| The massive consumption of fossil fuels has triggered serious air pollution,climate warming,and energy crisis,thus,developing clean renewable energy has been a task of top priority.In order to reduce carbon emissions,energy conversion and storage technologies represented by electrocatalytic CO2 reduction and hydrogen evolution are essential.Highly active electrocatalyst is the key point for efficient CO2 reduction and hydrogen production.Carbon-based materials are widely used in the electrochemical field due to their advantages of low cost,high surface area,high conductivity,and corrosion resistance.Heteroatom doping is an effective strategy for improving the catalytic activity of carbon materials.Therefore,this paper designs efficient catalysts for electrocatalytic CO2 reduction reaction(CO2RR)and hydrogen evolution reaction(HER)based on heteroatom-doped carbon materials:Metal-nitrogen-carbon catalysts show superior activity in CO2RR,but still require higher overpotentials to obtain a comparable activity as noble metals.Heteroatom doping in metalnitrogen-carbon is an effective strategy to improve the catalytic performance.Considering that many microorganisms have an intrinsic structure of metal-nitrogen coordination and are rich in various elements such as C,N,and P,in this paper,the nitrogen and phosphorus co-doped carbon with iron sites catalyst(P-Fe/NC-1000)was prepared by one-step pyrolysis using Shewanelia oneidensis MR-1 as the sole precursor.The CO Faraday efficiency reached 95%at a low overpotential of 390 mV,Tafel slope was 95 mV dec-1,and the reaction can keep stable for 12 h.Kinetic experiments and thermodynamic analysis proved that the excellent CO2RR performance was derived from the highly exposed Fe-N catalytic active sites and the P doping in carbon skeleton.The introduced P atoms could accelerate the dissociation of water and proton transfer,thus,boosting the protonation process of intermediates and promoting the formation of CO on Fe active sites.P can also improve the electronic structure of the Fe center and reduce the energy barrier of intermediates.A Zn-CO2 battery based on P-Fe/NC-1000 presented a high power density of 1.32 mW cm-2 and cycle charge-discharge for 30 h.Metal-free nitrogen-doped carbon is a good alternative to noble metal catalysts for HER,but due to its single active site,the hydrogen evolution potential is high.The doping of additional nonmetallic elements can enrich active sites,enhancing the reaction activity.In this paper,carbon nano fiber catalyst doped with nitrogen,sulfur and phosphorus(NSP/CNF-1000)were prepared by high temperature pyrolysis using the homogeneous precursor formed by thiourea,phytic acid,and carbon nanofiber.The temperature and raw material ratio were optimized.Thanks to the uniform distribution of N,S,and P in carbon skeleton and the synergistic effect among the three heteroelements,NSP/CNF-1000 exhibited outstanding HER catalytic activity and excellent stability in a wide pH range(0-14).The overpotential of NSP/CNF-1000 at 10 mA cm-2 current density was 389 mV(acid),416 mV(alkaline),and 466 mV(neutral),respectively.The performance can maintain stable during the reaction process exceeding 10 h.The low Tafel slope indicated that the catalyst had excellent reaction kinetics in acidic(109 mV dec-1),alkaline(136 mV dec-1),and neutral(221 mV dec-1)media.Theoretical analysis showed that three heteroatoms with different sizes and electronegativity were introduced into the carbon skeleton to induce the redistribution of charge density and spin density around carbon atoms,optimizing the adsorption of intermediates,and thus improving the HER activity of carbon materials.The heteroatom-doped carbon materials designed in this paper show excellent catalytic performance in CO2RR and HER,and the reaction mechanism on the catalysts is explored,which is of great significance for the development of carbon-based catalysts with low cost and high performance. |
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