Self-supporting network-structured MoS2/heteroatom-doped graphene as superior anode materials for sodium storage.

Layered graphene and molybdenum disulfide have outstanding sodium ion storage properties that make them suitable for sodium-ion batteries (SIBs). However, the easy and large-scale preparation of graphene and molybdenum disulfide composites with structural stability and excellent performance face enormous challenges. In this study, a self-supporting network-structured MoS2/heteroatom-doped graphene (MoS2/NSGs-G) composite is prepared by a simple and exercisable electrochemical exfoliation followed by a hydrothermal route. In the composite, layered MoS2 nanosheets and heteroatom-doped graphene nanosheets are intertwined with each other into self-supporting network architecture, which could hold back the aggregation of MoS2 and graphene effectively. Moreover, the composite possesses enlarged interlayer spacing of graphene and MoS2, which could contribute to an increase in the reaction sites and ion transport of the composite. Owing to these advantageous structural characteristics and the heteroatomic co-doping of nitrogen and sulfur, MoS2/NSGs-G demonstrates greatly reversible sodium storage capacity. The measurements revealed that the reversible cycle capacity was 443.9 mA h g-1 after 250 cycles at 0.5 A g-1, and the rate capacity was 491.5, 490.5, 453.9, 418.1, 383.8, 333.1, and 294.4 mA h g-1 at 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g-1, respectively. Furthermore, the MoS2/NSGs-G sample displayed lower resistance, dominant pseudocapacitive contribution, and faster sodium ion interface kinetics characteristic. Therefore, this study provides an operable strategy to obtain high-performance anode materials, and MoS2/NSGs-G with favorable structure and excellent cycle stability has great application potential for SIBs.

Thermal Migration Promotes the Formation of Manganese and Nitrogen Doped Polyhedral Surface for Boosted Oxygen Reduction Electrocatalysis.

Increasing the oxygen reduction reaction (ORR) catalytic activity of carbon-based electrocatalysts with robust stability is of great significance for their application. Herein, a feasible thermal migration strategy was proposed to construct manganese- and nitrogen-doped carbonaceous polyhedron frameworks coupled with manganese monoxide microrods (MnO-NC). Mn species were migrated to the surface of polyhedron frameworks, the shape of which was maintained at the high-temperature treatment. The Mn thermal migration not only created highly dispersed Mn-Nx active sites but also promoted graphitization, which benefited ORR electrocatalysis. Moreover, the MnO microrod-supported polyhedron frameworks provide beneficial mass transfer channels for electrocatalysis. Therefore, MnO-NC exhibited impressive ORR catalytic activity and stability in both alkaline and neutral electrolytes compared to commercial Pt/C catalysts. A magnesium-air battery (MAB) driven by MnO-NC delivered a high open circuit voltage and peak power density comparable to that driven by Pt/C. Notably, MnO-NC-driven MAB possessed a longer discharge time than the Pt/C-driven one, indicative of the superior catalytic performance of Mn-NC. This work provides a simple but effective strategy to construct carbonaceous framework electrocatalysts for boosted ORR, promoting the widespread application of metal-air batteries and fuel cells.

Robust Oxygen Reduction Electrocatalysis Enabled by Platinum Rooted on Molybdenum Nitride Microrods.

Robust oxygen reduction electrocatalysis is central to renewable fuel cells and metal-air batteries. Herein, Pt nanoparticles (NPs) rooted on porous molybdenum nitride microrods (Pt/Mo2N MRs) are rationally constructed toward the oxygen reduction reaction (ORR). Owing to the desired composition with strong electronic metal-support interactions (EMSIs) and a porous one-dimensional structure supporting ultrafine NPs, the developed Pt/Mo2N MRs possess much higher ORR mass and specific activities than commercial Pt/C. In situ Raman and density functional theory calculations reveal that the EMSI weakens the adsorption of intermediates over Pt/Mo2N MRs via an associative mechanism. Moreover, the porous Mo2N support stabilizes these high activities. Impressively, a homemade zinc-air battery driven by Pt/Mo2N MRs delivers excellent performance including a peak power density of 167 mW cm-2 and a high rate capability that ranged from 5 to 50 mA cm-2. This work highlights the role of EMSI in promoting robust ORR electrocatalysis, thus providing a promising approach for efficient and robust cathode materials for advanced metal-air batteries.

Diatomite waste derived N-doped porous carbon for applications in the oxygen reduction reaction and supercapacitors.

