC facilitates high accessibility, leading to a high current density of -315.2 mA cm-2 at -0.90 V. Theoretical calculations show the asymmetric sites in Zn1Sn1/SNC with ideal adsorption affinity lower the CO2 reduction barrier, thus improve the overall efficiency of CO2 reduction.

Mesoporous Boron-Doped Carbon with Curved B4C Active Sites for Highly Efficient H2O2 Electrosynthesis in Neutral Media and Air-Supplied Environments

Hydrogen peroxide (H2O2) electrosynthesis via the 2e- oxygen reduction reaction (ORR) is considered as a cost-effective and safe alternative to the energy-intensive anthraquinone process. However, in more practical environments, namely, the use of neutral media and air-fed cathode environments, slow ORR kinetics and insufficient oxygen supply pose significant challenges to efficient H2O2 production at high current densities. In this work, mesoporous B-doped carbons with novel curved B4C active sites, synthesized via a carbon dioxide (CO2) reduction using a pore-former agent, to simultaneously achieve excellent 2e- ORR activity and improved mass transfer properties are introduced. Through a combination of experimental analysis and theoretical calculations, it is confirmed that the curved B4C configuration, formed by mesopores in the carbon, demonstrates superior selectivity and activity for 2e- ORR due to its weaker interaction with *OOH intermediates compared to planar B4C in neutral media. Moreover, the mesopores facilitate oxygen supply and suppress the hydrogen evolution reaction, achieving a Faradaic efficiency of 86.2% at 150 mA cm-2 under air-supplied conditions, along with an impressive O2 utilization efficiency of 93.6%. This approach will provide a route to catalyst design for efficient H2O2 electrosynthesis in a practical environment.

Construction of PdCu Alloy Decorated on the N-Doped Carbon Aerogel as a Highly Active Electrocatalyst for Enhanced Oxygen Reduction Reaction

Fuel cells/zinc-air cells represent a transformative technology for clean energy conversion, offering substantial environmental benefits and exceptional theoretical efficiency. However, the high cost and limited durability of platinum-based catalysts for the sluggish oxygen reduction reaction (ORR) at the cathode severely restrict their scalability and practical application. To address these critical challenges, this study explores a groundbreaking approach to developing ORR catalysts with enhanced performance and reduced costs. We present a novel Pd3Cu alloy, innovatively modified with N-doped carbon aerogels, synthesized via a simple self-assembly and freeze-drying method. The three-dimensional carbon aerogel-based porous structures provide diffusion channels for oxygen molecules, excellent electrical conductivity, and abundant ORR reaction sites. The Pd3Cu@2NC-20% aerogel exhibits a remarkable enhancement in ORR activity, achieving a half-wave potential of 0.925 V, a limiting current density of 6.12 mA/cm2, and excellent long-term stability. Density functional theory (DFT) calculations reveal that electrons tend to transfer from the Pd atoms to the neighboring *O, leading to an increase in the negative charge around the *O. This, in turn, weakens the interaction between the catalyst surface and the *O and optimizes the elementary steps of the ORR process.

Facile synthesis of hierarchical core-shell carbon@ZnIn2S4 composite for boosted photothermal-assisted photocatalytic H2 production

Against the backdrop of energy shortage, hydrogen energy has attracted much attention as a green and clean energy source. In order to explore efficient hydrogen production pathways, we designed a composite photocatalyst with carbon-based core-shell photothermal-assisted photocatalytic system (Carbon@ZnIn2S4, denoted as C@ZIS). The well-designed catalyst C@ZIS composites demonstrated a photocatalytic hydrogen precipitation rate of 2.97 mmol g-1 h-1 even in the absence of the noble metal Pt co-catalyst. The incorporation of carbon-based core-shell photocatalysts into a photocatalytic reaction significantly affects the activity of the reaction by triggering a photothermal effect in the reaction solution. The results of the physicochemical experiments demonstrated that the carbon spheres in C@ZIS composite system could provide a greater number of active sites, thereby accelerating the electron transfer and separation efficiency, and thus enhancing the photocatalytic activity. The study presents an efficacious design concept for the development of efficacious carbon-based core-shell photothermal-assisted photocatalysts, which is anticipated to facilitate the efficient conversion of solar energy to hydrogen energy.

