RESUMEN
Actinide-based catalysts have been regarded as promising candidates for N2 fixation owing to their unique 5f orbital with flexible oxidation states. Herein, we report for the first time the dispersion of uranium (U) single atoms on TiO2 nanosheets via oxygen vacancy confinement for N2 electroreduction. The single-atom U catalyst exhibited a high NH3 yield of 40.57 µg h-1 mg-1, with a reasonably high Faraday efficiency of 25.77%, ranking first among the reported nitrogen-free catalysts. Isotope-labeling operando synchrotron infrared spectroscopy verifies that the key *N2Hy intermediate species was derived from the N2 gas of the feed. By using operando X-ray absorption spectroscopy, we found enhanced metal-support interaction between U single atoms and TiO2 lattice with more U-Olatt coordination under working conditions. Theoretical simulations suggest that the evolved 1Oads-U-4Olatt moieties act as a critical electron-feedback center, lowering the thermodynamic energy barrier for the N2 dissociation and the first hydrogenation step. This work provides the possibility of tailoring the interaction between metal active sites and supports for designing high-performance actinide-based single-atom catalysts.
RESUMEN
The emerging star of single atomic site (SAS) catalyst has been regarded as the most promising Pt-substituted electrocatalyst for oxygen reduction reaction (ORR) in anion-exchange membrane fuel cells (AEMFCs). However, the metal loading in SAS directly affects the whole device performance. Herein, we report a dual nitrogen source coordinated strategy to realize high dense Cu-N4 SAS with a metal loading of 5.61â wt% supported on 3D N-doped carbon nanotubes/graphene structure wherein simultaneously performs superior ORR activity and stability in alkaline media. When applied in H2 /O2 AEMFC, it could reach an open-circuit voltage of 0.90â V and a peak power density of 324â mW cm-2 . Operando synchrotron radiation analyses identify the reconstruction from initial Cu-N4 to Cu-N4 /Cu-nanoclusters (NC) and the subsequent Cu-N3 /Cu-NC under working conditions, which gradually regulate the d-band center of central metal and balance the Gibbs free energy of *OOH and *O intermediates, benefiting to ORR activity.
RESUMEN
Copper-based materials are efficient electrocatalysts for the conversion of CO2 to C2+ products, and most these materials are reconstructed in situ to regenerate active species. It is a challenge to precisely design precatalysts to obtain active sites for the CO2 reduction reaction (CO2 RR). Herein, we develop a strategy based on local sulfur doping of a Cu-based metal-organic framework precatalyst, in which the stable Cu-S motif is dispersed in the framework of HKUST-1 (S-HKUST-1). The precatalyst exhibits a high ethylene selectivity in an H-type cell with a maximum faradaic efficiency (FE) of 60.0 %, and delivers a current density of 400â mA cm-2 with an ethylene FE up to 57.2 % in a flow cell. Operando X-ray absorption results demonstrate that Cuδ+ species stabilized by the Cu-S motif exist in S-HKUST-1 during CO2 RR. Density functional theory calculations indicate the partially oxidized Cuδ+ at the Cu/Cux Sy interface is favorable for coupling of the *CO intermediate due to the modest distance between coupling sites and optimized adsorption energy.
RESUMEN
The electrocatalytic carbon dioxide reduction reaction (CO2RR) offers an attractive route to fuels and feedstocks from renewable energy. Gold is active for the electrochemical CO2RR to CO, while the competing hydrogen evolution reaction is unavoidable. Here, we report a synergistic strategy, via introducing atomically dispersed Fe to tune the electronic structure of the Au nanoparticle, to improve the CO selectivity. By using operando X-ray absorption and infrared spectroscopies, we reveal the dynamic structural evolution and the adsorption of reactant intermediates at the single-atom Fe1/Au interface. During the reaction, the interaction between Fe and Au atoms becomes stronger, and the Fe1/Au synergies affect the adsorption of reaction intermediates, thus improving the selectivity of CO up to 96.3% with a mass activity of 399 mA mg-1. These results highlight the significant importance of synergistic modulation for advancing the single-atom decorated nanoparticle catalysis.
RESUMEN
Developing new cathode-active materials for rechargeable batteries is important to fulfill the growing demands of energy transformation, storage, and utilization. Zeolitic transition-metal oxides based on vanadomolybdate, constructed by pentagon metal-oxygen clusters as building blocks and metal ions as linkers in a trigonal symmetry, are good candidates for cathodes of Na rechargeable batteries. The material is activated via amorphization of the crystal structure in the ab plane during discharging process, keeping the molecular structure of the building blocks stable, which causes high specific capacity and good cycle performance.
RESUMEN
Developing non-precious-metal bifunctional oxygen reduction and evolution reaction (ORR/OER) catalysts is a major task for promoting the reaction efficiency of Zn-air batteries. Co-based catalysts have been regarded as promising ORR and OER catalysts owing to the multivalence characteristic of cobalt element. Herein, the synthesis of Co nanoislands rooted on Co-N-C nanosheets supported by carbon felts (Co/Co-N-C) is reported. Co nanosheets rooted on the carbon felt derived from electrodeposition are applied as the self-template and cobalt source. The synergistic effect of metal Co islands with OER activity and Co-N-C nanosheets with superior ORR performance leads to good bifuctional catalytic performances. Wavelet transform extended X-ray absorption fine spectroscopy and X-ray photoelectron spectroscopy certify the formation of Co (mainly Co0 ) and the Co-N-C (mainly Co2+ and Co3+ ) structure. As the air-cathode, the assembled aqueous Zn-air battery exhibits a small charge-discharge voltage gap (0.82 V@10 mA cm-2 ) and high power density of 132 mW cm-2 , outperforming the commercial Pt/C catalyst. Additionally, the cable flexible rechargeable Zn-air battery exhibits excellent bendable and durability. Density functional theory calculation is combined with operando X-ray absorption spectroscopy to further elucidate the active sites of oxygen reactions at the Co/Co-N-C cathode in Zn-air battery.
RESUMEN
The development of cathode-active material of Li battery is important for the current emerging energy transferring and saving problems. A stable crystalline microporous complex metal oxide based on Mo, V, and Bi is an active and suitable material for Li battery. High capacity (380 Ah/kg) and stable cycle performance are achieved. X-ray absorption near-edge structure analyses demonstrate that the original Mo6+ and V4+ ions are reduced to Mo4+ and V3+ in the discharging process, respectively, which results in a 70-electron reduction per formula. The reduced metal ions can be reoxidized reversibly in the next charging process. Furthermore, extended X-ray absorption fine structure analyses reveal that the Mo-O bonds in the material are lengthened in the discharging process probably due to interaction with Li+ without change of the basic structure.