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The advancement of economical and readily available electrocatalysts for the oxygen reduction reaction (ORR) holds paramount importance in the advancement of fuel cells and metal‐air batteries. Recently, 2D non‐metallic materials have obtained substantial attention as viable alternatives for ORR catalysts due to their manifold advantages, encompassing low cost, ample availability, substantial surface‐to‐volume ratio, high conductivity, exceptional durability, and competitive activity. The augmented ORR performances observed in metal‐free 2D materials typically arise from heteroatom doping, defects, or the formation of heterostructures. Here, the authors delve into the realm of electrocatalysts for the ORR, pivoting around metal‐free 2D materials. Initially, the merits of metal‐free 2D materials are explored and the reaction mechanism of the ORR is dissected. Subsequently, a comprehensive survey of diverse metal‐free 2D materials is presented, tracing their evolutionary journey from fundamental concepts to pragmatic applications in the context of ORR. Substantial importance is given on the exploration of various strategies for enhancing metal‐free 2D materials and assessing their impact on inherent material performance, including electronic properties. Finally, the challenges and future prospects that lie ahead for metal‐free 2D materials are underscored, as they aspire to serve as efficient ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] 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. [ABSTRACT FROM AUTHOR]

[Display omitted] The optimization of the adsorption of oxygen-containing intermediates on platinum (Pt) sites of Pt-based electrocatalysts is crucial for the oxygen reduction reaction process. Currently, a large amount of researches mainly focus on modifying the bulk structure of the electrocatalysts, however, the vital role of solvent effect on the phase interfaces is often overlooked. Here, we successfully developed an electrocatalyst in which the ordered PtCo alloy anchors on the cobalt (Co) single-atoms/clusters decorated support (Co 1,n N C) and its surface is further optimized using hydrophobic ionic liquid (IL). Experimental studies and theoretical calculations indicate that compressive stress on Pt lattice contributed by intrinsic structure and the local hydrophobicity caused by IL on the surface can suppress the stabilization of *OH on Pt. This synergistic effect affords outstanding catalytic performance, exhibiting a half-wave potential (E 1/2) of 0.916 V vs. RHE and a mass activity (MA) of 1350.3 mA mg Pt −1 in 0.1 mol/L perchloric acid (0.1 M HClO 4) electrolyte, much better than the commercial Pt/C (0.849 V vs. RHE and 145.5 mA mg Pt −1 for E 1/2 and MA, respectively). Moreover, the E 1/2 of IL-PtCo/Co 1,n N C only lost 5 mV after 10,000 cyclic voltammetry (CV) cycles due to a strong and synergistic contact of the intermetallic PtCo alloy with the Co 1,n N C support and IL. This research provides an effective method for designing efficient electrocatalysts by combining intrinsic structure and surface modification. [ABSTRACT FROM AUTHOR]

[Display omitted] The sluggish kinetics and inferior stability of oxygen electrocatalyst in rechargeable zinc air battery (ZAB) hamper its industrialization. In this work, we activate cobalt telluride (CoTe) by introduction of metallic cobalt (Co) to modulate the work function to facilitate the electron transfer from Co to CoTe during oxygen catalysis; additionally, the three-dimensional porous carbon nanosheets (3DPC) are invited to reduce the resistance towards electrolyte/oxygen diffusion. Thereby, Co-CoTe@3DPC only demands 280 mV overpotential to reach 10 mA cm−2 under alkaline oxygen evolution reaction (OER) condition, relatively lower than commercial iridium oxides (IrO 2); besides, the operando electrochemical impedance spectroscopy (EIS) indicates a better resistance towards surface reconstruction than Co@3DPC leading to a superior stability. A Pt-like oxygen reduction reaction (ORR) performance, half-wave potential associated with kinetic current density, is achieved for Co-CoTe@3DPC. A maximum power density of 203 mW cm−2 is achieved and sustains for 800 h. Furthermore, the all-solid-state ZAB offers 97 mW cm−2. Theoretical calculation suggests that the incorporation of metallic Co to CoTe maintains the superb ORR activity and promotes the OER catalysis. [ABSTRACT FROM AUTHOR]

We introduce N-P pair into the carbon matrix to construct N,P-C electrocatalyst by a facile pyrolysis strategy. Benefiting from the moderate adsorption energy of *OH on the active sites (C adjacent to P atom in N-P), the achieved N,P-C-1000 displays outstanding alkaline ORR performance and high power density primary liquid and solid ZABs. [Display omitted] • N-P pair was introduced into the carbon matrix to construct N,P-C electrocatalyst by a facile pyrolysis strategy. • The catalyst exhibits superior ORR activity with a E 1/2 of 0.83 V, comparable to that of commercial 20 wt% Pt/C. • Its C-2p orbit has higher interaction strength with the intermediates, thus reducing the overall reaction energy barrier. • High power density primary liquid and solid ZABs are achieved using N,P-C-1000 as cathodic catalysts. Developing sustainable metal-free carbon-based electrocatalysts is essential for the deployment of metal-air batteries such as zinc-air batteries (ZABs), among which doping of heteroatoms has attracted tremendous interest over the past decade. However, the effect of the heteroatom covalent bonds in carbon matrix on catalysis was neglected in most studies. Here, an efficient metal-free oxygen reduction reaction (ORR) catalyst is demonstrated by the N-P bonds anchored carbon (termed N,P-C-1000). The N,P-C-1000 catalyst exhibits superior specific surface area of 1362 m2 g−1 and ORR activity with a half-wave potential of 0.83 V, close to that of 20 wt% Pt/C. Theoretical computations reveal that the p-band center for C-2p orbit in N,P-C-1000 has higher interaction strength with the intermediates, thus reducing the overall reaction energy barrier. The N,P-C-1000 assembled primary ZAB can attain a large peak power density of 121.9 mW cm−2 and a steady discharge platform of ∼1.20 V throughout 120 h. Besides, when served as the cathodic catalyst in a solid-state ZAB, the battery shows flexibility, conspicuous open circuit potential (1.423 V), and high peak power density (85.8 mW cm−2). Our findings offer a strategy to tune the intrinsic structure of carbon-based catalysts for improved electrocatalytic performance and shed light on future catalysts design for energy storage technologies beyond batteries. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) and oxygen evolutionc reaction (OER) are important chemical reactions for a rechargeable lithium–oxygen battery (LOB). Recently, high-entropy alloys and oxides have attracted much attention because they showed good electrocatalytic performance for oxygen evolution reaction (OER) and/or oxygen reduction reaction (ORR). In this study, we aimed to synthesize and characterize CoSn(OH)6 and two types of high-entropy perovskite hydroxides, that is, (Co0.2Cu0.2Fe0.2Mn0.2Mg0.2)Sn(OH)6 (CCFMMSOH) and (Co0.2Cu0.2Fe0.2Mn0.2Ni0.2)Sn(OH)6 (CCFMNSOH). TEM observation and XRD measurements revealed that the high-entropy hydroxides CCFMMSOH and CCFMNSOH had cubic crystals with sides of approximately 150–200 nm and crystal structures similar to those of perovskite-type CSOH. LSV measurement results showed that the high-entropy hydroxides CCFMMSOH and CCFMNSOH showed bifunctional catalytic functions for the ORR and OER. CCFMNSOH showed better catalytic performance than CCFMMSOH. [ABSTRACT FROM AUTHOR]

