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Regulating the coordination environment of transition-metal based materials in the axial direction with heteroatoms has shown great potential in boosting the oxygen reduction reaction (ORR). The coordination configuration and the regulation method are pivotal and elusive. Here, we report a combined strategy of matrix-activization and controlled-induction to modify the CoN4 site by axial coordination of Co—S (Co1N4-S1), which was validated by the aberration-corrected electron microscopy and X-ray absorption fine structure analysis. The optimal Co1N4-S1 exhibits an excellent alkaline ORR activity, according to the half-wave potential (0.897 V vs. reversible hydrogen electrode (RHE)), Tafel slope (24.67 mV/dec), and kinetic current density. Moreover, the Co1N4-S1 based Zn-air battery displays a high power density of 187.55 mW/cm2 and an outstanding charge—discharge cycling stability for 160 h, demonstrating the promising application potential. Theoretical calculations indicate that the better regulation of CoN4 on electronic structure and thus the highly efficient ORR performance can be achieved by axial Co—S. [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]

FeN4 moieties embedded in partially graphitized carbon are the most efficient platinum group metal free active sites for the oxygen reduction reaction in acidic proton‐exchange membrane fuel cells. However, their formation mechanisms have remained elusive for decades because the Fe−N bond formation process always convolutes with uncontrolled carbonization and nitrogen doping during high‐temperature treatment. Here, we elucidate the FeN4 site formation mechanisms through hosting Fe ions into a nitrogen‐doped carbon followed by a controlled thermal activation. Among the studied hosts, the ZIF‐8‐derived nitrogen‐doped carbon is an ideal model with well‐defined nitrogen doping and porosity. This approach is able to deconvolute Fe−N bond formation from complex carbonization and nitrogen doping, which correlates Fe−N bond properties with the activity and stability of FeN4 sites as a function of the thermal activation temperature. [ABSTRACT FROM AUTHOR]

Excessive CO2 emission due to a large amount of fossil fuel utilization has become a widespread concern, which causes both environmental and energy problems. To solve these issues, electrocatalytic and photocatalytic reduction of CO2 to produce value‐added chemicals have gained immense attention. Recently, metal–organic frameworks (MOFs) and their derived materials with high specific surface areas, controllable pore structures, and tunable chemical properties exhibit promising performance among the reported catalytic materials for CO2 conversion. This review describes the recent advances on the rational design and synthesis of MOF‐based electrocatalysts and photocatalysts for CO2 reduction. The importance of the catalytic processes is highlighted, followed by systematic understanding of MOF‐based catalysts for CO2 reduction through electrochemical and photochemical approaches. Special emphasis of this review is to introduce basic catalyst design strategies and synthesis methods as well as their resulting electrocatalysts and photocatalysts. One of the major goals is to elucidate the structures and properties that link to their catalytic activity, selectivity, and stability towards to CO2 reduction. We also outline the challenges in this research area and propose the potential strategies for the rational design and synthesis of high‐performance catalysts. Due to the controllable pore size distribution, high specific surface area, and the tunable properties, metal–organic framework (MOF)‐based electrocatalysts and photocatalysts have been recognized as promising candidates for CO2 reduction to value‐added chemicals. In this review recent advances are discussed in detail and the challenges and future directions are outlined. [ABSTRACT FROM AUTHOR]

Single-atom catalysts (SACs) with unitary active sites hold great promise for realizing high selectivity toward a single product in the CO 2 electroreduction reaction (CO 2 RR). However, achieving high Faradaic efficiency (FE) of multielectron products like methane on SACs is still challenging. Herein, we report a pressure-regulating strategy that achieves 83.5 ± 4% FE for the CO 2 -to-CH 4 conversion on the asymmetric Cu-N 2 sites, representing one of the best CO 2 -to-CH 4 performances. Elevated CO 2 pressure was demonstrated as an efficient way to inhibit the hydrogen evolution reaction via promoting the competing adsorption of reactant CO 2 , regardless of the nature of the active sites. Meanwhile, the asymmetric Cu-N 2 structure could endow the Cu sites with stronger electronic coupling with *CO, thus suppressing the desorption of *CO and facilitating the following hydrogenation of *CO to *CHO. This work provides a synergetic strategy of the pressure-induced reaction environment regulating and the electronic structure modulating for selective CO 2 RR toward targeted products.

