| With the energy shortage and water pollution becoming more and more serious,it is the primary task to seek sustainable green energy technology.Microbial fuel cell(MFC)is a new electrochemical system that directly converts the chemical energy stored by organic matter in sewage into electric energy by using the catalytic effect of electrogenic microorganisms.It has become a hot research topic in the field of environmental protection and energy in this century.However,the kinetics of the cathode Oxygen Reduction Reaction(ORR)of MFC is very slow.The performance of the cathode ORR catalyst is a key factor restricting the energy conversion efficiency and power output of fuel cells.The shortages of resources,high price and poor stability of traditional cathode precious metal catalysts(such as Pt-based catalysts)for MFC have limited the large-scale application of MFC.Therefore,the design and development of non-noble metal catalysts with high activity,good stability and low cost to replace the traditional noble metal catalysts is a hot spot in this field.At present,Co,Ni,Fe and other non-noble metal catalysts have been studied more,but their activity and stability need to be further improved to meet the requirements of industrial applications.In view of the above problems,this thesis is devoted to the study of cheap,excellent ORR performance and good stability of non-precious metal cobalt-based catalysts.The ORR performance and power generation performance of MFC are systematically studied to lay technical support for accelerating the large-scale industrial application of MFC.Specific research contents are as follows:1.Using Li Cl as the pore expanding agent,the 3D MOF structure was stripped into 2D layered structure by KCl.The Co/N-GO-T catalyst co-doped with Co and N was prepared by salt-melting pyrolysis of metal-organic framework Co0.5-Zn0.5-ZIF under nitrogen conditions.The results showed that:(1)The specific process of converting 3D MOF into 2D structure is discovered.KCl strips 3D MOF structure into 2D layered structure,and Li Cl plays the role of pore expanding.(2)With the increase of pyrolysis temperature,the total content of Grap-N and Pyri-N,which play a decisive role in the electrocatalytic activity of ORR,firstly increases and then decreases,and the generation of Co-Nx is beneficial to the improvement of the catalytic activity of cathode ORR;Pyrolysis products prepared at 800 oC have higher degree of graphitization and graphite defects,which are conducive to charge transfer in the ORR process.(3)Co0.5-Zn0.5/N-Go-800-MFC obtained a load voltage of0.62±0.05 V and a maximum power density close to that of Pt/C catalyst(0.97±0.04W·m-2),and an average COD removal rate of 95.95±0.9% and 34.66±0.7%coulomb efficiency was obtained in the sewage purification experiment.2.After self-polymerization of dopamine hydrochloride on the surface of Si O2 microspheres under alkaline conditions,ZIF-67 layers were grown on the surface to obtain multilayer spherical precursors.The hollow core-shell H-N-C@Co/N-C-3%Ni catalyst was prepared by pyrolysis-etching-impregnation-pyrolysis method.The results show that:(1)The pyrolytic carbonat-ion products have more Graph-N and Pyri-N and higher graphite carbonation and graphite defectsafter the introduction of PDA,which promote the ORR process of the catalyst.(2)Fourier-transform EXAFS spectroscopy at the Co K-edge showed a primary peak at ~1.42 ?,which corresponds to the Co-N scattering path.Fourier-transform EXAFS spectroscopy at the Ni K-edge showed a primary peak at ~2.15 ? that contributes to the Ni-Ni scattering path.(3)The current retention rate of H-N-C-@Co/N-C-3%Ni catalyst obtained by the introduction of Ni is 96.31%,which is nearly 10% higher than that of H-N-C@Co/N-C catalyst,indicating that the introduction of Ni can effectively improve the cycle stability of the catalyst for long time operation.(4)H-N-C@Co/N-C-3%Ni-MFC obtained a load voltage of 0.65±0.01 V and a maximum power density close to that of Pt/C catalyst(1.17±0.01W·m-2),and an average COD removal rate of 96.52±0.1% and 34.82±0.2% coulomb efficiency was obtained in the sewage purification experiment.3.A spherical bimetallic MOF with controllable size was synthesized by self-assembly of MOF fragments after hydrothermal treatment,and a multi-layer hollow Co-Ni alloy and N-co-doped carbon sphere catalyst(S-Co-Ni/N-C-T)were prepared by upstream and downstream pyrolysis with melamine as nitrogen source.The results showed that:(1)The lamellar bimetallic organic framework can be self-assembled into spherical S-Co-Ni-PTA-MOF under the action of structural regulator SDS,F127 and CTABby a hydrothermal reaction.(2)The total content of Pyri-N and Graph-N in the active site of S-Co-Ni/N-C-850 catalyst can be obtained by using melamine as nitrogen source at 850 oC for 3h,which can effectively improve the ORR activity.(3)Fourier-transform EXAFS spectroscopy at the Co K-edge showed a primary peak at ~1.42 ?,which corresponds to the Co-N scattering path and a wide absorption peaks of all the catalysts appear at ~ 2.22 ?,which belong to the absorption peaks of Co-Ni alloy.(4)The Co-Ni alloy effect in S-Co-Ni/N-C-850 catalyst significantly improves the stability of the catalyst,and the current retention rate reaches 96.2% after 450000 s.(5)S-Co-Ni/N-C-850-MFC obtained a load voltage of 0.63±0.03 V and a maximum power density close to that of Pt/C catalyst(1.04±0.04W·m-2),and an average COD removal rate of 96.52±1.3% and34.42±0.8%coulomb efficiency was obtained in the sewage purification experiment.4.A homogeneous hollow nanocube Co Ni alloy catalyst was prepared by ionic co-reduction precipitation method with nickel(II)acetylacetone and cobalt(II)acetylacetone as metal sources,urea as structure-directed regulator and hydrazine hydrate as reducing agent.The results show that:(1)The Co2Ni2 alloy with nano-cube structure could not be prepared by using CTAB and PVP instead of urea as structural regulator,which may be due to the failure of forming weak base solution system.(2)The Cox Niy HANCs catalyst showed wide absorption peaks at ~ 2.22 ? and ~ 2.21 ?at the near side of Fourier-transform EXAFS spectroscopy at the Co and Ni K-edge,which belonged to the absorption peaks of Co-Ni alloy.(3)The ORR stability of Co2Ni2 HANCs catalyst is extremely outstanding,and the current retention rate reaches 95.21% after 450000 s,indicating that metal alloying can effectively improve the cycle stability of the catalyst.Co2Ni2 HANCs-MFC achieved an average load voltage of 0.63±0.01 V and a maximum power density(1.03±0.01W·m-2)close to that of Pt/C catalyst.The COD removal rate of 96.27±1.2% and the coulomb efficiency of34.58±1.1% were obtained in the experiment of sewage cleaning treatment. |
PDF Full Text Request