[Display omitted] Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for the development of excellent bifunctional electrocatalysts, which are key functions in clean energy production. The emphasis of this study lies in the rapid design and investigation of 153 MN 4 –graphene (Gra)/ MXene (M 2 NO) electrocatalysts for ORR/OER catalytic activity using machine learning (ML) and density functional theory (DFT). The DFT results indicated that CoN 4 –Gra/Ti 2 NO had both good ORR (0.37 V) and OER (0.30 V) overpotentials, while TiN 4 –Gra/M 2 NO and MN 4 –Gra/Cr 2 NO had high overpotentials. Our research further indicated orbital spin polarization and d-band centers far from the Fermi energy level, affecting the adsorption energy of oxygen-containing intermediates and thus reducing the catalytic activity. The ML results showed that the gradient boosting regression (GBR) model successfully predicted the overpotentials of the monofunctional catalysts RhN 4 –Gra/Ti 2 NO (ORR, 0.39 V) and RuN 4 –Gra/W 2 NO (OER, 0.45 V) as well as the overpotentials of the bifunctional catalyst RuN 4 –Gra/W 2 NO (ORR, 0.39 V; OER, 0.45 V). The symbolic regression (SR) algorithm was used to construct the overpotential descriptors without environmental variable features to accelerate the catalyst screening and shorten the trial-and-error costs from the source, providing a reliable theoretical basis for the experimental synthesis of MXene heterostructures. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D GnP/MoS 2 and 3D (GnP/MoS 2)/MWNT composites are prepared by a facile, robust and ecofriendly method. • Effects of N-doping of GnPs and mass fraction of MWNTs on ORR activity are explored and rationalized. • Best synergistic ORR activity is obtained for N-doped catalyst with 3:1 2D-to-1D ratio. • Catalysts exhibit excellent stability and methanol resistance in alkaline medium. • Promising route to develop bifunctional ORR/OER catalysts. Nanocomposites have garnered attention for their potential as catalysts in electrochemical reactions vital for technologies like fuel cells, water splitting, and metal-air batteries. This work focuses on developing three-dimensional (3D) nanocomposites through aqueous phase exfoliation, non-covalent functionalization of building blocks with surfactants and polymers, and electrostatic interactions in solution leading to the nanocomposites assembly and organization. By combining molybdenum disulfide (MoS 2) layers with graphene nanoplatelets (GnPs) to form a binary 2D composite (MoS 2 /GnP), and subsequently incorporating multiwalled carbon nanotubes (MWNTs) to create ternary 3D composites, we explore their potential as catalysts for the oxygen reduction reaction (ORR) critical in fuel cells. Characterization techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction elucidate material composition and structure. Our electrochemical studies reveal insights into the kinetics of the reactions and structure–activity relationships. Both the (MoS 2 /GnP)-to-MWNT mass ratio and nitrogen-doping of GnPs (N -GnPs) play a key role on the electrocatalytic ORR performance. Notably, the (MoS 2 / N -GnP)/MWNT material, with a 3:1 mass ratio, exhibits the most effective ORR activity. All catalysts demonstrate good long-term stability and methanol crossover tolerance. This facile fabrication method and observed trends offer avenues for optimizing composite electrocatalysts further. [ABSTRACT FROM AUTHOR]

Ionic liquid modification for carbon-supported platinum (Pt/C) electrocatalysts to enhance their oxygen reduction reaction (ORR) activity has been well recognized. However, the research has only been reported on the low-Pt-loading Pt/C electrocatalysts, e.g., 20 wt%, while in practical applications, usually high-Pt-loading Pt/C electrocatalysts of 45–60 wt% are used. In this work, ionic liquid modification is systematically investigated for a Pt/C electrocatalyst with 60 wt% Pt loading for its ORR activity in the cathode in proton exchange membrane fuel cells (PEMFCs). Various adsorption amounts are studied on the catalyst surface. Different modification behavior is found. Mechanism exploration shows that the adsorption of ionic liquid mainly happens on the Pt electrocatalyst surface and in the micropores of the carbon support. The highest fuel cell power performance is achieved at an ionic liquid loading of 7 wt%, which is much higher than the 3 wt% reported for the low-Pt-loading Pt/C. [ABSTRACT FROM AUTHOR]

Trillion of cigarette butts are annually littered without being recycled. This work aims at valorizing the whole cigarette butts and their components (paper, filter and tobacco) into Fe‐Nx‐C electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The pristine wastes were pyrolyzed at 450 °C, activated with KOH at 700 °C, blended with iron phthalocyanine (FePc) precursor, and heat‐treated at 600 °C to produce a robust Fe‐Nx‐C material with ORR active units. The effect of the cigarette components on the final electrocatalytic activity was evaluated by thoroughly investigating the surface chemistry with XPS. The electrocatalysts displayed similar results among the different components in both media due to comparable surface chemistry, especially concerning the nitrogen functional groups. The highest performance was obtained in alkaline where the electrocatalysts from whole cigarettes and paper (CIGF_450 and CIGPF_450) showed an E1/2 of 0.89 V vs RHE, slightly larger than that of Pt/C with 40 wt % of Pt, which encouraged to replace Pt‐based electrocatalysts in alkaline fuel cells. [ABSTRACT FROM AUTHOR]

Climate change is showing its impacts now more than ever. The intense use of fossil fuels and the resulting CO2 emissions are mainly to blame, accentuating the need to develop further the available energy conversion and storage technologies, which are regarded as effective solutions to maximize the use of intermittent renewable energy sources and reduce global CO2 emissions. This work comprehensively overviews the most recent progress and trends in the use of transition metal-based electrocatalysts for three crucial reactions in electrochemical energy conversion and storage, namely, the oxygen evolution (OER), oxygen reduction (ORR), and hydrogen evolution (HER) reactions. By analyzing the state-of-the-art polyoxometalates (POMs) and metal-organic frameworks (MOFs), the performance of these two promising types of materials for OER, ORR, and HER is compared to that of more traditional transition metal oxides and alloy-based electrocatalysts. Both catalytic activity and stability are highly influenced by the adsorption energies of the intermediate species formed in each reaction, which are very sensitive to changes in the microstructure and chemical microenvironment. POMs and MOFs allow these aspects to be easily modified to fine-tune the catalytic performances. Therefore, their chemical tunability and versatility make it possible to tailor such properties to obtain higher electrocatalytic activities, or even to obtain derived materials with more compelling properties towards these reactions. [ABSTRACT FROM AUTHOR]

In the past decade, remarkable progress has been made in advancing heterogeneous single‐atom catalysts (SACs), propelled by their extraordinary properties such as unique activities, high selectivity, and efficient metal utilization. In contrast to their nanoparticle counterparts, SACs showcase distinct advantages, yet they are not exempt from limitations. A primary constraint lies in their relatively low metal content and lack of ensemble sites, potentially impacting overall catalytic activity. Stability concerns also arise, as isolated metal atoms may be prone to aggregation, oxidation, and other structural changes. To surmount these challenges, there is a burgeoning exploration of synergies between SACs and other active species, such as single atoms, atomic clusters, or nanoparticles. This approach holds promise for augmenting the efficiency of complex catalytic reactions. However, a systematic examination of their integration and potential synergy has been notably absent. This review strives to fill that gap by comprehensively exploring key interactions, complementary effects, and bifunctional roles of single atoms, atomic clusters and nanoparticles when combined in different compositions and configurations, especially for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) applications. Additionally, the review sheds new light on the underlying catalytic mechanisms by offering insights through specific case studies. In particular, it emphasizes the dynamic nature of each active species and their interactions within these innovative catalytic entities, specifically in the context of heterogeneous electrocatalytic processes, backed by compelling in situ and operando evidence. Concluding the discussion, the review addresses the current challenges and provides a glimpse into the prospects of these integrated catalytic systems in the future. The contents can serve as a valuable guide for the design of advanced catalysts, promoting the deliberate combination and synergy of binary or multiple active species to further advance the field of catalysis with a clear roadmap and easy assessments. [ABSTRACT FROM AUTHOR]

