Designed preparation of CoS/Co/MoC nanoparticles incorporated in N and S dual-doped porous carbon nanofibers for high-performance Zn-air batteries

Synthesis of Zr2ON2 via a urea-glass route to modulate the bifunctional catalytic activity of NiFe layered double hydroxide in a rechargeable zinc-air battery

The development of a highly efficient, stable, and low-cost bifunctional catalyst is imperative for facilitating the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, significant challenges are involved in extending its applications to rechargeable zinc-air batteries. This study presents a bifunctional catalyst, Zr2ON2@NiFe layered double hydroxide (LDH), that was developed by utilizing a urea-glass route for synthesizing the Zr2ON2 precursor, followed by riveting NiFe LDH nanosheets using a hydrothermal method. Specifically, the vertical distribution of NiFe LDH on the Zr2ON2 surface ensures the maximization of the number of accessible active sites and interfacial catalysis of NiFe LDH. Notably, Zr2ON2@NiFe LDH demonstrates ORR and OER bifunctional electrocatalytic behavior and high stability owing to its heterostructure and composition. Furthermore, a rechargeable zinc-air battery using a Zr2ON2@NiFe LDH electrocatalyst as the air cathode demonstrated a high peak power density (172 mW cm-2) and galvanostatic charge-discharge cycle stability (5 mA cm-2 over 443 h). Thus, this study presents an efficient and cost-effective strategy for the design of bifunctional electrocatalysts.

Precisely Engineering Asymmetric Atomic CoN4 by Electron Donating and Extracting for Oxygen Reduction Reaction

The development of nonpyrolytic catalysts featuring precisely defined active sites represents an effective strategy for investigating the fundamental relationship between the catalytic activity of oxygen reduction reaction (ORR) catalysts and their local coordination environments. In this study, we have synthesized a series of model electrocatalysts with well-defined CoN4 centers and nonplanar symmetric coordination structures. These catalysts were prepared by a sequential process involving the chelation of cobalt salts and 1,10-phenanthroline-based ligands with various substituent groups (phen(X), where X=OH, CH3, H, Br, Cl) onto covalent triazine frameworks (CTFs). By modulating the electron-donating or electron-withdrawing properties of the substituent groups on the phen-based ligands, the electron density surrounding the CoN4 centers was effectively controlled. Our results demonstrated a direct correlation between the catalytic activity of the CoN4 centers and the electron-donating ability of the substituent group on the phenanthroline ligands. Notably, the catalyst denoted as BCTF-Co-phen(OH), featuring the electron-donating OH group, exhibited the highest ORR catalytic activity. This custom-crafted catalyst achieved a remarkable half-wave potential of up to 0.80 V vs. RHE and an impressive turnover frequency (TOF) value of 47.4×10-3 Hz at 0.80 V vs. RHE in an alkaline environment.

Facile synthesis of FeNi alloy-supported N-doped Mo2C hollow nanospheres for the oxygen evolution reaction

The rapid depletion of fossil fuels results in significant environmental pollution. Consequently, researching environmentally friendly and cost-effective electrocatalysts with exceptional oxygen evolution reaction (OER) capabilities holds immense importance in enhancing the efficient utilization of resources. In this paper, a straightforward and cost-effective method was employed to produce Fe-Ni alloy-supported N-doped carbon hollow nanospheres (FeNi/Mo2C/NC) using self-assembled molybdenum dopamine spheres (Mo-PDA-HS) as a substrate. The inclusion of iron and nickel addressed the issue of aggregation and collapse in Mo-PDA-HS nanostructures at high temperatures, while adjusting the electronic structure of the composites to achieve efficient OER activity. The composite displayed a low overpotential (η10 mA = 304 mV) and a minimal Tafel slope (41.8 mV/dec-1). This study introduces a simple strategy for constructing structurally robust and non-aggregating Mo2C nanostructures, along with a direct method for designing cost-effective and high-performance catalysts for OER.

