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Lignin is an ideal carbon source material, and lignin-based carbon materials have been widely used in electrochemical energy storage, catalysis, and other fields. To investigate the effects of different lignin sources on the performance of electrocatalytic oxygen reduction, different lignin-based nitrogen-doped porous carbon catalysts were prepared using enzymolytic lignin (EL), alkaline lignin (AL) and dealkaline lignin (DL) as carbon sources and melamine as a nitrogen source. The surface functional groups and thermal degradation properties of the three lignin samples were characterized, and the specific surface area, pore distribution, crystal structure, defect degree, N content, and configuration of the prepared carbon-based catalysts were also analyzed. The electrocatalytic results showed that the electrocatalytic oxygen reduction performance of the three lignin-based carbon catalysts was different, and the catalytic performance of N-DLC was poor, while the electrocatalytic performance of N-ELC was similar to that of N-ALC, both of which were excellent. The half-wave potential (E 1/2 ) of N-ELC was 0.82 V, reaching more than 95% of the catalytic performance of commercial Pt/C (E 1/2 = 0.86 V) and proving that EL can be used as an excellent carbon-based electrocatalyst material, similar to AL.

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]

The development of precious metal-free (M-N-C) catalysts for the oxygen reduction reaction (ORR) is considered crucial for reducing fuel cell costs. Herein, Co-Zn/NC interconnected frameworks with uniformly dispersed Co nanoparticles and graphitic carbon are designed and successfully synthesized through the in situ growth of zeolitic imidazolate frameworks (ZIF67 and ZIF8) along with biomass nano-microfibrillar cellulose (MFC), followed by pyrolysis. A Co-Zn/NC composite is prepared by combining Co-Zn/NC with a perfluorosulfonic acid polymer. The Co-Zn/NC composite catalyst exhibits excellent ORR catalytic activity (E0 = 0.974 V vs. RHE, E1/2 = 0.858 V vs. RHE) and good long-term durability, with 90% current retention after 10000s, surpassing that of commercial Pt/C in alkaline media. The hierarchical porous structure, coupled with the uniform distribution of Co nanoparticles and nitrogen doping, contributes to superior electrocatalytic performance, while the interconnected frameworks and graphitic carbon ensure good stability. Additionally, the Co-Zn/NC composite demonstrates promising applications in acidic media. This strategy offers significant guidance to develop advanced non-precious metal carbon-based catalysts for highly efficient and stable ORR. [ABSTRACT FROM AUTHOR]

As the world faces an escalating energy crisis, the necessity of adopting alternative energy sources becomes increasingly evident. Despite challenges, the imperative to prioritise these eco‐friendly alternatives remains paramount in paving the way for a more sustainable and resilient future for our planet and its inhabitants. The pursuit of sustainable energy sources has brought the oxygen reduction reaction (ORR) into the spotlight as a crucial cathodic reaction in energy‐converting systems, notably fuel cells (FCs). These FCs hold tremendous promise in providing an eco‐friendly and efficient energy supply. However, the widespread implementation of FCs is hindered by their reliance on expensive and scarce noble metal catalysts, such as platinum (Pt), which pose economic and environmental challenges. Hence, this work reports the preparation, characterisation (FTIR, XPS, SEM and EDX) and application of four composites based on doped‐carbon materials (CM) and on the Wells‐Dawson POM salt K6⋅α‐[P2W12Mo6O62] ⋅ 19H2O (P2W12Mo6@MWCNT_N8, P2W12Mo6@MWCNT_N6, P2W12Mo6@MWCNT_S6, and P2W12Mo6@GF_S6) as ORR electrocatalysts in alkaline medium (pH=13). The successful doping of the carbon materials with nitrogen (N) and sulphur (S) and the incorporation of the polyoxometalate were verified through comprehensive structural characterisation. Overall, P2W12Mo6@MWCNT_N8 exhibited favourable onset potentials of 0.84 V vs. RHE, highlighting its high catalytic activity. Additionally, the catalyst showed excellent tolerance to methanol crossover, retaining 91 % of initial current, which is crucial for practical fuel cell applications. Furthermore, the P2W12Mo6@MWCNT_N8 catalyst showed commendable stability, retaining 81 % of its initial current after 36000 seconds at an operating potential of E=0.46 V vs. RHE. These encouraging results denote the significant potential of this electrocatalyst in advancing sustainable energy conversion technologies. [ABSTRACT FROM AUTHOR]

[Display omitted] Oxygen reduction reaction (ORR) is an essential half-reaction in next-generation energy storage and conversion systems, such as metal-air batteries and fuel cells. However, its practical application is restricted by the slow intrinsic kinetics, and the high price and low storage of noble metal electrocatalysts. Herein, unique CoFe nanoparticles encapsulated in N -doped carbon (CoFe-NC-Z8-900) with high content graphite-N derived from CoFe-g-C 3 N 4 @ZIF-8 via stepwise pyrolysis is reported as effective ORR catalysts. The increase of graphitic nitrogen content can enhance both the electrical conductivity and the adsorption of oxygen-containing intermediates, resulting in improved catalytic performance. Fortunately, CoFe-NC-Z8-900 exhibits an exceptionally high half-wave potential (E 1/2) of 0.914 V in a 0.1 M KOH solution. The excellent ORR electrocatalytic activity can be mainly attributed to the synergistic effect of the CoFe bimetal and the relatively high content of graphite-N. This study offers a unique method for creating powerful nitrogen-doped carbon coated metal nanoparticle electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] In this study, we present a bimetallic ion coexistence encapsulation strategy employing hexadecyl trimethyl ammonium bromide (CTAB) as a mediator to anchor cobalt–nickel (CoNi) bimetals in nitrogen-doped porous carbon cubic nanoboxes (CoNi@NC). The fully encapsulated and uniformly dispersed CoNi nanoparticles with the improved density of active sites help to accelerate the oxygen reduction reaction (ORR) kinetics and provide an efficient charge/mass transport environment. Zinc-air battery (ZAB) equipped CoNi@NC as cathode exhibits an open-circuit voltage of 1.45 V, a specific capacity of 870.0 mAh g−1, and a power density of 168.8 mW cm−2. Moreover, the two CoNi@NC-based ZABs in series display a stable discharge specific capacity of 783.0 mAh g−1, as well as a large peak power density of 387.9 mW cm−2. This work provides an effective way to tune the dispersion of nanoparticles to boost active sites in nitrogen-doped carbon structure, and enhance the ORR activity of bimetallic catalysts. [ABSTRACT FROM AUTHOR]

The search of active, stable and low costs catalysts for the oxygen reduction reaction (ORR) is crucial for the extensive use of fuel cells and metal–air batteries. The development of metal-free catalysts, instead of platinum-based materials, can dramatically reduce the cost and increase the efficiency of these devices. In this work, carbon nanohorns (CNHs) have been covalently functionalized with N-containing heterocycles by the Tour reaction protocol and tested as metal-free ORR catalysts. The insertion of N-functionalities favored the complete reduction of oxygen to hydroxyl ions, while their absence favored the production of hydrogen peroxide. With the aim of determining the N-species responsible for the ORR activity of CNHs, photoemission and electrochemical measurements were combined. Results suggest that protonated N is the main species involved in the ORR process, facilitating the adsorption of oxygen, with their consequent reduction to neutral hydrogenated N species. [ABSTRACT FROM AUTHOR]