The quest for alternatives to Pt as an oxygen reduction electrocatalyst, possessing high activity, stability, and abundant reserves, holds great significance for H2/O2 fuel cells. Recently, metal‐nitrogen‐carbon (M‐N‐C) electrocatalysts have garnered substantial attention as promising substitutes. These electrocatalysts not only exhibit well‐defined structures but also offer the flexibility to adjust the central metal atoms and coordination atoms. It is beneficial in elucidating the active sites during the catalytic process and in the design of highly active electrocatalysts. In this review, the real active site of M‐N‐C electrocatalyst‐driven ORR is investigated in depth by in situ characterization techniques such as X‐ray absorption spectroscopy, Raman spectroscopy, Fourier‐transform infrared spectroscopy. It′s worth noting that the catalytic activity of M‐N‐C electrocatalysts originates from the dynamic evolution of electrocatalyst structure. Subsequently, we review various synthetic strategies, including the wet chemistry method, spatial confinement, and template‐assisted method, aimed at the rational design of M‐N‐C electrocatalysts. Moreover, recent progresses of M‐N‐C electrocatalysts with varying configurations, encompassing single‐atom, and double‐atom electrocatalysts are discussed, Finally, summary and perspectives on the development of M‐N‐C are provided. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have been utilized as the ideal candidates to preciously construct electrocatalysts. However, the highly ordered degree of COFs renders the catalytic centers closely stacked, which limits the utilization efficiency of catalytic sites. Herein, we have first constructed dangling and staggered‐stacking aldehyde (–CHO) from [4 + 3] COFs as catalytic centers for 2e− oxygen reduction reaction (ORR). The new catalytic COFs have unreacted dangling ‐CHO out of the COFs' planes, which are more easily exposed in electrolytes than the sites in the frameworks. More importantly, these –CHO adopt staggered stacking models, and thus provide larger space for mass transport than those with eclipsed stacking models. In addition, by tuning the triratopic linkers in the COFs, the catalytic properties are well modulated. The optimized COF shows high selectivity and activity for 2e− ORR, with H2O2 selectivity of 91%, and mass activity of 12.2 A g−1, respectively. The theoretical calculation further reveals the higher activity for the pyridine‐contained B18C6‐PTTA‐COF due to the promoted binding ability of the intermediate OOH* at the carbon in dangling –CHO. This work provides us with a new insight into designing electrocatalysts based on COFs. [ABSTRACT FROM AUTHOR]

[Display omitted] Intermetallic compounds are emerging as promising oxygen reduction reaction (ORR) catalysts for fuel cells due to their typically higher activity and durability compared to disordered alloys. However, the preparation of intermetallic catalysts often requires high-temperature annealing, which unfortunately leads to adverse sintering of the metal nanoparticles. Herein, we develop a scalable site-selective sulfur anchoring strategy that effectively suppresses alloy sintering, ensuring the formation of efficient intermetallic electrocatalysts with small sizes and high ordering degrees. The alloy-support interactions are precisely modulated by selectively modifying the alloy-support interfaces with oxidized sulfur species, thus simultaneously blocking both the nanoparticle migration and Oswald ripening pathways for sintering. Using this strategy, sub-5 nm PtCo intermetallic electrocatalysts enclosed by two atomic layers of Pt shells have been successfully prepared even at a metal loading higher than 30 wt%. The intermetallic catalysts exhibit excellent ORR performances in both rotating disk electrode and membrane electrode assembly conditions with a mass activity of 1.28 A mg Pt −1 at 0.9 V (vs. RHE) and a power density of 1.0 W cm−2 at a current density of 1.5 A cm−2. The improved performances result from the enhanced Pt-Co electronic interactions and compressive surface strain generated by the highly ordering structure, while the atomic Pt shells prevent the dissolution of Co under highly acidic conditions. This work provides new insights to inhibit the sintering of nanoalloys and would promote the scalable synthesis and applications of platinum-based intermetallic catalysts. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) was initially evaluated as a potential preprocessing method for preparing biomass-based carbon electrocatalysts in this study. The AD pretreatment succeeded in the structural depolymerization and nitrogen enrichment of Hybrid Pennisetum, which provided favorable conditions to achieve efficient and homogeneous nitrogen introduction due to microorganism community enrichment and provided a porous structure by degradation of the biodegradable components. The resulted biochar exhibited improved physiochemical properties including higher specific surface areas, nitrogen content and graphitization degree than that obtained from pyrolyzing raw biomass. These improvements were positively correlated with the AD time and showed to have enhanced the performance in oxygen reduction reaction and practical microbial fuel cell applications. Amongst the investigated samples, the obtained biochar pretreated by AD for 15 days exhibited the most excellent performance with an onset potential of 0.17 V (VS. saturated calomel electrode) and the maximal power density of 543.2 mW cm−2 assembled in microbial fuel cells. This study suggested applying AD as a new biological pretreatment in the preparation of biomass-based electrocatalysts, and provided a unique pathway for fabricating high-performance biochar-based catalysts by structure optimization and N-containing active sites construction via gentle biological method, thereby providing a cost-effective method to fabricate metal-free catalysts for oxygen reduction reaction. Highlights: Anaerobic digestion pretreatment was conducted to assist electrocatalyst preparation. The biological pretreatment succeeded in carbohydrates decomposition and nitrogen enrichment. Pretreatment derived biochar significantly increased the ORR activity and microbial fuel cell performance. [ABSTRACT FROM AUTHOR]

The Mn-based catalysts with atomically dispersed Mn-SAs and MnP-NPs embedded in the porous and defective N, P co-doped carbon substrate by simple one-pot in situ doping-phosphatization strategy delivered excellent ORR performance. [Display omitted] • The MnSA-MnP-980℃ is synthesized by simple one-pot in situ doping-phosphatization strategy. • The existence of MnP NPs is conducive to increase the adsorption of intermediates on Mn SAs. • High value-added utilization of low cost FCC slurry. • The MnSA-MnP-980℃ exhibites excellent ORR performance in alkaline media. • Zn-air battery equipped with MnSA-MnP-980℃ displays power density superior to the commercial Pt/C. An electrocatalyst of single-atomic Mn sites with MnP nanoparticles (NPs) on N, P co-doped carbon substrate was constructed to enhance the catalytic activity of oxygen reduction reaction (ORR) through one-pot in situ doping-phosphatization strategy. The optimized MnSA-MnP-980℃ catalyst exhibits an excellent ORR activity in KOH electrolyte with a half-wave potential (E 1/2) of 0.88 V (vs. RHE), and the ORR current density of MnSA-MnP-980℃ maintained 97.9 % for over 25000 s chronoamperometric i-t measurement. When using as the cathode, the MnSA-MnP-980℃ displays a peak power density of 51 mW cm−2 in Zinc-Air batteries, which observably outperformed commercial Pt/C (20 wt%). The X-ray photoelectron spectroscopy reveal that the doped P atoms with a strong electron-donating effectively enhances electron cloud density of Mn SAs sites, facilitating the adsorption of O 2 molecules. Meanwhile, the introduction of MnP NPs can regulate the electronic structure of Mn SAs sites, making Mn SAs active sites exist in a low oxidation state and are less positively charged, which can supply electrons for ORR process to narrow the adsorption energy barrier of ORR intermediates. This work constructs novel active sites with excellent ORR properties and provides valuable reference for the development of practical application. [ABSTRACT FROM AUTHOR]

