Highly Active CoNi-CoN3 Composite Sites Synergistically Accelerate Oxygen Electrode Reactions in Rechargeable Zinc-Air Batteries

Reaching rapid reaction kinetics of oxygen reduction (ORR) and oxygen evolution reactions (OER) is critical for realizing efficient rechargeable zinc-air batteries (ZABs). Herein, a novel CoNi-CoN3 composite site containing CoNi alloyed nanoparticles and CoN3 moieties is first constructed in N-doped carbon nanosheet matrix (CoNi-CoN3/C). Benefiting from the high electroactivity of CoNi-CoN3 composite sites and large surface area, CoNi-CoN3/C shows a superior half-wave potential (0.88 V versus RHE) for ORR and a small overpotential (360 mV) for OER at 10 mA cm-2. Theoretical calculations have demonstrated that the introduction of CoNi alloys has modulated the electronic distributions near the CoN3 moiety, inducing the d-band center of CoNi-CoN3 composite site to shift down, thus stabilizing the valence state of Co active sites and balancing the adsorption of OER/ORR intermediates. Accordingly, the reaction energy trends exhibit optimized overpotentials for OER/ORR, leading to superior battery performances. For aqueous and flexible quasi-solid-state rechargeable ZABs with CoNi-CoN3/C as catalyst, a large power density (250 mW cm-2) and high specific capacity (804 mAh g-1) are achieved. The in-depth understanding of the electroactivity enhancement mechanism of interactive metal nanoparticles and metal coordinated with nitrogen (MNx) moieties is crucial for designing novel high-performance metal/nitrogen-doped carbon (M─N─C) catalysts.

Computational Insight into TM-N x Embedded Graphene Bifunctional Electrocatalysts for Oxygen Evolution and Reduction Reactions

Due to the energy crisis, development of bifunctional electrocatalysts for both oxygen evolution and reduction reactions is highly demanding. In this study, we have systematically investigated the bifunctional activity of metal (Co/Rh/Ir) and N co-doped graphene systems with varying N-dopant concentrations (TM-N _x @G, x = 0, 2, 4) using first-principles calculations. Charge transfer from the metal sites to the adsorbed intermediates and the adsorption free energy of the intermediates play important roles to help understand the potential-determining step and overpotential values for oxygen evolution reaction (OER)/oxygen reduction reaction (ORR). A dual volcano plot for all the systems using a common descriptor ΔG _OH* has been constructed. We find that the systems having ΔG _OH* values in the range of 0.40-0.70 eV can act as bifunctional electrocatalysts. Our study not only highlights the importance of metal and non-metal co-doped graphene as bifunctional catalysts but also can serve as a promising strategy for the design of efficient OER/ORR electrocatalysts.

Single atom catalysis for electrocatalytic ammonia synthesis

This review points out major challenges and outlook of NH3 synthesis via SACs. Summarizing the deficiencies of existing research can help researchers to continuously innovate and improve, and explore new research approaches.

Metal-Nitrogen-Carbon Catalysts of Specifically Coordinated Configurations toward Typical Electrochemical Redox Reactions

Metal-nitrogen-carbon (M-N-C) material with specifically coordinated configurations is a promising alternative to costly Pt-based catalysts. In the past few years, great progress is made in the studies of M-N-C materials, including the structure modulation and local coordination environment identification via advanced synthetic strategies and characterization techniques, which boost the electrocatalytic performances and deepen the understanding of the underlying fundamentals. In this review, the most recent advances of M-N-C catalysts with specifically coordinated configurations of M-N_x (x = 1-6) are summarized as comprehensively as possible, with an emphasis on the synthetic strategy, characterization techniques, and applications in typical electrocatalytic reactions of the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, CO₂ reduction reaction, etc., along with mechanistic exploration by experiments and theoretical calculations. Furthermore, the challenges and potential perspectives for the future development of M-N-C catalysts are discussed.

Activation of the methane C–H bond by Al- and Ga-doped graphenes: a DFT investigation

The potential of Al- and Ge-embedded graphene to activate the C–H bond of CH4 in the presence of a N2O molecule was studied using DFT calculations.