N -doped porous carbon monatomic iron catalysts (Fe SA /NPCs) obtained by polydopamine modification strategy were used for high efficiency oxygen reduction reactions and zinc-air batteries. [Display omitted] • Nitrogen doped porous carbon materials (NPCs) were prepared based on ZIF-L. • Stable hollow leaf-like morphology was maintained by coating PDA and nitrogen content was adjusted. • Fe SA was easily anchored on NPCs with luxuriant anchoring sites. • Fe SA /NPCs shows excellent electrochemical performance in oxygen reduction and zinc air batteries. Metal-nitrogen-carbon (M N C) catalysts, especially Fe N C catalysts, are considered promising candidates to replace Pt-based catalysts, but Fe N C catalysts still present certain challenges in controlled-synthesis and energy device applications. In this paper, through the modification strategy of poly-dopamine (PDA) to maintain 2D leaf morphology to obtain more active sites and further adjust the N content, N -doped porous carbon monatomic iron catalyst (Fe SA /NPCs) with rich-nitrogen content was prepared. XPS analysis showed that compared with C-ZIF-Fe, the contents of graphite nitrogen and pyridine nitrogen increased in Fe SA /NPCs. The hollow structure with defects and Fe-N 4 configuration of Fe single atom show more active sites for the catalyst, and positively promote the diffusion of reactants, oxygen exchange and electron transport, thus changing the reaction kinetics and promoting the improvement of ORR activity. Fe SA /NPCs electrocatalyst exhibits good half-wave potential and onset potential at low loading (E 1/2 = 0.93 V, E onset = 1.0 V). In addition, the methanol tolerance, stability and Tafel slope are better than those of commercial Pt/C. Excitingly, the zinc-air cell with Fe SA /NPCs as cathode material achieves a power density of 223 mW cm−2 and exhibits a long-term stability higher than 200 h. This work shows that nitrogen-doped porous carbon materials as well as iron monoatoms play important roles in improving electrocatalytic performance. [ABSTRACT FROM AUTHOR]

An efficient and low-cost oxygen catalyst for the oxygen reduction reaction (ORR) was developed by in situ growth of Mn-Mo oxide nanoparticles on nitrogen-doped carbon nanotubes (NCNTs). Doped nitrogen effectively increases the electron conductivity of the MnMoO4@NCNT complex and the binding energy between the Mn-Mo oxide nanoparticles and carbon nanotubes (CNTs), leading to fast charge transfer and more catalytically active sites. Combining Mn and Mo with NCNTs improves the catalytic activity and promotes both electron and mass transfers, greatly enhancing the catalytic ability for ORR. As a result, MnMoO4@NCNT exhibited a comparable half-wave potential to commercial Pt/C and superior durability, demonstrating great potential for application in renewable energy conversion systems. [ABSTRACT FROM AUTHOR]

Metal‐free carbon‐based catalysts have attracted significant attention owing to their unique electronic structure and excellent catalytic activity for the oxygen reduction reaction (ORR). Recently, several heteroatom‐doped carbon catalysts with ORR performances comparable with those of state‐of‐the‐art Pt‐based catalysts have been reported. However, the intrinsic influence of heteroatoms on the catalytic activity has not been thoroughly investigated to date. This paper reports porous carbons co‐doped with N and S, prepared using an ion‐exchange resin and tetramethylammonium cations, with an onset potential of 0.93 V versus reversible hydrogen electrode (RHE) and a half‐wave potential of 0.79 V versus RHE. First‐principles calculations reveal that the change in the atomic charge caused by the co‐doping of N and S is important for inducing a high ORR activity. This paper presents a rational synthetic strategy for metal‐free catalysts and provides fundamental insights into their electrocatalysis. [ABSTRACT FROM AUTHOR]

Metal/nitrogen-doped carbon single-atom catalysts (M−N−C SACs) show excellent catalytic performance with a maximum atom utilization and customizable tunable electronic structure. However, precisely modulating the M−Nx coordination in M−N−C SACs remains a grand challenge. Here, we used a N-rich nucleobase coordination self-assembly strategy to precisely regulate the dispersion of metal atoms by controlling the metal ratio. Meanwhile, the elimination of Zn during pyrolysis produced porous carbon microspheres with a specific surface area of up to 1151 m2 g−1, allowing maximum exposure of Co−N4 sites and facilitating charge transport in the oxygen reduction reaction (ORR) process. Thereby, the monodispersed cobalt sites (Co−N4) in N-rich (18.49 at%) porous carbon microspheres (CoSA/N−PCMS) displayed excellent ORR activity under alkaline conditions. Simultaneously, the Zn−air battery (ZAB) assembled with CoSA/N−PCMS outperformed Pt/C+RuO2-based ZABs in terms of power density and capacity, proving that they have good prospects for practical application. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene is currently recognized as one of the most promising catalysts for the oxygen reduction reaction (ORR). It has been demonstrated to act as a metal-free electrode with good electrocatalytic activity and long-term operation stability, excellent for the ORR in proton exchange membrane fuel cells (PEMFCs). As a consequence, intensive research has been dedicated to the investigation of this catalyst through varying the methodologies for the synthesis, characterization, and technologies improvement. A simple, scalable, single-step synthesis method for nitrogen-doped graphene oxide preparation was adopted in this paper. The physical and chemical properties of various materials obtained from different precursors have been evaluated and compared, leading to the conclusion that ammonia allows for a higher resulting nitrogen concentration, due to its high vapor pressure, which facilitates the functionalization reaction of graphene oxide. Electrochemical measurements indicated that the presence of nitrogen-doped oxide can effectively enhance the electrocatalytic activity and stability for ORR, making it a viable candidate for practical application as a PEMFC cathode electrode. [ABSTRACT FROM AUTHOR]

Graphene supported FeN5 active sites, exhibiting high activity and stability of oxygen reduction reaction, enable a H2-air fuel cell to decay little during the latter 20–100 h operation. [Display omitted] • Electrochemically-exfoliated graphene improves forming FeN 5 with NH 3. • Graphene benefits catalytic stability of oxygen reduction reaction. • Fuel cell keep stable with little decay in latter 80 h operation. • High half-wave potentials in alkaline medium (0.940 V). Metal-nitrogen-carbon catalytic material, generally thought as a promising low-cost electrocatalyst of oxygen reduction reaction (ORR), surfers from long-term catalytic durability for fuel cell and metal-air battery. Here, we describe an approach of synthesizing electrochemically exfoliated graphene supported penta-nitrogen coordinated iron exhibiting encouraging ORR catalytic activity and durability. The synthesized catalyst exhibits high half-wave potentials in alkaline medium (E 1/2 0.940 V) enabling high-performance zinc-air battery and in acidic condition for durable fuel cell with a high peak power density (630 mW cm−2). The current density of a proton exchange membrane fuel cell loading the catalyst as cathode tends to decay little after initial hours under H 2 -air measurement, remarkably inhibiting commonly decline tendency of iron–nitrogen-carbon catalysts. DFT calculation combined with extensive experimental investigations demonstrate that penta-nitrogen coordinated iron supported by graphene is thermodynamically stable, and thus benefits the catalytic stability of ORR. [ABSTRACT FROM AUTHOR]

The exploration of non-Pt catalysts with high electrocatalytic activity and durability is especially important for cathodic oxygen reduction reaction (ORR) in fuel cell. Here, cobalt and nitrogen doped hollow carbon sphere-bamboo like carbon nanotube (Co/NHCS-BCNT) is prepared by using SiO 2 sphere as sacrificial template. Co nanoparticles are confined in the cavity and top end of the in-situ formed BCNT, which can not only avoid the agglomeration of Co nanoparticles but also inhibit corrosion in caustic electrolyte. The synergistic effect between NHCS and well-dispersed Co particles makes Co/NHCS-BCNT have superior catalytic activity toward ORR. The electrochemical surface area (ECSA) of Co/NHCS-BCNT is 222 cm2, which is higher than those of NHCS (164 cm2) and HCS (135 cm2). The onset potential and half-wave potential of Co/NHCS-BCNT are 0.941 V and 0.814 V, respectively, which are close to commercial Pt/C (0.949 V, 0.807 V). The Tafel slope of Co/NHCS-BCNT (63.8 mV dec-1) is lower than that of Pt/C (71.7 mV dec-1). In addition, Co/NHCS-BCNT shows excellent durability and fuel selectivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Atomically distributed iron electrocatalyst is valid for oxygen reduction reaction (ORR). However, accurate regulation of the structure improving its intrinsic activity is a challenge. Herein, a dual-atom catalyst FeCu-NC with atomically distributed Fe and Cu co-anchored on porous N-doped carbon is obtained. The FeN 4 and CuN 3 couple sites bridged by two nitrogen atoms, exist as Fe(II,III)N 2 (µ 2 -N) 2 Cu(I,II)N moieties with the metal distance of ∼2.5 Å in the structure of FeCu-NC. The synergistic effect of Fe and Cu dual-atom reducing the dissociation energy of *OOH intermediate, allows an optimized 4e- ORR reaction pathway. The FeCu-NC exhibits high-efficiency ORR activity with the half-wave potential (E 1/2) of 0.889 V (vs RHE) and outstanding stability without obvious decay for the E 1/2 after 10,000 cycles. The FeCu-NC based Zn-air battery presents large specific capacity of 795 mAh g−1 and energy density of 998 Wh kg−1 as well as high charge-discharge cycling stability superior to the Pt/C. [Display omitted] • A dual-atom catalyst FeCu-NC with Fe(II,III)N 2 (µ 2 -N) 2 Cu(I,II)N moieties is prepared. • The synergistic effect of Fe and Cu clearly reduces the dissociation energy of *OOH. • The FeCu-NC has a high ORR activity in an optimized 4e- reaction pathway. • The FeCu-NC based Zn-air battery exhibits a large stable energy density. [ABSTRACT FROM AUTHOR]

