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The oxygen reduction reaction (ORR) is a crucial cathode reaction for developing quasi‐solid zinc–air batteries (QZABs) with high energy density. However, the activity and stability of catalysts under extreme conditions have not been fully explore. Herein, a series of systematic experiments and theoretical calculations have been conducted to investigate the potential of introducing FexCoy into nitrogen (N)‐doped porous carbon (NPC) via one‐step pyrolysis to form a core–shell structure that can effectively enhance the activity of the catalysts, particularly at low temperatures. Due to the difference in the work function of 5.12, 5.11, and 5.06 eV, the spin‐polarized charge is transferred to the pyridinic‐N site on the surface under the charge transfer. Consequently, the pyridinic‐N site on the surface exhibits varying degrees of magnetic moment 0.024 µB, which is crucial for forming OOH* and enhances ORR activity. The Fe5Co5@NPC catalyst is evaluated for QZABs at −40 °C and achieved a power density of up to 117.6 mW cm−2, which is only 18.7% lower than normal temperature, and a cycle life of up to 300 h. This study provides a means to realize the design of QZABs catalysts in extreme environments and explore their application potential. [ABSTRACT FROM AUTHOR]

Understanding the relationship between the electronic state of active sites and N2 reduction reaction (NRR) performance is essential to explore efficient electrocatalysts. Herein, atomically dispersed Fe and Mo sites are designed and achieved in the form of well‐defined FeN4 and MoN4 coordination in polyphthalocyanine (PPc) organic framework to investigate the influence of the spin state of FeN4 on NRR behavior. The neighboring MoN4 can regulate the spin state of Fe center in FeN4 from high‐spin (dxy2dyz1dxz1dz21dx2−y21) to medium‐spin (dxy2dyz2dxz1dz21), where the empty d orbitals and separate d electron favor the overlap of Fe 3d with the N 2p orbitals, more effectively activating N≡N triple bond. Theoretical modeling suggests that the NRR preferably takes place on FeN4 instead of MoN4, and the transition of Fe spin state significantly lowers the energy barrier of the potential determining step, which is conducive to the first hydrogenation of N2. As a result, FeMoPPc with medium‐spin FeN4 exhibits 2.0 and 9.0 times higher Faradaic efficiency and 2.0 and 17.2 times higher NH3 yields for NRR than FePPc with high‐spin FeN4 and MoPPc with MoN4, respectively. These new insights may open up opportunities for exploiting efficient NRR electrocatalysts by atomically regulating the spin state of metal centers. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction towards hydrogen peroxide (H2O2) provides a green alternative route for H2O2 production, but it lacks efficient catalysts to achieve high selectivity and activity simultaneously under industrial-relevant production rates. Here we report a boron-doped carbon (B-C) catalyst which can overcome this activity-selectivity dilemma. Compared to the state-of-the-art oxidized carbon catalyst, B-C catalyst presents enhanced activity (saving more than 210 mV overpotential) under industrial-relevant currents (up to 300 mA cm−2) while maintaining high H2O2 selectivity (85–90%). Density-functional theory calculations reveal that the boron dopant site is responsible for high H2O2 activity and selectivity due to low thermodynamic and kinetic barriers. Employed in our porous solid electrolyte reactor, the B-C catalyst demonstrates a direct and continuous generation of pure H2O2 solutions with high selectivity (up to 95%) and high H2O2 partial currents (up to ~400 mA cm−2), illustrating the catalyst's great potential for practical applications in the future. Oxygen reduction reaction provides an environmentally-benign route for hydrogen peroxide production but lacks efficient catalysts to achieve high selectivity and activity simultaneously. Here, the authors report a boron-doped carbon catalyst which shows great promise with outstanding performance. [ABSTRACT FROM AUTHOR]

Mn and N codoped carbon materials are proposed as one of the most promising catalysts for the oxygen reduction reaction (ORR) but still confront a lot of challenges to replace Pt. Herein, a novel gas‐phase migration strategy is developed for the scale synthesis of atomically dispersed Mn and N codoped carbon materials (g‐SA‐Mn) as highly effective ORR catalysts. Porous zeolitic imidazolate frameworks serve as the appropriate support for the trapping and anchoring of Mn‐containing gaseous species and the synchronous high‐temperature pyrolysis process results in the generation of atomically dispersed Mn‐Nx active sites. Compared to the traditional liquid phase synthesis method, this unique strategy significantly increases the Mn loading and enables homogeneous dispersion of Mn atoms to promote the exposure of Mn‐Nx active sites. The developed g‐SA‐Mn‐900 catalyst exhibits excellent ORR performance in the alkaline media, including a high half‐wave potential (0.90 V vs reversible hydrogen electrode), satisfactory durability, and good catalytic selectivity. In the practical application, the Zn–air battery assembled with g‐SA‐Mn‐900 catalysts shows high power density and prominent durability during the discharge process, outperforming the commercial Pt/C benchmark. Such a gas‐phase synthetic methodology offers an appealing and instructive guide for the logical synthesis of atomically dispersed catalysts. [ABSTRACT FROM AUTHOR]