Hydrogen Peroxide Electrosynthesis via Selective Oxygen Reduction Reactions Through Interfacial Reaction Microenvironment Engineering

The electrochemical two-electron oxygen reduction reaction (2e- ORR) offers a compelling alternative for decentralized and on-site H2O2 production compared to the conventional anthraquinone process. To advance this electrosynthesis system, there is growing interest in optimizing the interfacial reaction microenvironment to boost electrocatalytic performance. This review consolidates recent advancements in reaction microenvironment engineering for the selective electrocatalytic conversion of O2 to H2O2. Starting with fundamental insights into interfacial electrocatalytic mechanisms, an overview of various strategies for constructing the favorable local reaction environment, including adjusting electrode wettability, enhancing mesoscale mass transfer, elevating local pH, incorporating electrolyte additives, and employing pulsed electrocatalysis techniques is provided. Alongside these regulation strategies, the corresponding analyses and technical remarks are also presented. Finally, a summary and outlook on critical challenges, suggesting future research directions to inspire microenvironment engineering and accelerate the practical application of H2O2 electrosynthesis is delivered.

Refining Metal-Free Carbon Nanoreactors through Electronic and Geometric Comodification for Boosted H2O2 Electrosynthesis toward Efficient Water Decontamination

Hydrogen peroxide (H2O2) electrosynthesis using metal-free carbon materials via the 2e- oxygen reduction pathway has sparked considerable research interest. However, the scalable preparation of carbon electrocatalysts to achieve satisfactory H2O2 yield in acidic media remains a grand challenge. Here, we present the design of a carbon nanoreactor series that integrates precise O/N codoping alongside well-regulated geometric structures targeting high-efficiency electrosynthesis of H2O2. Theoretical computations reveal that strategic N/O codoping facilitates partial electron transfer from C sites to O sites, realizing electronic rearrangement that optimizes C-site adsorption of *OOH. Concurrently, the O-O bond in *OOH is strengthened by charge transfer from antibonding to π-orbitals, stabilizing the O-O bond and preventing its dissociation. The carbon nanoreactor with a hollow bowl geometry also facilitates the mass transport of O2 and H2O2, achieving an H2O2 selectivity of 96% in acidic media. Furthermore, a flow cell integrated with the refined nanoreactor catalyst achieves an impressive H2O2 production rate of 2942.4 mg L-1 h-1, coupled with stable operation of nearly 80 h, surpassing the state-of-the-art metal-free analogs. The feasibility of the electro-synthesized H2O2 is further demonstrated to be highly efficient in wastewater remediation.

Engineering of Single-Atomic Sites for Electro- and Photo-Catalytic H2O2 Production

Direct electro- and photo-synthesis of H2O2 through the 2e- O2 reduction reaction (ORR) and H2O oxidation reaction (WOR) offer promising alternatives for on-demand and on-site production of this chemical. Exploring robust and selective active sites is crucial for enhancing H2O2 production through these pathways. Single-atom catalysts (SACs), featuring isolated active sites on supports, possess attractive properties for promoting catalysis and unraveling catalytic mechanisms. This review first systematically summarizes significant advancements in atomic engineering of both metal and nonmetal single-atom sites for electro- and photo-catalytic 2e- ORR to H2O2, as well as the dynamic behaviors of active sites during catalytic processes. Next, the progress of single-atom sites in H2O2 production through 2e- WOR is overviewed. The effects of the local physicochemical environments on the electronic structures and catalytic behaviors of isolated sites, along with the atomic catalytic mechanism involved in these H2O2 production pathways, are discussed in detail. This work also discusses the recent applications of H2O2 in advanced chemical transformations. Finally, a perspective on the development of single-atom catalysis is highlighted, aiming to provide insights into future research on SACs for electro- and photo-synthesis of H2O2 and other advanced catalytic applications.