Single atom catalysts (SACs) are constituted by isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and amorphous carbon. The thermal stability, electronic properties, and catalytic activities of the metal center can be controlled via manipulating the neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomical dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased. Furthermore, new possibilities are offered to easily control the selectivity of a given transformation process as well as to improve turnover frequencies and turnover numbers of target reactions. Among them, Fe--N--C single atom catalysts own special electronic structure, and have been widely used in many fields of electrocatalysis. This review aims to summarize the synthesis of Fe--N--C based on anchoring individual iron atoms on carbon/graphene. The spin-related properties of Fe--N--C catalysts are described, including the relation between spin and electron structure of Fe--Nx as well as the coupling between electronic structure of Fe--Nx and electronic (orbit) of CO2, N2 and O2. Next, mechanistic investigations conducted to understand the specific behavior of Fe--N--C catalysts are highlighted, including C, N, O electro-reduction. Finally, some issues related to the future developments of Fe--N--C are put forward and corresponding feasible solutions are offered. [ABSTRACT FROM AUTHOR]

Cathodic oxygen reduction reaction is a decisive factor for fuel cell. In this work, for the first time, we demonstrated the synthesis of N -doped carbon hollow spheres derived from conjugated microporous polymers. The resulting sample remained the inherent porosity and N component with hollow spherical morphology, which exhibits excellent ORR performance with higher limiting current density and stability than that of commercial Pt/C catalyst in alkaline solution. [Display omitted] The exploitation non-precious or metal-free electrocatalysts of oxygen reduction reaction (ORR) is of significance for construction of next-generation fuel cells. In this work, hollow-spherical conjugated microporous polymers (CMPs) comprising porphyrin units were synthesized as precursors to prepare N -doping porous carbon spheres (CMP-NP-x) by a direct pyrolysis method. The as-resulted CMP-NP-x exhibited spherical morphology with hollow structure similar to that of CMPs precursors. The BET surface area of CMP-NP-x can be tailored by the pyrolysis temperature varying from 868 m2 g−1 to 1118 m2 g−1. According to XPS analysis, the pyrrolic N content in the sample decreased but the graphitic N and pyridinic N increased with increasing of the pyrolysis temperature from 800 °C to 1000 °C. Taking advantages of porous structure with large accessible surface areas and N species active sites, the resulting CMP-NP-x showed superior ORR activity and methanol tolerance to commercial Pt/C catalyst. In particular, CMP-NP-900 possesses the highest onset potential (0.930 V), half-wave potential (0.857 V) and limiting current density of 4.45 mA cm−2, compared with Pt/C catalyst and other samples, making it a promising metal-free catalyst superior to commercial Pt/C catalyst in alkalic condition. [ABSTRACT FROM AUTHOR]

[Display omitted] Nitrogen- and transition metal-dual doped carbon materials with low cost and high catalytic performances are considered as one of promising alternatives for noble metal catalysts in acceleration of oxygen reduction reaction (ORR). In this work, three-dimensional (3D) self-supporting superstructures of iron carbide (Fe 3 C) nanoclusters entrapped in manganese (Mn)- and nitrogen (N)-dual doped carbon nanosheets covered with double-sided nanoneedles carbon arrays (Fe 3 C/Mn,N-NCAs) are simply synthesized by a coordination pyrolysis method, in which dicyandiamide mainly behaves as nitrogen source and 1-(2-pyridylazo)-2-naphthol (PAN) as carbon source. Integration of the unique 3D self-supporting superstructures and synergistic effects of the multi-compositions, the as-obtained catalyst displays appealing ORR performance such as the much positive onset potential (E onset = 0.98 V vs. RHE) and half-wave potential (E 1/2 = 0.88 V vs. RHE), as well as a just 10 mV negative shift in E 1/2 after 2000 cycles, surpassing commercial Pt/C. This work provides some valuable perspectives for preparation of high-efficiency and low-cost non-noble metal ORR electrocatalysts in energy transformation and storage correlated systems. [ABSTRACT FROM AUTHOR]

Numerous active sites and hierarchical pore structures are important for improving catalytic performance for the oxygen reduction reaction (ORR). In this work, a series of iron-nitrogen-doped porous carbon materials (Fe– N –C) with ORR catalytic activity were prepared by a one-step pyrolysis method using enzymolytic lignin as the raw material, soy protein isolate and iron chloride as dopants. The results showed that the samples with the best performance have abundant Fe-Nx active sites and mesoporous structures. At the same time, the electrocatalytic results indicate that the half-wave potential of catalyst was 0.84 V, which reached 96.55% of commercial Pt/C catalysts (E 1/2 = 0.86 V), it still preserves an initial current density of 92%, after 10,000 s of circulation, which is much better than Pt/C (86%). Due to the low cost, high activity and stable ORR property, the prepared non-precious metal electrocatalyst will play an important role in the applications of fuel cells. • Porous carbons prepared by a one-step pyrolysis method using enzymolytic lignin. • Successful doping of iron and nitrogen into the framework of mesoporous carbons. • Superior oxygen reduction activity for Fe–N codoped porous carbon. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synergistic effect of carbon edges and dopants towards ORR was predicted by DFT. • Well-designed N -GNRs contain both heteroatom-doping and abundant edge sites. • Best ORR property was obtained for N -GNRs compared to other control samples. • The synergistic effect was again demonstrated by experimental facts. Decoration with alien atoms and increasing the edge content are two valid ways to activate the oxygen reduction reaction (ORR) property of nanocarbons. To further enhance their intrinsic activity and explore the underlying ORR mechanism, graphene nanoribbons (GNRs) were selected as an ideal catalyst model. Theoretical simulations have predicted that with the synergistic effect between heteroatom-doping and edge sites, the ORR activity can be significantly improved. Inspired by this, N -GNRs were synthesized via the oxidative unzipping of CNTs followed by nitrogen incorporation with urea. Ample edges and nitrogen doping sites were detected by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. As a result, N -GNRs exhibited remarkably higher ORR properties in terms of onset and half-wave potentials, Tafel slopes, electron transfer number and methanol tolerance than either GNRs, the control sample without doping, or N -CNTs, the control sample without abundant edges, simply clarifying the significance of synergy between dopants and edges. Thus, this work provides a simple but efficient strategy to fabricate high-performance oxygen reduction catalysts. [ABSTRACT FROM AUTHOR]