Aqueous Zn-iodine (Zn-I 2 ) conversion batteries with iodine redox chemistry suffers the severe polyiodide shuttling and sluggish redox kinetics, which impede the battery lifespan and rate capability. Herein, an ultrastable Zn-I 2 battery is introduced based on single-atom Fe-N-C encapsulated high-surface-area carbon (HC@FeNC) as the core-shell cathode materials, which accelerate the I - /I 3 - /I° conversion significantly. The robust chemical-physical interaction between polyiodides and Fe-N 4 sites tightly binds the polyiodide ions and suppresses the polyiodide shuttling, thereby significantly enhancing the coulombic efficiency. As a result, the core-shell HC@FeNC cathode endows the electrolytic Zn-I 2 battery with an excellent capacity, remarkable rate capability, and an ultralong lifespan over 60 000 cycles. More importantly, a practical 253 Wh kg -1 pouch cell shows good capacity retention of 84% after 100 cycles, underscoring its considerable potential for commercial Zn-I 2 batteries., (© 2024 Wiley‐VCH GmbH.)

Metal single-atom catalysts are promising in electrochemical CO 2 reduction reaction (CO 2 RR). The pores and cavities of the supports can promote the exposure of active sites and mass transfer of reactants, hence improve their performance. Here, iron oxalate is added to ZIF-8 and subsequently form hollow carbon nanocages during calcination. The formation mechanism of the hollow structure is studied in depth by controlling variables during synthesis. Kirkendall effect is the main reason for the formation of hollow porous carbon nanocages. The hollow porous carbon nanocages with Fe single atoms exhibit better CO 2 RR activity and CO selectivity. The diffusion of CO 2 facilitated by the mesoporous structure of carbon nanocage results in their superior activity and selectivity. This work has raised an effective strategy for the synthesis of hollow carbon nanomaterials, and provides a feasible pathway for the rational design of electrocatalysts for small molecule activation., (© 2023 Wiley-VCH GmbH.)

An Fe-N-C catalyst with an FeN 4 active moiety has gained ever-increasing attention for the oxygen reduction reaction (ORR); however, the catalytic performance is sluggish in acidic solutions and the regulation is still a challenge. Herein, Fe-Mo dual-metal sites were constructed to tune the ORR activity of a mononuclear Fe site embedded in porous nitrogen-doped carbon. The cracking of O-O bonds is much more facile on the Fe-Mo atomic pair site due to the preferred bridge-cis adsorption model of oxygen molecules. The downshift of the Fe d band center when an Mo atom is introduced to the FeN x configuration optimizes the absorption-desorption behavior of ORR intermediates in the FeMoN 6 active moiety, thus boosting the catalytic performance. The construction of dual-metal atom sites to regulate the catalytically active moiety paves the way for boosting the electrocatalytic performance of other similar non-precious-metal catalysts.

Excessive CO 2 emission due to a large amount of fossil fuel utilization has become a widespread concern, which causes both environmental and energy problems. To solve these issues, electrocatalytic and photocatalytic reduction of CO 2 to produce value-added chemicals have gained immense attention. Recently, metal-organic frameworks (MOFs) and their derived materials with high specific surface areas, controllable pore structures, and tunable chemical properties exhibit promising performance among the reported catalytic materials for CO 2 conversion. This review describes the recent advances on the rational design and synthesis of MOF-based electrocatalysts and photocatalysts for CO 2 reduction. The importance of the catalytic processes is highlighted, followed by systematic understanding of MOF-based catalysts for CO 2 reduction through electrochemical and photochemical approaches. Special emphasis of this review is to introduce basic catalyst design strategies and synthesis methods as well as their resulting electrocatalysts and photocatalysts. One of the major goals is to elucidate the structures and properties that link to their catalytic activity, selectivity, and stability towards to CO 2 reduction. We also outline the challenges in this research area and propose the potential strategies for the rational design and synthesis of high-performance catalysts., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)