Application Of MOF-based Bimetallic Electrocatalysts In Oxygen Evolution Reaction

As the rate-limiting reaction of water electrolysis,oxygen evolution reaction（OER）requires the high-efficiency,stable and low-cost non-noble metal-based catalysts to replace noble metal-based catalysts.Metal-organic frameworks（MOFs）are used to catalyze OER due to their high porosity and abundant active sites.However,the inherent defects of poor conductivity and stability limit its catalytic activity for OER.Therefore,exploring suitable preparation methods to improve the conductivity of MOFs and derivatizing MOFs are the effective strategies to improve the catalytical activity of MOF.In this paper,around the electrochemical preparation of bimetallic MOF electrocatalysts,the synthesis of MOF and its derivatives is explored and their application to electrocatalyze OER is also investigated.The details are as follows:（1）Iron cobalt bimetallic MOF,FeCo-BTC_cdep and FeCo-BTC_adep,supported by the nickel foam（NF）were in-situ prepared by cathodic electrodeposition（CE）and anodic electrodeposition（AE）,respectively.The effects of deposition potential,deposition time and Fe/Co metal composite ratio on the morphology,structure and electrochemical properties of FeCo-BTC_cdep were systematically discussed.The effects of scanning cycles,deposition potential and deposition time on the electrochemical properties of FeCo-BTC_adep.And the difference in morphology,structure and electrochemical activity between FeCo-BTC_cdep and FeCo-BTC_adep was discussed.The experimental results show that when the deposition potential is-1.3 V,the deposition time is 40 min,and the Fe/Co molar ratio is 2:1,FeCo-BTC_cdep has the best electrochemical activity.When j is 10 m A·cm^-2,the OER overpotential is only169 m V,and the Tafel slope is 58.4 m V·dec^-1,which FeCo-BTC_cdep has the higher electrocatalytical activity than FeCo-BTC_adep.This is attributed to the enhanced mechanical stability and electrical conductivity from the in-situ preparation of MOFs,the good intrinsic activity from the Fe/Co synergy,and the large specific surface area and rapid ion transport from the porous structure of the MOF materials.（2）A two-dimensional sheet bimetallic MOF,FeNi-CA/NF,was prepared via CE method.The effects of deposition potential,deposition time and Fe/Ni metal composite ratio on its electrocatalytic OER activity were explored.When the deposition potential is-1.6 V,the deposition time is 30 min,and the Fe/Ni molar ratio is 1:1,FeNi-CA/NF has the best electrochemical activity.The Tafel slope is 86.1m V·dec^-1.When j is 10 m A·cm^-2,the OER overpotential is 216 m V.To improve the poor conductivity of MOFs,FeNi-CA/NF was derivatized.FeNi-CA/NF was oxidized via high temperature calcination to obtain NiFeO/NF.The effect of calcination temperature on the morphology,structure and electrochemical performance of NiFeO/NF was discussed.FeNi-CA/NF was vulcanized via the hydrothermal method to prepare FeNiS/NF.The effects of hydrothermal temperature and hydrothermal time on the electrochemical properties of FeNiS/NF were discussed.The advantages of the two-dimensional structure of MOF,the synergistic effect between MOF and oxide or sulfide in-situ transformed from MOF and the mixed valence states of Fe and Ni endow the two materials with excellent electrocatalytic activity on OER.NiFeO/NF-350 obtained from calcining FeNi-CA/NF at 350℃and FeNiS/NF-90-8 obtained by hydrothermal treating FeNi-CA/NF at 90℃for 8 h have overpotentials of 146 and 113 m V respectively when the current density reaches 10m A·cm^-2,and the Tafel slopes are 76.4 and 51.3 m V·dec^-1.Especially,the overpotential only rises to 353 and 327 m V when j reaches 100 m A·cm^-2.Moreover,the two materials also have good performance in the stability test with j higher than100 m A·cm^-2 and up to 100 h,indicating a satisfactory for application.