Preparation And Electrocatalytic Properties Of Three Dimensional Porous Transition Metal Based Phosphorus/Sulfur Nanoelectrodes

The increasing depletion of traditional fossil fuels and the issues involved in environmental pollution have caused an urgent demand for exploring clean and sustainable energy resources.Hydrogen（H₂）as a promising green energy is an ideal energy carrier to replace fossil fuels due to its advantages of possessing both high combustion heat and high energy capacity over the other fuels.Water electrolysis is a significant approach to produce hydrogen among all the technologies for generating hydrogen.However,the bottleneck of high energy consumption and low efficiency in the process of water electrolysis needs to be solved urgently.It is one of the effective aproaches to improve the electrolysis water efficiency by designing highly efficient electrocatalysts to reduce high overpotential toward either the electrochemical hydrogen evolution reaction（HER）on the cathode or the oxygen evolution reaction（OER）on the anode.In this paper,the preparation and electrocatalytic performances of non noble metal electrode materials for water splitting were systematically reported.The main results are as follows:（1）A three-dimensional self-supported ternary NiS-Ni₉S₈-NiSe nanorod（NR）array has been successfully in situ constructed by a two-step facile hydrothermal route on nickel foam（NF）.The as-synthesized NiS-Ni₉S₈-NiSe-NR array cathode only requires overpotentials as low as 120 and 112 mV to drive 10 mA cm^-2 for hydrogen evolution reaction in 0.5 M H₂SO₄ and 1.0 M KOH solution,respectively,demonstrating optimized electrocatalytic activity and long-term durability.Density functional theory calculation（DFT）reveals that after Se doping Se 3d orbitals are bonded to Ni 3d orbitals and S p orbitals near Fermi level,attesting a significant electron transfer between nickel and selenium atoms.（2）The NiO/NF nanoparticle（NP）precursor was obtained through anodizing and calcining treatment,followed phosphating reaction with sodium hypophosphite and red phosphorus,Ni₂P/NF NPs and Ni₅P₄-NiP₂/NF nanosheet（NS）array were sucessfully fabricated,respectively.On the basis of optimal experiments with anodizing temperature,we found that electrodes anodized of 20 min demonstrate optimized electrocatalytic performance,and the order of catalytic activity was Ni₅P₄-NiP₂/NF>Ni₂P/NF>NiO/NF.Moreover,as-prepared Ni₅P₄-NiP₂/NF NSs array not only exhibits excellent electrocatalytic properties and stability for hydrogen evolution and oxygen evolution in three-electrode system,but displays exceptionally high electrocatalytic activity toward overall water splitting in two-electrode configuration.The Ni₅P₄-NiP₂/NF//Ni₅P₄-NiP₂/NF system only requires cell voltage of 1.47 V to attain current density of 10 mA cm^-2 and catalytic performance shows negligible degradation under continuous electrolysis for 8hours,corroborating an admirable long-term durability for water splitting.（3）Cu₂S rhombic dodecahedra（RD）particles were prepared through a simple hydrothermal method on copper foam（CF）,and the effects of reaction temperature,time and ratio of reactants on catalytic performances were employed.It was found that as-prepared Cu₂S/CF RDs obtained under the condition of 180℃for 9 h with S/Cu molar ratio of 5 exhibit optimized bifunctional electrocatalytic performances for HER and OER.In addition,two pieces of Cu₂S/CF RDs were directly used as both the anode and cathode to practically electrocatalyze water splitting.The Cu₂S/CF//Cu₂S/CF system offers catalytic current density of 10 mA cm^-2 at a cell voltage of 1.72 V and exhibits excellent stability for full water splitting.