Quantum-Sized Co Nanoparticles with Rich Vacancies Enabled the Uniform Deposition of Lithium Metal and Fast Polysulfide Conversion

The notorious polysulfide shuttling and uncontrollable Li-dendrite growth are the main obstacles to the marketization of Li-S batteries. Herein, a dual-functional material consisting of vacancy-rich quantum-sized Co nanodots anchored on a mesoporous carbon layer (v-Co/meso-C) is proposed. This material exposes more active sites to improve its reaction performance and simultaneously realizes excellent lithiophilicity and sulfiphilicity characteristics in Li-S electrochemistry. As Li metal deposition hosts, v-Co/meso-C shows small nucleation overpotential, low polarization, and ultra-long cycling stability in both half and symmetric cells, as confirmed by experimental studies. On the S cathode side, experimental and theoretical calculations demonstrate that v-Co/meso-C enhances the adsorption of polysulfides and boosts their catalytic conversion rate. This, in turn, suppresses the shuttle effect of polysulfides and improves sulfur utilization efficiency. Finally, a shuttle-free and dendrite-free v-Co/meso-C@Li//v-Co/meso-C@S full cell is fabricated, exhibiting excellent rate performance (739 mAh g-1 at 5.0 C) and good cyclability (capacity decay rate is 0.033% and 0.035% per cycle at 2.0 and 5.0 C, respectively). Even a pouch cell with high sulfur loading (5.5 mg cm-2) and lean electrolyte/sulfur (4.8 µL mg-1) can still work 50 cycles with 80% capacity retention rate. This study shows far-reaching implications in the design of dendrite-free, shuttle-free Li-S batteries.

Phenolic multiple kinetics-dynamics and discrete crystallization thermodynamics in amorphous carbon nanostructures for electromagnetic wave absorption

The lack of a chemical platform with high spatial dimensional diversity, coupled with the elusive multi-scale amorphous physics, significantly hinder advancements in amorphous electromagnetic wave absorption (EWA) materials. Herein, we present a synergistic engineering of phenolic multiple kinetic dynamics and discrete crystallization thermodynamics, to elucidate the origin of the dielectric properties in amorphous carbon and the cascade effect during EWA. Leveraging the scalability of phenolic synthesis, we design dozens of morphologies from the bottom up and combine with in-situ pyrolysis to establish a nanomaterial ecosystem of hundreds of amorphous carbon materials. Based on controlled discrete crystallization, nano-curvature regulation of spatial inversion symmetry-breaking structures, and surface electric field enhancement from multi-shell structures, the multi-scale charge imbalance triggers intense polarization. Both experiments and theories show that each scale is essential, which collectively drives broadband absorption (8.46 GHz) and efficient dissipation (-54.77 dB) of EWA performance. Our work on the amorphous nanostructure platform and the cascade effect can contribute to uncovering the missing pieces in amorphous physics and EWA research.

Mesoporous carbon hollow spheres based sensitive SPME probes for in vivo sampling analysis of selected plant hormones in Chinese aloes

Phytohormones are a class of endogenous substances that separately or synergistically regulate the growth, development, and differentiation of plants. Accurately and efficiently detecting and monitoring the concentration of plant hormones in living plants is of significant importance. Herein, a novel mesoporous carbon hollow spheres (MCHS)-based in vivo solid phase microextraction (SPME) probe was designed for in vivo sampling of plant hormones. The designed MCHS features the advantages of high surface area, porous shells, and large hollow spaces, facilitating the dynamic adsorption and enrichment of target phytohormone. In addition, a cationic polyelectrolyte, (poly (diallyl dimethyl ammonium chloride) (PDDA), was further modified onto the MCHS to expedite the extraction process by electrostatic interaction. Utilizing the MCHS@PDDA probe in combination with HPLC-MS/MS facilitated the continuous monitoring of three plant hormones (abscisic acid (ABA), indole-3-acetic acid (IAA), and gibberellin (GA3)) in Chinese aloe. The detection limit of this method was 0.016-0.090 μg/L, the linear range was 10-1000 μg/L, and both the RSD of the single probe (n = 6) and probe-to-probe test (n = 6) were less than 7.2 %. This method had excellent accuracy and good reproducibility comparable to the traditional sample pretreatment method. Ultimately, this established in-vivo SPME method was successfully adopted to quantify three selected plant hormones in living Chinese Aloes, providing a new method for the long-term monitoring of endogenous active substances in living system.

