| The shortage of energy and the worsening environmental problems have attracted wide attention.Currently,an important part of the sustainable development chain is electrochemical storage and conversion devices,such as fuel cells,electrochemical reduction of carbon dioxide,water and nitrogen.Electrocatalysts play an important role in these electrochemical reactions.As one of the leading catalysts,single-atom catalysts have become a research hotspot in the field of catalysis.However,most of the catalysts still use rare precious metals,such as Pt and Ru,which increase the manufacturing cost and hinder the large-scale production and commercial application of the catalysts.As a new,cheap and environmentally friendly carbon-based material,biomass has attracted much attention in the field of electrocatalysis.In this paper,in order to further reduce the catalyst cost,realize the efficient preparation of the catalyst and ensure its catalytic performance comparable to that of the commercial Pt/C catalyst,an electrocatalytic material with high catalytic activity and stability was prepared by combining iron with abundant biomass carbon material.The results show that the biomass carbon-based materials have their own unique structures and excellent electro-catalytic properties after being treated at different temperatures.When combined with iron（especially iron atoms）,the activity of the catalyst is further enhanced.The main research work is as follows:1.Using spores as carbon source,the carbon-based catalyst derived from biomass was obtained through one-step pyrolysis,and the N content and defect size in the catalyst were adjusted by controlling pyrolysis temperature.The results showed that the ORR activity of spore-750 was similar to that of nitrogen-doped carbon in previous literatures.Spore-1150 showed more excellent ORR activity and stability.Spore-1150had an initial potential of 0.96 V.In addition,the electron transfer number of spore-1150 was 3.9.The spore-750 electron transfer number was 3.2,indicating that the ORR process of mixing two and four electrons was experienced.2.Active metal loading on the surface of carbon materials is one of the main means to improve catalytic activity.The biomass carbon-based material（CS）derived from spores was used as the carrier to load iron to achieve better catalytic performance.Firstly,Fe@CS catalysts with different loading capacities were prepared by controlling the amount of iron source in the precursor.The optimal loading capacity was 0.98 wt%according to the electrochemical test results.Subsequently,the carbonization temperature of spores was regulated.The results showed that the optimum carbonization temperature was 800°C.Finally,a series of temperature gradient samples show that the optimum temperature for iron-loaded pyrolysis is 800°C.The electrocatalytic ORR results showed that the optimal sample Fe@CS-800 800 showed a better initial potential of 0.97 V（vs.RHE）than Pt/C in 0.1 m KOH,and a half-wave potential beyond Pt/C 70 m V,with a Tafel slope（50.8 m V/dec）less than Pt/C（60.6m V/dec）.In addition,in 0.5 m H2SO4,Fe@CS-800 800 also showed better ORR performance than Pt/C,which was mainly reflected in a larger limit current density and a half-wave potential 10 m V beyond Pt/C.3.The prepared Fe@CS-800 800 catalyst was used to assemble rechargeable zinc-air batteries.Assembled liquid zinc-air battery showed an open circuit potential（1.516 V）close to that of most catalyst cathodes,and a power density of 73.2 m W/cm~2at a current density of about 120 m A/cm~2.At the current density of 2 m A/cm~2,the performance of the Fe@CS-800 800 zinc-air battery was basically similar to that of the Pt/C+Ru O2.Then,the flexible zinc-air cell was also assembled.The Fe@CS-800 800air cathode exhibited an open circuit potential of 1.33 V under different bending conditions.At the current density of 2 m A/cm~2,the flexible zinc-air cell driven by Fe@CS-800 800 has poor stability（only 41 cycles）. |
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