The Synthesis Of Fe-Based Single Atom Catalysts Based On Biomass-Derived Carbon And Industrial Spend Acid For Oxygen Reduction Reaction

The excessive consumption of fossil fuels has resulted in energy shortage and climate change.Therefore,it is urgent to develop efficient clean energy technologies to reduce the reliance to fossil fuels.In recent years,metal-air batteries have been considered as highly promising clean energy conversion devices.Among them,zinc-air batteries（ZAB）feature the advantages of environmental friendliness,low cost as well as toxic substances-free.Nontheless,the slow kinetic process of oxygen reduction reaction（ORR）in ZABs greatly hinders their energy conversion efficiency,which requires to be promoted by catalysts.As a benchmark for ORR catalysts,precious metal-based catalysts,e.g.Pt/C,suffer from resource scarcity and high cost,which largely limit their large-scale application.Therefore,non-noble metal catalysts with high electrocatalytic activity and stability have gained great attraction.Currently,transition metal single-atom catalysts（SACs）,with M-N-C structures（M=Fe,Co,Ni,Cu,Zn,etc.）exhibiting good catalytic performance,is considered as one of the most promising materials to replace precious metal catalysts among all reported non-precious metal-based electrocatalysts.Usually,the precursors containing metals and carbon materials containing nitrogen are widely used for the synthesis of M-N-C SACs.Here,we designed a greener and more effective strategy for SAC preparation using inexpensive biomass materials as nitrogen-containing carbon precursors and industrial waste acid（SA）as an iron source.The main research contents are as follows:（1）Preparation and ORR performance of porous iron based SAC（Si O₂/Si-FeNSC）derived from coffee grounds and industrial waste acids.In this system,Si O₂/Si-FeNSC single-atom catalyst has been prepared using coffee grounds（CW）and industrial waste acid（SA）as precursors.The Si O₂/Si-FeNSC was characterized by a series of characterization methods,and the results showed that Si O₂/Si-FeNSC possess high specific surface area and Fecontent with monoatomic dispersion.In addition,the catalyst exhibited excellent electrocatalytic performance with the half-wave potential E_1/2=0.889 V vs.RHE,the Tafel slope of 60.34 m V dec^-1,the power density of 196m W cm^-2 and a stable charge/discharge of more than 280 h at a current density of 5 m A cm^-2.The electrocatalytic activity and stability of the catalyst were far superior to those of commercial Pt/C catalyst.Importantly,as cheap and readily available raw materials,CW and SA can be used to prepare high-performance Fe-N-C monoatomic catalysts,which have important application values.（2）Preparation and ORR performance of porous iron based monoatomic catalyst（FeNC-SAC-LS）derived from lotus seed and industrial waste acid.We report a green and economical strategy to prepare Fe-N-C SACs for efficient ORRs using iron-containing industrial SA and lotus clips（LS）as raw materials.SA has two unique advantages in the reaction process.First,Fe³⁺can act as Lewis acid to hydrolyze the lignin in LS and act as"scissors"to cut some of the molecular bonds of lignin,generating abundant defects.Second,the iron source of SA is embedded in the microchannels.After high temperature pyrolysis,Feions can be further immobilized in the LS carbon matrix.The synthesized FeNC-SAC-LS catalyst with a half-wave potential of 0.866 V vs.RHE,which was attributed to its high specific surface area,hierarchical porous structure and highly accessible single-atom active sites.The ZAB assembled using the FeNC-SAC-LS showed high power density(140.2 m W cm^-2)and long-term stability.（3）Preparation and ORR performance of porous Iron based monoatomic catalyst（FeNC-SS）derived from shrimp shell powder and industrial waste acid.In this work,shrimp shell and SA were used to prepare a cheap and stable ORR catalyst,which was applied to the air cathode of ZAB.The FeNC-SS exhibited high electrocatalytic activity,with the half-wave potential of up to 0.858 V vs.RHE and a Tafel slope of 58.97 m V dec^-1.The ORR kinetic process of electrocatalysts was investigated by rotating ring disk electrode（RRDE）test,and the four-electron reduction pathway was pointed out,which was also experimentally verified by RRDE voltammetry.The average electron transfer number for each reduced oxygen molecule was calculated to be about 3.98,surpassing most literature reports.This experiment achieved waste utilization and provided a simple and environmentally friendly strategy for preparing SACs.