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Highlights: Oxygen-coordinated single-atom Mn catalyst was fabricated via introducing oxygen functional groups rich bacterial cellulose as the adsorption regulator through a combined impregnation–pyrolysis–etching synthetic route. Mn–O–C as the electrocatalyst exhibits superior electrocatalytic activity toward ammonia synthesis with a maximum NH3 yield rate of 1476.9 ± 62.6 μg h−1 cm−2 at − 0.7 V (vs. RHE) and a faradaic efficiency of 89.0 ± 3.8% at − 0.5 V (vs. RHE) under ambient conditions. Electrocatalytic mechanism of Mn–(O–C2)4 site for nitrate reduction reaction is unveiled by a combination of in situ spectroscopy characterization and computational study. Electrocatalytic nitrate reduction reaction has attracted increasing attention due to its goal of low carbon emission and environmental protection. Here, we report an efficient NitRR catalyst composed of single Mn sites with atomically dispersed oxygen (O) coordination on bacterial cellulose-converted graphitic carbon (Mn–O–C). Evidence of the atomically dispersed Mn–(O–C2)4 moieties embedding in the exposed basal plane of carbon surface is confirmed by X-ray absorption spectroscopy. As a result, the as-synthesized Mn–O–C catalyst exhibits superior NitRR activity with an NH3 yield rate (RNH3) of 1476.9 ± 62.6 μg h−1 cm−2 at − 0.7 V (vs. reversible hydrogen electrode, RHE) and a faradaic efficiency (FE) of 89.0 ± 3.8% at − 0.5 V (vs. RHE) under ambient conditions. Further, when evaluated with a practical flow cell, Mn–O–C shows a high RNH3 of 3706.7 ± 552.0 μg h−1 cm−2 at a current density of 100 mA cm−2, 2.5 times of that in the H cell. The in situ FT-IR and Raman spectroscopic studies combined with theoretical calculations indicate that the Mn–(O–C2)4 sites not only effectively inhibit the competitive hydrogen evolution reaction, but also greatly promote the adsorption and activation of nitrate (NO3−), thus boosting both the FE and selectivity of NH3 over Mn–(O–C2)4 sites. [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]

Simultaneously increasing the activity and stability of the single-atom active sites of M–N–C catalysts is critical but remains a great challenge. Here, we report an Fe–N–C catalyst with nitrogen-coordinated iron clusters and closely surrounding Fe–N4 active sites for oxygen reduction reaction in acidic fuel cells. A strong electronic interaction is built between iron clusters and satellite Fe–N4 due to unblocked electron transfer pathways and very short interacting distances. The iron clusters optimize the adsorption strength of oxygen reduction intermediates on Fe–N4 and also shorten the bond amplitude of Fe–N4 with incoherent vibrations. As a result, both the activity and stability of Fe–N4 sites are increased by about 60% in terms of turnover frequency and demetalation resistance. This work shows the great potential of strong electronic interactions between multiphase metal species for improvements of single-atom catalysts. It is challenging to break the activity–stability trade-off in Fe–N–C fuel cell catalysts. Here, the authors show that interactions between iron atoms and clusters accelerate reaction kinetics and suppress demetalation to improve fuel cell stability. [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]

Atomic interface regulation is thought to be an efficient method to adjust the performance of single atom catalysts. Herein, a practical strategy was reported to rationally design single copper atoms coordinated with both sulfur and nitrogen atoms in metal-organic framework derived hierarchically porous carbon (S-Cu-ISA/SNC). The atomic interface configuration of the copper site in S-Cu-ISA/SNC is detected to be an unsymmetrically arranged Cu-S1N3 moiety. The catalyst exhibits excellent oxygen reduction reaction activity with a half-wave potential of 0.918 V vs. RHE. Additionally, through in situ X-ray absorption fine structure tests, we discover that the low-valent Cuprous-S1N3 moiety acts as an active center during the oxygen reduction process. Our discovery provides a universal scheme for the controllable synthesis and performance regulation of single metal atom catalysts toward energy applications. Engineering the coordination environment of single atom catalysts offers to opportunity to optimize electrocatalytic activity. In this work, the authors prepare an unsymmetrical Cu-S1N3 single atom site on porous carbon with high performance in the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Highlights: Precisely located S doping of atomic Fe-N4 in Fe(N3)(N–C–S) motif was realized. This S doping renders weakened *OH binding and faster charge transfer on Fe-N4. Fe-NSC showed excellent oxygen reduction reaction performance with onset potential ~ 1.09 V and half-wave potential ~ 0.92 V.Immobilizing metal atoms by multiple nitrogen atoms has triggered exceptional catalytic activity toward many critical electrochemical reactions due to their merits of highly unsaturated coordination and strong metal-substrate interaction. Herein, atomically dispersed Fe-NC material with precise sulfur modification to Fe periphery (termed as Fe-NSC) was synthesized, X-ray absorption near edge structure analysis confirmed the central Fe atom being stabilized in a specific configuration of Fe(N3)(N–C–S). By enabling precisely localized S doping, the electronic structure of Fe-N4 moiety could be mediated, leading to the beneficial adjustment of absorption/desorption properties of reactant/intermediate on Fe center. Density functional theory simulation suggested that more negative charge density would be localized over Fe-N4 moiety after S doping, allowing weakened binding capability to *OH intermediates and faster charge transfer from Fe center to O species. Electrochemical measurements revealed that the Fe-NSC sample exhibited significantly enhanced oxygen reduction reaction performance compared to the S-free Fe-NC material (termed as Fe-NC), showing an excellent onset potential of 1.09 V and half-wave potential of 0.92 V in 0.1 M KOH. Our work may enlighten relevant studies regarding to accessing improvement on the catalytic performance of atomically dispersed M-NC materials by managing precisely tuned local environments of M-Nx moiety. [ABSTRACT FROM AUTHOR]