A novel strategy to prepare COF-derived carbon materials mediated by volatile guest molecule for efficient electrocatalytic oxygen reduction reaction is reported. [Display omitted] Covalent organic framework (COF) derived metal-free carbon materials have emerged as promising electrocatalysts for the oxygen reduction reaction (ORR). Herein, a volatile guest molecule mediated-pyrolysis strategy was explored on a designed thiophene-rich and imine-linked COF. Through the modulation of guest mediators (iodine and sulfur), the properties of the as-obtained carbon materials can be well regulated. The optimized nitrogen and sulfur dual-doped carbon electrocatalyst demonstrates remarkable ORR activity with a half-wave potential of 0.87 V and impressive durability, with only an 8% current loss over 21 h. The corresponding assembled zinc-air battery has a comparable power density (60 mW cm−2) to that of the commercial Pt/C. It is proposed that the coexistence of the guest mediators iodine and sulfur in the channels of COFs could prevent the loss of N species. The enhanced N content and N/S ratio are assumed to be responsible for the ORR performance. This study puts forward a novel strategy to prepare COF-derived carbon materials mediated by volatile guest molecules, which may provide new insights into the development of metal-free ORR catalysts. [ABSTRACT FROM AUTHOR]

Plasma etching treatment is an effective strategy to improve the electrocatalytic activity, but the improvement mechanism is still unclear. In this work, a nitrogen‐doped carbon nanotube‐encased iron nanoparticles (Fe@NCNT) catalyst is synthesized as the model catalyst, followed by plasma etching treatment with different parameters. The electrocatalytic activity improvement mechanism of the plasma etching treatment is revealed by combining the physicochemical characterizations and electrochemical results. As a result, highly active metal–nitrogen species introduced by nitrogen plasma etching treatment are recognized as the main contribution to the improved electrocatalytic activity, and the defects induced by plasma etching treatment also contribute to the improvement of the electrocatalytic activity. In addition, the prepared catalyst also demonstrates superior ORR activity and stability than the commercial Pt/C catalyst. [ABSTRACT FROM AUTHOR]

Studying the ORR activity of platinum-based electrocatalysts is an urgent task in the development of materials for proton-exchange membrane fuel cells. The catalytic ink composition and the formation technique of a thin layer at the RDE play a significant role in studying ORR activity. The use of a polymer ionomer in the catalytic ink provides viscosity as well as proton conductivity. Nafion is widely used as an ionomer for research both at the RDE and in the MEA. The search for ionomers is a priority task in the development of the MEA components to replace Nafion. The study also considers the possibility of using the LF4-SK polymer as an alternative ionomer. The comparative results on the composition and techniques of applying the catalytic layer using LF4-SK and Nafion ionomers are presented, and the influence of the catalytic ink composition on the electrochemical characteristics of commercial platinum–carbon catalysts and a highly efficient platinum catalyst based on an N-doped carbon support is assessed. [ABSTRACT FROM AUTHOR]

Climate change is showing its impacts now more than ever. The intense use of fossil fuels and the resulting CO2 emissions are mainly to blame, accentuating the need to develop further the available energy conversion and storage technologies, which are regarded as effective solutions to maximize the use of intermittent renewable energy sources and reduce global CO2 emissions. This work comprehensively overviews the most recent progress and trends in the use of transition metal-based electrocatalysts for three crucial reactions in electrochemical energy conversion and storage, namely, the oxygen evolution (OER), oxygen reduction (ORR), and hydrogen evolution (HER) reactions. By analyzing the state-of-the-art polyoxometalates (POMs) and metal-organic frameworks (MOFs), the performance of these two promising types of materials for OER, ORR, and HER is compared to that of more traditional transition metal oxides and alloy-based electrocatalysts. Both catalytic activity and stability are highly influenced by the adsorption energies of the intermediate species formed in each reaction, which are very sensitive to changes in the microstructure and chemical microenvironment. POMs and MOFs allow these aspects to be easily modified to fine-tune the catalytic performances. Therefore, their chemical tunability and versatility make it possible to tailor such properties to obtain higher electrocatalytic activities, or even to obtain derived materials with more compelling properties towards these reactions.

Currently, the development of nonmetallic oxygen reduction reaction (ORR) catalysts based on heteroatomic-doped carbon materials is receiving increaseing attention in the field of fuel cells. Here, we used enzymolytic lignin (EL), melamine, and thiourea as carbon, nitrogen, and sulfur sources and NH4Cl as an activator to prepare N- and S-codoped lignin-based polyporous carbon (ELC) by one-step pyrolysis. The prepared lignin-derived biocarbon material (ELC-1-900) possessed a high specific surface area (844 m2 g−1), abundant mesoporous structure, and a large pore volume (0.587 cm3 g−1). The XPS results showed that ELC-1-900 was successfully doped with N and S. ELC-1-900 exhibited extremely high activity and stability in alkaline media for the ORR, with a half-wave potential (E1/2 = 0.88 V) and starting potential (Eonset = 0.98 V) superior to those of Pt/C catalysts and most non-noble-metal catalysts reported in recent studies. In addition, ELC-1-900 showed better ORR stability and methanol tolerance in alkaline media than commercial Pt/C catalysts. [ABSTRACT FROM AUTHOR]

The use of platinum-free (Pt) cathode electrocatalysts for oxygen reduction reactions (ORRs) has been significantly studied over the past decade, improving slow reaction mechanisms. For many significant energy conversion and storage technologies, including fuel cells and metal–air batteries, the ORR is a crucial process. These have motivated the development of highly active and long-lasting platinum-free electrocatalysts, which cost less than proton exchange membrane fuel cells (PEMFCs). Researchers have identified a novel, non-precious carbon-based electrocatalyst material as the most effective substitute for platinum (Pt) electrocatalysts. Rich sources, outstanding electrical conductivity, adaptable molecular structures, and environmental compatibility are just a few of its benefits. Additionally, the increased surface area and the simplicity of regulating its structure can significantly improve the electrocatalyst's reactive sites and mass transport. Other benefits include the use of heteroatoms and single or multiple metal atoms, which are capable of acting as extremely effective ORR electrocatalysts. The rapid innovations in non-precious carbon-based nanomaterials in the ORR electrocatalyst field are the main topics of this review. As a result, this review provides an overview of the basic ORR reaction and the mechanism of the active sites in non-precious carbon-based electrocatalysts. Further analysis of the development, performance, and evaluation of these systems is provided in more detail. Furthermore, the significance of doping is highlighted and discussed, which shows how researchers can enhance the properties of electrocatalysts. Finally, this review discusses the existing challenges and expectations for the development of highly efficient and inexpensive electrocatalysts that are linked to crucial technologies in this expanding field. [ABSTRACT FROM AUTHOR]

