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The effects of different N-types coordinated with single atomic sites (SASs) on the oxygen reduction reaction (ORR) has not been deeply explored. Herein, we first predicted by density functional theory (DFT) calculations that pyridinic-N and graphitic-N on Fe SAS can cooperatively enhance ORR activity. Then, Fe SASs containing both pyridinic-N and graphitic-N were synthesised by a dual-nitrogen strategy. The Fe SASs supported on a 3D N-doped carbon nanotubes/graphene network structure (Fe–N–C/GC) with more pyridinic-N and graphitic-N sites were prepared by a dual nitrogen strategy. The highly active Fe–N4 sites and 3D structure enabled the outstanding ORR performance of Fe–N–C/GC with a half-wave potential of 0.85 V and a limiting current density of 6.05 mA cm−2, which is comparable to the performance of Pt/C in alkaline media. Furthermore, the assembled H2/O2 fuel cell with Fe–N–C/GC can deliver a peak power density of 406 mW cm−2 and an open-circuit voltage of 0.90 V, exceeding those of previously reported Fe-related catalysts. DFT calculations demonstrated that the anti-bonding dz2, dxz, and dyz orbitals of the Fe atom had higher filling degrees, which reduced the energy barrier for the formation of oxygen intermediates and promoted ORR activity. This was ascribed to the synergistic effect between pyridinic-N and graphitic-N sites. [ABSTRACT FROM AUTHOR]

The emerging star of single atomic site (SAS) catalyst has been regarded as the most promising Pt‐substituted electrocatalyst for oxygen reduction reaction (ORR) in anion‐exchange membrane fuel cells (AEMFCs). However, the metal loading in SAS directly affects the whole device performance. Herein, we report a dual nitrogen source coordinated strategy to realize high dense Cu−N4 SAS with a metal loading of 5.61 wt% supported on 3D N‐doped carbon nanotubes/graphene structure wherein simultaneously performs superior ORR activity and stability in alkaline media. When applied in H2/O2 AEMFC, it could reach an open‐circuit voltage of 0.90 V and a peak power density of 324 mW cm−2. Operando synchrotron radiation analyses identify the reconstruction from initial Cu−N4 to Cu−N4/Cu‐nanoclusters (NC) and the subsequent Cu−N3/Cu−NC under working conditions, which gradually regulate the d‐band center of central metal and balance the Gibbs free energy of *OOH and *O intermediates, benefiting to ORR activity. [ABSTRACT FROM AUTHOR]

Dual‐metal single‐atom catalysts exhibit superior performance for oxygen reduction reaction (ORR), however, the synergistic catalytic mechanism is not deeply understood. Herein, we report a dual‐metal single‐atom catalyst consisted of Cu−N4 and Zn−N4 on the N‐doped carbon support (Cu/Zn−NC). It exhibits high‐efficiency ORR activity with an Eonset of 0.98 V and an E1/2 of 0.83 V, excellent stability (no degradation after 10 000 cycles), surpassing state‐of‐the‐art Pt/C and great mass of Pt‐free single atom catalysts. Operando XANES demonstrates that the Cu−N4 as active center experiences the change from atomic dispersion to cluster with the cooperation of Zn−N4 during ORR process, and then turns to single atom state again after reaction. DFT calculation further indicates that the adjustment effect of Zn on the d‐orbital electron distribution of Cu could benefit to the stretch and cleavage of O‐O on Cu active center, speeding up the process of rate determining step of OOH*. [ABSTRACT FROM AUTHOR]

Corrigendum: Reconstruction of Highly Dense Cu-N4 Active Sites in Electrocatalytic Oxygen Reduction Characterized by Operando Synchrotron Radiation In the Acknowledgments section of this Research Article one of the grant numbers (U20A200537) is incorrect. The revised Acknowledgment is: "We gratefully acknowledge the support of this research by the National Natural Science Foundation of China (U20A20250, 22179034, 91961111, 22005078). [Extracted from the article]