Correction to: I Nature Communications i https://doi.org/10.1038/s41467-018-07850-2, published online 21 December 2018. These authors contributed equally: Yuanjun Chen, Shufang Ji, Shu Zhao. [Extracted from the article]

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]

[Display omitted] • The unique Pt-O-Cu structure is constructed on the 2.5Pt-2Cu/Fe 2 O 3 catalyst. • The Pt-O-Cu site shows the best reactivity for EWGS reaction. • The Pt-O-Cu site balances the binding ability of CO and the activation of OH–. • The Pt-O-Cu structure greatly boots the capability in antioxidation of Pt. Electrochemical water–gas shift (EWGS) reaction is an emerging technology with energy-saving and environmental-friendly advantages to produce high-purity hydrogen form the waste gas containing CO. However, it remains a significant challenge to design superior activity and highly durable EWGS electrocatalysts, particularly with low content of noble metals. Herein, a series of Pt-xCu/Fe 2 O 3 (x = 0, 2, 5) catalysts are synthesized by the complexation precipitation method to construct coupling sites between Pt and CuOx, aiming to optimize the adsorption of CO and the activation of OH–. The obtained 2.5Pt-2Cu/Fe 2 O 3 catalyst presents a unique Pt-O-Cu structure, delivering a much lowest onset potential, high specific activity, and excellent mass activity (1.5 A·mg Pt -1) at 0.73 V (vs. RHE), which is over 15 and 3 times that of commercial Pt/C (20%) and unmodified Pt/Fe 2 O 3 catalyst, respectively. Meanwhile, the in-situ X-ray absorption results demonstrate that the facilitated interaction among the Pt-O-Cu structure promotes the high durability of the 2.5Pt-2Cu/Fe 2 O 3 catalyst and the operability at high potential. More importantly, the moderate binding of CO and moderate activation of OH* are suggested for boosting the reactivity in the CO electro-oxidation reaction. In particular, the fabricated Pt||2.5Pt-2Cu/Fe 2 O 3 , employed in coupling the HER and CO electro-oxide reaction, shows a remarkable hydrogen production of about 98 mmol H2 ·h−1·mg Pt −1 at 0.8 V (vs. RHE). This work also definitely confirms the possibility of the catalyst being applied to produce hydrogen under practical conditions with different concentrations of CO, even being applied in the purification of trace CO in a hydrogen-rich atmosphere. [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]

Electrochemical production of hydrogen peroxide (H 2 O 2) is a sustainable and environmentally benign process. The electrochemical oxygen reduction process (ORR) via a two electron pathway (2e- ORR) offers a practical method for on-site H 2 O 2 generation. As an earth-abundant catalyst, the cobalt-nitrogen coordinated systems integrated into the carbon matrix (Co-NC) has caused wide attention for its high activity in 2e- ORR. Even though most of the reported Co-NC catalysts have classical planar Co-N 4 coordination, axial coordination engineering has recently emerged as an effective way to control the active sites in the axial direction by using different coordination ligands. The structure-function link between the Co-N configuration of non-planar coordination and 2e- ORR activity is, however, not fully understood. An axial-N coordinated Co-N 5 motif embedded in hierarchically porous graphite-3R carbon (Co-N 5 C) was effectively synthesized using a template-sacrificing method. The Co-N 5 C has a high selectivity for 2e- ORR and a high H 2 O 2 molar production rate of up to 6.78 mol peroxide/g catalyst /h in acidic media, both of which are better than its Co-N 4 counterpart. DFT analyses demonstrate that axial-N ligands regulated the d -band center of the Co atom in the Co-N 5 C catalyst, inducing a shift in Δ G *OOH near the Sabatier volcano plot's peak (Δ G *OOH = 4.22 eV). This optimized the binding of the *OOH intermediate and then enhanced the protonation of *OOH to produce H 2 O 2 more efficiently. [Display omitted] • A Co-N 5 C catalyst containing an axial-N ligand was synthesized for the effective ORR. • Co-N 5 C, with graphite-3R phase, showed a specific BET surface area of 801.6 m2/g. • Co-N 5 C exhibited a high selectivity for 2e- ORR and H 2 O 2 molar production rate. • Co-N 5 C possessed a high active SD and high intrinsic kinetic TOF. [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]

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]

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]

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]

• A hierarchically Fe, N CO doped porous carbon material is synthesized as robust catalyst for CO 2 electroreduction. • The Faradaic efficiency of CO reaches 96 % with an ultra-low overpotential of 470 mV and excellent durability. • The Fe-N 4 O stucture was found having a better catalytic performance than Fe-N 4 for CO 2 electroreduction to CO. Electrochemical reduction of carbon dioxide (CO 2) is a potentially useful step in energy storage and greenhouse gas alleviation. Here we demonstrate for the first time a Fe-N 4 O-doped nanoporous carbon as robust electrocatalyst for CO 2 reduction, where the five-coordinated Fe-N 4 O structure works as catalytically active site. It exhibits a high faradaic efficiency of 96 % towards CO with partial current density of -5.4 mA cm−2 at low overpotential of 470 mV. First-principles density functional theory calculations reveal that the free energy barrier for *CO desorption is greatly reduced on Fe-N 4 O site compared to Fe-N 4 , resulting in a higher selectivity to CO for a wider electrochemical window. This work opens up new possibilities for improving the catalytic performance of metal-N-C electrocatalysts by regulating the co-ordination of metal atom. [ABSTRACT FROM AUTHOR]