Transition Metal/Porous Carbon Composites:Preparation And Electrocatalysis Application

Porous carbon is often used as a carrier material for catalysts because of its good electrical conductivity,large specific surface area,and excellent chemical stability.Precious metal materials currently have excellent catalytic effect.However,their high expense and poor stability severely hamper their large-scale applications.Therefore,the development of non-precious metal catalysts,especially transition metal catalysts,has become one of the research hotspots in the field of electrochemistry.The purpose of this paper is to prepare several transition metal/porous carbon composites.The unique porous structure of porous carbon is beneficial to improve the dispersion of transition metals,expose more active sites,and improve the catalytic performance of composites.Moreover,transition metal is encapsulated into porous carbon that can increase stability during the catalytic process or during the pickling.In this paper,several transition metal/porous carbon?such as graphene aerogel,porous carbon fiber and macroporous carbon?composites were prepared,including nickel nitride supported on graphene aerogel?Ni₃N/GA?,zirconium-based metal-organic framework?zirconium ion as the center and iron porpHyrin as ligand?loaded onto large pore carbon?Zr-PorMOF/MPC?,cobalt-iron selenide supported on porous carbon fiber?CoFe₂Se₄/PCF?,and iron-cobalt alloy supported on porous carbon fiber?FeCo@PCNF-T?.These composite modified electrodes were used as electroanalysis and used in oxygen reduction.The main content is follows:?1?We prepared a novel enzyme-free glucose and hydrogen peroxide?H₂O₂?sensor based on Ni₃N nanoparticles on conductive 3D graphene aerogels?Ni₃N/GA?.The Ni₃N/GA has been successfully synthesized by using hydrothermal reaction,freeze-dried and then calcined under NH₃ atmosphere.The obtained Ni₃N/GA composites were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray pHotoelectron spectroscopy?XPS?,nitrogen adsorption-desorption isotherms.The results demonstrate that 3D GA has an interconnected macroporous framework and could provide multidimensional electrons/ions transport pathways,which is advantageous for electrons/ions passing.Secondly,3D GA carrier could effectively prevent the aggregation of Ni₃N particles,which increase active sites for electrocatalysis.The results show the obtained3D Ni₃N/GA composites exhibit excellent electrochemical performance toward glucose oxidation and H₂O₂ reduction with larger catalytic rate constant K_cat value of 3.75×10³ M^-1 s^-1 and 1.24×10³ M^-1 s^-1,respectively.As a glucose sensor,the obtained electrode provides a wide detection range of 0.1-7645.3?M,fast response time within 3 s,high sensitivity of 905.6?A mM^-1 cm^-2 and low detection limit of 0.04?M.For detection of H₂O₂,this prepared sensor offers a wide detection range?5?M-75.13 mM?,fast response time?within 5 s?,sensitivity(101.9?A mM^-1 cm^-2)and low detection limit?1.80?M?.This enzyme-free glucose and H₂O₂sensor display satisfactory selectivity,reproducibility and long-term storage stability.Additionally,the sensor can also be used for glucose and H₂O₂ detection in human blood serum.?2?We prepared a Zr-PorMOF/MPC composite by a simple one-step solvothermal method through growing Zr-PorMOF on macroporous carbon?MPC?.Porphyrin-base MOFs combining the structural adjustable of MOFs and the specific catalytic activity of biomimetic catalysts play an important role in electrocatalysis.A series of characterization show that the roles of MPC as follow:Firstly,MPC could avoid the agglomeration of Zr-PorMOF particles and increase the specific surface area;Secendly,MPC could improve the electrochemical stability of Zr-PorMOF particles;At last,MPC could reduce the electron transfer resistance.Therefore,MPC plays the role of the conductive bridges to provide facile charge transport.The obtained Zr-PorMOF/MPC composites exhibit much better electrocatalytic activity for the reduction of hydrogen peroxide?H2O2?than the pristine Zr-PorMOF due to the synergy of Zr-PorMOF and MPC.This enzyme-free H2O2 sensor shows two linear relationships in the ranges 0.5–137?M(R²=0.991,sensitivity=66?A mM^-1)and 137-3587?M(R²=0.993,sensitivity=16?A mM^-1),with a low over-potential at-0.2 V,a fast response time within 1 s and a low limit of detection of 0.18?M.Moreover,Zr-PorMOF/MPC composites were used to simultaneously detect uric acid?UA?,xanthine?XA?and hypoxanthine?HX?.These three substances are degradation products of purine metabolism.In addition,Zr-PorMOF/MPC composites can be used to develop multifunctional biosensors.?3?We prepared a novel pHenolic sensor based on CoFe₂Se₄/PCF.The CoFe₂Se₄/PCF has been successfully prepared by using electrospinning[Polyacrylonitrile?PAN?/Prussian blue analogues/CaCO₃]and then calcined under atmospHere of selenium powder.The results demonstrate that the skeleton of the porous carbon fiber prevents aggregation of CoFe₂Se₄nanoparticles and can expose more active sites.In addition,porous carbon fibers provide a continuous conductive path that promotes material and electron transport.The results show the obtained 3D CoFe₂Se₄/PCF nanocomposite exhibits excellent electrochemical properties while simultaneous testing of HQ,CC and RS.The obtained electrode provides wide detection ranges of 0.5–200?M,0.5–190?M and 5–350?M and low detection limit of 0.08?M,0.15?M and 1.36?M for HQ,CC and RS,respectively.The as-prepared pHenolic sensor displays satisfactory selectivity,reproducibility and long-term storage stability.In addition,the sensor can also be used for HQ,CC and RS detection of actual samples.?4?We prepared a novel ORR electrocatalyst of iron-cobalt?FeCo?alloy nanoparticles embedded on N-doped porous carbon nanofibers?FeCo@PCNF-T?by electrospinning of[PAN/Prussian blue analogues/CaCO3]and post-calcination treatment.The obtained catalysts with bimetallic active sites show unique three-dimensional?3D?hierarchical meso/macropores structures.FeCo alloy nanoparticles are encapsulated into graphitic carbon that can increase stability and provide additional catalytic active sites.Under the optimized condition,FeCo@PCNF-800 displays excellent ORR electrocatalytic activity in alkaline solutions,with a more positive half-wave potential(E_1/2 of 0.854 V vs RHE)and larger limited-diffusion current density(j of 6.012 mA cm^-2)than those of 20 wt.%Pt/C(E_1/2 of0.849 V and j of 5.710 mA cm^-2).In addition,FeCo@PCNF-800 also exhibits comparable ORR electrocatalytic activity in acidic solutions to those of 20 wt.%Pt/C with onset potential and half-wave potential as more positive as 0.843V vs RHE and 0.739 V vs RHE,respectively.Moreover,FeCo@PCNF-800 exhibits excellent tolerance towards methanol,stability and a four-electron pathway in both basic and acidic solutions.The excellent ORR electrocatalytic activity performance of FeCo@PCNF-800 is attributed to the synergistic effect of the FeCo alloy nanoparticles and N-doped porous carbon nanofibers.The synergistic effect can improve the mass and charge transport capability and increase active sites of FeCo-N-C.Furthermore,this work offers a new insight for the reasonable design and development of efficient non-noble metal electrocatalysts for challenging electrochemical energy-related technologies.