Biomass waste recycling and utilization is of great significance for improving ecological environments and relieving the current energy crisis. Waste diatomite with an adsorbed mass of yeast protein resulting from beer filtration is feasibly converted into N-doped porous carbon (NPC) via high temperature thermal treatment. The resulting NPC inherits the three-dimensional hierarchical structure of the diatomite, with a unique rich-pore feature composed of micro/meso/macropores, which is beneficial for high exposure of the electrocatalytic sites and ion transfer and diffusion. The NPC compounds with controllable nitrogen doping are used for the oxygen reduction reaction (ORR) and in a supercapacitor. NPC-2 exhibits a half-wave potential of 0.801 V comparable to that (0.812 V) of commercially available Pt/C in alkaline media, along with a good methanol tolerance capacity and long-term stability for the ORR. Furthermore, as an electrode material, a symmetric supercapacitor based on NPC-2 manifests an outstanding specific capacitance of 151.5 F g-1 at a current density of 1 A g-1 and a considerable capacitance retention of 90.5% after a cycling performance test of 10 000 cycles. The NPC-2 based symmetric SC delivered an energy density of 13.47 W h kg-1 at a power density of 400 W kg-1. This work highlights the environmental significance of converting waste diatomite into metal-free ORR catalysts and electrode materials for energy conversion and storage technologies.

Control of the interface graphitized/amorphous carbon of biomass-derived carbon microspheres for symmetric supercapacitors.

Rational interface control of porous carbon electrode materials is of significance for achieving efficient supercapacitors. Herein, biomass-derived carbon microspheres with a highly graphitized porous surface and amorphous subsurface were well constructed via a flexible coupled catalysis-activation process. The unique structure not only endows the carbon microspheres with rapid electron transfer but also an ultra-high specific surface area. Owing to the optimized graphitized/amorphous structure, the obtained graphitized and activated starch-derived carbon microspheres display obviously impressive energy storage capability among the reported starch-derived carbon materials, even though they were evaluated in a narrow voltage window. The assembled symmetrical supercapacitor based on the optimized carbon microspheres exhibits a high capacitance of 198 F g-1 at 1 A g-1, a high energy density of 14.67 W h kg-1 at a power density of 4142.80 W kg-1, robust cycle performance, and good rate performance in alkaline aqueous electrolyte. This work provides a strategy for flexible construction of biomass-derived carbon electrode materials, with an optimized graphitized/amorphous and porous structure, for boosted energy storage in supercapacitor applications.

Short-range amorphous carbon nanosheets for oxygen reduction electrocatalysis.

Selectively creating active sites that can work well in different media as much as possible remains an open challenge for the widespread application of sustainable metal air batteries and fuel cells. Herein, short-range amorphous nitrogen-doped carbon nanosheets (NCS) coupled with partially graphitized porous carbon architecture were reported, and were prepared via flexible salt-assisted calcination strategy and followed by a simple cleaning process. The short-range amorphous structure not only significantly promotes the exposure of electrochemically active sites of carbon defects with less protonation in acidic medium, but also maintains the structural stability and electron conduction of the NCS. This unique structure endows the NCS (0.832 V) with efficient ORR electrocatalytic performance with a high half-wave potential (E 1/2) comparable to that of commercial Pt/C (0.837 V) in alkaline electrolyte and an impressive E 1/2 of 0.64 V in harsh acidic medium, making it outstanding among the reported analogous metal-free carbon electrocatalysts. In addition, the NCS manifests robust stability for ORR electrocatalysis with little change in the catalytic activity after accelerated stability tests. This work will provide a feasible inspiration to the construction of carbon nanomaterials with high active site density for efficient energy conversion-related electrochemical reactions.

Scalable Preparation of the Chemically Ordered Pt-Fe-Au Nanocatalysts with High Catalytic Reactivity and Stability for Oxygen Reduction Reactions.

Carbon-supported Au-Pt xFe y nanoparticles were synthesized via microwave heating polyol process, followed by annealing for the formation of the ordered structure. The structure characterizations indicate that Au is alloyed with intermetallic Pt-Fe nanoparticles and therefore the surface electronic properties are tuned. The electrochemical tests show that the microwave heating polyol process is more effective than oil bath heating polyol process for synthesizing the highly active catalysts. The introduction of trace Au (0.2 wt % Au) significantly improves the oxygen reduction reaction (ORR) catalytic activity of Pt xFe y catalysts. Au-PtFe/C-H (0.66 A/mgPt) and Au-PtFe3/C-H (0.63 A/mgPt) prepared in a batch of 10.0 g show significantly improved catalytic activities than their counterparts (PtFe/C-H and PtFe3/C-H) as well as commercial Johnson Matthey Pt/C (0.17 A/mgPt). In addition, the as-prepared Au-PtFe/C-H and Au-PtFe3/C-H display highly enhanced stability toward the ORR compared to the commercial Pt/C. The superior catalytic performance is attributed to the synergistic effect of chemically ordered intermetallic structure and Au. This work provides a scalable synthesis of the multimetallic chemically ordered Au-Pt xFe y catalysts with high ORR catalytic performance in acidic condition.