Room‐temperature sodium–sulfur (RT Na–S) batteries have attracted extensive attention because of their low cost and high specific energy. RT Na–S batteries, however, usually suffer from sluggish reaction kinetics, low reversible capacity, and short lifespans. Herein, it is shown that chain‐mail catalysts, consisting of porous nitrogen doped carbon nanofibers (PCNFs) encapsulating Co nanoparticles (Co@PCNFs), can activate sulfur via electron engineering. The chain‐mail catalysts Co@PCNFs with a micrograde hierarchical structure as a freestanding sulfur cathode (Co@PCNFs/S) can provide space for high mass loading of sulfur and polysulfides. The electrons can rapidly transfer from chain‐mail catalysts to sulfur and polysulfides during discharge–charge processes, therefore boosting its conversion kinetics. As a result, this freestanding Co@PCNFs/S cathode achieves a high sulfur loading of 2.1 ± 0.2 mg cm−2, delivering a high reversible capacity of 398 mA h g−1 at 0.5 C (1 C = 1675 mA g−1) over 600 cycles and superior rate capability of an average capacity of 240 mA h g−1 at 5 C. Experimental results, combined with density functional theory calculations, demonstrate that the Co@PCNFs/S can efficiently improve the conversion kinetics between the polysulfides and Na2S via transferring electrons from Co to them, thereby realizing efficient sulfur redox reactions.
Noble metal catalysts, especially Pt, have been widely used for electrochemical energy conversion, including in fuel cells, [1,2] water electrolysis, [3,4] metal-air batteries, [5] and N 2 /CO 2 to fuel conversion. [6][7][8] However, because of the scarcity of Pt, increasing its usage efficient is a significant way to reduce the cost of production. [9][10][11] An efficient strategy is to downsize catalysts, which has been regarded as one of the most effective The rational synthesis of single-layer noble metal directly anchored on support materials is an elusive target to accomplish for a long time. This paper reports well-defined single-layer Pt (Pt-SL) clusters anchored on ultrathin TiO 2 nanosheets-as a new frontier in electrocatalysis. The structural evolution of Pt-SL/TiO 2 via self-assembly of single Pt atoms (Pt-SA) is systematically recorded. Significantly, the Pt atoms of Pt-SL/TiO 2 possess a unique electronic configuration with PtPt covalent bonds surrounded by abundant unpaired electrons. This Pt-SL/TiO 2 catalyst presents enhanced electrochemical performance toward diverse electrocatalytic reactions (such as the hydrogen evolution reaction and the oxygen reduction reaction) compared with Pt-SA, multilayer Pt nanoclusters, and Pt nanoparticles, suggesting an efficient new type of catalyst that can be achieved by constructing single-layer atomic clusters on supports.
The electrochemical nitrogen reduction reaction (NRR) to directly produce NH3 from N2 and H2O under ambient conditions has attracted significant attention due to its ecofriendliness. Nevertheless, the electrochemical NRR presents several practical challenges, including sluggish reaction and low selectivity. Here, bi-atom catalysts have been proposed to achieve excellent activity and high selectivity toward the electrochemical NRR by Ma and his co-workers. It could accelerate the kinetics of N2-to-NH3 electrochemical conversion and possess better electrochemical NRR selectivity. This work sheds light on the introduction of bi-atom catalysts to enhance the performance of the electrochemical NRR.
Noble metals have been widely applied as catalysts in chemical production, energy conversion, and emission control [1][2][3], but their high cost and scarcity are major obstacles for any large-scale practical applications. It is therefore of great interest to explore new active material systems that require less mass loading of noble metal catalysts but with even better performance. Recently, intense research has been devoted towards downsizing the noble metals into single-atom catalysts (SACs) [4,5]. SACs, with single-atom active centers, were first reported by Qiao et al. [4]. They synthesized a single Pt atom catalyst supported on FeO x (Pt 1 /FeO x ), which offered extremely high efficiency on an atomic percent basis and showed excellent performance towards CO oxidation.There is no doubt that SACs offer superior performance towards some catalytic reactions, because of the unsaturated coordination environment of their metal species and highly active valence electrons. In addition, the surface free energy of metal species reaches a maximum in SACs [6-10]. Nevertheless, it is worth noting that the catalytic selectivity plays an important part in catalytic reactions, and the SACs may limit application in some multi-electron catalytic processes [5]. In this case, we propose that if single atoms could assemble to monatomic layer clusters (mALCs), they would exhibit higher catalytic activity and selectivity than SACs. Unlike SACs [11][12][13], the mALCs materials are expected to be stable and to keep its structure under realistic catalytic conditions, which outperformes well-defined monatomic layer.The coordination environment of mALCs will be more saturated than that of single atoms, which indicates mALCs materials could be more stable during catalytic reaction. In addition, under the realistic reaction condition, the atoms of mALCs could work in synergy to catalyze the reaction. For example, neighboring Pt monomers showed better catalytic performance and lower activation energy than single Pt atoms towards CO 2 reduction; meanwhile, these neighboring Pt monomers did not aggregate during the catalytic reaction [8]. It is generally believed that the support materials could affect electronic configuration of noble metal atoms by rearranging the molecular orbitals. This phenomenon results in modification of local charge density in catalyst surface. Based on the combination ways between noble metal atoms and matrix atoms, there are two models to describe the interaction between noble metal atoms and matrix atoms corresponding to the simulating charge density maps, as shown in Fig. 1. For SACs, if the single noble atom is anchored by three or four matrix atoms, its charge density will be affected only by matrix atoms. Its low-coordination environment results in a high activity.In contrast, if the single atoms assemble to monatomic layer clusters (for example, two atoms or four atoms), their energy states and charge density will be determined by both matrix atoms and neighboring noble atoms through the hybridization. Mor...
Core-shell structured bimetallic platinum-metal (PtÀ M) nanoparticles, as a new class of active and stable nanocatalysts, have shown many advantages in increasing the utilization of precious Pt and improving electrocatalytic performances. Here, a core-shell Pt 3 Co@Pt supported on porous graphitic carbon (denoted as Pt 3 Co@Pt/C) is synthesized via a simple thermal method, and further used as an efficient electrocatalyst for oxygen reduction reaction (ORR) in the direct methanol fuel cell. An atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) measurement combining with line-profile analysis reveals that the average thickness of Pt-shell is around 0.4-0.6 nm, forming an ultrathin catalytic layer. Given its unique geometric and electronic structure, the as-prepared Pt 3 Co@Pt/C displays highly enhanced electrocatalytic ORR activity and stability, boosted anti-methanol poisoning ability with a high onset potential and an exceptional half-wave potential in 0.1 M HClO 4 solution. Impressively, its mass activity (0.71 mA mg Pt À 1) and specific activity (2.75 mA cm Pt À 2) for ORR are 3.7-and 8.1-fold higher than those of commercial Pt/C catalyst, respectively. The Pt 3 Co@Pt/C nanocatalysts show remarkable tolerance against methanol poisoning, evidenced by the in situ Fourier-transform infrared (FTIR) spectroscopy. This work points out a path for the design of high-performance nanocatalysts for accelerating the development of clean energy technologies involving ORR.
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