Photovoltaic-driven stable electrosynthesis of H2O2 in simulated seawater and its disinfection application

Electrosynthesis of H2O2 through O2 reduction in seawater provides bright sight on the H2O2 industry, which is a prospective alternative to the intensively constructed anthraquinone process. In this work, a photovoltaic-driven flow cell system is built for the electrosynthesis of H2O2 in simulated seawater using N-doped carbon catalysts. The N-doped carbon catalysts with multiple N-doped carbon defects can achieve a record-high H2O2 production rate of 34.7 mol gcatalyst -1 h-1 under an industrially relevant current density of 500 mA cm-2 and a long-term stability over 200 h in simulated seawater (0.5 M NaCl). When driven by the photovoltaic system, a H2O2 solution of ∼1.0 wt% in 0.5 M NaCl is also obtained at about 700 mA cm-2. The obtained solution is applied for disinfection of mouse wounds, with a removal rate of 100% for Escherichia coli and negligible toxicity to living organisms. It provides bright prospects for large-scale on-site H2O2 production and on-demand disinfection.

Engineering Three-Dimensional Interconnected Pores with Plentiful Edge Sites via a Confined Space for Enhanced Oxygen Reduction

N-Doped carbon sheets based on edge engineering provide more opportunities for improving oxygen reduction reaction (ORR) active sites. However, with regard to the correlation between porous structural configurations and performances, it remains underexplored. Herein, a silica-assisted localized etching method was employed to create two-dimensional mesoporous carbon materials with customizable pore structures, abundant edge sites, and nitrogen functionalities. The mesoporous carbon exhibited superior electrocatalytic performance for the ORR compared to that of a 20 wt % Pt/C catalyst, achieving a half-wave potential of 0.88 V versus RHE, situating them in the leading level of the reported carbon electrocatalysts. Experimental data suggest that the edge graphitic nitrogen sites played a crucial role in the ORR process. The three-dimensional interconnected pores provided a high density of active sites for the ORR and facilitated the efficient transport of electrons. These unique properties make the carbon sheets a promising candidate for highly efficient air cathodes in rechargeable Zn-air batteries.

Advanced Nanocarbons Toward two-Electron Oxygen Electrode Reactions for H2O2 Production and Integrated Energy Conversion

Hydrogen peroxide (H2O2) plays a pivotal role in advancing sustainable technologies due to its eco-friendly oxidizing capability. The electrochemical two-electron (2e-) oxygen reduction reaction and water oxidation reaction present an environmentally green method for H2O2 production. Over the past three years, significant progress is made in the field of carbon-based metal-free electrochemical catalysts (C-MFECs) for low-cost and efficient production of H2O2 (H2O2EP). This article offers a focused and comprehensive review of designing C-MFECs for H2O2EP, exploring the construction of dual-doping configurations, heteroatom-defect coupling sites, and strategic dopant positioning to enhance H2O2EP efficiency; innovative structural tuning that improves interfacial reactant concentration and promote the timely release of H2O2; modulation of electrolyte and electrode interfaces to support the 2e- pathways; and the application of C-MFECs in reactors and integrated energy systems. Finally, the current challenges and future directions in this burgeoning field are discussed.

Combination of nanoparticles with single-metal sites synergistically boosts co-catalyzed formic acid dehydrogenation

The development of hydrogen technologies is at the heart of a green economy. As prerequisite for implementation of hydrogen storage, active and stable catalysts for (de)hydrogenation reactions are needed. So far, the use of precious metals associated with expensive costs dominates in this area. Herein, we present a new class of lower-cost Co-based catalysts (Co-SAs/NPs@NC) in which highly distributed single-metal sites are synergistically combined with small defined nanoparticles allowing efficient formic acid dehydrogenation. The optimal material with atomically dispersed CoN2C2 units and encapsulated 7-8 nm nanoparticles achieves an excellent gas yield of 1403.8 mL·g-1·h-1 using propylene carbonate as solvent, with no activity loss after 5 cycles, which is 15 times higher than that of the commercial Pd/C. In situ analytic experiments show that Co-SAs/NPs@NC enhances the adsorption and activation of the key intermediate monodentate HCOO*, thereby facilitating the following C-H bond breaking, compared to related single metal atom and nanoparticle catalysts. Theoretical calculations show that the integration of cobalt nanoparticles elevates the d-band center of the Co single atoms as the active center, which consequently enhances the coupling of the carbonyl O of the HCOO* intermediate to the Co centers, thereby lowering the energy barrier.

