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Coupling the structure advantages of platinum (Pt)-based active composites, transition-metal single sites, and porous carbon is highly desirable to reduce the Pt usage in proton-exchange membrane fuel cells (PEMFCs) but remains a great challenge. Herein, we report the in situ construction of synergistic oxygen reduction reaction (ORR) catalysts with intermetallic PtZn alloy nanoparticles confined in mesoporous carbon doped with atomic Co–N4 and Zn–N4 moieties. Mesoporous carbon doped with Co–N4 and Zn–N4 moieties could be fabricated by carbonization of CoSO4-doped ZIF-8 precursors and SO42– has been verified to be responsible for the formation of mesopores and defects with narrow pore size distribution. More importantly, systematical characterizations revealed that Pt could in situ alloy with Zn–N4 sites, which could effectively prevent the agglomeration of Pt during high-temperature treatment, leading to the formation of uniform and well-dispersed PtZn nanoparticles with a mean diameter of ∼3.06 nm. The as-synthesized PtZn@Meso/Zn1Co1/NC shows an excellent mass activity of 490 mA mgPt–1 @ 0.9 V as well as excellent durability with an activity retention of 79% after 20,000 potential cycles in 0.1 M HClO4, showing that the nanoarchitecture of the mesopore-encased PtZn alloy has a high resistance to migration due to the pore confinement effect and anchoring effect of the support. In addition to developing robust Pt-based catalysts, this study also lays out a straightforward strategy for designing synergistic catalysts, which might have far-reaching implications for fuel cells and beyond. [ABSTRACT FROM AUTHOR]

Enhancing the homodispersion of Pt nanoparticles and their interaction with carbon supports is a promising strategy for improving the activity and stability of Pt-based catalysts in proton-exchange membrane fuel cells. We have developed a highly efficient and durable catalyst by confining Pt nanoparticles in a mesoporous carbon support doped with single Fe atoms (named as Pt/Meso Fe1-NC). The Pt/Meso Fe1-NC catalyst, which combined the pore confinement effect with the electronic metal–support interaction strategy, exhibited enhanced activity with a half-wave potential of 0.915 V and a mass activity of 0.566 A/mgPt. The observed improvement is ascribed to the electronic regulation between Pt and single Fe atoms, facilitated by the electron transfer from Pt to single Fe atoms. Moreover, the pore confinement and electronic metal–support interaction contributes to the superior durability with a negligible loss of 6 mV after 30 000 cycles in 0.1 M HClO4. The approach developed in this study offers a pathway to synthesize outstanding hybrid ORR catalysts. [ABSTRACT FROM AUTHOR]

To achieve practical application of fuel cell, it is vital to develop highly efficient and durable Pt‐free catalysts. Herein, we prepare atomically dispersed ZnNC catalysts with Zn‐Pyrrolic‐N4 moieties and abundant mesoporous structure. The ZnNC‐based anion‐exchange membrane fuel cell (AEMFC) presents an ultrahigh peak power density of 1.63 and 0.83 W cm−2 in H2‐O2 and H2‐air (CO2‐free), and also exhibits long‐term stability with more than 120 and 100 h for H2‐air (CO2‐free) and H2‐O2, respectively. Density functional calculations further unveil that the Zn‐Pyrrolic‐N4 structure is the origin of high activity of as‐synthesized ZnNC catalyst, while the Zn‐Pyridinic‐N4 moiety is inactive for oxygen reduction reaction (ORR), which successfully explain the puzzle why most Zn‐metal‐organic framework ‐derived ZnNC catalysts in previous reports did not present good ORR activity because of their Zn‐Pyridinic‐N4 moieties. This work offers a new route for speeding up development of AEMFCs. [ABSTRACT FROM AUTHOR]

Fine‐tuning single‐atom catalysts (SACs) to surpass their activity limit remains challenging at their atomic scale. Herein, we exploit p‐type semiconducting character of SACs having a metal center coordinated to nitrogen donors (MeNx) and rectify their local charge density by an n‐type semiconductor support. With iron phthalocyanine (FePc) as a model SAC, introducing an n‐type gallium monosulfide that features a low work function generates a space‐charged region across the junction interface, and causes distortion of the FeN4 moiety and spin‐state transition in the FeII center. This catalyst shows an over two‐fold higher specific oxygen‐reduction activity than that of pristine FePc. We further employ three other n‐type metal chalcogenides of varying work function as supports, and discover a linear correlation between the activities of the supported FeN4 and the rectification degrees, which clearly indicates that SACs can be continuously tuned by this rectification strategy. [ABSTRACT FROM AUTHOR]

Combining isolated atomic active sites with those in nanoparticles for synergizing complex multistep catalysis is being actively pursued in the design of new electrocatalyst systems. However, these novel systems have been rarely studied due to the challenges with synthesis and analysis. Herein, a synergistically catalytic performance is demonstrated with a 0.89 V (vs reversible hydrogen electrode) onset potential in the four‐step oxygen reduction reaction (ORR) by localizing tungsten single atoms around tungsten nitride nanoparticles confined into nitrogen‐doped carbon (W SAs/WNNC). Through density functional theory calculations, it is shown that each of the active centers in the synergistic entity feature a specific potential‐determining step in their respective reaction pathway that can be merged to optimize the intermediate steps involving scaling relations on individual active centers. Impressively, the W SAs/WNNC as the air cathode in all‐solid‐state Zn‐air and Al‐air batteries demonstrate competitive durability and reversibility, despite the acknowledged low activity of W‐based catalyst toward the ORR. [ABSTRACT FROM AUTHOR]

