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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]

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]

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]

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]

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]

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]