As low-cost electrocatalysts for oxygen reduction reaction applied to fuel cells and metal-air batteries, atomic-dispersed transition metal-nitrogen-carbon materials are emerging, but the genuine mechanism thereof is still arguable. Herein, by rational design and synthesis of dual-metal atomically dispersed Fe,Mn/N-C catalyst as model object, we unravel that the O2 reduction preferentially takes place on FeIII in the FeN4 /C system with intermediate spin state which possesses one eg electron (t2g4eg1) readily penetrating the antibonding π-orbital of oxygen. Both magnetic measurements and theoretical calculation reveal that the adjacent atomically dispersed Mn-N moieties can effectively activate the FeIII sites by both spin-state transition and electronic modulation, rendering the excellent ORR performances of Fe,Mn/N-C in both alkaline and acidic media (halfwave positionals are 0.928 V in 0.1 M KOH, and 0.804 V in 0.1 M HClO4), and good durability, which outperforms and has almost the same activity of commercial Pt/C, respectively. In addition, it presents a superior power density of 160.8 mW cm−2 and long-term durability in reversible zinc–air batteries. The work brings new insight into the oxygen reduction reaction process on the metal-nitrogen-carbon active sites, undoubtedly leading the exploration towards high effective low-cost non-precious catalysts. The working mechanism of several low-cost electrocatalyst materials is still arguable. Here the authors show a model Fe,Mn/N-C catalyst where the oxygen reduction preferentially takes place on Fe(III) sites with the intermediate spin state (t2g4 eg1) caused by the adjacent Mn-N moieties. [ABSTRACT FROM AUTHOR]

Iron‐nitrogen‐carbon materials are being intensively studied as the most promising substitutes for Pt‐based electrocatalysts for the oxygen reduction reaction (ORR). A rational design of the morphology and porous structure can promote the accessibility of the active site and the reactants/products transportation, accelerating the reaction kinetics. Herein, 1D porous iron/nitrogen‐doped carbon nanorods (Fe/N‐CNRs) with a hierarchically micro/mesoporous structure are prepared by pyrolyzing the in situ polymerized pyrrole on the surface of Fe‐MIL‐88B‐derived 1D Fe2O3 nanorods (MIL: Material Institut Lavoisier). The Fe2O3 nanorods not only partially dissolve to generate Fe3+ for initiating polymerization but serve as templates to form the 1D structure during polymerization. Furthermore, the pyrrole coated Fe2O3 nanorod architecture prevents the porous structure from collapsing and protects Fe from aggregation to yield atomic Fe‐N4 moieties during carbonization. The obtained Fe/N‐CNRs display exceptional ORR activities (E1/2 = 0.90 V) and satisfactory long‐term durabilities, exceeding those for Pt/C. Furthermore, the unprecedented Fe/N‐CNRs catalytic performance is demonstrated with Zn‐air batteries, including a superior maximum power density (181.8 mW cm−2), specific capacity (998.67 W h kg−1), and long‐term durability over 100 h. The prominent performance stems from the unique 1D structure, hierarchical pore system, high surface area, and homogeneously dispersed single‐atom Fe‐N4 moieties. [ABSTRACT FROM AUTHOR]

A zinc‐based single‐atom catalyst has been recently explored with distinguished stability, of which the fully occupied Zn2+ 3d10 electronic configuration is Fenton‐reaction‐inactive, but the catalytic activity is thus inferior. Herein, we report an approach to manipulate the s‐band by constructing a B,N co‐coordinated Zn‐B/N‐C catalyst. We confirm both experimentally and theoretically that the unique N2‐Zn‐B2 configuration is crucial, in which Zn+(3d104s1) can hold enough delocalized electrons to generate suitable binding strength for key reaction intermediates and promote the charge transfer between catalytic surface and ORR reactants. This exclusive effect is not found in the other transition‐metal counterparts such as M‐B/N‐C (M=Mn, Fe, Co, Ni and Cu). Consequently, the as‐obtained catalyst demonstrates impressive ORR activity, along with remarkable long‐term stability in both alkaline and acid media. This work presents a new concept in the further design of electrocatalyst. [ABSTRACT FROM AUTHOR]