Metal phthalocyanines (MPcs) have highly conjugated π electron systems and metal atoms acting as active centers, and so exhibit excellent electrocatalytic performance during the oxygen reduction reaction (ORR). However, these complexes also tend to undergo aggregation and exhibit poor electrical conductivity and minimal durability, all of which hinder their large‐scale industrial applications. In the present study, iron phthalocyanine (FePc) is applied to hollow carbon shells (HCSs) to generate an ORR catalyst containing single Fe atoms(HCS‐O‐FePc). The HCSs have numerous N/O‐based surface functional groups that promote the formation of Fe−O bonds with the FePc held in an axial coordination position. These axial Fe−O bonds disrupt the electron symmetry in the plane of the FePc molecules, which facilitate electron transfer. 1100HCS‐O‐FePc exhibits an onset potential of 0.98 V (vs RHE), a half‐wave potential of 0.91 V (vs RHE), an electron transfer number of 3.90, and durability better than that of a 20 % commercial Pt/C catalyst. Electrochemical impedance spectroscopy demonstrates that the ORR process over this material likely proceeds via a rapid 2+2 electron mechanism. This composite displays excellent oxygen reduction properties and is a promising alternative to Pt‐based ORR catalysts. [ABSTRACT FROM AUTHOR]

Atomically dispersed Pt species are advocated as a promising electrocatalyst for the oxygen reduction reaction (ORR) to boost noble metal utilization efficiency. However, when assembled on various substrates, isolated Pt single atoms are often demonstrated to proceed through the two‐electron ORR pathway due to the unfavorable O─O bond cleavage thermodynamics in the absence of catalytic ensemble sites. In addition, although their distinct local coordination environments at the exact single active sites are intensively explored, the interactions and synergy between closely neighboring single atom sites remain elusive. Herein, atomically dispersed Pt monomers strongly interacting on a Mo2C support is demonstrated as a model catalyst in the four‐electron ORR, and the beneficial interactions between two closely neighboring and yet non‐contiguous Pt single atom sites (named as quasi‐paired Pt single atoms) are shown. Compared to isolated Pt single atom sites, the quasi‐paired Pt single atoms deliver a superior mass activity of 0.224 A mg−1Pt and near‐100% selectivity toward four‐electron ORR due to the synergistic interaction from the two quasi‐paired Pt atom sites in modulating the binding mode of reaction intermediates. Our first‐principles calculations reveal a unique mechanism of such quasi‐paired configuration for promoting four‐electron ORR. [ABSTRACT FROM AUTHOR]

The modulation effect has been widely investigated to tune the electronic state of single‐atomic M‐N‐C catalysts to enhance the activity of oxygen reduction reaction (ORR). However, the in‐depth study of modulation effect is rarely reported for the isolated dual‐atomic metal sites. Now, the catalytic activities of Fe‐N4 moiety can be enhanced by the adjacent Pt‐N4 moiety through the modulation effect, in which the Pt‐N4 acts as the modulator to tune the 3d electronic orbitals of Fe‐N4 active site and optimize ORR activity. Inspired by this principle, we design and synthesize the electrocatalyst that comprises isolated Fe‐N4/Pt‐N4 moieties dispersed in the nitrogen‐doped carbon matrix (Fe‐N4/Pt‐N4@NC) and exhibits a half‐wave potential of 0.93 V vs. RHE and negligible activity degradation (ΔE1/2=8 mV) after 10000 cycles in 0.1 M KOH. We also demonstrate that the modulation effect is not effective for optimizing the ORR performances of Co‐N4/Pt‐N4 and Mn‐N4/Pt‐N4 systems. [ABSTRACT FROM AUTHOR]

Self‐powered sensing systems (SPSSs) are critical components in smart portable electronic devices. Zinc‐air batteries (ZABs) as promising energy devices provide a great opportunity to develop novel SPSS for sensing applications owing to the merit of high open‐circuit potential. Herein, hierarchically porous single‐atom iridium embedded nitrogen‐doped carbon (SA‐Ir/NC) is reported as an efficient catalyst for the oxygen reduction reaction (ORR) in the neutral ZABs, enabling the SPSSs towards glucose detection with a high sensitivity and stable output signal. The resultant SA‐Ir/NC shows superior ORR activity and stability to commercial Pt/C in neutral electrolytes. According to the theoretical calculations, IrN5 active sites in SA‐Ir/NC exhibit moderate adsorption free energy to reaction intermediates, giving SA‐Ir/NC excellent four‐electron ORR activity and well‐enhanced H2O2 tolerance. When SA‐Ir/NC is applied as an air cathode, the as‐prepared ZABs display a large open‐circuit voltage of 1.42 V, a remarkable power density of 90.4 mW cm−2, and excellent long‐term stability. After being integrated with glucose oxidase, the SPSSs are successfully established for sensitive detection of glucose based on a competitive model, holding great promise in biosensing applications. [ABSTRACT FROM AUTHOR]

The development of inexpensive and highly efficient nonprecious metal catalysts to substitute Pt in the alkaline oxygen reduction reaction is an appealing idea in the energy field. Herein, a Mn oxygen reduction electrocatalyst with a half‐wave potential (E1/2) as high as 0.910 V under an alkaline oxygen reduction reaction process is developed, and the dynamic atomic structure change of the highly efficient Mn single‐atomic site is investigated using operando X‐ray absorption spectroscopy. These results demonstrate that the low‐valence MnL+N4 is the active site during the oxygen reduction process. Density functional theory reveals that facile electron transfer from MnL+N4 to adsorbed *OH species plays a key role in the excellent electrocatalytic performance. Moreover, when assembled as the cathode in a zinc–air battery, this MnN4 material shows high power density and excellent durability, demonstrating its promising potential to substitute the Pt catalyst in practical devices. [ABSTRACT FROM AUTHOR]