Ultrasmall 2 D Cox Zn2-x (Benzimidazole)4 Metal-Organic Framework Nanosheets and their Derived Co Nanodots@Co,N-Codoped Graphene for Efficient Oxygen Reduction Reaction

The development of nonprecious metal-nitrogen-carbon (M-N-C) materials with efficient metal utilization and abundant active sites for the oxygen reduction reaction (ORR) is of great significance for fuel cells and metal-air batteries. Ultrasmall 2 D Co_x Zn_2-x (benzimidazole)₄ [Co_x Zn_2-x (bim)₄ ] bimetallic metal-organic framework (MOF) nanosheets (≈2 nm thick) are synthesized by a novel bottom-up strategy and then thermally converted into a core-shell structure of sub-5 nm Co nanodots (NDs) wrapped with 2 to 5 layers of Co,N-codoped graphene (Co@FLG). The size of the Co NDs in Co@FLG could be precisely controlled by the Co/Zn ratio in the Co_x Zn_2-x (bim)₄ nanosheet. As an ORR electrocatalyst, the optimized Co@FLG exhibits an excellent half-wave potential of 0.841 V (vs. RHE), a high limiting current density of 6.42 mA cm^-2 , and great stability in alkaline electrolyte. Co@FLG also has great ORR performance in neutral electrolyte, as well as in Mg-air batteries. The experimental studies and DFT calculations reveal that the high performance of Co@FLG is mainly attributed to its great O₂ absorptivity, which is endowed by the abundant Co-N_x and pyridinic-N in the FLG shell and the strong electron-donating ability from the Co ND core to the FLG shell. This elevates the e_g orbital energy of Co^II and lowers the activation energy for breaking the O=O/O-O bonds. This work sheds light on the design and fabrication of 2 D MOFs and MOF-derived M-N-C materials for energy storage and conversion applications.

Atomically dispersed metal–nitrogen–carbon catalysts for fuel cells: advances in catalyst design, electrode performance, and durability improvement

The review provides a comprehensive understanding of the atomically dispersed metal–nitrogen–carbon cathode catalysts for proton-exchange membrane fuel cell applications.

A single-atom catalyst of cobalt supported on a defective two-dimensional boron nitride material as a promising electrocatalyst for the oxygen reduction reaction: a DFT study

Single-atom catalysts present extraordinary catalytic performance towards various reactions. In this work, the possibility of single Co atoms supported by the experimentally available defective two-dimensional boron nitride material (2D-BN) with boron vacancies (Co/BN) as a potential catalyst for the oxygen reduction reaction (ORR) was investigated by density functional theory. Co/BN has a similar active center to the cobalt nitride species, which have been proved to be effective ORR catalysts. It is found that Co atoms bind with the defective 2D-BN strongly to ensure the stability of Co/BN. Moreover, all of the ORR intermediates can be adsorbed on Co/BN. Especially, the HOOH species is found to be unstable and decomposes into two OH species immediately, suggesting that the ORR process occurs on Co/BN only through a direct 4e- pathway. Along the favorable pathway, the reduction of O2 to OOH is the rate-limiting step with a largest activation barrier of 0.30 eV and the maximum free energy change is 0.82 eV. Co/BN exhibits competitive ORR activity with that of CoN3 embedded graphene and Pt-based catalysts. These results should be enlightening to understand the ORR mechanism on Co/BN and design novel single-atom catalysts for the ORR and other electrocatalysis reactions.

Theoretical analysis of oxygen reduction reaction activity on single metal (Ni, Pd, Pt, Cu, Ag, Au) atom supported on defective two-dimensional boron nitride materials

Single metal atom supported by a defective two-dimensional boron nitride material is a promising ORR catalyst.

Single tungsten atom supported on N-doped graphyne as a high-performance electrocatalyst for nitrogen fixation under ambient conditions

A promising highly efficient and inexpensive W@N-doped graphyne electrocatalyst for N₂ fixation has been predicted by first-principle calculation.