Electrocatalysts with high efficiency and low cost are always urgently needed for oxygen reduction reaction (ORR). As a new carbon allotrope, graphdiyne (GDY) has received much attention due to its unique chemical structure containing sp- and sp2-hybridized carbons, and intrinsic electrochemical activity ascribed to its inherent conductivity. Herein, we prepared two graphdiyne materials named GDY nanotube and nitrogen-doped GDY (NGDY) nanotube via cross-coupling reactions on the surface of Cu nanowires. As metal-free catalysts, their electrocatalytic activities for ORR were demonstrated. The results showed that the NGDY nanotube presents more excellent electrochemical performance than that of the GDY nanotube, including more positive potential and faster kinetics and charge transfer process. The improvement can be ascribed to the greater number of structural electrocatalytic active sites from nitrogen atoms as well as the hollow nanotube morphology, which is beneficial to the adsorption of oxygen and acceleration of the catalytic reaction. This work helps develop high-quality graphdiyne-based electrocatalysts with well-defined chemical structures and morphologies for various electrochemical reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] Exploiting clean, highly efficient energy storage and conversion device like Zn-air battery is of significance for alleviating the energy and environmental crises of this society. Metal organic coordination polymers/frameworks have been regarded as ideal templates to synthesize non-noble metal catalysts for a long time. However, the high density of metal nodes inevitably leads to the heavy aggregation of metal nanoparticles during thermolysis transformation process, which greatly hinders the maximizing of electrochemical performances. Herein, covalent organic framework (COF) has been employed to anchor the quantificational Fe ions (COF-Fe) and then confined into the macropores of g-C 3 N 4 to improve the dispersion of metal active sites and avoid severe aggregation during high temperature pyrolysis. After calcination, the metal nanoparticles highly dispersed Fe-CFN catalysts can be obtained. The optimal Fe-CFN-800 catalysts exhibit excellent ORR and OER performances with the potential difference between ORR and OER of merely 0.723 V. Moreover, experimental way and DFT theoretical calculations are also employed to disclose the reaction mechanism. Finally, the all-solid-state and aqueous Zn-air batteries assembled with the optimized Fe-CFN-800 as cathode present excellent performances with high peak power density, flexible rate performance, strong discharge stability and long-term charge–discharge cycling performance. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) plays a pivotal role in electrochemical energy conversion and chemical production. Two‐electron (2e−) charge transfer for oxygen reduction is considered a promising method for the on‐site production of hydrogen peroxide (H2O2), which requires electrocatalysts with high H2O2 selectivity and ORR activity. Noble metal alloys (e.g., Pt‐Hg and Pd‐Hg) have been prevalent materials of choice due to their desirable intrinsic activity, but their scarcity and high cost seriously hinder their widespread application in practice. Self‐doped heteroatomic carbon‐based electrocatalysts, derived from abundant and inexpensive biomass, have emerged as attractive candidates for on‐site H2O2 production. This review summarizes the fundamentals and recent advances in H2O2 production via 2e− ORR, including basic catalytic mechanisms, the influence of electrolyte pH and porous structure of catalysts, selectivity assessment methods, determination of the cumulative H2O2 concentration, development of biomass‐derived carbon‐based catalyst, and electrochemical device designs. Current challenges and proposed opportunities are also presented with an emphasis on large‐scale electrochemical H2O2 synthesis. [ABSTRACT FROM AUTHOR]

Electrochemical oxygen reduction reaction (ORR) is an attractive and alternative route for the on‐site production of hydrogen peroxide (H2O2). The electrochemical synthesis of H2O2 in neutral electrolyte is in early studying stage and promising in ocean‐energy application. Herein, N‐doped carbon materials (N‐Cx) with different N types are prepared through the pyrolysis of zeolitic imidazolate frameworks. The N‐Cx catalysts, especially N‐C800, exhibit an attracting 2e− ORR catalytic activity, corresponding to a high H2O2 selectivity (≈95%) and preferable stability in 0.5 m NaCl solution. Additionally, the N‐C800 possesses an attractive H2O2 production amount up to 631.2 mmol g−1 h−1 and high Faraday efficiency (79.8%) in H‐type cell. The remarkable 2e− ORR electrocatalytic performance of N‐Cx catalysts is associated with the N species and N content in the materials. Density functional theory calculations suggest carbon atoms adjacent to graphitic N are the main catalytic sites and exhibit a smaller activation energy, which are more responsible than those in pyridinic N and pyrrolic N doped carbon materials. Furthermore, the N‐C800 catalyst demonstrates an effective antibacterial performance for marine bacteria in simulated seawater. This work provides a new insight for electro‐generation of H2O2 in neutral electrolyte and triggers a great promise in ocean‐energy application. [ABSTRACT FROM AUTHOR]

Due to their low cost, accessibility of resources, and improved stability and durability, carbon‐based nanomaterials have attracted significant attention as cathode materials for oxygen reduction reactions. These materials also exhibit intrinsic physical and electrochemical features. However, their potential for use in fuel cells is constrained by low ORR activity and slow kinetics. Carbon nanomaterials can be functionalized and doped with heteroatoms to change their morphologies and generate a large number of oxygen reduction active sites to lessen the problems. Doping the carbon lattice with heteroatoms like N, S, and P and functionalizing the carbon structure with −OCH3, −F, −COO−, −O− are two of these modifications that can change specific properties of the carbon nanomaterials like expanding interlayer distance, producing a large number of active sites, and enhancing oxygen reduction activity. When compared to pristine carbon‐based nanomaterials, these doped and functionalized carbon nanomaterials, including their composites, exhibit accelerated rate performance, outstanding stability, and higher methanol tolerance. This article summarizes the most recent developments in heteroatom‐doped and functionalized carbon‐based nanomaterials, covering different synthesis approaches, characterization methods, electrochemical performance, and oxygen reduction reaction mechanisms. As cathode materials for fuel cell technologies, the significance of heteroatom co‐doping and transition metal heteroatom co‐doping is also underlined. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is a key cathodic reaction in energy-converting systems, such as fuel cells (FCs). Thus, it is of utmost importance to develop cost-effective and efficient electrocatalysts (ECs) without noble metals to substitute the Pt-based ones. This study focuses on polyoxometalate (POM)-based ECs for ORR applications. A Wells–Dawson POM salt K7 [P2W17(FeOH2)O61].·20H2O was immobilised onto graphene flakes and multiwalled carbon nanotubes doped with nitrogen, denominated as P2W17Fe@GF_N8 and P2W17Fe@MWCNT_N8. The successful preparation of the composites was proved with various characterisation techniques, including FTIR, XPS and SEM. Both materials showed good ORR performance in an alkaline medium with similar potential onset values of ~0.84 V vs. RHE and diffusion-limiting current densities of −3.9 and −3.3 mA cm−2 for P2W17Fe@MWCNT_N8 and P2W17Fe@GF_N8, respectively. Furthermore, both composites presented low Tafel slopes (48–58 mV dec−1). Chronoamperometric tests revealed that the as-prepared nanocomposites rendered a significant improvement achieving between 90 and 94% of current retention in tolerance to methanol in comparison with Pt/C, and moderate to good long-term electrochemical stability with current retentions comprised between 68 and 88%. This work reinforces the use of POMs as important electroactive species for the preparation of alternative ORR electrocatalysts, exhibiting good activity, stability and selectivity towards the ORR in the presence of methanol. [ABSTRACT FROM AUTHOR]

Abstract Plasma etching treatment is an effective strategy to improve the electrocatalytic activity, but the improvement mechanism is still unclear. In this work, a nitrogen‐doped carbon nanotube‐encased iron nanoparticles (Fe@NCNT) catalyst is synthesized as the model catalyst, followed by plasma etching treatment with different parameters. The electrocatalytic activity improvement mechanism of the plasma etching treatment is revealed by combining the physicochemical characterizations and electrochemical results. As a result, highly active metal–nitrogen species introduced by nitrogen plasma etching treatment are recognized as the main contribution to the improved electrocatalytic activity, and the defects induced by plasma etching treatment also contribute to the improvement of the electrocatalytic activity. In addition, the prepared catalyst also demonstrates superior ORR activity and stability than the commercial Pt/C catalyst.