Metal-nitrogen-carbon (M-N-C) catalysts with M-N x (x = 2 or 4) sites on graphene substrate are researched intensively nowadays. However, the simple and repetitive hexatomic ring structure of graphene limits the exploration of novel efficient active sites for catalysis. Herein, a new carbon material, hydrogen-substituted graphdiyne (HsGDY), is designed as the substrate to develop new active sites. Benefiting from the unique sp and sp2 hybridized carbon atoms of HsGDY, aromatic rings in HsGDY can fix Fe single atoms, creating novel FeC 6 and FeNC 5 active sites. The as-synthesized Fe-N-HsGDY catalyst displays much higher activity than commercial Pt/C and is found to be one of the highest activities among the reported non-noble metal catalysts for oxygen reduction reaction (ORR). FeNC 5 site with graphitic-N has been verified experimentally and theoretically as an efficient active site for ORR. Those results indicate that the rational choice of specific substrate materials with novel structures will broaden the path of creating new active sites with efficient activity. [Display omitted] • The uniform dispersion of the single Fe atoms in Fe(N/C)6 coordination structures in the Fe-N-HsGDY sample was synthesized. • The FeNC5 with graphitic-N active site for Fe-N-HsGDY was revealed to be a novel and highly active ORR reaction site. • The Fe-N-HsGDY with unique active sites exhibits excellent performance for ORR in both acid and alkaline environment. [ABSTRACT FROM AUTHOR]

Carbon‐supported precious metal single‐atom catalysts (PM SACs) have shown promising application in proton exchange membrane fuel cells (PEMFCs). However, the coordination principle of the active site, consisting of one PM atom and several coordinating anions, is still unclear for PM SACs. Here, a sequential coordination method is developed to dope a large amount of PM atoms (Ir, Rh, Pt and Pd) into a zeolite imidazolate framework (ZIF), which are further pyrolyzed into nitrogen‐coordinated PM SACs. The PM loadings are as high as 1.2–4.5 wt%, achieving the highest PM loadings in ZIF‐derived SACs to date. In the acidic half‐cell, Ir1‐N/C and Rh1‐N/C exhibit much higher oxygen reduction reaction (ORR) activities than nanoparticle catalysts Ir/C and Rh/C. In the contrast, the activities of Pd1‐N/C and Pt1‐N/C are considerably lower than Pd/C and Pt/C. Density function theory (DFT) calculations reveal that the ORR activity of PM SAC depends on the match between the OH* adsorption on PM and the electronegativity of coordinating anions, and the stronger OH* adsorption is, the higher electronegativity is needed for the coordinating anions. PEMFC tests confirm the active‐site coordination principle and show the extremely high atomic efficiency of Ir1‐N/C. The revealed principle provides guidance for designing future PM SACs for PEMFCs. [ABSTRACT FROM AUTHOR]

The transition metal phosphides have gradually emerged as promising electrocatalysts candidate for oxygen reduction reaction in recent years. As a research hotspot of transition metal phosphides, exploring their mechanism of catalytic activity and the influence of unique morphology is of great significance. In this study, a series of yolk‐shell structure catalysts are fabricated only by pyrolyzing cyclophosphazene microspheres and metal salt without using any other templates, which M2P (M=Fe, Co, Ni) act as the core and N, P co‐doped carbon as the shell. The yolk‐shell structures aim to overcome the inferior conductivity and aggregation problems traditionally existed in application of transition metal phosphides through combination of transition metal phosphides and doped carbon materials. The prepared Fe2P/NPC, Co2P/NPC and Ni2P/NPC catalysts exhibit excellent ORR catalytic activity through the four‐electron pathway, together with large electrochemically active surface area, superior stability and admiring methanol tolerance. What came first: yolk or shell? A series of yolk‐shell structure M2P/NPC catalysts are fabricated by general method without templates for efficient oxygen reduction in alkaline condition. [ABSTRACT FROM AUTHOR]

Abstract: Developing hybrid carbon materials with unique micro/nanostructured and multicomponent features is of great importance in catalysis, energy storage, and energy conversion. Herein, we demonstrate the formation of a novel kind of hybrid carbon material, that is, bimetallic nanoparticles supported by ultrathin (≈5.5 nm) and porous carbon nanosheets, by the pyrolysis of preformed bimetallic metal–organic framework nanosheets. This hybrid carbon nanostructure combines the advantages of highly exposed nanoparticles that are readily accessible to the reactant, multiple active sites such as metal–metal and metal–nitrogen sites and ultrathin carbon layers, and highly efficient electron transport. Owing to these unique features, the bimetallic carbon nanosheets exhibit excellent electrocatalytic performance for the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Abstract: The environmentally friendly synthesis of highly active Fe‐N‐C electrocatalysts for proton‐exchange membrane fuel cells (PEMFCs) is desirable but remains challenging. A simple and scalable method is presented to fabricate FeII‐doped ZIF‐8, which can be further pyrolyzed into Fe‐N‐C with 3 wt % of Fe exclusively in Fe‐N4 active moieties. Significantly, this Fe‐N‐C derived acidic PEMFC exhibits an unprecedented current density of 1.65 A cm−2 at 0.6 V and the highest power density of 1.14 W cm−2 compared with previously reported NPMCs. The excellent PEMFC performance can be attributed to the densely and atomically dispersed Fe‐N4 active moieties on the small and uniform catalyst nanoparticles. [ABSTRACT FROM AUTHOR]

The development of low-cost, efficient, and stable electrocatalysts for the oxygen reduction reaction (ORR) is desirable but remains a great challenge. Herein, we made a highly reactive and stable isolated single-atom Fe/N-doped porous carbon (ISA Fe/CN) catalyst with Fe loading up to 2.16 wt %. The catalyst showed excellent ORR performance with a half-wave potential ( E1/2) of 0.900 V, which outperformed commercial Pt/C and most non-precious-metal catalysts reported to date. Besides exceptionally high kinetic current density ( Jk) of 37.83 mV cm−2 at 0.85 V, it also had a good methanol tolerance and outstanding stability. Experiments demonstrated that maintaining the Fe as isolated atoms and incorporating nitrogen was essential to deliver the high performance. First principle calculations further attributed the high reactivity to the high efficiency of the single Fe atoms in transporting electrons to the adsorbed OH species. [ABSTRACT FROM AUTHOR]