In addition to C, H and O, some biomass is also rich in mineral elements. The recovery and utilization of special mineral elements is of great significance to prepare functional materials and alleviate the current energy shortage. Herein, we describe a facile strategy for making full use of the chemical composition (C, Fe) and special structure of red blood cells (RBCs) from waste pig blood to fabricate a dual metal (Fe, Co)-nitrogen (N)-doped porous carbon catalyst by pyrolysis of a mixture of RBCs biomass, cobaltous acetate, and melamine. The porous catalyst displays a comparable activity for oxygen reduction reaction (ORR) to that of commercial Pt/C catalyst, with a half-wave potential of 0.821 VvsRHE in alkaline media and 0.672 VvsRHE in acid electrolyte. Especially, the as-prepared catalyst shows excellent methanol tolerance and stability in both acidic and alkaline electrolytes, which is superior to commercial Pt/C catalysts. The excellent ORR activity of FeCo-N/C(RBC) can be ascribed to the porous morphology and the cooperation between metal and nitrogen species. This work provides a novel idea of exploiting the composition of renewable biomass to modulate the activity and stability of carbon-based ORR catalysts. [ABSTRACT FROM AUTHOR]

A template-free pyrolysis approach is proposed to fabricate nitrogen and sulfur doped hollow mesoporous carbon sphere (N/S-HMCS). The unique hollow/mesoporous nanostructure and abundant N, S-doped active sites prompt the optimal N/S-HMCS 900 exhibits satisfactory electrocatalysis in oxygen electroreduction for high-performance Zn-air battery. [Display omitted] • A nitrogen, sulfur dual-doped hollow mesoporous carbon sphere (N/S-HMCS) is fabricated by a simple yet efficient template-free pyrolysis approach. • The N/S-HMCS 900 exhibits high oxygen reduction reaction (ORR) activities with an excellent half-wave potential and high methanol tolerance. • The optimal electrocatalyst can be used as air electrode materials in high-performance zinc-air batteries. • Density functional theory (DFT) calculations reveal that N, S-dual dopant can create extra active sites with higher catalytic activity than the isolated N -dopant. The construction of hollow mesoporous carbon nanospheres (HMCS) avoiding the use of traditional soft/hard templates is highly desired for nanoscience yet challenging. Herein, we report a simple and straightforward template-free strategy for preparing nitrogen, sulfur dual-doped HMCSs (N/S-HMCSs) as oxygen reduction reaction (ORR) electrocatalysts. The unique hollow spherical and mesoporous structure was in-situ formed via a thermally initiated hollowing pathway from an elaborately engineered covalent triazine framework. Regulation of pyrolysis temperatures contributed to precisely tailoring of the shell thickness of HMCSs. The resulting N/S-HMCS 900 (pyrolyzed at 900 °C) possessed high N and S contents, large specific surface areas, rich and uniform mesopores distribution. Consequently, as a metal-free ORR electrocatalyst, N/S-HMCS 900 exhibits a high half-wave potential, excellent methanol tolerance and great long-term durability. Additionally, density functional theory calculations demonstrate that N, S-dual dopant can create extra active sites with higher catalytic activity than the isolated N -dopant. This strategy provides new insights into the construction of hollow and mesoporous multi-heteroatom-doped carbon materials with tunable nanoarchitecture for various electrochemical applications. [ABSTRACT FROM AUTHOR]

The metal-nitrogen-carbon (M-N-C) type oxygen reduction reaction (ORR) catalysts are promising for hydroxide exchange membrane fuel cells, but catalysts with further improved performance are challenging. Here, we report the efficient improvement of the ORR activity of M-N-C catalysts by employing highly polarizable metal cation Ag+. Ag, Fe single atomic sites embedded in concave nitrogen doped carbon (Ag 1 Fe 1 /CNC) is successfully synthesized and shows high performance towards ORR, indicating by both the ultra-high half-wave potential of 0.917 V and membrane electrolyte assembly performance of peak power density up to 1.26 W cm−2. The binding energy of the ORR intermediates on the highly polarizable Ag site in Ag 1 Fe 1 /CNC was significantly tuned by the adjacent Fe site by more than 0.2 eV, and thus leading to a low theoretical ORR overpotential of only 0.398 V. The employment of the highly polarizable metal cation brings a novel and efficient approach to construct highly active catalysts. [Display omitted] • High performance oxygen reduction reaction catalyst Ag 1 Fe 1 /CNC is synthesized. • The highly polarizable Ag site shows ultra-high catalytic activity. • The Ag sites are significantly affect by the adjacent metals. • High membrane electrolyte assembly performance is achieved by using Ag 1 Fe 1 /CNC. [ABSTRACT FROM AUTHOR]

• Fe-N-C catalyst was prepared using FePc, dicyandiamide and CDC/graphene composite. • DCDA helps to mitigate metal agglomeration and boosts Fe-N x active site formation. • FeN-CDC/G/DCDA catalyst (E 1/2 = 0.76 V) outperforms FeN-CDC/G catalyst (E 1/2 = 0.70 V) • RRDE results display good selectivity for 4e− ORR pathway of FeN-CDC/G/DCDA (n = 3.9) The focus in the development of catalysts doped with transition metals aims to replace platinum group metal catalysts in fuel cells. However, these non-precious metal catalysts exhibit limited performance in acidic environment for the oxygen reduction reaction (ORR) due to issues such as metal agglomeration and the subsequent loss of active sites. Herein, we synthesised catalysts doped with iron and nitrogen on a composite material consisting of carbide-derived carbon (CDC) and graphene (G), employing an additional nitrogen source dicyandiamide (DCDA), denoted as FeN-CDC/G/DCDA. Our physico-chemical analysis unveiled that the inclusion of DCDA was effective in mitigating metal agglomeration during the synthesis process and increasing the presence of Fe-N x sites in the catalysts. Notably, the FeN-CDC/G/DCDA catalyst exhibited enhanced ORR activity in acid media with half-wave potential (E 1/2) of 0.76 V, surpassing the performance of the FeN-CDC/G catalyst, which had an E 1/2 value of 0.70 V. Furthermore, the rotating ring-disk electrode results indicated a reduced formation of hydrogen peroxide when employing the FeN-CDC/G/DCDA catalyst. The findings from this study represent a significant step towards the development of efficient catalysts for fuel cells, underscoring the pivotal role of additional nitrogen doping and its positive impact on the ORR performance. [ABSTRACT FROM AUTHOR]

Developing bifunctional catalysts to oxygen reduction (ORR) and oxygen evolution reactions (OER) is of vital to the practical application of rechargeable Zn-air batteries. Herein, an N-doped carbon-based catalyst (FeCo-NC-St) was prepared by using starch as a basic material which was transferred to defective carbon particles. The fresh starch-derived carbon is favor of the doping of nitrogen atoms to form more N-related ORR active sites. The existence of cobalt further positively regulates the OER activity of FeCo-NC-St. Resultantly, FeCo-NC-St shows 0.837 V of ORR E 1/2 and 1.611 V of OER E 10 which is slightly lower than the 0.850 V of ORR E 1/2 for Pt/C but far better than the 1.723 V of OER E 10 for the benchmark RuO 2 , revealing the superior bifunctional activities of FeCo-NC-St. Practically, the Zn-air battery with FeCo-NC-St outputs 1.505 V of open circuit voltage, 1.15–1.25 V of working voltage and 937.51 mW h g−1 Zn of specific energy density at 10 mA cm−2. The Zn-air battery also exhibits remarkable rechargeability and long-term durability, demonstrating the promising potential to substitute the precious Pt/Ru-based catalysts in the practical applications. An N-doped carbon-based catalyst (FeCo-NC-St) was prepared by using starch as a basic material. The resultant catalyst exhibits superior bifunctional catalytic activity to ORR and OER. [Display omitted] • An N-doped carbon-based bifunctional catalyst was fabricated. • Starch was utilized as a sustainable material. • The starch-derived carbon was favor of the doping of nitrogen atoms. • OER performance was positively regulated by cobalt element. • The catalyst exhibits satisfactory activity to ORR and OER. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis route: a straightforward, solvent-free, and one-step pyrolysis approach. • Well-dispersed tetragonal ZrO 2 , appropriate N dopants, and hierarchical pores. • Synergistic catalytic effect endow good ORR performance and high power density. An innovative, high-performance, non-noble-metal-based oxygen reduction reaction (ORR) catalyst must be developed utilizing a new and cost-effective technique. ZrO 2 has the merits of high stability, low toxicity, good catalytic activity, and low enthalpy for atomic oxygen adsorption. However, the poor conductivity restricts its application as an ORR catalyst. Here, we successfully prepared ZrO 2 nanoparticles / nitrogen-rich two-dimensional carbon nanosheet composites as ORR catalysts using a straightforward, solvent-free, one-step pyrolysis approach. Due to the unique component and structure characteristics, ZrO 2 @N-C-900 demonstrates remarkable ORR performances in alkaline electrolytes, such as high half-wave potential (0.82 V vs. RHE), higher current density (J L = 6.4 mA cm−2), and outstanding long term stability (95 % for 36,000 s). Especially, when used in a Zn-air battery, ZrO 2 @N-C-900 exhibited a power density of 148 mW cm−2, exceeding that of 20 % Pt/C. [ABSTRACT FROM AUTHOR]

