Mesoporous Surface-Sulfurized Fe-Co3O4 Nanosheets Integrated with N/S Co-Doped Graphene as a Robust Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reactions.

Playing a significant role in electrochemical energy conversion and storage systems, heteroatom-doped transition metal oxides are key materials for oxygen-involving reactions. Herein, mesoporous surface-sulfurized Fe-Co3O4 nanosheets integrated with N/S co-doped graphene (Fe-Co3O4-S/NSG) were designed as composite bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). Compared with the Co3O4-S/NSG catalyst, it exhibited superior activity in the alkaline electrolytes by delivering an OER overpotential of 289 mV at 10 mA cm-2 and an ORR half-wave potential of 0.77 V vs. RHE. Additionally, Fe-Co3O4-S/NSG kept stable at 4.2 mA cm-2 for 12 h without significant attenuation to render robust durability. This work not only demonstrates the satisfactory effect of the transition-metal cationic modification represented by iron doping on the electrocatalytic performance of Co3O4, but it also provides a new insight on the design of OER/ORR bifunctional electrocatalysts for efficient energy conversion.

Achieving job-synergistic polysulfides adsorption-conversion within hollow structured MoS2/Co4S3/C heterojunction host for long-life lithium-sulfur batteries.

Lithium-sulfur batteries are considered one of the most promising next-generation energy storage devices owing to their ultrahigh theoretical energy density and environmental friendliness. However, the sluggish electrode reaction kinetics of the sulfur cathode and shuttle effects of lithium polysulfide (LiPSs) restrict their active material utilization and cycling stability. Herein, a hollow, free-standing MoS2/Co4S3/C heterojunction was fabricated and employed as a cathode host for high-performance lithium-sulfur batteries (LSBs). The unique hollow nanostructured MoS2/Co4S3/C can achieve job-synergistic polysulfide adsorption-conversion, in which the conductive nitrogen-doped carbon framework facilitates rapid electron/ion diffusion; polar Co4S3 species provide strong chemisorption capability and endow intrinsic catalytic sites towards LiPSs, and MoS2 serves as a nanocrystal to accelerate the reaction dynamics. As a result, MoS2/Co4S3/C/S exhibited high reversible specific capacities at 2C and was maintained at 394 mAh g-1 after 1000 cycles, with a 0.04% capacity decay rate. Impressively, the high reversible specific capacities with high sulfur loading of 4.1 mg cm-2 were maintained at 906.7 mAh g-1.

Balanced capture and catalytic ability toward polysulfides by designing MoO2-Co2Mo3O8 heterostructures for lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries, as the next generation of energy storage systems, are currently limited by insufficient capture ability and sluggish catalytic reaction kinetics, thus leading to serve the shuttle effect of lithium polysulfides (LiPSs). Realizing the accelerated conversion of polysulfides in the cathode host of Li-S batteries is an effective way to improve its coulombic efficiency. The essence of fast conversion relies on enhanced oxidation reaction kinetics by virtue of the metal catalyst, but the generation of various intermediates exacerbate the complexity of the system and perplex the perfect operation of batteries relying on only one catalyst. In this work, the xMoO2:yCo2Mo3O8 heterostructures were designed, in which controlling the content of cobalt could balance the capture capability towards LiPSs by MoO2 and catalytic ability of liquid-solid conversion by Co2Mo3O8 catalytic sites. Therefore, utilizing synergy effect of MoO2-Co2Mo3O8 heterostructure enhances capture and catalytic ability toward polysulfides in Li-S batteries. As a result, the 9MoO2:2Co2Mo3O8-based cathode delivers excellent reversibility of 880 mA h g-1 after 100 cycles at 0.2C and 509 mA h g-1 after 1000 cycles at 1C with 0.056% capacity decay each cycle. This work provides a new method for synthesizing heterostructures by doping metals. Moreover, it promotes the understanding of balancing and promoting the capture capacity and catalytic conversion ability toward LiPSs.

Engineering the electronic and strained interface for high activity of PdMcore@Ptmonolayer electrocatalysts for oxygen reduction reaction.

Alloyed nanoparticles with core-shell structures provide a favorable model to modulate interfacial interaction and surface structures at the atomic level, which is important for designing electrocatalysts with high activity and durability. Herein, core-shell structured Pd3M@Pt/C nanoparticles with binary PdM alloy cores (M = Fe, Ni, and Co) and a monolayer Pt shell were successfully synthesized with diverse interfaces. Among these, Pd3Fe@Pt/C exhibited the best oxygen reduction reaction catalytic performance, roughly 5.4 times more than that of the commercial Pt/C catalyst used as reference. The significantly enhanced activity is attributed to the combined effects of strain engineering, interfacial electron transfer, and improved Pt utilization. Density functional theory simulations and extended X-ray absorption fine structure analysis revealed that engineering the alloy core with moderate lattice mismatch and alloy composition (Pd3Fe) optimizes the surface oxygen adsorption energy, thereby rendering excellent electrocatalytic activity. Future researches may use this study as a guide on the construction of highly effective core-shell electrocatalysts for various energy conversions and other applications.

Transition Metal Nitride Coated with Atomic Layers of Pt as a Low-Cost, Highly Stable Electrocatalyst for the Oxygen Reduction Reaction.

The main challenges to the commercial viability of polymer electrolyte membrane fuel cells are (i) the high cost associated with using large amounts of Pt in fuel cell cathodes to compensate for the sluggish kinetics of the oxygen reduction reaction, (ii) catalyst degradation, and (iii) carbon-support corrosion. To address these obstacles, our group has focused on robust, carbon-free transition metal nitride materials with low Pt content that exhibit tunable physical and catalytic properties. Here, we report on the high performance of a novel catalyst with low Pt content, prepared by placing several layers of Pt atoms on nanoparticles of titanium nickel binary nitride. For the ORR, the catalyst exhibited a more than 400% and 200% increase in mass activity and specific activity, respectively, compared with the commercial Pt/C catalyst. It also showed excellent stability/durability, experiencing only a slight performance loss after 10,000 potential cycles, while TEM results showed its structure had remained intact. The catalyst's outstanding performance may have resulted from the ultrahigh dispersion of Pt (several atomic layers coated on the nitride nanoparticles), and the excellent stability/durability may have been due to the good stability of nitride and synergetic effects between ultrathin Pt layer and the robust TiNiN support.