Interface Design Of Transition Metal Based Catalytic Electrode And Its Application In Water Splitting

The technology of splitting water to produce hydrogen makes it possible for orderly mitigation of many problems induced by the massive burning of fossil fuels,such as the greenhouse effect,to achieve the overall goal of carbon peak and carbon neutrality.However,the reaction involved in this technique is kinetically slow and occurs at a high.Recently,Pt and Ir/Ru noble metals are used to catalyze the hydrogen evolution and oxygen evolution semi-reactions（HER and OER）in industry,respectively.But the scarcity and high cost of noble metals limit their long-term large-scale application.Therefore,it is particularly important to explore efficient and cheap non-noble metal catalysts.In this paper,layered double hydroxide（LDHs）is used as the entry point,nickel foam（NF）is used as the substrate,LDHs type free-standing electrodes were synthesized through a simple one-step electrodeposition method.The free-standing electrodes can not only improve the low conductivity of LDHs effectively,but also avoid the use of binder,simplify the electrode preparation process and reduce the cost.Furthermore,compared with the hydrothermal method,a commonly adopted way for LDHs synthesis,the preparation time of this method is greatly shortened.Meanwhile,the experiment focused on metal doping.The loading and electron density of LDHs were adjusted by optimizing deposition time and doping concentration,respectively.And the synergistic effect of polymetals was utilized to improve the HER and OER performance of LDHs.The specific contents are as follows;1.CoFeLDHs was applied to OER catalysis.The Ni/CoFeLDH electrode with deposition time of 200 s has the highest OER catalytic activity.Overpotentials at 50 and 100 m A cm^-2 are324 and 333 m V,respectively.SEM and TEM images show that the morphology of CoFeLDHs is nanosheet with array structure.Amorphous MOOH（M=Co,Fe）was reconstituted from CoFeLDHs nanosheets after OER.Compared with the OER catalytic performance and XPS of CoFeLDHs powder catalyst,the higher catalytic activity of Ni/CoFeLDH is mainly attributed to the interface electron coupling effect between CoFeLDHs catalyst and NF substrate.In addition,its high OER catalytic activity is also closely related to good wettability.2.Cr doped CoFeLDHs was synthesized by one-step electrodeposition and applied to HER catalysis.The CoFeCrLDH electrode with the optimized deposition time of 100 s and the doping concentration of 10%has the highest hydrogen evolution activity.At the current output of 10 m A cm^-2,the overpotential of CoFeCrLDH electrode is only 201 m V while the CoFeLDH electrode needs 234 m V.The Co peaks in the CoFeLDH are shifted by the introduction of Cr,which confirms the synergistic electronic interaction between metal ions.Meanwhile,Cr doping produces a large number of oxygen defects.Both are the main reasons for the improvement of hydrogen evolution activity.3.Cr and Fe（II）doped Ni Zn LDHs were synthesized and applied to HER and OER catalysis.Both the doping of Cr and Fe can improve the catalytic performance of HER and OER of Ni Zn LDHs.Among them,Cr-Ni Zn LDH electrode with deposition time of 200 s and doping concentration of 2%has the highest catalytic activity of both HER and OER.The overpotentials of HER and OER to reach the current density of 50 m A cm^-2 are 266 m V and292 m V,respectively.Cr doping causes Ni Zn LDH to produce more high-valence cations and oxygen vacancies,which increases the number of active sites and accelerates the process of electron transfer.After analysis,MOOH（M=Ni）reconstitution also occurs in Cr-Ni Zn LDH during OER.This work provides a new idea for simplifying the preparation process of efficient LDHs electrocatalysts.