Molecular-level design of Fe-N-C catalysts derived from Fe-dual pyridine coordination complexes for highly efficient oxygen reduction

A Superior Bifunctional Electrocatalyst in Which Directional Electron Transfer Occurs Between a Co/Ni Alloy and Fe─N─C Support

Stable, efficient, and economical bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are needed for rechargeable Zn-air batteries. In this study, a directional electron transfer pathway is exploited in a spatial heterojunction of CoyNix@Fe─N─C heterogeneous catalyst for effective bifunctional electrolysis (OER/ORR). Thereinto, the Co/Ni alloy is strongly coupled to the Fe─N─C support through Co/Ni─N bonds. DFT calculations and experimental findings confirm that Co/Ni─N bonds play a bridging role in the directional electron transfer from Co/Ni alloy to the Fe─N─C support, increasing the content of pyridinic nitrogen in the ORR-active support. In addition, the discovered directional electron transfer mechanism enhances both the ORR/OER activity and the durability of the catalyst. The Co0.66Ni0.34@Fe─N─C with the optimal Ni/Co ratio exhibits satisfying bifunctional electrocatalytic performance, requiring an ORR half-wave potential of 0.90 V and an OER overpotential of 317 mV at 10 mA cm-2 in alkaline electrolytes. The assembled rechargeable zinc-air batteries (ZABs) incorporating Co0.66Ni0.34@Fe─N─C cathode exhibits a charge-discharge voltage gap comparable to the Pt/C||IrO2 assembly and high robustness for over 60 h at 20 mA cm-2.

Identifying and tailoring C–N coupling site for efficient urea synthesis over diatomic Fe–Ni catalyst

Electrocatalytic urea synthesis emerged as the promising alternative of Haber–Bosch process and industrial urea synthetic protocol. Here, we report that a diatomic catalyst with bonded Fe–Ni pairs can significantly improve the efficiency of electrochemical urea synthesis. Compared with isolated diatomic and single-atom catalysts, the bonded Fe–Ni pairs act as the efficient sites for coordinated adsorption and activation of multiple reactants, enhancing the crucial C–N coupling thermodynamically and kinetically. The performance for urea synthesis up to an order of magnitude higher than those of single-atom and isolated diatomic electrocatalysts, a high urea yield rate of 20.2 mmol h⁻¹ g⁻¹ with corresponding Faradaic efficiency of 17.8% has been successfully achieved. A total Faradaic efficiency of about 100% for the formation of value-added urea, CO, and NH₃ was realized. This work presents an insight into synergistic catalysis towards sustainable urea synthesis via identifying and tailoring the atomic site configurations.

The direct electrocatalytic synthesis of urea via C–N coupling is of great significance. The authors report a diatomic catalyst with bonded Fe–Ni pairs to improve the efficiency of electrochemical urea synthesis from nitrate and CO₂.

Synthesis of poly (2,6-diaminopyridine) using a rotating packed bed toward efficient production of polypyrrole-derived electrocatalysts

Synthesis of pyridinic-rich polymer is a key step in obtaining high-performance polypyrrole-derived electrocatalysts for oxygen reduction reaction. A straightforward and controllable synthesis method is highly favored to efficiently manupulate the...

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.

Enhanced electrocatalytic oxygen reduction reaction for Fe-N4-C by the incorporation of Co nanoparticles

Oxygen reduction reaction (ORR) catalytic activity can be improved by means of enhancing the synergy between transition metals. In this work, a novel porous Fe-N₄-C nanostructure containing uniformly dispersed Co nanoparticles (CoNPs) is prepared by an assisted thermal loading method. The as-prepared Co@Fe-N-C catalyst shows enhanced ORR activity with a half-wave potential (E_1/2) of 0.92 V vs. RHE, which is much higher than those of the direct pyrolysis CoNP-free sample Fe-N-C (E_1/2 = 0.85 V) and Pt/C (E_1/2 = 0.90 V) in alkaline media. It exhibits remarkable stability with only a 10 mV decrease in E_1/2 after 10 000 cycles and an outstanding long-term durability with 85% current remaining after 60 000 s. In acidic media, this catalyst exhibits catalytic activity with an E_1/2 of 0.79 V, comparable to Pt/C (E_1/2 = 0.82 V). X-ray absorption fine spectroscopy analysis revealed the presence of active centres of Fe-N₄. Density functional theory calculations confirmed the strong synergy between CoNPs and Fe-N₄ sites, providing a lower overpotential and beneficial electronic structure and a local coordination environment for the ORR. The incorporation of CoNPs on the surface of Fe-N₄-C nanomaterials plays a key role in enhancing the ORR catalytic activity and stability, providing a new route to prepare efficient Pt-free ORR catalysts.

Highly Efficient Multifunctional Co-N-C Electrocatalysts with Synergistic Effects of Co-N Moieties and Co Metallic Nanoparticles Encapsulated in a N-Doped Carbon Matrix for Water-Splitting and Oxygen Redox Reactions

Electrochemical water-splitting reactions (hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)) and oxygen redox reactions (oxygen reduction reaction (ORR) and OER) are core processes for electrochemical water-splitting devices, rechargeable metal-air batteries, and regenerative fuel cells. Developing highly efficient non-noble multifunctional catalysts in the same electrolyte is an open challenge. Herein, efficient Co-N-C electrocatalysts with a mixed structure comprising Co-N moieties and Co nanoparticles encapsulated in a N-doped carbon layer were prepared via pyrolysis of a new structure of Co-coordinated bis(imino)pyridine polymer constructed by 2,6-diacetylpyridine and 3,3'-diaminobenzidine. Results demonstrate that Co ion sources have a remarkable impact on the final Co-N-C performance. The Co-N-C catalyst prepared using cobalt acetate as a precursor displays remarkable overall multifunctional performance. It needs only a cell voltage of 1.66 V (obtained from the half-cell test) for the water-splitting reaction (HER/OER) to reach 10 mA·cm^-2 in 1.0 M KOH, and the overall oxygen redox activity (OER/ORR) is 0.72 V in 0.1 M KOH, outperforming the reported nonprecious metal catalysts. The excellent activity is attributable to the synergistic effects between active sites with encapsulated metallic Co for HER and OER and Co-N moieties for ORR.

Core-Shell Fe3O4@NCS-Mn Derived from Chitosan-Schiff Based Mn Complex with Enhanced Catalytic Activity for Oxygen Reduction Reaction

A core-shell type of Fe3O4/NCS-Mn composite was prepared by pyrolyzing a precursor fabricated by coating a chitosan-Schiff base Mn complex on Fe3O4 cores. For comparison purposes, the Fe3O4@NCS sample in the absence of Mn and the Fe3O4@NC sample derived from just chitosan coating Fe3O4 were also prepared. Among the three catalysts, Fe3O4@NCS-Mn demonstrates the best electrocatalytic activity compared to commercial Pt/C (20%) for oxygen reduction reaction (ORR). The average of the transferred electron number (n) approached 3.6 in the range of −0.3 to −0.8 V (vs. Ag/AgCl). Moreover, the catalyst exhibited high stability and durability against methanol and may potentially be a promising ORR catalyst for fuel cells.