Pore engineering of Porous Materials: Effects and Applications

Porous materials, characterized by their controllable pore size, high specific surface area, and controlled space functionality, have become cross-scale structures with microenvironment effects and multiple functions and have gained tremendous attention in the fields of catalysis, energy storage, and biomedicine. They have evolved from initial nanopores to multiscale pore-cavity designs with yolk-shell, multishells, or asymmetric structures, such as bottle-shaped, multichambered, and branching architectures. Various synthesis strategies have been developed for the interfacial engineering of porous structures, including bottom-up approaches by using liquid-liquid or liquid-solid interfaces "templating" and top-down approaches toward chemical tailoring of polymers with different cross-linking degrees, as well as interface transformation using the Oswald ripening, Kirkendall effect, or atomic diffusion and rearrangement methods. These techniques permit the design of functional porous materials with diverse microenvironment effects, such as the pore size effect, pore enrichment effect, pore isolation and synergistic effect, and pore local field enhancement effect, for enhanced applications. In this review, we delve into the bottom-up and top-down interfacial-oriented synthesis approaches of porous structures with advanced structures and microenvironment effects. We also discuss the recent progress in the applications of these collaborative effects and structure-activity relationships in the areas of catalysis, energy storage, electrochemical conversion, and biomedicine. Finally, we outline the persisting obstacles and prospective avenues in terms of controlled synthesis and functionalization of porous engineering. The perspectives proposed in this paper may contribute to promote wider applications in various interdisciplinary fields within the confined dimensions of porous structures.

Advancing H2O2 electrosynthesis: enhancing electrochemical systems, unveiling emerging applications, and seizing opportunities

Hydrogen peroxide (H2O2) is a highly desired chemical with a wide range of applications. Recent advancements in H2O2 synthesis center on the electrochemical reduction of oxygen, an environmentally friendly approach that facilitates on-site production. To successfully implement practical-scale, highly efficient electrosynthesis of H2O2, it is critical to meticulously explore both the design of catalytic materials and the engineering of other components of the electrochemical system, as they hold equal importance in this process. Development of promising electrocatalysts with outstanding selectivity and activity is a prerequisite for efficient H2O2 electrosynthesis, while well-configured electrolyzers determine the practical implementation of large-scale H2O2 production. In this review, we systematically summarize fundamental mechanisms and recent achievements in H2O2 electrosynthesis, including electrocatalyst design, electrode optimization, electrolyte engineering, reactor exploration, potential applications, and integrated systems, with an emphasis on active site identification and microenvironment regulation. This review also proposes new insights into the existing challenges and opportunities within this rapidly evolving field, together with perspectives on future development of H2O2 electrosynthesis and its industrial-scale applications.

Efficient Neutral H2O2 Electrosynthesis from Favorable Reaction Microenvironments via Porous Carbon Carrier Engineering

The efficient electrosynthesis of hydrogen peroxide (H2O2) via two-electron oxygen reduction reaction (2e- ORR) in neutral media is undoubtedly a practical route, but the limited comprehension of electrocatalysts has hindered the system advancement. Herein, we present the design of model catalysts comprising mesoporous carbon spheres-supported Pd nanoparticles for H2O2 electrosynthesis at near-zero overpotential with approximately 95 % selectivity in a neutral electrolyte. Impressively, the optimized Pd/MCS-8 electrocatalyst in a flow cell device achieves an exceptional H2O2 yield of 15.77 mol gcatalyst -1 h-1, generating a neutral H2O2 solution with an accumulated concentration of 6.43 wt %, a level sufficiently high for medical disinfection. Finite element simulation and experimental results suggest that mesoporous carbon carriers promote O2 enrichment and localized pH elevation, establishing a favorable microenvironment for 2e- ORR in neutral media. Density functional theory calculations reveal that the robust interaction between Pd nanoparticles and the carbon carriers optimized the adsorption of OOH* at the carbon edge, ensuring high active 2e- process. These findings offer new insights into carbon-loaded electrocatalysts for efficient 2e- ORR in neutral media, emphasizing the role of carrier engineering in constructing favorable microenvironments and synergizing active sites.

