ABSTRACT
Reconstructing metal-organic framework (MOFs) toward a designed framework structure provides breakthrough opportunities to achieve unprecedented oxygen evolution reaction (OER) electrocatalytic performance, but has rarely, if ever, been proposed and investigated yet. Here, the first successful fabrication of a robust OER electrocatalyst by precision reconstruction of an MOF structure is reported, viz., from MOF-74-Fe to MIL-53(Fe)-2OH with different coordination environments at the active sites. Due to the radically reduced eg -t2g crystal-field splitting in Fe-3d and the much suppressed electron-hopping barriers through the synergistic effects of the O species the efficient OER of in MIL-53(Fe)-2OH is guaranteed. Benefiting from this desired electronic structure, the designed MIL-53(Fe)-2OH catalyst exhibits high intrinsic OER activity, including a low overpotential of 215 mV at 10 mA cm-2 , low Tafel slope of 45.4 mV dec-1 and high turnover frequency (TOF) of 1.44 s-1 at 300 mV overpotential, over 80 times that of the commercial IrO2 catalyst (0.0177 s-1 ).Consistent with the density functional theory (DFT) calculations, the real-time kinetic simulation reveals that the conversion from O* to OOH* is the rate-determining step on the active sites of MIL-53(Fe)-2OH.
ABSTRACT
Developing efficient earth-abundant MoS2 based hydrogen evolution reaction (HER) electrocatalysts is important but challenging due to the sluggish kinetics in alkaline media. Herein, a strategy to fabricate a high-performance MoS2 based HER electrocatalyst by modulating interface electronic structure via metal oxides is developed. All the heterostructure catalysts present significant improvement of HER electrocatalytic activities, demonstrating a positive role of metal oxides decoration in promoting the rate-limited water dissociation step for the HER mechanism in alkaline media. The as-obtained MoS2 /Ni2 O3 H catalyst exhibits a low overpotential of 84 mV at 10 mA cm-2 and small charge-transfer resistance of 1.5 Ω in 1 m KOH solution. The current density (217 mA cm-2 ) at the overpotential of 200 mV is about 2 and 24 times higher than that of commercial Pt/C and bare MoS2 , respectively. Additionally, these MoS2 /metal oxides heterostructure catalysts show outstanding long-term stability under a harsh chronopotentiometry test. Theoretical calculations reveal the varied sensitivity of 3d-band in different transition oxides, in which Ni-3d of Ni2 O3 H is evidently activated to achieve fast electron transfer for HER as the electron-depletion center. Both electronic properties and energetic reaction trends confirm the high electroactivity of MoS2 /Ni2 O3 H in the adsorption and dissociation of H2 O for highly efficient HER in alkaline media.
ABSTRACT
Two D-π-A-π-D type solvatochromic fluorescence probes (JT1 and JT2) based on triphenylamine have been synthesized. The photophysical and electrochemical properties of these probes as well as their solvatochromic behavior were studied. The Stokes shifts of JT1 and JT2 reach 175 nm (6417.0 cm-1) and 218.6 nm (9916.7 cm-1) in the acetonitrile solution, respectively. There is an excellent linear correlation between the Stokes shifts and the ET (30) solvent polarity values in different solvents. The high responsiveness of JT1 and JT2 to solvent polarity makes them promising candidates for solvatochromic fluorescence probes, especially for the detection of the polarity of non-proton solvents or the content of water in tetrahydrofuran.