This work reveals the crucial role of compressive lattice strain for the effective modulation of electronic metal-support interaction, which provides valuable guidance to the rational design of advanced ORR catalysts by lattice strain engineering. [Display omitted] • A structurally ordered PtCo/NCS-5 catalyst is successfully synthesized by a facile natural ligand annealing strategy. • The effective coupling of PtCo and NCS is proven to be beneficial to the improvement of ORR activity. • The electronic interaction between PtCo and NCS is explored through both characterizations and DFT calculations. • The crucial role of compressive lattice strain for the enhanced electronic interaction of PtCo/NCS-5 is revealed. Atomically ordered intermetallic catalysts have great potential for catalyzing efficient oxygen reduction reaction (ORR), while the coupling of metal and support are not emphasized enough. Herein, we report an atomically ordered PtCo bimetallic catalyst coupled with N-doped ultrathin carbon shells (PtCo/NCS) for ORR by a facile natural ligand annealing strategy. The formed NCS prevents the high-temperature sintering of catalysts by physical confinement, and the coupling effect results in a stronger affinity between PtCo and NCS for PtCo/NCS. The optimal PtCo/NCS-5 exhibits more exceptional activity and durability, outperforming commercial Pt/C and Pt 3 Co/C catalysts (C-Pt 3 Co/C). It is proved that PtCo and NCS synergically account for the enhanced ORR performance for PtCo/NCS-5. More importantly, the compressive lattice strain effectively promotes electron redistribution and optimizes the electronic structure for PtCo/NCS-5. This work further deepens the understanding of catalytic mechanisms and provides new insight into the rational design of advanced electrocatalysts toward ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • A highly efficient Fe SAs/NPs@NC catalyst for boosting the ORR is developed. • A synergistic effect stemming from the isolated Fe-N x and metallic Fe is uncovered. • The catalyst showed high ORR activity and stability superior to the commercial Pt/C. • The Zn-air battery exhibits high power density and excellent cycling stability. Herein, a proof-of-concept study on the evaluation of Fe nanoparticles (Fe NPs) encapsulated by nitrogen-doped carbon to Fe single atoms (Fe SAs) for boosting the oxygen reduction reaction (ORR) catalytic activity toward Zn-air batteries was reported. Specifically, unlike Fe SAs encapsulated by nitrogen-doped carbon (Fe SAs@NC), the Fe SAs and Fe NPs co-embedded in nitrogen-doped carbon (Fe SAs/NPs@NC) derived from a pyrolysis and acid dissolution protocols exhibits excellent ORR performance with good stability and remarkable methanol tolerance in alkaline solutions. Combining a series of experimental analyses, the strong interaction between the atomically dispersed Fe-N x and adjacent Fe NPs in altering the electronic structure of isolated Fe-N x sites could weaken the binding energies of the ORR intermediates on Fe SAs/NPs@NC, resulting in an enhanced electrocatalytic kinetics than Fe SAs@NC and Pt/C catalysts. This strategy not only offers a new way for synthesis highly efficient Fe-N/C catalysts toward ORR, but also provides the new insights into the understanding of the mechanism of adjacent Fe NPs encapsulated by nitrogen-doped carbon to Fe SAs sites. [ABSTRACT FROM AUTHOR]

A nitrogen and sulfur codoped carbon-based catalyst (Fe-NS-AG-C) to oxygen reduction reaction (ORR) is prepared by pyrolyzing a precursor from iron chloride, thiourea, anhydrous glucose and carbon black. Glucose is transformed to carbon sheets with defect-rich structures which are highly active to the anchoring of nitrogen and sulfur atoms. Correspondingly, the 3.35 at% and 0.63 at% contents of nitrogen and sulfur in Fe-NS-AG-C are heavily higher than the 0.71 at% and 0.26 at% in the controlled catalyst Fe-NS-C (without glucose). The edge-oriented pyridinic N is easily formed as ORR active sites with the C-S structure. A dual mesopore-dominated microstructure is also constructed by the carbon sheets to favor the mass transfer in the reaction process. As a result, the Fe-NS-AG-C presents outstanding ORR performance with more positive half wave potential, greater limiting current density, and better methanol tolerance than the benchmark Pt/C catalyst. The Zn-air battery assembled with Fe-NS-AG-C outputs 1.48 V of open circuit voltage, 156 mW cm−2 of maximum power density, and 1.26 V of work voltage, 785 mAh g−1 Zn of specific capacity and 983 mWh g−1 Zn of specific energy density at 10 mA cm−2 of discharge current density. • Glucose was pyrolized to carbon sheets with defect-rich structures. • The defect enriched carbon sheets are active to the doping of nitrogen and sulfur. • A dual mesopore-dominated microstructure was constructed by the carbon sheets. • The N, S-codoped carbon catalyst shows excellent catalytic performance to oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

A nitrogen-doped carbon-based catalyst (Fe-C-CG) to oxygen reduction reaction (ORR) is synthesized by pyrolyzing a precursor from coffee grounds, iron chloride and commercial carbon black in ammonia atmosphere. The coffee grounds are pyrolyzed to carbon particles with diameters about 20 nm with the facilitation of carbon black. The carbon nanoparticles show higher reactive activity with ammonia to achieve the doping of nitrogen atoms to carbon with 3.33 at% of content in Fe-C-CG, which is greater than 0.47 at% in the product from commercial carbon black (Fe-C). Resultantly, the Fe-C-CG exhibits high ORR activity with 0.87 V of half wave potential and 5.48 mA cm−2 of limited diffusion current, which highly surpass the 0.71 V, 4.19 mA cm−2 for Fe-C, and are comparable with 0.86 V and 4.52 mA cm−2 for Pt/C catalyst, respectively. The Zn-air battery assembled with Fe-C-CG delivers 142 mW cm−2 of maximum power density and 774 mAh g−1 Zn of specific capacity, and can stably work at 1.212–1.257 V of discharge voltage at 10 mA cm−2. This work provides a strategy to prepare a nonprecious metal and nitrogen doped carbon catalyst to ORR by using biomass as the basic material. • A nitrogen doped carbon-based oxygen catalyst was fabricated from biomass coffee grounds. • Coffee grounds were pyrolyzed to ultrafine carbon nanoparticles. • The nanoparticles have highly reaction activity with ammonia. • The catalyst shows excellent catalytic activity to oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Nitrogen coordinated Fe single atoms (Fe-N x SAs) anchored in carbon support is one of the most efficient electrocatalysts for oxygen reduction reaction (ORR). Engineering the microenvironment of Fe-N x sites to achieve enhanced activity is still challenging. Herein, we theoretically demonstrate that nitrogen dopants in carbon skeletons can optimize the adsorption of ORR intermediates on Fe-N 4 sites. Then, we introduce a rational strategy to anchor Fe-N 4 sites in nitrogen-rich carbon support with abundant tubular channels (Fe-SAs@NCTCs). Fe-SAs@NCTCs exhibits encouraging ORR performance with a half-wave potential of 0.91 V in 0.1 M KOH and 0.80 V in 0.1 M HClO 4. The assembled rechargeable Zn–air battery presents high power density and operates steadily with a narrow voltage gap of 0.76 V for 650 h. The results verify that the outstanding ORR activity can be attributed to the abundant nitrogen dopant, hierarchical porous structure, and abundant tubular channels. [Display omitted] • DFT reveals that Fe-(N-C 2) 4 -2N achieves optimal adsorptions of ORR intermediates. • Fe-SAs@NCTCs possesses abundant Fe SAs in nitrogen-rich carbon support. • Hierarchical porous structure with tubular channels renders rapid mass transport. • Fe-SAs@NCTCs exhibits remarkable ORR performances in alkaline and acidic media. • Zn–air battery assembled using Fe-SAs@NCTCs shows excellent performance. [ABSTRACT FROM AUTHOR]