A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal-organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-N x single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials. [ABSTRACT FROM AUTHOR]

Developing single-atomic site (SAS) catalysts for oxygen reduction reaction (ORR) with superior activities in the renewable-energy initiatives is critical but remains challenging. Herein, exceptional SAS Fe boosted by adjacent graphene-encapsulated Fe 3 C nanocrystals (Fe 3 C@C-Fe SAS) is constructed for ORR. Because of the strong synergistic effects between SAS Fe and Fe 3 C@C nanocrystals, Fe 3 C@C-Fe SAS shows robust ORR performance in the neutral electrolyte with the onset potential of 0.99 V and negligible activity loss after 30 k cycles of an accelerated durability test, much better than that of Pt/C catalyst. Notably, the integrated zinc-air battery in the neutral system exhibits an outstanding peak power density of 74.8 mW/cm2 and durability over 100 h, representing a state-of-the-art PGM-free ORR catalyst. More importantly, the density functional theory (DFT) calculations shed light on that the introduction of Fe 3 C@C nanocrystals is favorable for the activation of O 2 molecules and desorption of OH* on the Fe SAS, resulting in accelerated reaction kinetics and promising ORR activity. Given the explicit structure-performance relationships for Fe 3 C@C-Fe SAS, this work provides a new strategy for the design of more advanced energy-based electrocatalysts. [Display omitted] • Fe 3 C@C enhanced single-atomic site Fe catalyst (Fe 3 C@C-Fe SAS) is fabricated. • The optimized Fe 3 C@C-Fe SAS manifests outstanding ORR performance at neutral conditions. • The introduction of Fe 3 C@C is verified to optimize the adsorption/desorption of intermediates on Fe SAS. [ABSTRACT FROM AUTHOR]

Controllable synthesis of 2D carbon nanosheets with high heteroatom‐doping level, large specific surface area, and hierarchically pore structure is difficult and desired. In this work, a novel and simple self‐sacrificing in situ formed dual‐template strategy is first developed to synthesize N/S codoped hierarchically porous carbon nanosheets. The in‐situ formed g‐C3N4 and amorphous ZnO act as self‐sacrificing templates on account of their thermal decomposition and evaporation at higher temperature. The N/S codoped hierarchically porous carbon nanosheets simultaneously possess high heteroatom‐doping level (N: 10.51 wt%; S: 1.71 wt%), large specific surface area (904.63 m2 g−1), and abundant hierarchically porous structure. Particularly, this material possesses a high content of pyridinic‐N and pyrrolic‐N configuration (65.66%). These unique structure advantages of N/S codoped hierarchically porous carbon nanosheets contribute to high oxygen reduction electrocatalytic activity in both basic and acidic environments. Additionally, as the anode material for sodium‐ion batteries, the material also displays a high reversible capacity of 270.1 mAh g−1 at a current density of 100 mA g−1 and high stability (160.1 mAh g−1 after 2000 cycles at 1000 mA g−1 with a capacity retention of 82.3%). These results indicate a great potential of the material in energy conversion and storage applications. A novel and simple self‐sacrificing dual‐template strategy is first developed to synthesize N/S codoped hierarchically porous carbon nanosheets (S‐N‐HPCS). The S‐N‐HPCS material exhibits greatly enhanced oxygen reduction catalytic performance and improved sodium storage property. These results indicate a great potential of the material in energy conversion and storage applications. [ABSTRACT FROM AUTHOR]

Isolated single‐atom iron catalysts with excellent oxygen reduction reaction (ORR) reactivity and outstanding stability are prepared by a cage‐encapsulated‐precursor pyrolysis strategy. In their Communication on page 6937 ff., D. Wang, Y. Li, and co‐workers show experimentally and theoretically that it is essential for the high ORR performance to maintain the iron centers as isolated atoms as well as to incorporate nitrogen. [ABSTRACT FROM AUTHOR]

The reasonable design and construction of single-atom electrocatalysts with low-cost and excellent intrinsic activity for oxygen reduction reaction (ORR) is indispensable in metal-air batteries. Herein, a facile isolation anchoring strategy was reported for in situ formation of porous N-doped carbon catalysts (Fe 1 /NC) rich in Fe single atoms. The d -glucose, zinc gluconate and N-rich histidine were deployed as spatial isolation agents and anchoring agents to inhibit iron atom aggregation during the high-temperature pyrolysis. The as-synthesized Fe 1 /NC catalyst shows remarkable stability and superior ORR electrocatalytic activity under both alkaline and acidic conditions owing to highly dispersed Fe–N 4 sites, especially with a half-wave potential up to 0.91 V in 0.1 M KOH, exceeding 60 mV compared with Pt/C. Notably, the Fe 1 /NC-based Zn-air battery exhibits maximal power density of 164 mW cm−2, large specific capacities of 769 mA h g Zn −1, excellent cycle stability over 300 h, and great potential in renewable energy conversion electronics. A facile isolation anchoring strategy was reported to synthesize the Fe single-atom electrocatalyst that exhibits excellent ORR catalytic efficiency and long-term stability in both three electrodes system and zinc-air battery due to the abundant Fe–N 4 active sites. [Display omitted] • A facile isolation anchoring strategy was reported to prepare Fe single-atom electrocatalyst. • d -glucose, zinc gluconate and N-rich histidine were deployed as spatial isolation and anchoring agents. • The electrocatalysts exhibit superior ORR performance due to the abundant Fe–N 4 active sites. • The Zn-air battery assembled with Fe 1 /NC displays a high discharge specific capacity and excellent cyclic stability. [ABSTRACT FROM AUTHOR]

