ABSTRACT
Metal-organic framework (MOF) nanosheets with attractive chemical and structural properties have been considered as prominent oxygen evolution reaction (OER) electrocatalysts, while the insufficient exposed active sites and low electrical conductivity of MOFs limit their electrocatalytic activity and further industrial applications. Herein, a unique strategy to remarkably boost electrocatalytic OER activity of one Ni-based MOF is developed by the simultaneous incorporation of Fe3+ ions and BF4- anions within its layer structure. The optimized electrocatalyst NiFe-MOF-BF4--0.3 NSs shows superior OER activity with a required ultralow overpotential of 237 mV at 10 mA cm-2, a small Tafel slope of 41 mV dec-1, and outstanding stability in an alkaline medium. The experimental and density functional theory (DFT) calculation results verify that the interactions between metal (M) ions and BF4- anions (defined as M···F, M = Ni or Fe) in this catalyst can adjust the adsorption abilities of oxygen intermediates and lower the free energy barrier of the potential-determining step by tailoring its electronic structure, thereby remarkably boosting its OER activity. This protocol provides new insights into surface and structure engineering of 2D MOFs, leading to greatly enhanced electrocatalytic OER performance.
ABSTRACT
The development of metal-organic frameworks (MOFs) as high-efficiency electrocatalysts for water splitting has attracted special attention due to their unique structural features including high porosity, large surface areas, high concentrations of active sites, uniform pore sizes and shapes, etc. Most of the related reports focus on the in situ generation of high-efficiency electrocatalysts by annealed MOFs. However, the pyrolysis process usually destroys the porous structure of MOFs and reduces the number of active sites due to the absence of organic ligands and agglomeration of metal centers. In this work, we prepared unique NiCo-MOF hollow nanospheres (NiCo-MOF HNSs) by a solvothermal method and further fabricated Fe-doped NiCo-MOF HNSs (Fe@NiCo-MOF HNSs) by a simple impregnation-drying method. Significant enhancement of electrocatalytic activity of Fe@NiCo-MOF HNSs was witnessed because of the doped Fe. Compared with the parent NiCo-MOF HNSs, the optimized Fe@NiCo-MOF HNSs exhibited a lower overpotential of 244 mV at 10 mA·cm-2 with a smaller Tafel slope of 48.61 mV·dec-1, which was lowered by ca. 90 mV due to the influence of Fe doping on the electronic structure of the active centers of Ni and Co. The above materials also displayed excellent stability without obvious activity decay for at least 16 hours. These findings present a new entry in the design and fabrication of high-efficiency MOF-based electrocatalysts for energy conversion.
ABSTRACT
As an important two-dimensional material, layered double hydroxides (LDHs) show considerable potential in electrocatalytic reactions. However, the great thickness of the bulk LDH materials significantly limits their catalytic activity. In this work, we report ultrathin NiFe-LDH nanosheets with sulfate interlayer anions (Ni6Fe2(SO4)(OH)16·7H2O) (U-LDH(SO4 2-)), which can be synthesized in gram-scale by a simple solvothermal method. The U-LDH(SO4 2-) shows excellent stability and great electrocatalytic performance in OER with a current density of 10 mA cm-2 at a low overpotential of 212 mV and a small Tafel slope of 65.2 mV dec-1, exhibiting its great potential for a highly efficient OER electrocatalyst.
ABSTRACT
Design and synthesis of non-noble metal electrocatalysts with high activity and durability for the electrolysis of water is of great significance for energy conversion and storage. In this work, we prepared a series of Fe-doped MoS2 nanomaterials by simple one-pot solvothermal reactions of (NH4)2MoS4 with FeCl3·6H2O. An optimized working electrode of Fe-MoS2-5 displayed high hydrogen evolution reaction (HER) activity with a relatively small overpotential of 173 mV to achieve a current density of 10 mA cm-2 in 0.5 M H2SO4, along with no significant change in catalytic performance even after 1000 cyclic voltammetry (CV) cycles. Fe-MoS2 nanoparticles on nickel foam (NF; denoted as Fe-MoS2/NF) exhibited an overpotential of 230 mV at 20 mA cm-2 for the oxygen evolution reaction (OER) and 153 mV at 10 mA cm-2 for the HER in 1.0 M KOH electrolyte. Fe-MoS2/NF was stable for more than 140 h under these conditions. Furthermore, the two electrode system of Fe-MoS2/NF (anode)//Fe-MoS2/NF (cathode) electrodes demonstrated excellent electrocatalytic activity toward overall water splitting with a low potential of 1.52 V at 10 mA cm-2 in 1.0 M KOH electrolyte.
ABSTRACT
The development of bifunctional non-noble metal electrocatalysts demonstrating high activity and stability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great significance for renewable and clean energy. In this work, we report hierarchically structured integrated Fe-MoS2/Ni3S2/NF (NF = nickel foam) materials prepared by a facile in situ solvothermal method, and among them, the Fe-doped MoS2 was assembled into spine-like nanorods. The optimized electrocatalyst (denoted as Fe-MoS2/Ni3S2/NF-2) demonstrated excellent activity and durability for performing the HER and OER in an alkaline electrolyte (pH = 14) with low overpotentials of 130.6 mV and 256 mV (vs. RHE) at a current density of 10 mA cm-2, as well as no significant loss in catalytic performance even after 2000 cyclic voltammetry (CV) cycles. An outstanding durability of 180 h could be achieved for OER. The overall water splitting made up of the two-electrode system with Fe-MoS2/Ni3S2/NF-2 as both the anode and the cathode required a voltage of only 1.61 V to drive a current density of 10 mA cm-2 along with an outstanding long-term stability of 20 h, displaying its great potential for application in water splitting. The effective construction of multi-component synergistic structures shows a good pathway for high-performance electrocatalysis and energy storage.
