Studies On Oxygen Evolution Reaction Performance Of 3D Ni-Fe-based Electrocatalysts At Large Current Densities

The extraction and burning of fossil fuels such as coal,oil and natural gas have produced a large number of greenhouse gases and harmful substances,which has brought the energy crisis and many environmental problems.The storage of discontinuous wind and solar energy as hydrogen through electrolyzed water is an important way to alleviate energy and environmental issues.The catalysts for oxygen evolution reaction(OER),such as iron,cobalt and nickel,have become the focus of recent research.The development of efficient and stable nickel-iron-based(Ni-Fe-based)OER electrocatalysts is still facing the challenges of industrial applications at high current densities.Herein,we developed novel 3D ternary hybrid electrocatalysts.Owing to the synergistic effect and their strong coupling effect,the 3D Fe0-NixSy/NF,?-Fe2O3@Ni2P/Ni(PO3)2/NF and r-FeOOH/?-Ni(OH)2 hybrids achieve a superior electrocatalytic OER performance at ultra-high current densities in alkaline electrolyte.A novel 3D ultrasmall Fe0 coupled nickel sulfides(Fe0-NixSy)nanosheets hybrid supported on Ni foam through one-step gas-solid reaction between 3D Ni foam with S powder.In such a 3D hybrid system,the ultrasmall Fe0 nanoparticles with the size of?2 nm are uniformly anchored onto the surface of NixSy nanosheets with?33 nm average thickness and?400 nm lateral size that are homogeneously grown on the Ni foam.The resulting 3D Fe0-NixSy/NF hybrid shows excellent electrocatalytic activity and stability towards OER in 1.0 M KOH,achieving extremely-high current densities of 1000 and 1500 mA cm-2 at low potentials of 1.57 and 1.60 V,respectively.This is the best performance among all previously reported Ni-Fe-based sulfides OER electrocatalysts,and even superior to state-of-the-art Ir/C catalyst at the same current densities.The synergistic effect between the Fe0 and NixSy as well as unique 3D hierarchical structure of the 3D Fe0-NixSy/NF hybrid contributes to the excellent OER catalytic activity.Further combining with a silicon photovoltaic cell,the 3D Fe0-NixSy/NF hybrid electrocatalyst could enable highly efficient solar-driven overall-water-splitting.A novel 3D strongly coupled ternary hybrid composed of Ni2P/Ni(PO3)2 and Fe2O3 grown on the 3D Ni foam through a disproportionation reaction.In such a hybrid system,the ?-Fe2O3@Ni2P/Ni(PO3)2 nanoparticles with?200 nm lateral size and?300 nm transverse size were orderly grown on the Ni foam.The 3D?-Fe2O3@Ni2P/Ni(PO3)2/NF hybrid showed an excellent activity and robust stability for OER in 1.0 M KOH,achieving extremely low potentials of 1.57 and 1.60 V at ultra-high current densities of 500 and 1000 mA cm-2,respectively,which are practically the lowest potentials among all previously reported Ni-Fe-based phosphides/phosphates OER electrocatalysts,and even exceed the state-of-the-art Ir/C catalyst.The outstanding OER activity can be attributed to the synergetic effect and the strong coupling effect between the Fe2O3 and Ni2P/Ni(PO3)2.In situ Raman spectroscopy revealed that the NiOOH and FeOOH phases were the real active species in the ?-Fe2O3@Ni2P/Ni(PO3)2/NF for OER.In addition to the admirable OER activity and stability,the bifunctional 3D ?-Fe2O3@Ni2P/Ni(PO3)2/NF delivered cell voltages of 1.93,2.48,and 3.02 V at 100,500,and 1000 mA cm-2 toward overall water splitting,respectively.A novel binary hybrid of strongly coupled crystalline a-Ni(OH)2 with amorphous reduced FeOOH heterostructure coated on 3D Ni foam(NF)was developed via a fast reduction method.In such a hybrid system,the r-FeOOH/?-Ni(OH)2 with-10 nm particle sizes was uniformly grown on the surface of the 3D NF.The resulted 3D r-FeOOH/?-Ni(OH)2/NF,possessing strong coupling effects,exhibited excellent OER performance in basic electrolyte with low potentials of 1.54 V under 100 mA cm-2,1.62 V under 1,000 mA cm-2,and 1.66 V under 1,500 mA cm-2,respectively,which are almost the lowest potentials among all previously reported Ni-Fe-based OER electrocatalysts,even exceeding benchmark Ir/C.The real active phase for the OER was NiOOH species confirmed by ex-situ X-ray photoelectron spectroscopy(ex-suit XPS)and in-situ electrochemical Raman spectra.Furthermore,bifunctional 3D r-FeOOH/?-Ni(OH)2/NF delivered the cell voltages of 2.32 and 2.78 V under 500 and 1,000 mA cm-2 respectively for overall water splitting.In this paper,the oxygen evolution reaction performance at large current densities was improved by 3D Ni-Fe-based electrocatalysts,inspiring a way to synthesize Ni-Fe-based hybrid toward the energy conversion applications,such as hydrogen evolution reactions,nitrogen reduction reactions,and CO2 reduction reactions.