A template-engaged multistep synthesis process is developed to fabricate ultrathin carbon nanosheets assembled hierarchical nanoboxes embedded with dense Mo-N 4 active sites, which exhibited excellent activity and superb stability for oxygen reduction reaction. [Display omitted] • Unique hierarchical SA-Mo-C nanoboxes were fabricated via a template-engaged multistep synthesis process. • Comprehensive characterizations including EXAFS reveal Mo-N 4 atomic sites were formed and densely dispersed in the SA-Mo-C nanoboxes. • SA-Mo-C nanoboxes exhibited better ORR performance compared to commercial Pt/C catalysts. Construction of single-atom catalysts (SACs) with maximally exposed active sites remains a challenging task mainly because of the lack of suitable host matrices. In this study, hierarchical N -doped carbon nanoboxes composed of ultrathin nanosheets with dispersed atomic Mo (denoted as hierarchical SA-Mo-C nanoboxes) were fabricated via a template-engaged multistep synthesis process. Comprehensive characterizations, including X-ray absorption fine structure analysis, reveal the formation of Mo-N 4 atomic sites uniformly anchored on the hierarchical carbon nanoboxes. The prepared catalysts offer structural and morphological advantages, including ultrathin nanosheet units, unique hollow structures and abundant active Mo-N 4 species, that result in excellent activity with a half-wave potential of 0.86 V vs. RHE and superb stability for the oxygen reduction reaction in 0.1 M KOH; thus, the catalysts are promising air–cathode catalysts for Zn-air batteries with a high peak power density of 157.6 mW cm−2. [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 Fe–N–C electrocatalysts are attracting more attentions as one most promising transition metal based single-atom catalyst towards the oxygen reduction reaction (ORR). However, the inaccessibility of internal Fe-N x active sites and insufficient stability hinder their large-scale application. Herein, a facile benzoate-assisted self-template strategy which could dramatically enhance the oxygen reduction reaction catalytic performance and stability of ZIF-8 derived atomically dispersed Fe–N–C catalysts (Fe-SA/Meso-C) is developed. The sodium benzoate used in the present work is effective for promoting the formation of Fe–N–C catalysts with denser accessible active sites as well as mesopores with diameters ranging from 2.5 to 5 nm. These structural advantages make the synthesized Fe-SA/Meso-C catalysts afford excellent electrocatalytic performance for the ORR in 0.1 M KOH with a positive half-wave potential (E 1/2) of 0.926 V vs. RHE and exceptionally high kinetic current density (J k) of 92.5 mA cm−2 at 0.85 V. Beyond that, Fe-SA/Meso-C shows outstanding long-term stability with over 90% activity retain after 90 h chronoamperometry i-t test as well as superior tolerance to methanol crossover. More importantly, the assembled zinc-air battery with Fe-SA/Meso-C as the cathode material achieves a high peak power density of 166.2 mW cm−2 and a high specific capacity of 776.1 mA h g−1. Our results reveal that small mesopores in atomically dispersed Fe–N–C electrocatalysts could facilitate mass transport, increase the accessibility of active sites and optimize the interface between electrolyte and carbon matrix, thus optimizing their electrocatalytic performance for the ORR. This work paves a way to the design and synthesis of stable single-atom electrocatalysts with optimized structure, electrochemical performance and promising applications. Ultrastable and highly catalytically active single-atom iron electrocatalysts (Fe-SA/Meso-C) with exclusively Fe–N 4 sites dispersed on ZIF-8 derived mesoporous N-doped carbon frameworks have been synthesized by a novel benzoate-assisted self-template strategy without acid leaching assistance. [Display omitted] [ABSTRACT FROM AUTHOR]

High-efficient and long-cycle air cathodes are crucial for the development of rechargeable zinc-air batteries (ZABs). Herein, we develop a strategy of micro-spherical cobalt-doped Fe 5 (PO 4) 4 (OH) 3 ·H 2 O (Co-FPOH), synthesized by a novel water-oil two-phase hydrothermal method, which was used as ORR/OER bifunctional electrocatalyst for ZABs. The change of local electronic distribution is identified by doping of Co into Fe 5 (PO 4) 4 (OH) 3 ·H 2 O (FPOH), effectively improving the electrocatalytic performance of the resulted Co-FPOH. The OER overpotential of Co-FPOH (290 mV) far outperforms state-of-the-art RuO 2 (350 mV); the ORR catalytic reaction of Co-FPOH is near 4e-, almost reaching the theoretical value of Pt/C (n = 4.00). The ZAB assembled with Co-FPOH as an air electrode exhibits an ultralong cycling lifetime of 450 h at 5 mA cm−2, a super high peak power density of 167.8 Wh cm−2, a high open circuit voltage of about 1.42 V and a large discharge specific capacity of 817 mAh g Zn −1 at 10 mA cm−2. The proposed Co-FPOH is expected to outperform precious metal electrocatalysts as a potential bifunctional electrocatalyst for advanced ZABs. Also, this work offers a novel strategy to synthesize excellent bifunctional electrocatalysts for this kind of energy-related electrocatalytic reactions. [Display omitted] Bifunctional electrocatalyst of Co-FPOH was synthesized by a novel water-oil two-phase hydrothermal method, which exhibited a long-cycle stability of up to 450 h at a current density of 5 mA cm−2 and a super high power density of 167.8 mW cm−2. ● A strategy of Co-FPOH is designed for ORR/OER bifunctional electrocatalyst. ● The local electronic distribution contributes to high-efficient electrocatalysis. ● ZABs assembled with Co-FPOH demonstrate excellent electrochemical performances. [ABSTRACT FROM AUTHOR]

