Metal Organic Frameworks Based Electrocatalysts For Oxygen Reduction And Hydrogen Evolution Reaction:preparation And Characterization

Herein,a facile and efficient strategy for achieving stable Fe and Co single atoms catalysis anchoring on nitrogen-doped porous carbon??Fe,Co?SACs/N-C?with large surface area(764.7 m²g^-1)and high metal loading?1.6 wt.%?is reported.First,Fe?III?through one-step jointly nucleate with a pre-designed bimetallic Zn/Co metal organic framework?BMOF?to form Fe?acac?₃@ZnCo-BMOF,and then?Fe,Co?SACs/N-C is obtained by pyrolysis and sequential reduction process,during which BMOF is transformed into nitrogen-doped porous carbon matrix.The obtained?Fe,Co?SACs/N-C exhibit good ORR performance with a half-wave potential?0.72 V?that is slightly negative compared with commercial Pt/C?0.81 V?in 0.1 M HClO₄,in 0.1 M PBS,half-wave potential of this catalyst is 0.81 V.More importantly,under alkaline conditions?0.1 M KOH?,the half-wave potential of this catalyst is 0.85 V,20 mV positive than commercial Pt/C?0.83 V?.At the same time,we also explore that the difference activity in acidic and alkaline conditions maybe attributed to the protonation of pyridine N.Kinetics studies had been found that the electrocatalytic reaction of?Fe,Co?SACs/N-C was a fast 4-electron process in acidic,neutral and alkaline electrolyte,which was essential for good ORR catalytic performance.More importantly,even after3000 cycles scanning,the half-wave potential of?Fe,Co?SACs/N-C only had 13 and 7mV decrease in acidic and alkaline electrolytes,respectively,which demonstrated its superior stability.Furthermore,?Fe,Co?SACs/N-C had excellent tolerance to methanol crossover in both acidic and alkaline environments.The outstanding performance,which was comparable to commercial Pt/C,?Fe,Co?SACs/N-C catalyst with potential application prospect for PEMFCs and metal-air batteries.Moreover,the established facile one-step joint nucleation method can play an exemplary role for the preparation of other bimetallic single atom materials.By using UIO-66 as the precursor,porous FeP@PC was prepared by chemical vapor deposition of FeCl₃,in-situ carbonization,phosphating and HF etching.The morphology,crystal structure,elemental composition and valence states of FeP@PC were characterized by field emission transmission electron microscopy?FE-TEM?,X-raydiffraction?XRD?,X-rayphotoelectronspectroscopy?XPS?and Brunauer-Emmett-Teller?BET?measurements.Results showed that FeP@PC maintained the original porous nano-octahedral structure and had a high specific surface area of 83 m²g^-1.For linear sweep voltammetry and electrochemical impedance spectroscopy measurements,the catalyst FeP@PC only needed overpotential of 156 mV to driven current density of 10 mA cm^-2.Meanwhile,the Tafel slope,the electron-transfer resistance and the electrochemically active surface area of the catalyst were calculated to be 84 mV dec^-1,44?and 13.9 mF cm^-1,respectively.In order to evaluate the durability and stability of the catalyst,12 h-chronoamperometry and1000-cycle cyclic voltammetry measurements were also conducted and no obvious activity decay was observed.The remarkable electrocatalytic activity and stability were not only ascribed to porous nature and the high surface area of the catalyst,but also to the protection affects of the carbon shell for FeP particles.In short,FeP@PC exhibited comparable HER activity to most non-noble metal catalysts for hydrogen evolution and the strategy by introduction of other metal active sites into MOFs provide new enlightenment for development of HER catalysts.