Ce-Modified Flowerlike NiFe-MOF Nanostructure Based on Ion Competitive Coordination for Enhancing the Oxygen Evolution Reaction

Abstract

Metal−organic framework (MOF) has become a popular electrocatalyst for the oxygen evolution reaction (OER) because of its large specific surface area and adjustable porosity. Nevertheless, the electrochemical performance of MOFs has been greatly limited by poor intrinsic conductivity and catalytic activity. Herein, we report a Ce-doped nanoflower-like MOF material Ce@ NiFe-MOF-5 via a facile ion competitive coordination effect and doping method. Benefiting from the nanoflower structure formed by the stacking of nanosheets, a large number of active sites can be exposed, which favors electron/mass transfer during water oxidation. The coordination substitution of Ce ions not only promoted an increase in the number of active sites on the surface of the nanosheets but also optimized the electronic structure of pristine NiFe-MOF. The well-designed Ce@NiFe-MOF-5 catalysts exhibited superior OER performance under basic conditions, which only required an overpotential of 258 mV at a current density of 10 mA cm −2 and a Tafel slope of 54.44 mV dec −1 . Moreover, when Ce@NiFe-MOF-5 served as an anode and Pt/C as a cathode, the two-electrode system only needed 1.56 V to drive overall water splitting at 10 mA cm −2 .

(FeMnCe)-co-doped MOF-74 with significantly improved performance for overall water splitting

“…Dalton Therefore, the introduction of the Ce element can effectively reduce charge-transport impedance and improve the electron transfer rate, thereby promoting electrocatalytic kinetics. As reported in previous literature, [67][68][69][70][71] rare earth elements can effectively modulate the electronic structures and reduce the H* absorption energy, further promoting HER activity. In a word, the above comparative results of the EIS test further demonstrated the importance and effectiveness of the 3d-4f mixed metal strategy.…”

“…74,75 The percentage of Ce 4+ decreases after the test, which may be due to the reduction of Ce 4+ to Ce 3+ during the OER. 71 More discussion about XPS results for initial FeMn 6 Ce 0.5 -MOF-74/NF can be found in the ESI. † The above comparison of XPS further proves the change of electronic states in FeMn 6 Ce 0.5 -MOF-74/NF electrode materials during the electrochemical test.…”

3D nanostructured Ce-doped CoFe-LDH/NF self-supported catalyst for high-performance OER

“…When the current density was 10 mA cm −2 , the overpotential of this material was as low as 254 mV; 28 Wei's team doped Ce ions into flowerlike NiFe-MOF nanostructure, showing an oxygen evolution overpotential of 258 mV at 10 mA cm −2 and a Tafel slope of 54.44 mV dec −1 . 29 Significantly, previous researches found that the partial replacement of Fe 3+ by Ce 3+ or La 3+ affected the electronic structure of CoFe LDH, which could reduce the crystallite size and enhance the electronic coordination in the system. 30,31 Usually, powdered OER catalysts need to be coated on the electrode with a polymer binder, which hinders the utilization of pore volume, porosity of catalysts, and reachability of the active sites.…”