Metal-free carbon-based electrocatalysts for oxygen reduction reaction (ORR) have received considerable attention owing to their abundance and low cost. However, designing carbon-based electrocatalysts with excellent performance in a facile manner remains a challenge. In this work, porous nitrogen-doped carbon nanosheet (PNCNs) catalysts with high contents of graphitic N and defects were readily prepared via a simple self-doping method, in which coal-based graphene quantum dots (GQDs) were used as the carbon and nitrogen resource. Based on the results, PNCNs-900 (obtained at 900 °C) displayed good ORR performance, with a half-wave potential (E 1/2) of 0.80 V. It also exhibited high stability and methanol tolerance compared with commercial Pt/C. Experimental investigations and theoretical calculations prove that the increased ORR electrocatalytic activity of PNCNs-900 is due to the synergistic effect of a large number of defects and graphitic N. Furthermore, its higher electrocatalytic activity for ORR also benefits from the porous lamellar structure, which facilitates the mass transfer process. This study offers a novel approach for developing effective ORR catalysts and for the high value-added utilization of coal resources. In this work, porous nitrogen-doped carbon nanosheets (PNCNs) were prepared by a simple template-assisted assembly strategy from coal-based graphene quantum dots. PNCNs-900 (obtained at 900 °C) displays good oxygen reduction reaction (ORR) performance and outperforms stability compared with commercial Pt/C. Characterization and density functional theory (DFT) calculation displayed that the synergistic effect of large number of defects and graphitic N in PNCNS-900 was responsible for the improvement of ORR activity. [Display omitted] • PNCNs-900 catalyst was synthesized using coal-based graphene quantum dots. • PNCNs-900 catalyst exhibits the better ORR stability compared with commercial Pt/C. • Synergistic effect of graphitic nitrogen and defect improves electrocatalytic activity for ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchically porous carbon is synthesized via topological changing strategy. • Single Fe atom catalyst was successfully synthesized by pore confined method. • The Fe-SA/HPC showed superior catalytic activity toward ORR. • The excellent performance is clarified by the DFT theory. • The active site is optimized by the synergistic effect of defects and graphite-N. The requirement of sustainable energy is of great significance for easing the energy shortage crisis, in which the oxygen reduction reaction (ORR) in metal-air batteries and fuel cells plays a crucial role in efficient energy conversion. The development of noble-metal-free, efficient, and stable ORR electrocatalysts is highly desirable but remains a significant challenge. Herein, we report an atomically dispersed Fe and N co-doped hierarchically porous carbon (Fe-SA/HPC) catalyst derived from two-dimensional leaf-like ZIF-L with preeminent ORR activity. The Fe-SA/HPC catalyst, benefitting from hierarchically porous structure and rich highly-dispersed active sites of FeN x , put up ORR performance with a half-wave potential (E 1/2) of 0.91 V vs. the reversible hydrogen electrode (RHE) in 0.1 M KOH electrolyte. The current density with a 0.382 mg cm−2 loading of catalyst in a rotating disk electrode (RDE) test can reach 24.65 mA cm−2 at 0.8 V, which is nearly twice that of commercial 20 wt% Pt/C. Density functional theory calculations demonstrate that the co-regulation of defects and graphitic nitrogen can optimize the local electronic redistribution for active sites and endow them with a lower free-energy barrier towards the ORR. This work provides certain inspiration for the development of highly reactive atomic metal catalysts through rational topology structure engineering and nitrogen moiety regulation. [ABSTRACT FROM AUTHOR]

Developing bifunctional ORR&OER electrocatalysts with high activity and stability is challenging for practical application of rechargeable Zinc air batteries. Herein, an ionic liquid strategy is proposed for construction of FeCo alloys encapsulated in nitrogen-doped carbon as bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). By taking advantages of the unique properties such as solvent effect and low volatility, ionic liquid serves as solvent to disperse metal ions in the precursor preparation and nitrogen-containing carbon source during pyrolysis. The FeCo alloy nanoparticles encapsulated in the N-doped carbon matrix show a homogeneous distribution with average sizes of 50–100 nm. Such a core-shell structure endows the catalyst with both high ORR and OER activity and robust stability in alkaline environments. Especially, the half-wave potential (E 1/2) for ORR is 0.86 V and the overpotential (E over) for OER to reach the 10 mA·cm−2 current density is only 280 mV. Furthermore, the obtained bifunctional electrocatalyst also displays high efficiency and great durability when applied in the rechargeable Zn-air battery. The specific capacity and energy density at the discharge current density of 10 mA·cm−2 reach up to 741.5 mAh·g−1 and 830.1 Wh kg−1, respectively. It's envisioned that this ultra-facile method would be applicable to synthesize highly efficient catalysts for other energy conversion systems. • The FeCo@NC electrocatalyst is prepared through a facile two-step method by employing the ionic liquid ([EMIM][DCA]). • The FeCo@NC electrocatalyst exhibits excellent ORR and OER activity and stability in alkaline environments. • The FeCo@NC based Zn-air battery displays high efficiency and good reversibility. [ABSTRACT FROM AUTHOR]