Coupling Ni Single Atomic Sites with Metallic Aggregates at Adjacent Geometry on Carbon Support for Efficient Hydrogen Peroxide Electrosynthesis

Single atomic catalysts have shown great potential in efficiently electro-converting O2 to H2O2 with high selectivity. However, the impact of coordination environment and introduction of extra metallic aggregates on catalytic performance still remains unclear. Herein, first a series of carbon-based catalysts with embedded coupling Ni single atomic sites and corresponding metallic nanoparticles at adjacent geometry is synthesized. Careful performance evaluation reveals NiSA/NiNP-NSCNT catalyst with precisely controlled active centers of synergetic adjacent Ni-N4S single sites and crystalline Ni nanoparticles exhibits a high H2O2 selectivity over 92.7% within a wide potential range (maximum selectivity can reach 98.4%). Theoretical studies uncover that spatially coupling single atomic NiN4S sites with metallic Ni aggregates in close proximity can optimize the adsorption behavior of key intermediates *OOH to achieve a nearly ideal binding strength, which thus affording a kinetically favorable pathway for H2O2 production. This strategy of manipulating the interaction between single atoms and metallic aggregates offers a promising direction to design new high-performance catalysts for practical H2O2 electrosynthesis.

Linking atomic to mesoscopic scales in multilevel structural tailoring of single-atom catalysts for peroxide activation

A key challenge in designing single-atom catalysts (SACs) with multiple and synergistic functions is to optimize their structure across different scales, as each scale determines specific material properties. We advance the concept of a comprehensive optimization of SACs across different levels of scale, from atomic, microscopic to mesoscopic scales, based on interfacial kinetics control on the coupled metal-dissolution/polymer-growth process in SAC synthesis. This approach enables us to manipulate the multilevel interior morphologies of SACs, such as highly porous, hollow, and double-shelled structures, as well as the exterior morphologies inherited from the metal oxide precursors. The atomic environment around the metal centers can be flexibly adjusted during the dynamic metal-oxide consumption and metal-polymer formation. We show the versatility of this approach using mono- or bi-metallic oxides to access SACs with rich microporosity, tunable mesoscopic structures and atomic coordinating compositions of oxygen and nitrogen in the first coordination-shell. The structures at each level collectively optimize the electronic and geometric structure of the exposed single-atom sites and lower the surface *O formation barriers for efficient and selective peroxidase-type reaction. The unique spatial geometric configuration of the edge-hosted active centers further improves substrate accessibility and substrate-to-catalyst hydrogen overflow due to tunable structural heterogeneity at mesoscopic scales. This strategy opens up new possibilities for engineering more multilevel structures and offers a unique and comprehensive perspective on the design principles of SACs.

Recent Advances in Carbon-Based Single-Atom Catalysts for Electrochemical Oxygen Reduction to Hydrogen Peroxide in Acidic Media

Electrochemical oxygen reduction reaction (ORR) via the 2e- pathway in an acidic media shows great techno-economic potential for the production of hydrogen peroxide. Currently, carbon-based single-atom catalysts (C-SACs) have attracted extensive attention due to their tunable electronic structures, low cost, and sufficient stability in acidic media. This review summarizes recent advances in metal centers and their coordination environment in C-SACs for 2e--ORR. Firstly, the reaction mechanism of 2e--ORR on the active sites of C-SACs is systematically presented. Secondly, the structural regulation strategies for the active sites of 2e--ORR are further summarized, including the metal active center, its species and configurations of nitrogen coordination or heteroatom coordination, and their near functional groups or substitute groups, which would provide available and proper ideas for developing superior acidic 2e--ORR electrocatalysts of C-SACs. Finally, we propose the current challenges and future opportunities regarding the acidic 2e--ORR pathway on C-SACs, which will eventually accelerate the development of the distributed H2O2 electrosynthesis process.