Abstract The stability of nanoparticles is a major challenge in thermal and electrocatalysis. This is especially true for core‐shell nanoparticles where only a few monolayers of noble metal protect the usually non‐noble core material. In this work, we utilize the practical nobility concept to engineer stable core‐shell nanoparticles with a self‐passivating core material. Specifically, tantalum carbide as core material in combination with a 1–3 monolayer thick platinum shell exhibits exceptional stability in aqueous media. The core‐shell catalyst shows no sign of structural changes after 10,000 degradation cycles up to 1.0 VRHE. Due to the efficient passivation of tantalum carbide at the solid/liquid interface, the dissolution reduces by a factor of eight compared to bare Pt. Our findings confirm that passivating core materials are highly beneficial for the stabilization of core‐shell nanomaterials in aqueous media. They open up new ways for the rational design of cost‐efficient but stable non‐noble core – platinum shell nanoparticles where harsh, oxidizing conditions are employed.

The oxygen reduction reaction (ORR) plays a pivotal role in electrochemical energy conversion and chemical production. Two‐electron (2e−) charge transfer for oxygen reduction is considered a promising method for the on‐site production of hydrogen peroxide (H2O2), which requires electrocatalysts with high H2O2 selectivity and ORR activity. Noble metal alloys (e.g., Pt‐Hg and Pd‐Hg) have been prevalent materials of choice due to their desirable intrinsic activity, but their scarcity and high cost seriously hinder their widespread application in practice. Self‐doped heteroatomic carbon‐based electrocatalysts, derived from abundant and inexpensive biomass, have emerged as attractive candidates for on‐site H2O2 production. This review summarizes the fundamentals and recent advances in H2O2 production via 2e− ORR, including basic catalytic mechanisms, the influence of electrolyte pH and porous structure of catalysts, selectivity assessment methods, determination of the cumulative H2O2 concentration, development of biomass‐derived carbon‐based catalyst, and electrochemical device designs. Current challenges and proposed opportunities are also presented with an emphasis on large‐scale electrochemical H2O2 synthesis.

Co 4 N@NCNTs with superior ORR and OER activity and stability were prepared by triazole -assisted in-situ pyrolysis of MOF-74/TZ. [Display omitted] • Co 4 N@NCNTs were prepared by triazole -assisted in-situ pyrolysis of MOF-74/TZ. • The possible structure outward contract evolution mechanism of Co 4 N@NCNTs was investigated. • Co 4 N@NCNT-900 showed superior ORR and OER catalytic activity and stability. • A ZAB with Co 4 N@NCNT-900 air cathode delivers higher power density and specific capacity. The design of high-performance oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) dual-functional catalysts is not only important for the further applications of zinc-air batteries (ZABs) but also a major challenge in the field of energy conversion. The cheap 1,2,4-triazole (1,2,4-TZ) can be decomposed easily by heat, making it a high research value in carbon catalysts derived from metal-organic frameworks (MOFs). Here, Co 4 N particles encapsulated at the top of N -doped carbon nanotubes (Co 4 N@NCNTs) were conveniently prepared by 1,2,4-TZ-assisted pyrolysis of Co-MOF-74 for the first time. Owing to the excellent activity of Co 4 N particles and the highly graphitized N -doped carbon nanotubes (NCNTs), Co 4 N@NCNTs obtained at 900 °C (Co 4 N@NCNT-900) exhibited astonishing catalytic performance in both ORR and OER, and high reversible oxygen bifunctional activity (ΔE = 0.685 V). Moreover, Co 4 N@NCNT-900 displayed a larger discharge power density (122 mW cm−2), a better specific capacity (811.8 mAh g−1), and more excellent durability during the ZAB test, implying that Co 4 N@NCNT-900 can act as a bifunctional high active catalyst in ZABs. [ABSTRACT FROM AUTHOR]

[Display omitted] Developing highly efficient, low-cost, and stable bifunctional oxygen electrocatalysts is essential for the wide popularization of rechargeable Zn-air batteries. Combining zero-dimensional metal nanoparticles with two-dimensional metal oxide nanosheets is an appealing strategy to balance performance and cost. However, the precise construction of these composites remains a great challenge, and their interaction mechanisms lack thorough study. Herein, a cobalt-oxide-based bifunctional oxygen electrocatalyst comprising a rich Co-CoO heterointerface (CoO/Co@NG) was synthesized via a NaCl sealing-assisted pyrolysis strategy. The NaCl crystals played the role of a closed nanoreactor, which facilitated the formation of a CoO-Co heterojunction. Experimental results and theoretical calculations confirmed that the ingeniously constructed heterojunction expedited the oxygen reduction reaction and oxygen evolution reaction kinetics, which is superior to Pt/C. When serving as the air electrode in an assembled liquid-state Zn-air battery, the battery shows high power density (215 mW cm−2), specific capacity (710 mAh g zn −1), and outstanding durability (720 h at 10 mA cm−2). This work provides an innovative avenue to design high-performance heterojunction electrocatalysts for perdurable Zn-air batteries. [ABSTRACT FROM AUTHOR]

Much attention has been paid to the development of high‐performance electrocatalytic reactions by exploiting the plasmonic properties of noble metal nanoparticles. In this study, ultrathin Pt layers with different coverage ratios were prepared on plasmonic octahedral Au nanoparticles (NPs) by underpotential deposition (UPD) of Cu followed by redox replacement with Pt. The effect of the Cu UPD cycle on the deposited Cu and redox‐substituted Pt layers on octahedral Au NPs was investigated to evaluate the electrocatalytic activity of Pt‐decorated octahedral NPs for the oxygen reduction reaction (ORR). By varying the number of cycles of Cu UPD and Pt replacement, the coverage by the Pt layer on the Au NPs could be easily controlled. The resulting Pt‐coated octahedral Au NPs exhibited three times higher specific activity for ORR than commercial Pt/C nanocatalysts due to the deposited Pt layer reflecting the {111} plane of the core. The ORR activity of Pt‐coated octahedral Au NPs could be enhanced by photoexcitation with monochromatic LED irradiation, and the increase in enhancement factor was even greater when irradiated with a wavelength that could efficiently excite the localized surface plasmon resonance (LSPR) of the NPs. Analysis shows that this improvement is due to improved diffusion of oxygen to the electrode. [ABSTRACT FROM AUTHOR]

