Construction And Performance Of Highly Active Transition Metal-based Oxygen Evolution Electrocatalyst

Nowdasys,the energy crisis and environmental issues have attracted great attention from human beings,so the development of new energy is urgent.The technology of producing hydrogen by water splitting is more and more popular among researchers.One of the half reactions of water splitting is oxygen evolution reaction?OER?.OER is a slow four-electron reaction,and its slow reaction rate will limit the efficiency of water splitting to generate H₂.Noble metals such as Ir and its compounds are active OER electrocatalysts with excellent performance,but high cost and insufficient resources,resulting in a limited range of applications.Recently,research on low-cost transition metal-based catalysts has become a hot spot.Numerous studies have confirmed that the OER performance of the transition bimetallic compound electrocatalyst is better than that of the corresponding single metal compounds.In addition,combining the catalyst with nickel foam?NF?with high electrical conductivity,greatly increases the rate of electron transport,which can further improve the activity and stability of the material.The catalytic performance of the double transition metal compounds still has much room for improvement.In this paper,modification methods such as non-metal P element doping,heterostructure construction,and introduction of Fe are used to construct ternary transition metal compounds.These are three methods to further improve the catalytic activity of cobalt-nickel bimetallic compounds.The specific research contents are as follows:?1?P-doping is an effective strategy to improve the OER performance of the catalysts.In most literatures,P-doped catalysts are bulk doped,and the effect of P doping on the surface of the catalyst for OER has not been reported.In this paper,a three-step method?hydrothermal+calcination+phosphating?was used to synthesize P-doped nickel cobaltate on the NF substrate?P-NiCo₂O₄/NF?and study its OER performance.The P element was successfully modified on the surface of NiCo₂O₄nanowires was proved by the result of XRD and XPS.In 1 M KOH,the P-NiCo₂O₄/NF electrode has an overpotential of 279 mV at a current density of 10 mA cm^-2,which is better than NiCo₂O₄/NF?310 mV?.And long-term electrolysis experiments show that the P-NiCo₂O₄/NF electrode has good stability.In addition,the P-NiCo₂O₄/NF||P-NiCo₂O₄/NF electrode requires 1.68 V to achieve a current density of 10 mA cm^-2 and it also exhibits excellent stability.These results indicate that surface phosphating is an effective method to improve the OER performance of NiCo₂O₄/NF electrode materials.?2?A heterostructured Ni₃S₂-Co₉S₈ nanowires was fabricated on the NF substrate by using a simple two-step hydrothermal method.This heterostructure can form a large number of OER active sites.Electrochemical characterization show that the Ni₃S₂-Co₉S₈/NF electrode exhibits excellent OER activity in 1 M KOH,requiring only 294mV to achieve a current density of 20 mA cm^-2.This may be attributed to the defect hetero-interface between Co₉S₈ and Ni₃S₂ nanocryatal grains with excellent electrical conductivity.Furthermore,Ni₃S₂-Co₉S₈/NF electrode has excellent stability for a total of 60 h.This method of preparing Ni₃S₂-Co₉S₈ heterostructure catalyst can provide some inspiration for the design of non-precious metal electrocatalysts.In addition,the electrocatalytic oxidation performance of H₂O₂ on Ni₃S₂-Co₉S₈ electrode was studied.The results indicate that the-OOH oxidation step in the OER four-electron reaction of the Ni₃S₂-Co₉S₈/NF electrode is a fast kinetic process,not the rate-determining step.?3?A FeNiCo ternary transition metal compound catalyst(Fe_x Ni_1-xCo₂-S,x=0,0.25,0.5,1)was synthesized on NF by a two-step hydrothermal method.And the OER performance of Fe_xNi_1-xCo₂-S/NF electrodes was studied in 1 M KOH.The results of XRD,TEM and XPS show that Fe_xNi_1-xCo₂-S is a mixture of Co₅(O_9.48H_8.52)NO₃ with low crystallinity and S-containing amorphous compounds.Fe_xNi_1-xCo₂-S/NF electrode has excellent OER catalytic activity.Among them,Fe_0.5Ni_0.5Co₂-S/NF has the best OER performance,the overpotentials at the current density of 50 and 100 mA cm^-22 are only228 and 250 mV.The performance of this electrode is superior to most reported transition metal catalysts.At the same time,Fe_0.5Ni_0.5Co₂-S/NF electrode has good electrochemical stability.