[Display omitted] • FeSb-NC diatomic catalysts with a new local structure were synthesized. • The FeSb-NC shows excellent ORR performance in both acid and alkaline media. • The FeSb-NC-based PEMFC and ultralow temperature (−40 °C) Zn-air batter exhibit high peak power densities. • DFT calculation reveals the synergistic catalytic mechanism of SbN 4 and FeN 4 OH species. Dual atom catalysts (DAC) have attracted extensive concerns due to the combinatorial diversity of two central sites and their synergistic effects for boosting oxygen reduction reaction (ORR). However, how the synergistic effect modulates the local electronic structure and thus enhances the ORR activity is still ambiguity. Here, we successfully synthesize FeSb-NC diatomic catalysts with a new local structure of FeN 4 OH-SbN 4 , which is identified by synchrotron X-ray adsorption fine spectroscopy. The FeSb-NC shows excellent ORR activity with half-wave potentials of 0.795 V in 0.1 M HClO 4 and 0.905 V in 0.1 M KOH. Importantly, the FeSb-NC-based proton exchange membrane fuel cell exhibits a peak power density (PPD) of 0.4 W cm−2 at 1 bar H 2 /air condition, and the current density at 0.6 V iR-free reaches 0.673 A cm−2. Furthermore, the FeSb-NC-based solid-state Zn-air battery exhibits an ultrahigh PPD of 57.5 mW cm−2 at −40 °C ultralow temperature, apparently superior to Fe-NC and Pt/C – based ones. DFT calculations further reveal the synergistic catalytic mechanism of SbN 4 and FeN 4 OH species, i.e. SbN 4 could act as a lateral coordination site to enhance reaction kinetics and adsorption ability of FeN 4 OH species, and thus significantly boosts ORR performance. This work provides a new route of lateral coordination for the design of diatomic catalysts. [ABSTRACT FROM AUTHOR]

• Pt/MnOx and Pt/MnO electrocatalysts were prepared for the oxygen reduction reaction. • Pt-based electrocatalysts showed high utilization efficiency of Pt. • Both Pt-based catalysts exhibited good ORR stability. Electrocatalyst for oxygen-reduction reaction (ORR) is crucial for metal-air batteries, in which Pt-based materials are the benchmark catalysts for ORR. However, the high cost and limited supplies of Pt limit its broad use in commercial applications. Designing highly efficient Pt electrocatalysts can reduce material cost and enable commercial success for a wide variety of electrochemical technologies. Herein, we prepared Pt/MnO x and Pt/MnO electrocatalysts via deposition–precipitation and H 2 –reduction approaches. The Pt mass activities towards the ORR at 0.7 V for the Pt/MnO x , and Pt/MnO catalysts were 4.0 and 3.7 A mg Pt −1, respectively, which were 20, and 18.5 times as commercial 20% Pt/C catalyst. The transferred electron numbers (n) were 3.6 and 4.0 for Pt/MnO x and Pt/MnO, respectively. Moreover, Pt/MnO catalyst exhibited a good ORR stability after 500 cycles compared to Pt/MnO x catalyst in 0.1 M KOH. [ABSTRACT FROM AUTHOR]

Developing low-cost and high-performance non-precious metal oxygen reduction reaction (ORR) catalysts for fuel cells is highly desirable but still full of challenges. In this work, oxygen-doped carbonaceous polypyrrole nanotubes (OCPN) are synthesized by a KOH-activated assisted method and Ag nanoparticles are grown in situ on OCPN. The resultant Ag/OCPN catalysts possess comparable excellent activity with commercial Pt/C (onset potential is −0.003 V vs. SCE) in alkaline solution, which is ascribed to the synergistic effect of Ag nanoparticles and the unique properties of OCPN. The best ORR property of Ag/OCPN demonstrated that the oxygen in the catalyst can facilitate the ORR. Moreover, superior stability and methanol tolerance deserve to be mentioned. [ABSTRACT FROM AUTHOR]

Abstract: A facile method using polystyrene‐b‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) micelles is demonstrated to synthesize N/FeN4‐doped hollow carbon nanospheres (N/FeN4‐CHNS) with high electrocatalytic activity for oxygen reduction reactions (ORRs). Uniform spherical micelles with PS core and P4VP shell are prepared by exposing PS‐b‐P4VP in a mixture of ethanol/tetrahydrofuran. Pyridinic N in shell cooperates with Fe3+ to induce an in situ polymerization of pyrrole. Tuning molecular composition of PS‐b‐P4VP can form hollow carbon spheres with controlled size down to sub‐100 nm that remains challenge using traditional hard template strategies. N/FeN4‐CHNS possesses a series of desirable properties as electrode materials, including easy fabrication, high reproducibility, large surface area, and highly accessible porous surface. This electrocatalyst exhibits excellent ORR activity (onset potential of 0.976 V vs reversible hydrogen electrode (RHE) and half‐wave potential of 0.852 V vs RHE), higher than that of commercial Pt/C (20 wt%) in an alkaline media, and shows a good activity in an acidic media as well. In addition to its higher stability and methanol tolerance than Pt/C in both alkaline and acidic electrolytes, highly competitive single cell performance is achieved in a proton exchange membrane fuel cell. This work provides a general approach to preparing functionalized small hollow nanospheres based on self‐assembly of block copolymers. [ABSTRACT FROM AUTHOR]