We report the development of a novel electrocatalyst composed of nanoarchitectured spinel cobalt manganese oxide and graphene for the oxygen reduction reaction (ORR). A combination of co-precipitation and hydrothermal methods achieved the unique nanoarchitecture of the electrocatalyst. The formation of CoMn2O4 electrocatalyst was confirmed by X-ray diffraction, transmission electron microscopy, and other spectroscopic and microscopic techniques. In addition to synthesizing CoxOy and MnxOy as control electrocatalysts, we created a physical mixture of CoMn2O4 and graphene to investigate the impact of their interface on electrocatalytic activity. Our findings indicate that CoMn2O4/graphene exhibits improved ORR activity, stability, and methanol tolerance in an alkaline medium. This enhancement can be attributed to the synergistic effect and strong interface interaction between CoMn2O4 and graphene. This study demonstrates the potential of the proposed electrocatalyst as a cost-effective and eco-friendly alternative for oxygen reduction in fuel cells applications. [ABSTRACT FROM AUTHOR]

With the increasing demand for green and efficient energy storage devices， advanced technologies for clean energy conversion have attracted close attention from researchers. Fuel cells with environmental friendliness and high energy conversion efficiency are promising alternatives to traditional energy sources. However， Pt catalysts with high commercialization degrees in the industrial catalysis field have some problems， such as high cost， poor stability and weak anti-toxicity ability， which limits the further development of fuel cells. The development of non-Pt oxygen reduction reaction （ORR） catalysts with abundant reserves， low cost and excellent performance is an effective way to improve the efficiency of fuel cells. In this paper， based on the research results at home and abroad in recent years， various types of non-Pt system ORR catalysts， including non-precious metal and non-metal catalysts， are systematically introduced. The advantages， disadvantages and modification strategies of various catalysts are summarized， and challenges and prospects for the development of ORR electrocatalysts are put forward. [ABSTRACT FROM AUTHOR]

The development of efficient non-precious metal electrocatalysts for oxygen reduction reaction (ORR) to replace Pt-based methods is crucial for the applications of fuel cells and metal–air batteries. In this study, a bimetallic M-N-C catalyst with highly dispersed dual-atom Fe/Mn-Nx sites immobilized on N-doped bamboo-like carbon nanotubes is prepared by the ball-milling and calcination of dual-MOFs as precursors. The rich N-doping and abundant M–Nx species contribute to the excellent intrinsic ORR activity of the catalyst, and the unique bamboo-like nanotubes morphology is beneficial for facilitating electron transfer and mass transport while simultaneously enabling the exposure of active sites. As expected, the optimized Z-Fe1Mn1-NC catalyst exhibits efficient ORR activity with a half-wave potential (E1/2) of 0.80 V in acid and 0.82 V in alkaline, and a higher electrochemical stability with the current density maintained at 91% (in 0.1 M KOH) and 86% (0.1 M HClO4) of its initial current density after 15 h of a chronoamperometric test at a high potential of 0.7 V. When further applied to Zn–air batteries, the catalyst also delivers a high open-circuit voltage, large power density, and outstanding rate performance. This work provides a novel means of designing dual metal M–Nx site-based M-N-C catalysts for ORR sustainable energy applications. [ABSTRACT FROM AUTHOR]

The design of highly efficient promoters for the oxygen reduction reaction (ORR) is an important challenge in the large‐scale distribution of proton exchange membrane (PEM) fuel cells. Hygroscopic cerium oxide (CeO2) is here proposed as co‐catalyst in combination with Pt. Physical chemical characterizations, by means of X‐ray diffraction, vibrational spectroscopy, morphological and thermal analyses, were carried out, demonstrating high water affinity of the synthesized CeO2 nanoparticles. Composite catalysts (i. e., Pt : CeO2 1 : 0.5 and 1 : 1 wt:wt), were studied by either rotating disk electrode (RDE) and fuel cell tests performed at 80 °C and 110 °C. Interestingly, the cell adopting the Pt : CeO2 1 : 0.5 catalyst enabled the achievement of high power densities reaching ∼80 and ∼35 mW cm−2 under low relative humidity and high temperatures. This result demonstrates that tuning material surface properties (e. g. oxygen vacancies) could significantly boost the electrochemical performance of cathodes as a combined result of optimized water retention and improved ORR kinetic. [ABSTRACT FROM AUTHOR]

As an eco-friendly oxidant and energy carrier, H2O2 is used in various fields. The industrial production of H2O2 mostly depends on the large-scale anthraquinone oxidation processes with high costs. Electrocatalytic production of H2O2 has attracted attention as a renewable and cost-effective approach to replace traditional ones. With the recent development of oxygen reduction reaction (ORR) catalysts, remarkable progress in electrocatalysts for electrocatalytic H2O2 production by 2e- ORR has been reported. This review summarizes a detailed overview of the recent progress in 2e- ORR for H2O2 production with the mechanism and various efficient catalysts. The catalysts were divided into three parts: noble metal-based catalyst, non-noble metal-based catalyst, and non-metalbased catalyst. The influences of the catalytic activity and selectivity were also discussed. Finally, this review explores the prospects of electrocatalytic 2e- ORR for H2O2 synthesis and potential research directions for electrocatalysts. It aims to offer guidance in designing efficient 2e- ORR electrocatalysts and inspire further innovation in electrocatalytic H2O2 synthesis. [ABSTRACT FROM AUTHOR]

One of the most popular solutions for electrochemical energy storage is metal–air batteries, which could be employed in electric vehicles or grid energy storage. Metal–air batteries have a higher theoretical energy density than lithium-ion batteries. The crucial components for the best performance of batteries are the air cathode electrocatalysts and corresponding electrolytes. Herein, we present several of the latest studies on electrocatalysts for air cathodes and bifunctional oxygen electrocatalysts for aqueous zinc–air and aluminium–air batteries. [ABSTRACT FROM AUTHOR]

The preparation of porous carbon from biomass flour as high-performance electrocatalysts for oxygen reduction reaction (ORR) was reported in this paper. The fast and vigorous pyrolysis of flour was induced in the presence of magnesium nitrate, by which MgO nanoparticles were introduced as nano-template to create numerous nanopores and to increase the specific surface area (SSA). The pore structure, SSA and elemental dopant were influenced by the ratio of biomass to magnesium nitrate and calcination temperature. A highly hierarchical micro-meso-macroporous carbon, which was calcined at 1000 °C and had a high SSA of 1880 m2 g−1, exhibited the best ORR performance in terms of fast ORR kinetic, superior stability and excellent methanol tolerance. [ABSTRACT FROM AUTHOR]

As a key role in hindering the large-scale application of fuel cells, oxygen reduction reaction has always been a hot issue and nodus. Aiming to explore state-of-art electrocatalysts, this paper reviews the latest development of nonmetallic catalysts in oxygen reduction reactions, including single atoms doped with carbon materials such as N, B, P or S and multi-doped carbon materials. Afterward, the remaining challenges and research directions of carbon-based nonmetallic catalysts are prospected. [ABSTRACT FROM AUTHOR]