Shifting electrochemical oxygen reduction towards 2e– pathway to hydrogen peroxide (H2O2), instead of the traditional 4e– to water, becomes increasingly important as a green method for H2O2 generation. Here, through a flexible control of oxygen reduction pathways on different transition metal single atom coordination in carbon nanotube, we discovered Fe-C-O as an efficient H2O2 catalyst, with an unprecedented onset of 0.822 V versus reversible hydrogen electrode in 0.1 M KOH to deliver 0.1 mA cm−2 H2O2 current, and a high H2O2 selectivity of above 95% in both alkaline and neutral pH. A wide range tuning of 2e–/4e– ORR pathways was achieved via different metal centers or neighboring metalloid coordination. Density functional theory calculations indicate that the Fe-C-O motifs, in a sharp contrast to the well-known Fe-C-N for 4e–, are responsible for the H2O2 pathway. This iron single atom catalyst demonstrated an effective water disinfection as a representative application. Hydrogen peroxide can be produced alternatively using green inputs such as air, water, and sunlight but this requires a selective catalyst. Here the authors report an iron single atom catalyst that can convert oxygen into hydrogen peroxide with a selectivity of above 95% in both alkaline and neutral pH. [ABSTRACT FROM AUTHOR]

A metalorganic gaseous doping approach for constructing nitrogen‐doped carbon polyhedron catalysts embedded with single Fe atoms is reported. The resulting catalysts are characterized using scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, and X‐ray absorption spectroscopy; for the optimal sample, calculated densities of Fe–Nx sites and active N sites reach 1.75812 × 1013 and 1.93693 × 1014 sites cm‐2, respectively. Its oxygen reduction reaction half‐wave potential (0.864 V) is 50 mV higher than that of 20 wt% Pt/C catalyst in an alkaline medium and comparable to the latter (0.78 V vs 0.84 V) in an acidic medium, along with outstanding durability. More importantly, when used as a hydrogen–oxygen polymer electrolyte membrane fuel cell (PEMFC) cathode catalyst with a catalyst loading as low as 1 mg cm‐2 (compared with a conventional loading of 4 mg cm‐2), it exhibits a current density of 1100 mA cm‐2 at 0.6 V and 637 mA cm‐2 at 0.7 V, with a power density of 775 mW cm‐2, or 0.775 kW g–1 of catalyst. In a hydrogen–air PEMFC, current density reaches 650 mA cm‐2 at 0.6 V and 350 mA cm‐2 at 0.7 V, and the maximum power density is 463 mW cm‐2, which makes it a promising candidate for cathode catalyst toward high‐performance PEMFCs. An atomic Fe‐doped MOF‐derived carbon polyhedron with high active‐center density and ultra‐high performance toward polymer electrolyte membrane fuel cells (PEMFC) is fabricated using a novel metallorganic gaseous doping strategy, which is a promising candidate for high‐performance practical PEMFC. [ABSTRACT FROM AUTHOR]

Modification of the microenvironment of metal- and nitrogen-coordinated nanocarbons (M-N-Cs) is critical in regulating their electronic structure and thus catalytic selectivity toward the oxygen reduction reaction (ORR). Introducing heteroatoms into the carbon matrix of M-N-Cs could affect the coordination configuration and charge density of the metal centers, but it has rarely been applied to improve the ORR selectivity for H 2 O 2 electrosynthesis. Here we show that doping phosphorus (P) atoms into the carbon substrate of a Co-N-C catalyst lengthens the Co−N bond, decreases the electron density of the Co, and weakens the adsorption strength of the key *OOH intermediate on the active sites, as demonstrated by both experimental and theoretical results. Consequently, this P-doped Co-N-C catalyst presents outstanding catalytic performance toward the 2e− ORR with an early onset potential of 0.81 V (vs. the reversible hydrogen electrode), exceptional H 2 O 2 selectivity above 90% in a wide potential range from 0.1 V to 0.7 V (maximum value of ∼ 97% at 0.5 V) and a large turnover frequency (2.36 ± 0.15 s−1 at 0.65 V) in alkaline electrolyte, superior to almost all previously reported counterparts. Moreover, an unprecedented H 2 O 2 production rate up to 11.2 mol H 2 o 2 g catalyst − 1 h − 1 with long-term durability (110 h) is obtained when the catalyst is assessed as a gas diffusion layer in a practical flow cell. [Display omitted] • A new P-doped Co-N-C catalyst is designed with elongated Co−N bond, decreased electron density and optimized *OOH adsorption. • Both experiments and theories show that the P dopants can effectively regulate the ORR pathway of the Co-N-C catalyst. • The P-doped Co-N-C catalyst presents outstanding 2e− ORR activity and selectivity along with a high H 2 O 2 production rate. [ABSTRACT FROM AUTHOR]