In this work, a category of Fe 3 C-containing Fe/N/C mesoporous material has been fabricated by carbonizing the mixture of uric acid, Iron (Ⅲ) chloride anhydrous and carbon support (XC-72) under different pyrolysis temperature. Of all these samples, pyrolysis temperature (800 °C) becomes the most crucial factor in forming Fe 3 C active sites which synergizes with high content of graphitic N to catalyze oxygen reduction reaction (ORR). X-ray absorption fine structure spectroscopy (XAFS) is used to exhibit that the space structure around Fe atoms in the catalyst. This kind of catalyst possesses comparable ORR properties with commercial 20% Pt/C (onset potential is 0 V vs. Ag/AgCl in 0.1 M KOH), the average transfer electron number is 3.84 reflecting the 4-electron process. Moreover, superior stability and methanol tolerance deserve to be mentioned. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three-dimensional ordered macroporous frameworks with NiN 4 sites were obtained. • 3DOM Ni N C was highly efficiency for ORR and OER performances in neutral condition. • The neutral zinc-air batteries exhibited outstanding long term stability of 580 cycles at 1.0 mA cm−2. • The failure mechanism of air electrode in neutral condition was revealed. Neutral zinc-air batteries prevent the carbon based catalysts from being oxidized during cycling, which show excellent potential for long-term energy storage. Three-dimensional ordered macroporous nitrogen doped carbon frameworks with NiN 4 (3DOM Ni N C) were constructed by in situ reaction of Ni nanoparticles and dicyandiamide. The 3DOM Ni N C bifunctional catalysts exhibit comparable oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) efficiency and stablity. The 3D interconnected structure of 3DOM Ni N C provides sufficient channel for mass transfer, resulting in high power density (35 mW cm−2) and long cycle life (580 cycles) of neutral zinc-air batteries. Meanwhile the failure mechanism in neutral electrolyte was discussed. [ABSTRACT FROM AUTHOR]

Binuclear iron (III) phthalocyanine (bi-FePc) and iron (III) phthalocyanine (FePc) are synthesized in situ on graphene nanosheets (GNS) by a microwave-assisted method. TEM, ultraviolet–visible spectroscopy and Raman spectroscopy confirm that bi-FePc is supported on GNS through π–π interactions. The catalytic activity of the bi-FePc/GNS and FePc/GNS composites in the oxygen reduction reaction (ORR) is investigated by CV and RDE measurements. The bi-FePc/GNS composite shows a more positive onset potential (0.12 V vs . Hg/Hg 2 SO 4 ) for the ORR than FePc/GNS (−0.02 V vs . Hg/Hg 2 SO 4 ), and a four-electron mechanism similar to commercial Pt/C (0.22 V vs . Hg/Hg 2 SO 4 ). Moreover, bi-FePc/GNS exhibits good stability with 100% retention after 36,000 s, while Pt/C has a retention of only 50% after the same period. Additionally, bi-FePc/GNS shows higher tolerance toward methanol than the Pt/C catalyst. XPS and X-ray absorption fine structure spectroscopy demonstrate that compared with FePc/GNS, bi-FePc/GNS possesses a higher concentration of Fe 3+ and smaller skeleton radius of the phthalocyanine ring, which has a square-planar structure that evidently favors the ORR. Thus, bi-FePc/GNS is a promising candidate as a cathode catalyst in direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

Three different pentacoordinate iron phthalocyanine (FePc) electrocatalysts with an axial ligand (pyridyl group, Py) anchored to multi-walled carbon nanotubes (MWCNTs) are prepared by a microwave method as high performance composite electrocatalysts (FePc–Py/MWCNTs) for the oxygen reduction reaction (ORR). For comparison, tetracoordinate FePc electrocatalysts without an axial ligand anchored to MWCNTs (FePc/MWCNTs) are assembled in the same way. Ultraviolet–visible spectrophotometry (UV–Vis), Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HRTEM) are used to characterize the obtained electrocatalysts. The electrocatalytic activity of the samples is measured by linear sweep voltammetry (LSV), and the onset potential of all of the FePc–Py/MWCNTs electrocatalysts is found to be more positive than that of their FePc/MWCNTs counterparts. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy are employed to elucidate the relationship between molecular structure and electrocatalytic activity. XPS indicates that higher concentrations of Fe 3+ and pyridine-type nitrogen play critical roles in determining the electrocatalytic ORR activity of the samples. XAFS spectroscopy reveals that the FePc–Py/MWCNTs electrocatalysts have a coordination geometry around Fe that is closer to the square pyramidal structure, a higher concentration of Fe 3+ , and a smaller phthalocyanine ring radius compared with those of FePc/MWCNTs. [ABSTRACT FROM AUTHOR]

Reducing the usage of noble metals, such as platinum-based catalysts for oxygen reduction reaction (ORR) is pressingly demanded towards the practical applications of proton-exchange membrane fuel cells. One promising way is to develop Pt single atom catalysts (SACs), which, however, are plagued by their preference toward two-electron ORR pathway as well as stability issue. Herein, a single-atom alloy (SAA) catalyst with platinum-cobalt (Pt-Co) dual sites encapsulated in nitrogen-doped graphitized carbon nanotubes (Pt 1 Co 100 /N-GCNT) consisting of isolated Pt atoms decorated on the surface of Co nanoparticles was reported. Based on complementary spectroscopic characterizations and first-principle calculations, we propose that the unique Pt-Co dual sites in SAA facilitates the adsorption and dissociation of oxygen, particularly for the immobilization of OOH* intermediate and the dissociation of OH* intermediate, and thus result in high-efficiency four-electron ORR pathway. Consequently, the Pt 1 Co 100 /N-GCNT SAA catalyst achieves a mass activity of 0.81 A mg–1 Pt at 0.90 V (versus the reversible hydrogen electrode) in 0.1 M HClO 4 electrolyte, outperform commercial Pt/C catalyst for 5.4 times. The superior stability of the SAA catalyst was reflected by the results from the 30,000 potential-scanning cycles combined with the post characterization of the catalyst. [Display omitted] • A single atom alloy (SAA) catalyst with well-defined platinum-cobalt (Pt-Co) dual sites was reported. • The unique Pt-Co dual sites in SAA facilitates the immobilization of OOH* intermediate and the dissociation of OH* intermediate. • The rationally designed PtCo SAA was found to have 4e- ORR activity in acidic media and exhibited high activity and durability. [ABSTRACT FROM AUTHOR]