Dual-atomic-site catalysts (DASCs), as an extension of single-atom catalysts (SACs), have attracted increasing attention owing to the synergistic effect. However, the study of DASCs is still at the early stages and mainly based on metal atom pairs. More experimental and theoretical exploration needed for further guiding the reasonable design of diatomic active sites. Herein, remarkable activity for oxygen reduction reaction (ORR) of Se 1 -NC single-atom catalyst was discovered, and then Fe/Se dual-atom catalysts were constructed to demonstrate the dual-atom sites synergistic effect. Encouraging, the Fe 1 Se 1 -NC catalyst displays significant enhancement for ORR towards Fe 1 -NC and Se 1 -NC in both alkaline and acid electrolytes. Spectroscopic characterizations and theoretical calculations reveal that there are multiple effects for the introduction of Se, especially for supplying new active sites, and effectively tuning charge redistribution and the spin-state of Fe active sites, which presenting a new strategy to improve the electrochemical performance based on the metal-nonmetal dual-atomic-site catalysts. Atomically dispersed metal(Fe) and non-metal (Se) dual atoms anchored on nitrogen-doped carbon for the first time. The co-exist of Fe-N 5 moiety and SeC 2 dual active sites displays significant synergetic enhancement for ORR towards Fe 1 -NC and Se 1 -NC. This work provides a unique insights of atomical introducing of non-metal active sites for rational design of more effective catalysts. [Display omitted] • Metal(Fe) and nonmetal(Se) dual-atom sites are prepared for the first time, which displays significant enhancement for ORR. • DFT calculations indicate that the co-exist of Fe and Se dual-atomic-site is more beneficial to *OH desorption process. • Se atom has several functions: (1) adjust the electronic state of the Fe-N X. (2) Serve as ORR site. (3) Create rich pores. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly dispersed Co atoms anchored in porous N-doped carbon is synthesized. • The p –Co–N–C exhibits excellent activity and selectivity for H 2 O 2 electrosynthesis. • The p –Co–N–C shows promising application for the degradation of organic pollutants. Cobalt–nitrogen–carbon (Co–N–C) materials exhibit great potential for H 2 O 2 electrosynthesis through the oxygen reduction reaction (ORR). However, the encapsulated Co nanoparticles reduce the Faradic efficiency of H 2 O 2 production. Herein, highly dispersed cobalt atoms anchored in porous N-doped carbon (p –Co–N–C) via a carbonization-alkalization-acidification strategy are prepared and prove to be efficient for H 2 O 2 electrosynthesis in acidic media. The H 2 O 2 selectivity on the p –Co–N–C is over 90%, which is three times higher than that of Co nanoparticles encapsulated in N-doped carbon. Notably, the p –Co–N–C displays a H 2 O 2 production rate of 2,460.8 mg L−1h−1 and a malachite green degradation rate of 90% within 8 min when employed in a flow cell. The enhanced performance of p –Co–N–C for H 2 O 2 electrosynthesis originates from the highly dispersed Co–N x species and hierarchical porous architecture. The Co–N x species can provide active sites for O 2 and reaction intermediate adsorption and the hierarchical porous architecture can promote the diffusion of H 2 O 2 into the bulk solution. This work provides a facile synthesis strategy for non-precious metal materials in various energy-related applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Single-Cu-atoms and Cu clusters anchored nitrogen-doped porous carbon is developed. • As-prepared porous carbon shows ultra-high specific surface area of 3264 m2 g−1. • The catalysts exhibit the pH-universal electrocatalytic activity for oxygen reduction reaction. • The catalytic activity in acidic medium outperforms all of reported Cu-based catalysts. • The enhanced activity can be attributed to the synergistic effects of single-Cu-atom and Cu cluster. Oxygen reduction reaction (ORR) plays a significant role in many renewable energy storage and conversion devices. Various kinds of transition metal-based electrocatalysts were developed to promote the ORR. Among them, Cu-based catalysts were rarely studied due to their intrinsic de-active feature in bulk state, especially in acidic medium. In this work, single Cu atoms and Cu clusters-anchored nitrogen-doped porous carbons are rationally developed. As electrocatalysts for ORR, half-wave potential (E 1/2) of 0.88 V and diffusion limiting current density (J L) of 5.88 mA cm−2 can be achieved in 0.1 M KOH, exceeding the most of reported non-precious catalysts and commercial Pt/C. Significantly, as-prepared catalysts exhibit the state-of-the-art performance in acidic medium among all of reported Cu-based catalysts with the E 1/2 of 0.80 V and J L of 5.86 mA cm−2. Theoretical calculations indicate that the nitrogen-coordinated Cu atoms are the dominating active sites, and the neighboring Cu cluster increases the electron density of d orbitals of single-Cu-atom, which weakened the O-O interaction, thus further boost ORR performance. This work not only presents a facile strategy to fabricate efficient catalysts but also identifies the great potential of Cu based materials for ORR in both alkaline and acidic media. [ABSTRACT FROM AUTHOR]

[Display omitted] • Influence of Fe bonded with different type N on the stability of ORR was analyzed. • Fe-N-C catalyst with high pyridinic N content was successfully prepared. • Fe-N-C with high pyridinic N content presents much enhanced ORR stability. • The practical value of catalyst was tested in PEMFC and Zn-air cell. Developing advanced non-precious metal catalysts towards acidic oxygen reduction reaction (ORR) is critical for electrochemical energy conversion devices. Fe-N-C catalysts are demonstrated to be the most promising alternatives to platinum-based catalysts for ORR. Herein, Fe single atoms (SAs) coordinated by pyridinic nitrogen catalysts (denoted as Fe-pyridinic N-C) are synthesized through pyrolysis of ZIF-8 encapsulating ferrocene. Owing to the synergistic effects between Fe SAs and pyridinic N, Fe-pyridinic N-C exhibits remarkable ORR activity and outstanding stability in acid media, evidenced by golden kinetic current density of 9.71 mA cm−2 at 0.8 V, along with only 21 mV decrease in half-wave potential after 20,000 cycles. Theoretical calculations demonstrate that pyridine-type N possesses stronger binding energy with Fe SAs compared with pyrrole-type N, in other words, high pyridinic N content will help stabilize the catalyst. This study will be of great significance for the development of non-noble metal catalysts towards ORR with enhanced stability in acidic media. [ABSTRACT FROM AUTHOR]

Via a simple microwave-assistance without template and metal ligand, nitrogen doped porous carbon polyhedrals supported Fe and Ni dual single-atomic catalysts (FeNi-DACs-PNCH) were sucessfully prepared, and exhibited superb ORR performances with positive E 1/2 (0.89 V vs RHE), excellent durability and strong tolerance to methanol and SCN- in alkaline media. Moreover, with FeNi-DSAs-PNCH as the air cathode and zinc foil as the anode, an assembled Zn-air battery exhibits a higher open-circuit voltage of 1.48 V and a larger specific capacity of 802.18 mAh g−1 than that of the Pt/C-based Zn-air battery (1.37 V and 664.78 mAh g−1, respectively). [Display omitted] • Dual single-atomic catalysts prepared via microwave-aid with no template and metal ligand. • The catalysts have porous structure, large surface area and abundant active sites. • The catalysts showed high ORR activity superior to the commercial Pt/C. • The proposed Zn-air battery exhibits a promising practical application prospect. • DFT calculation verified the d-band center modulating for boosted ORR catalysis. Constructing dual-metal single-atom catalysts (DSAs) now stands for a unique and worthwhile strategy for developing high-efficiency electrocatalysts for oxygen reduction reaction (ORR). However, the facile synthesis of DSAs uniformly located on nitrogen porous carbon materials is still challenging. Herein, Fe and Ni dual-metal single-atomic active sites uniformly located on nitrogen doped porous carbon polyhedrals (FeNi-DSAs-PNCH) are successfully prepared by a facile and rapid microwave-assisted adsorption and subsequent pyrolysis process with free template and free metal ligand. The FeNi-DSAs-PNCH catalyst exhibits boosted ORR activity and long time stability. Experimental investigations and density functional theory calculation results verify that, besides the hierarchical porous structure, large specific surface area and abundant catalytic active sites, the adjacent Ni-Nx atomic sites can modulate the d-band center of Fe-Nx single atomic active centers and balance the adsorption–desorption affinities to O 2 molecules and oxygen-containing intermediates on Fe-Nx, thus leading to an superior ORR activity with a more positive half-wave potential (0.89 V vs. RHE) than the single Fe or Ni atomic catalyst and the commercial Pt/C catalyst. Moreover, with FeNi-DSAs-PNCH as the air cathode and zinc foil as the anode, an assembled Zn-air battery exhibits a higher open-circuit voltage of 1.48 V and a larger specific capacity of 802.18 mAh g−1 than that of the Pt/C-based Zn-air battery (1.37 V and 664.78 mAh g−1, respectively). This work develops a convenient strategy for preparing dual-metal single-atomic cataysts as promising substitutes for the commercial Pt/C catalysts in the practical energy conversion applications, and also offers experimental and theoretical guidance for rational designing and improvement of ORR and other catalysts by tailoring the d-band center of the active sites. [ABSTRACT FROM AUTHOR]