Durability of carbon-supported Fe single-atom catalysts has remained a critical issue for metal-air batteries. Herein, Fe single atoms with adjacent Fe nanoclusters supported on nitrogen-doped carbon aerogels (NCA/Fe SA+NC) are prepared via a facile two-step pyrolysis procedure using biomass hydrogels as the precursor and template. The Fe atomic centers are found to exhibit an increased 3d electron density and decreased magnetic moment by the nanoclusters. This markedly enhances the oxygen reduction reaction activity and anti-oxidation stability of the FeN 4 sites, as compared to the nanocluster-free counterparts. With NCA/Fe SA+NC as the cathode catalysts, a flexible zinc-air battery delivers a remarkable performance even at −40 °C, with an open circuit voltage as high as 1.47 V, power density 49 mW cm−2, and excellent durability after 2300 continuous recharging/charging cycles. The performance is even higher at ambient temperature. These results highlight the significance of electronic manipulation in enhancing the durability of single atom catalysts. [Display omitted] • Carbon aerogels from two-step pyrolysis of biomass hydrogels. • Fe single atoms with adjacent Fe nanoclusters supported on carbon aerogels. • Increased 3d electron density and decreased magnetic moment of Fe atomic centers. • Enhanced ORR stability and activity of the FeN 4 sites. • High performance and stability of flexible Zn-air batteries at low temperatures. [ABSTRACT FROM AUTHOR]

A facile polymer-silicon-dual-template strategy is developed to construct mesoporous carbon spheres with densely and accessible atomic Fe-Nx sites. This result in an efficient air electrode with 3D hierarchically porous frameworks, which leads to enhanced mass transfer and consequently superior aluminum-air flow battery performance. [Display omitted] • Dens Fe-Nx sites coupled mesoporous carbon spheres are constructed by a facile dual-template strategy. • Single atomic Fe-Nx moieties could serve as highly active and stable centers for catalyzing ORR. • The 3D porous air electrode accelerates oxygen transfer and enhances accessibility of Fe-Nx sites. • The assembled aluminum-air flow battery delivers high gravimetric energy density and superior discharging stability. Single atomic iron modified nitrogen-doped carbons (SA Fe-N-C) are promising alternatives to Pt-based counterparts for facilitating the sluggish oxygen reduction reaction (ORR). However, both the low density of Fe-Nx active sites and their less utilization render these catalysts inefficient. To address these issues, a synergistic polymer-silicon dual templates strategy is reported to fabricate dense SA Fe-Nx sites on mesoporous carbon spheres (SA-Fe-Nx-MPCS). Thanks to the dense and accessible SA Fe-Nx sites, the SA-Fe-Nx-MPCS exhibits better ORR catalytic activity and stability than the commercial Pt/C catalyst. Moreover, the SA-Fe-Nx-MPCS result in a 3D porous framework with abundant channels in air cathode, facilitating mass transfer and enhancing accessibility of Fe-Nx moieties. The assembled aluminum-air flow battery exhibits a large peak power density of 130 mW cm−2 and a high gravimetric energy density of ca. 2905 Wh kg Al −1, as well as a superior stable discharging voltage over 300 h. [ABSTRACT FROM AUTHOR]

• A bifunctional Fe-Ni atomic pair is developed as high performance ORR and OER electrocatalyst. • The interplay between charge itineration and spin polarization of electrons is elucidated for the first time. • The potential difference from ORR to OER (ΔE) is 0.691 V. Charge and spin manipulations of electrons are considered to be of great significance in boosting the catalytic activity of M N C electrocatalysts. However, to the best of our knowledge, most current studies focus only on the charge engineering, the interplay between spin and charge is not well understood, and the simultaneous manipulation of both charge and spin remains challenging. Herein, we show that the cooperative interplay between charge itineration and spin-polarization of electrons has a profound impact on the catalytic behavior through density functional theory (DFT) calculations for the first time. Following this concept, we report a Fe-Ni atomic pair as a superior bifunctional catalyst for high performance ORR and OER, with a very small potential difference (ΔE) of 0.691 V. We confirm that the coexistence of Fe 3d itinerant charge and moderate spin polarization (magnetic moment: 1.48 μ B) is responsible for the superior functional catalytic activity for the Fe Ni atomic pairs. [ABSTRACT FROM AUTHOR]