Metal-phthalocyanine (MPc) macrocyclic catalysts have been perceived as promising alternatives to Pt and Pt-based catalysts for the oxygen reduction reaction (ORR). However, the effect of different MPc molecular structures on the ORR has rarely been reported in depth. Herein, iron-phthalocyanine polymers (poly-FePcs) and multi-walled carbon nanotubes (MWCNTs) composites with different structures were synthesized using microwave method. The relationship between their molecular structure and electrocatalytic activity was fully revealed by density functional theory (DFT) and X-ray fine absorption spectroscopy (XAFS). DFT calculations revealed that the introduction of halogen atoms can increase the ion potential (IP) and the dioxo-binding energy () of the poly-FePcs. Meanwhile, their conjugated structure not only facilitates electronic transmission, but also significantly increases . XAFS analysis indicated that the poly-FePc/MWCNTs composites had a square planar structure and a smaller of phthalocyanine ring (Fe-N 4 structure) skeleton structure radius when a larger conjugated structure or introduced halogen atoms was present. The experimental results suggest that the these changes in properties arising from the different structures of the MPc macrocyclic compounds led to a huge effect on their ORR electrochemical activities, and provide a guide to obtaining promising electrochemical catalysts. [ABSTRACT FROM AUTHOR]

Multi-walled carbon nanotubes (MWCNTs) supported iron phthalocyanine (FePc), binuclear iron phthalocyanine (bi-FePc) and iron polyphthalocyanine (FePPc) were prepared by a solvothermal process. The resulting FePc/MWCNTs, bi-FePc/MWCNTs and FePPc/MWCNTs were heat-treated in argon (Ar) atmosphere at various temperatures ranging from 500 to 900 °C to obtain optimized catalysts for the oxygen reduction reaction (ORR). The crystal structure, morphology and chemical environment of the catalysts were examined by ultraviolet-visible (UV–Vis) spectroscopy, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS). The electrocatalytic activity of the obtained catalysts was measured using a rotating disk electrode (RDE) technique in 0.5 mol L −1 H 2 SO 4 solution saturated with oxygen. The ORR activity of the heat-treated FePPc/MWCNTs was found to be better than that of the heat-treated bi-FePc/MWCNTs and FePc/MWCNTs. Furthermore, the heat-treatment temperature greatly influenced the catalytic ORR ability of the catalysts. The FePPc/MWCNTs heat-treated at 800 °C exhibited a four-electron transfer process and the best ORR activity (E ORR = 0.79 V vs. RHE), methanol resistance, and stability (current loss = 13% at –0.13 V vs. Hg/Hg 2 SO 4 after 55 h). XPS indicated that pyridine-type nitrogen, not graphitic-N, played a critical role in determining the electrocatalytic ORR activity of the amples. XAFS showed that the coordination geometry around Fe was close to square planar in structure, suggesting that the Fe-N 4 structure was produced by the high temperature treatment. [ABSTRACT FROM AUTHOR]

The thorough understanding of ORR mechanism provides insights into the design of efficient ORR catalysts. Despite remarkable progress has been made in the development of Cu–N–C ORR catalysts, fundamental understanding of molecular governing factors is still lacking. The carbon matrix with varying π-electron delocalization degree can modulate electron density at the metal ion center rather than merely acting as the electron-conducting path. A volcano relationship is established between oxygen-reduction intrinsic activity and full-width at half-maxima (FWHM) of C 1s photoemission spectra (depicting electron donating/withdrawing capability of carbon matrix to metal ion center). The mechanistic origin of ORR on carbon matrix, N–C sites, and Cu sites in Cu–N–C catalyst in different reaction regions is also illuminated. This work will be likely to offer a new insight in the development of more selective and durable Cu–N–C catalysts for zinc-air batteries. ga1 • Cu moieties can be successfully anchored on mesoporous N-doped carbon. • Mechanism of ORR on carbon matrix, N–C sites, and Cu sites is elucidated. • Cu sites mainly function in diffusion-controlled region. • A volcano relationship is obtained between ORR and FWHM of C 1s for Cu–N–C. • Cu–N–C-900 exhibits the best ORR due to the optimal intermolecular hardness. [ABSTRACT FROM AUTHOR]

• Graphitic N dopants embedded in carbon matrix boost the intrinsic activity of single-atom FeN 4 sites. • 3D interconnected pores of ordered mesoporous carbon framework endow dense Fe-N-C sites accessible. • Fe-N-C/N-OMC provides a half-wave potential of 0.93 V, a kinetic current density of 57.4 mA cm-2, a turnover frequency (TOF) of 38.4 s-1 and a mass activity of 66.4 A mg Fe -1 towards ORR in 0.1 M KOH. • Fe-N-C/N-OMC shows a half-wave potential of 0.73 V towards ORR in 0.5 M H 2 SO 4 , comparable to Pt/C. Single-atom Fe-N-C electrocatalysts have emerged as the most promising oxygen reduction reaction (ORR) catalyst. However, the low Fe loading and inaccessibility of Fe-N-C sites limit the overall ORR activity. Here, we report an efficient single-atom electrocatalyst (Fe-N-C/N-OMC) with Fe-N-C sites embedded in three-dimensional (3D) N-doped ordered mesoporous carbon framework. Fe-N-C/N-OMC shows high half-wave potential, kinetic current density, turnover frequency and mass activity towards ORR in alkaline electrolyte. Experiments and theoretical calculations suggest that the ultra-high ORR activity stems from the boosted intrinsic activity of FeN 4 sites by graphitic N dopants, high density of accessible active site generated by high Fe and N loadings and ordered mesoporous carbon structure as well as facilitated mass and electron transport in 3D interconnected pores. Fe-N-C/N-OMC also shows comparable ORR activity to Pt/C in acidic electrolyte. As the cathode for zinc-air battery, Fe-N-C/N-OMC exhibits high open-circuit voltage, high power density and remarkable durability. [ABSTRACT FROM AUTHOR]