Study Of Ni₃S₂ Electrocatalysts On Oxygen Evolution Performance

Hydrogen energy has gradually received essential attention from energy industries worldwide in recent years.Hydrogen production from electrolytic water splitting is expected to be the best way to produce hydrogen energy on a large scale due to its greater efficiency and higher purity of hydrogen production.Ru O₂ and Ir O₂are the noble metal-based oxygen evolution reaction（OER）catalysts with the most mature process.However,their high cost,scarce reserves,and poor stability have seriously hindered their wide application.Alternatively,transition metal catalysts could balance the cost and properties,which are the promising electrocatalytic OER materials for large-scale applications.Among these,transition metal sulfide electrode materials are important owing to their abundant reserves,unique structural features,and tunable electronic structures.Ni₃S₂ electrocatalysts have extensively been studied owing to their high Ni metal contents and unique physicochemical properties.However,the following issues still limit its further application as an electrocatalyst:1)the charge from the guest hydrogen evolution reaction（HER）material must cross the heterogeneous interface to reach the Ni₃S₂ during the electrolytic water splitting,which slows down the overall charge transfer rate;2)how to apply the simple and low cost means to increase the proportion of high-valent metals in the Ni₃S₂ to facilitate the conversion of the surface portion to the actual active phase Ni OOH during the OER process,as well as increasing the active surface area.Therefore,to solve the above issues,heterostructure engineering,electronic structure modulation engineering,and morphology modulation strategies are employed to improve the electrolytic water splitting performance.The details of the study are as follows:（1）A low-cost,efficient,and stable bifunctional Fe₅Ni₄S₈/Ni₃S₂ electrocatalyst was obtained by integrating Fe₅Ni₄S₈ with HER activity into Ni₃S₂ nanoarrays using a hydrothermal method.The hydrophilicity of pretreated Fe₅Ni₄S₈ was quite high,whereas the rod-shaped Ni₃S₂ structure had a large number of radial active sites.Additionally,the high-conductivity of Fe₅Ni₄S₈ and nickel foam provided a double-channel structure for rapid internal charge transfer.Ultimately,Fe₅Ni₄S₈,rod Ni₃S₂nanoarrays,and nickel foam substrates form an interconnected network-like structure,which facilitates the catalytic activity of OER,HER,and enhances the reaction kinetics of overall water splitting.To achieve a current density of 10 m A cm^-2 in 1.0M KOH solution,only overpotentials of 248 and 94 m V were required.Moreover,the voltage of the constructed Fe₅Ni₄S₈/Ni₃S₂||Fe₅Ni₄S₈/Ni₃S₂ double-electrode battery system was only 1.64 V@10 m A cm^-2,but the battery could have run for at least 120h at an industrial current density of 500 m A cm^-2.Therefore,this work proposes a rational heterogeneous structure design strategy for bifunctional electrocatalysts applied to overall water splitting.（2）High OER activity electrocatalysts were obtained by co-doping Co/Fe metals into Ni₃S₂ via a simple single-step hydrometric method by adjusting the ratio of bimetal doping.A series of characterization revealed that the introduction of Co/Fe co-dopant increased the active sites and improved the electroconductibility,while the electronic structure of Ni₃S₂ was optimized.Meanwhile,Fe-induced high-valence Ni contributed to the production of the OER active phase Ni OOH.The unique dendritic crystal morphology facilitated the disclosure of the active sites and expansion of mass transfer channels.The optimized sample required a low overpotential of 146 m V to excite a current density of 10 m A cm^-2 in 1.0 M KOH solution.The optimized sample also operated stably for at least 86 h.This work provides new research ideas for designing efficient,stable,and low-cost non-precious metal catalysts with high electrical conductivity and multiple active sites.