Phase Engineering of Molybdenum Carbide-Cobalt Heterostructures for Long-Lasting Zn-Air Batteries

Developing highly active and robust oxygen catalysts is of great significance for the commercialization of Zn-air batteries (ZABs) with long-life stability. Herein, heterostructured catalysts comprising molybdenum carbide and metallic Co are prepared by a simple dicyandiamide-assisted pyrolysis strategy. Importantly, the crystalline phase of molybdenum carbide in the catalysts can be carefully regulated by adjusting the CoMo-imidazole precursor and dicyandiamide ratio. The electronic configuration of Co and Mo centers as well as the phase-dependent oxygen reduction reaction performance of these heterostructures (β-Mo2C/Co, β-Mo2C/η-MoC/Co, and η-MoC/Co) was disclosed. A highly active η-MoC/Co cathode enables ZABs with outstanding long-term stability over 850 h with a low voltage decaying rate of 0.06 mV·h-1 and high peak power density of 162 mW·cm-2. This work provides a new idea for the rational design of efficient and stable cathode catalysts for ZABs.

Nanocapsule of MnS Nanopolyhedron Core@CoS Nanoparticle/Carbon Shell@Pure Carbon Shell as Anode Material for High-Performance Lithium Storage

MnS has been explored as an anode material for lithium-ion batteries due to its high theoretical capacity, but low electronic conductivity and severe volume change induce low reversible capacity and poor cycling performance. In this work, the nanocapsule consisting of MnS nanopolyhedrons confined in independent, closed and conductive hollow polyhedral nanospheres is prepared by embedding MnCO₃ nanopolyhedrons into ZIF-67, followed by coating of RF resin and gaseous sulfurization/carbonization. Benefiting from the unique nanocapsule structure, especially inner CoS/C shell and outer pure C shell, the MnS@CoS/C@C composite as anode material presents excellent cycling performance (674 mAh g^-1 at 1 A g^-1 after 300 cycles; 481 mAh g^-1 at 5 A g^-1 after 300 cycles) and superior rate capability (1133.3 and 650.6 mAh g^-1 at 0.1 and 4 A g^-1), compared to the control materials (MnS and MnS@CoS/C) and other MnS composites. Kinetics measurements further reveal a high proportion of the capacitive effect and low reaction impedance of MnS@CoS/C@C. SEM and TEM observation on the cycled electrode confirms superior structural stability of MnS@CoS/C@C during long-term cycles. Excellent lithium storage performance and the convenient synthesis strategy demonstrates that the MnS@CoS/C@C nanocapsule is a promising high-performance anode material.

Boosting the activity and stability via synergistic catalysis of Co nanoparticles and MoC to construct a bifunctional electrocatalyst for high-performance and long-life rechargeable zinc-air batteries

The high overpotential of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) leading to slow air cathode kinetics is still a major challenge for zinc-air batteries (ZABs), hindering the commercialization of ZABs. With the advantages of cost-effectiveness and feasibility of synthesis at room temperature, zeolite imidazole frameworks (ZIFs) are regarded as advanced precursors. But a majority of ZIF-derived catalysts show only one catalytic activity, which limits their performance in ZABs as well as the cycling stability. In addition, molybdenum carbide (MoC) is recognized as an excellent candidate for renewable energy conversion due to its good chemical resistance and thermal stability. Herein, we report a ZIF-67-derived Co/MoC-NC multiphase doped carbon bifunctional ORR/OER catalyst with multiple active sites for the cathode of ZABs. The synergistic catalysis of Co nanoparticles and MoC nanoparticles in Co/MoC-NC which are embedded in a thin layer of N-doped graphitic carbon and immobilized on N-doped graphitic carbon, respectively, demonstrates superior ORR catalytic performance and durability both under alkaline and acidic conditions (E_1/2 = 0.87 V in 1.0 M KOH and E_1/2 = 0.76 V in 0.5 M H₂SO₄). Simultaneously, Co/MoC-NC also exhibits favorable OER performance (10 mA cm^-2, η = 320 mV) in 1 M KOH. Furthermore, a remarkable peak-power density of 215.36 mW cm^-2 and great cycling stability could be achieved while applying Co/MoC-NC in the cathode of ZABs (over 300 h). This work will provide a viable design concept for designing and synthesizing multifunctional catalysts to construct rechargeable ZABs.