Ce-based materials have been widely used in photocatalysis and other fields because of their rich redox pairs and oxygen vacancies, despite research on the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) remaining scare. However, most pristine cerium-based materials, such as CeO2, are non-conductive materials. Therefore, how to obtain highly conductive and stable OER/ORR electrocatalysts is currently a hot research topic. To overcome these limitations, researchers have proposed a variety of strategies to promote the development of Ce-based electrocatalysts in recent years. This progress report focuses on reviewing new strategies concerning three categories of Ce-based electrocatalysts: metal–organic framework (MOF) derivatives, structure tuning, and polymetallic doping. It also puts forward the main existing problems and future prospects. The content of cerium in the crust is about 0.0046%, which is the highest among the rare earth elements. As a low-cost rare earth material, Ce-based materials have a bright future in the field of electrocatalysis due to replacing precious metal and some transition metals. [ABSTRACT FROM AUTHOR]

Biomass-derived porous carbon has gained significant attention as a cost-effective and sustainable material in non-noble metal carbon-based electrocatalysts for the oxygen reduction reaction (ORR). However, during the preparation of transition metal catalysts based on biomass-derived porous carbon, the agglomeration of transition metal atoms often occurs, leading to a notable decline in catalytic activity. In this study, we present a straightforward synthetic approach for the preparation of nitrogen-enriched soybean-derived porous carbon (Co@SP-C-a) as an electrocatalyst for the ORR. To achieve this, we employed a two-step method. In the first step, a chemical activator (KCl) was utilized to enhance the porosity of the self-doped nitrogen biomass carbon material. In the second step, a constant pressure drop funnel technique was employed to uniformly disperse bimetal cobalt/zinc-based zeolitic imidazolium frameworks (ZIF-L and ZIF-67) containing different metal ions (Zn2+ and Co2+) into the activated biomass carbon material. Subsequent high-temperature calcination of the ZIF-L and ZIF-67@SP-C-a composite precursor yielded the Co@SP-C-a catalyst. The obtained catalyst exhibited remarkable ORR activity in an alkaline solution (Eonset = 0.89 V, E1/2 = 0.83 V, JL = −6.13 mA·cm−2) and exceptional long-term stability. This study presents an effective strategy to prevent the agglomeration of metal nanoparticles when integrating them with biomass-based carbon materials, thus leading to enhanced catalytic performance. [ABSTRACT FROM AUTHOR]

[Display omitted] The development of a convenient and universal strategy for the synthesis of inorganic–organic hybrid nanomaterials with phenolic coating on the surface is of special significance for the preparation of electrocatalysts. In this work, we report an environmentally friendly, practical, and convenient method for one-step reduction and generation of organically capped nanocatalysts using natural polyphenol tannic acid (TA) as reducing agents and coating agents. TA coated metal (Pd, Ag and Au) nanoparticles are prepared by this strategy, among which TA coated Pd nanoparticles (PdTA NPs) show excellent oxygen reduction reaction activity and stability under alkaline conditions. Interestingly, the TA in the outer layer makes PdTA NPs methanol resistant, and TA acts as molecular armor against CO poisoning. We propose an efficient interfacial coordination coating strategy, which opens up new way to regulate the interface engineering of electrocatalysts reasonably and has broad application prospects. [ABSTRACT FROM AUTHOR]

Abstract Much attention has been paid to the development of high‐performance electrocatalytic reactions by exploiting the plasmonic properties of noble metal nanoparticles. In this study, ultrathin Pt layers with different coverage ratios were prepared on plasmonic octahedral Au nanoparticles (NPs) by underpotential deposition (UPD) of Cu followed by redox replacement with Pt. The effect of the Cu UPD cycle on the deposited Cu and redox‐substituted Pt layers on octahedral Au NPs was investigated to evaluate the electrocatalytic activity of Pt‐decorated octahedral NPs for the oxygen reduction reaction (ORR). By varying the number of cycles of Cu UPD and Pt replacement, the coverage by the Pt layer on the Au NPs could be easily controlled. The resulting Pt‐coated octahedral Au NPs exhibited three times higher specific activity for ORR than commercial Pt/C nanocatalysts due to the deposited Pt layer reflecting the {111} plane of the core. The ORR activity of Pt‐coated octahedral Au NPs could be enhanced by photoexcitation with monochromatic LED irradiation, and the increase in enhancement factor was even greater when irradiated with a wavelength that could efficiently excite the localized surface plasmon resonance (LSPR) of the NPs. Analysis shows that this improvement is due to improved diffusion of oxygen to the electrode.

Abstract The design of highly efficient promoters for the oxygen reduction reaction (ORR) is an important challenge in the large‐scale distribution of proton exchange membrane (PEM) fuel cells. Hygroscopic cerium oxide (CeO2) is here proposed as co‐catalyst in combination with Pt. Physical chemical characterizations, by means of X‐ray diffraction, vibrational spectroscopy, morphological and thermal analyses, were carried out, demonstrating high water affinity of the synthesized CeO2 nanoparticles. Composite catalysts (i. e., Pt : CeO2 1 : 0.5 and 1 : 1 wt:wt), were studied by either rotating disk electrode (RDE) and fuel cell tests performed at 80 °C and 110 °C. Interestingly, the cell adopting the Pt : CeO2 1 : 0.5 catalyst enabled the achievement of high power densities reaching ∼80 and ∼35 mW cm−2 under low relative humidity and high temperatures. This result demonstrates that tuning material surface properties (e. g. oxygen vacancies) could significantly boost the electrochemical performance of cathodes as a combined result of optimized water retention and improved ORR kinetic.

Covalent organic frameworks (COFs) have emerged as promising electrocatalysts due to their controllable architectures, highly exposed molecular active sites, and ordered structures. In this study, a series of porphyrin-based COFs (TAPP-x-COF) with various transition metals (Co, Ni, Fe) were synthesized via a facile post-metallization strategy under solvothermal synthesis. The resulting porphyrin-based COFs showed oxygen reduction reaction (ORR) activity with a trend in Co > Fe > Ni. Among them, TAPP-Co-COF exhibited the best ORR activity (E1/2 = 0.66 V and jL = 4.82 mA cm−2) in alkaline media, which is comparable to those of Pt/C under the same conditions. Furthermore, TAPP-Co-COF was employed as a cathode in a Zn-air battery, demonstrating a high power density of 103.73 mW cm–2 and robust cycling stability. This work presents a simple method for using COFs as a smart platform to fabricate efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

Bifunctional oxygen electrocatalysts constructed with the separate active sites of ORR and OER have shown excellent performance in rechargeable zinc-air battery. [Display omitted] High activity, excellent durability, and low-cost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts are highly required for rechargeable zinc (Zn)-air batteries. Herein, we designed an electrocatalyst by integrating the ORR active species of ferroferric oxide (Fe 3 O 4) and the OER active species of cobaltous oxide (CoO) into the carbon nanoflower. By well regulating and controlling the synthesis parameters, Fe 3 O 4 and CoO nanoparticles were uniformly inserted into the porous carbon nanoflower. This electrocatalyst can reduce the potential gap between the ORR and OER to 0.79 V. The Zn-air battery assembled with it exhibited an open-circuit voltage of 1.457 V, a stable discharge of 98 h, a high specific capacity of 740 mA h g−1, a large power density of 137 mW cm−2, as well as good charge/discharge cycling performance, exceeding the performance of platinum/carbon (Pt/C). This work provides references for exploring highly efficient non-noble metal oxygen electrocatalysts by tuning ORR/OER active sites. [ABSTRACT FROM AUTHOR]