Study On Preparation And Performance Of Non-noble Metal Electrocatalysts

With the fast development of the economy,fossil energy depletion and environmental degradation are major problems facing mankind in this century.Researchers have been committed to developing new,green and environmentally friendly clean energy sources to solve the current serious energy and environmental problems from the source.Fuel cells,zinc-air batteries,and water splitting are considered as promising energy conversion and storage devices.Currently,most of the electrochemical reactions involved in the above devices require noble metals(Pt,RuO2,IrO2,etc.)as catalysts,and the high cost of the catalysts limits the rapid development of corresponding devices.In this respect,research and development of non-precious metal electrocatalysts to substitute noble metal catalysts is one of pivotal issues that need to be urgently solved.This thesis mainly carried out the research on synthesis and regulation of non-noble metal catalysts(including Fe,Co,Ni,Cu,etc.),and further investigated the application of the prepared electrocatalysts in oxygen reduction reaction(ORR),oxygen precipitation reaction(OER)and hydrogen reduction reaction(HER).The main contents and innovations are:1.The surfactant-assisted method was used to synthesize the single atom iron catalyst(labeled as SA-Fe/NG).In acidic media,the half-wave potential of SA-Fe/NG was only 30 mV lower than 20 wt%Pt/C,while in alkaline media it was 30 mV higher than 20 wt%Pt/C.The proton exchange membrane fuel cell assembled based on the SA-Fe/NG catalyst exhibited a high power density of 823 mW cm-2.The combination of experimental results and density functional theory(DFT)calculations revealed that the origin of high ORR activity of SA-Fe/NG was from Fe-pyrrole-N species.2.The surfactant-assisted method was used to synthesize an electrocatalyst with single atom cobalt dispersed on nitrogen-doped graphite nanosheets(labeled as CoN4/NG).The CoN4/NG catalyst exhibited excellent electrocatalytic activity.The half-wave potential of the ORR was 0.87 V(vs.RHE),and for OER,only 380 mV overpotential was required to reach 10 mA cm-2.In addition,liquid zinc-air batteries and flexible zinc-air batteries using CoN4/NG catalyst as air electrodes both exhibited excellent charge-discharge performance,large power density,and long-term stability.3.The surfactant-assisted method was used to synthesize a single atom copper(labeled as SA-Cu/NG)electrocatalyst.The catalyst had higher ORR catalytic performance than 20 wt%Pt/C in alkaline solution.Experimental results and DFT calculations confirmed that the atomic configuration of SA-Cu/NG was a mononuclear copper ion coordinated by two nitrogen and two carbon atoms(Cu-N2C2)embedded in a graphene substrate.DFT reveals the reconstruction of Cu-N2C2 surface active sites in the basic ORR process,which was caused by the dynamic adsorption of atomic oxygen(O*)intermediates on the Cu-C site(labeled Cu-N2C2-O).Theoxygen-reconstructed Cu-N2C2-O structure was the true active species of ORR in alkaline medium.4.Co,N co-doped carbon nanotube/graphene heterostructure bi-functional ORR and HER catalyst(Co/NCNT/NG)was synthesized by a one-dimensional/two-dimensional(1D/2D)hybrid strategy.Co/NCNT/NG heterostructure catalysts not only showed an ORR half-wave potential of 0.85 V(vs.RHE),but for acidic HER,the low overpotential at a current density of 10 mA/cm2 was 123 mV.The excellent performance of the Co/NCNT/NG catalyst was attributed to the unique 1D/2D carbon nanotube/graphene heterostructure,in which the 1D and 2D structures provided different catalytic active sites for HER and ORR(including metal Co,CoNx and NC).5.To successfully synthesize FeNi alloy and nitrogen co-doped porous carbon(FeNi-NC)electrocatalyst,peanut shell was used as the precursor and a small amount of iron and nickel salts were added as non-noble metal sources.The catalyst showed an ORR electrocatalytic activity similar to that of 20 wt%Pt/C.At the same time,it also had satisfactory OER performance.Furthermore,the self-made zinc-air battery using FeNi-NC as an oxygen electrode had an excellent charge-discharge performance and long-term cycle stability,which was better than a 20 wt%Pt/C+IrO2 based battery.6.Growth of vertical CoTe and NiTe nanoarrays on nickel foam(labeled as CoTeNR/NF and NiTeNR/NF)as bifunctional OER and HER electrocatalysts.Under alkaline conditions,CoTeNR/NF catalyst not only possessed excellent OER performance(low overpotential of 350 mV to drive current density of 100 mA/cm2),but also had excellent HER activity(only 202 mV overpotential can reach the current density of 10 mA/cm2).We also combined experimental results with DFT to discover that the real OER active site was derived from the in-situ generated β-CoOOH(1014)species,which successfully illustrated the bottleneck of the true active site of metal telluride.