Single atom sites (SAS) often undergo structural recombination in oxygen reduction reaction (ORR), while the effect of valence state and reconstruction on active centers needs to be investigated thoroughly. Herein, the Mn-SAS catalyst with uniform and precise Mn-N 4 configuration is rationally designed. We utilize operando synchrotron radiation to track the dynamic evolution of active centers during ORR. Under the applied potential, the structural evolution of Mn-N 4 into Mn-N 3 C and further into Mn-N 2 C 2 configurations is clarified. Simultaneously, the valence states of Mn are increased from +3.0 to +3.8 and then decreased to +3.2. When the potential is removed, the catalyst returned to its initial Mn +3.0 -N 4 configuration. Such successive evolutions optimize the electronic and geometric structures of active centers as evidenced by theory calculations. The evolved Mn +3.8 -N 3 C and Mn +3.2 -N 2 C 2 configurations respectively adjust the O 2 adsorption and reduce the energy barrier of rate-determining step. Thus, it can achieve an onset potential of 0.99 V, superior stability over 10,000 cycles, and a high turnover frequency of 1.59 s -1 at 0.85 VRHE. Our present work provides new insights into the construction of well-defined SAS catalysts by regulating the valence states and configurations of active centers., (© 2023 Wiley-VCH GmbH.)

The emerging star of single atomic site (SAS) catalyst has been regarded as the most promising Pt-substituted electrocatalyst for oxygen reduction reaction (ORR) in anion-exchange membrane fuel cells (AEMFCs). However, the metal loading in SAS directly affects the whole device performance. Herein, we report a dual nitrogen source coordinated strategy to realize high dense Cu-N 4 SAS with a metal loading of 5.61 wt% supported on 3D N-doped carbon nanotubes/graphene structure wherein simultaneously performs superior ORR activity and stability in alkaline media. When applied in H 2 /O 2 AEMFC, it could reach an open-circuit voltage of 0.90 V and a peak power density of 324 mW cm -2 . Operando synchrotron radiation analyses identify the reconstruction from initial Cu-N 4 to Cu-N 4 /Cu-nanoclusters (NC) and the subsequent Cu-N 3 /Cu-NC under working conditions, which gradually regulate the d-band center of central metal and balance the Gibbs free energy of *OOH and *O intermediates, benefiting to ORR activity., (© 2022 Wiley-VCH GmbH.)

Dual-metal single-atom catalysts exhibit superior performance for oxygen reduction reaction (ORR), however, the synergistic catalytic mechanism is not deeply understood. Herein, we report a dual-metal single-atom catalyst consisted of Cu-N 4 and Zn-N 4 on the N-doped carbon support (Cu/Zn-NC). It exhibits high-efficiency ORR activity with an E onset of 0.98 V and an E 1/2 of 0.83 V, excellent stability (no degradation after 10 000 cycles), surpassing state-of-the-art Pt/C and great mass of Pt-free single atom catalysts. Operando XANES demonstrates that the Cu-N 4 as active center experiences the change from atomic dispersion to cluster with the cooperation of Zn-N 4 during ORR process, and then turns to single atom state again after reaction. DFT calculation further indicates that the adjustment effect of Zn on the d-orbital electron distribution of Cu could benefit to the stretch and cleavage of O-O on Cu active center, speeding up the process of rate determining step of OOH*., (© 2021 Wiley-VCH GmbH.)

Development of efficient and durable non-Pt catalysts for hydrogen evolution reaction (HER) in acid media is highly desirable. Iron nitride has emerged as a promising catalyst for its cost-effective nature, but the corresponding acidic stability must be promoted. Herein, phosphorus-decorated Fe 2 N and reduced graphene oxide (P-Fe 2 N/rGO) composite are designed and synthesized. X-ray photoelectron spectroscopy and X-ray absorption fine structure (XAFS) show that a thin layer amorphous iron phosphide is coated on the surface of Fe 2 N nanoparticles, which could be responsible for the well resistance of chemical corrosion in acidic media. Meanwhile, the P-decoration could tune the electronic state and coordination environment of iron atom as evidenced by XAFS, resulting in dramatically enhanced electrocatalytic activity of P-Fe 2 N/rGO. Density functional theory calculations reveal that both the P-connected N atoms and the Fe atoms in P-Fe 2 N/rGO catalyst are the main active sites for H* adsorption. The hydrogen-binding free energy |ΔG H* | value is close to zero for P-Fe 2 N/rGO, suggesting a good balance between the Volmer and Heyrovsky/Tafel steps in HER kinetics. As expected, P-Fe 2 N/rGO catalyst could achieve a low η onset of 22.4 mV, a small Tafel plot of 48.7 mV dec -1 , and remarkable stability for HER in acid electrolyte., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)