• Co/Co 9 S 8 nanoparticles decorated N, S dual-doped carbon leaves was prepared via DTO molecule coating leaf-shaped ZIFs. • The functionality of DTO simultaneously optimizes 2D nanostructure and component (S doping) by the confinement effect. • The Co/Co 9 S 8 -NCL-30 exhibits excellent ORR performance, stability and zinc-air battery performance. [Display omitted] Substituting costly Pt-based oxygen reduction reaction (ORR) catalysts with highly active and stable non-precious metal catalysts is a great challenge in zinc-air batteries. Herein, we fabricated Co/Co 9 S 8 nanoparticles decorated nitrogen, sulfur dual-doped carbon leaves (Co/Co 9 S 8 -NCL) with outstanding ORR performance by pyrolysis of dithiooxamide (DTO) molecule modified two-dimensional (2D) leaf-shaped zeolitic imidazolate framework (ZIF-L). The functionality of DTO simultaneously optimizes 2D nanostructure and component (S doping) by the confinement effect due to the coordination interaction between S atoms of DTO and Co2+ in ZIF-L. Benefiting from the synergistic effect between Co-N x sites and Co/Co 9 S 8 species coupled with unique two-dimensional N, S-codoped carbon leaves, the resulting Co/Co 9 S 8 -NCL-30 exhibits a remarkable ORR activity with a half-wave potential of 0.852 V comparable to Pt/C (0.843 V) and outstanding long-term stability. Impressively, the Zn-air battery with Co/Co 9 S 8 -NCL-30 achieves high power density of 112 mW cm−2 and specific capacity of 799 mAh g−1 Zn. This work will present a new pathway to prepare highly active and durable 2D transition metal-based carbon nanomaterials in zinc-air batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • Melamine was added to intrigue the self-assembly of Cu/Zn MOF nanosheet. • In situ trapped N-rich molecules benefit the formation of pores and Cu-N 4 sites. • Cu-SAs/NSs display remarkable ORR activity and excellent stability. • Cu-SAs/NSs exhibit superb performance when used in rechargeable Zn–air battery. • The strategy can be extended to prepare other metal-based single atoms. The development of noble-metal-free single atom electrocatalysts (SAECs) with both remarkable activity and durability for oxygen reduction reaction (ORR) are in great demand for large-scale commercialization of proton-exchange membrane fuel cells and metal-air batteries. Here, we developed a novel strategy to fabricate high-performance Cu-SAs/NSs from pyrolysis of two-dimensional (2D) Cu/Zn bimetallic MOF. Specifically, nitrogen-rich molecules (melamine) were deliberately added to intrigue the self-assembly of Cu/Zn bimetallic MOF, and contribute to the formation of highly porous structure and abundant Cu-N 4 active sites. With the enhanced accessibility of active sites and mass transport, the as-developed Cu-SAs/NSs display a remarkable ORR performance in alkaline media, outperforming the benchmark Pt/C and most of platinum group metals (PGMs)-free electrocatalysts reported to date. Notably, this facile strategy can be extended to fabricate other transition metal (TM, TM = Fe, Co, Ni)-based single atoms. This work presents a novel and general strategy to construct carbon-based SAECs towards ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu 0.6 -N-CNFs were prepared using SCC as an organometallic copper source. • The Cu-N 4 chelating structure in SCC was retained in the Cu 0.6 -N-CNFs. • The Cu 0.6 -N-CNFs exhibited ORR activity similar to that of commercial Pt/C catalysts. Single-atom catalysts (SACs) have attracted much attention in the field of oxygen reduction reactions (ORR) as a result of their high selectivity and effective atom utilization. Cu SACs are particularly difficult to prepare since copper is prone to agglomeration, which leads to the formation of metal particles. In this study, using sodium copper chlorophyllin (SCC) as an organometallic copper source, carbon nanofibers incorporating Cu-N 4 structures were prepared using electrospinning technology. This new type of Cu SAC has a huge surface area (1005.615 m2·g) and a 3D network structure, which are conducive to the exposure of more active sites as well as to electron conduction and material transport. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy revealed that the Cu-N 4 structure was preserved in the electrocatalyst, and was responsible for the catalytic activity towards the ORR. The Cu–N-CNFs exhibited higher catalytic activity and greater stability than commercial Pt/C in an alkaline medium, suggesting the possibility of using Cu SACs to replace commercial Pt/C electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • A surface functional group regulation strategy was proposed for H 2 O 2 production. • The optimized CoNCF-HNO 3 exhibits satisfactory 2e− ORR selectivity in acid medium. • Positive correlation between C-O-C content and 2e− ORR selectivity was disclosed. • A sterilization system for water disinfection was developed based on CoNCF-HNO 3. Electrochemical synthesis has emerged as a promising alternative method for industrial production of hydrogen peroxide (H 2 O 2). Although transition metal-nitrogen-carbon moieties have been regarded as efficient catalysts for oxygen reduction reaction (ORR), they are generally established for four-electron (4e−) pathway, rather than two-electron (2e−) one for selective generation of H 2 O 2. Herein, we propose a strategy to achieve cobalt-carbon hybrids with high 2e− selectivity for H 2 O 2 production in acidic media via tailoring their surface structure and coordination environment. The correlation between 2e− ORR selectivity of the fabricated monolithic electrodes, i.e. Co nanoparticles embedded in N-doped oxo carbon framework (CoNCF), and their oxygen-containing functional groups is revealed. In particular, an excellent H 2 O 2 selectivity over 91 % in 0.05 M H 2 SO 4 is achieved, which exceeds most of previously reported 2e− ORR electrocatalysts. Moreover, a sterilization system for water disinfection is constructed, demonstrating potential practical applications. The smart design of multi-active sites and porous monolithic architecture opens a new avenue for preparing advanced electrode for H 2 O 2 generation and other environment/energy-related systems. [ABSTRACT FROM AUTHOR]

The high-quality hollow N-doping carbon nanoflowers (h-N-CFs) with nanosheets subunits are synthesized by using 2,5-diaminobenzoic acid-1,3,5-benzenetricarboxaldehyde (DABA-BTCO) complex nanoflowers as the self-template and nitrogen resource. The as-prepared h-N-CFs at 800 ℃ has excellent electrocatalytic oxygen reduction activity in both alkaline and neutral electrolytes, good long-term stability and eminent methanol tolerance, which is equal or even better than Pt/C electrocatalyst. [Display omitted] • Hollow N-doping carbon nanoflowers (h-N-CFs-800) are successfully prepared. • Covalent complexes act as calcination precursors and activated nitrogen sources. • Hollow and porous structure of h-N-CFs-800 increase the number of active sites. • The high ORR activity due to the unique hollow structure and abundant N doping. • h-N-CFs-800 has excellent ORR activity in both alkaline and neutral electrolytes. The synthesis of economic carbon-based metal-free catalysts with high electroactivity for the oxygen reduction reaction (ORR) is still a huge challenge for energy storage and conversion devices. Herein, the hollow N-doped carbon nanoflowers (h-N-CFs) with nanosheets subunits were synthesized by using 3,5-diaminobenzoic acid-1,3,5-benzenetricarboxaldehyde (DABA-BTCO) complex nanoflowers as the self-template and nitrogen resource. Various physical characterizations show that h-N-CFs with hollow and porous architecture have a high surface area (1390.3 m2g−1) and abundant activated N atoms (i.e., graphitic N and pyridinic N). Electrochemical measurements demonstrate that h-N-CFs synthesized at 800 °C can be used as an efficient metal-free ORR catalyst with prominent electroactivity and stability due to hollow architecture, abundant pores, and high N-doping content. Meanwhile, h-N-CFs also show eminent ORR selectivity (i.e., methanol tolerance) in alkaline media, which markedly surpasses benchmark Pt/C catalyst in the presence of methanol. [ABSTRACT FROM AUTHOR]

A simple method for the mechanochemical synthesis of an effective metal-free electrocatalyst for the oxygen reduction reaction was demonstrated. A nitrogen-doped carbon material was obtained by grinding a mixture of graphene oxide and melamine in a planetary ball mill. The resulting material was characterized by XPS, EPR, and Raman and IR spectroscopy. The nitrogen concentration on the N-bmGO surface was 5.5 at.%. The nitrogen-enriched graphene material (NbmGO has half-wave potential of −0.175/−0.09 V and was shown to possess high activity as an electrocatalyst for oxygen reduction reaction. The electrocatalytic activity of NbmGO can be associated with a high concentration of active sites for the adsorption of oxygen molecules on its surface. The high current retention (93% for 12 h) after continuous polarization demonstrates the excellent long-term stability of NbmGO. [ABSTRACT FROM AUTHOR]