Synthesis And Electrocatalytic Performance Of Carbon-Based Non-noble Hybrid Nanocatalysts

With the increasing exploitation and consumption of fossil fuels,the problems of energy crisis and environmental pollution are increasing prominent.Recently,fuel cells,metal-air batteries and water electrolytic cell have attracted extensive attention because of their green,renewable energy conversion properties,which are the fronties and hotspots of current research.Oxygen reduction reaction(ORR),oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)are three critical processes within abovementioned systems,which need excellent electrocatalysts to boost the reaction efficiency because of their sluggish reaction kinitics.At present,Pt-based precious metal catalysts are mainly used for ORR and HER,while Ir-and Ru-based precious metal catalysts are mainly used for OER.However,the high cost and scarcity of noble mental have limited their widespread application.Consequently,developing low cost,high active and stable catalysts based on non-noble systems in the clean energy filed has become one of the core issues to be solved.In the present work,a series of new non-noble metal carbon-based nanocatalysts have been designed and fabricated based on composite strategy,and the electrocatalytic performances were systematically investigated.The main contents are as follows:(1)Bacterial cellulose with 3D network structure was used as carbon skeleton precursor,and polydopamine in-situ formed on the surface of bacterial cellulose can be further transformed to N-doped carbon nanoparticles supported on the carbon nanofibers network(NCN@CF).Reasearch shows that this strategy enables the effective improvement of the mass density of active species(N-doped carbon),specific surface area as well as the final yield of catalysts.The electrochemical analysis shows that the ORR performances of as-fabricated catalyst are better than benchmark Pt/C in alkaline medium.Notably,when this catalyst is used as air electrode catalyst,the as-constructed Zn-air battery presents a larger peak power density of 168 m W cm^-2,higher specific capacity of 720.5 m Ah g^-1 and energy density of 900.0 Wh kg_Zn^-1,showing a good application prospect.(2)Na₂HPO₄ was used to promote the polymerization of dopamine instead of the Tris buffer solution,which meanwhile serves as the phosphorus source,a composite catalyst integrating Co₂P nanoparticles and N,P co-doped carbon(Co₂P/NPCF)was obtained,which exhibits excellent catalytic performances for ORR and OER.The electrochemical analysis shows that its E_onset,E_1/2 and Tafel slope are 0.94 V?0.85 V and 52 m V dec^-1 in 0.1 M KOH,respectively,all of which are better than benchmark Pt/C.The overpotential for OER is 370 m V at a current density of 10 m A cm^-2,indicating a better catalytic performance than the commercial RuO₂.Co₂P/NPCF-based primary Zn-air battery reaches the maximum power density of 160 m W cm^-2,and when discharging for 110 h at a current density of 10 m A cm^-2,the voltage gap only decreases 55 m V.For the Co₂P/NPCF-based rechargeable Zn-air battery,after 160 cycles at a current density of 10 m A cm^-2,the voltage gap of charge-discharge does not change obviously,exhibiting good device cycle stability.(3)A ZIF-67-derived composite catalyst containing metallic Co nanoparticles embedded N-doped carbon layer(Co@NCL)was fabricated which uses water as solvent medium,it is expected to solve the environmental pollution caused by the use of organic solvents in the traditional preparation process.Reaserch shows that the as-fabricated catalyst exhibits excellent trifuctional electrocatalytic activities.As a catalyst for ORR,its E_onset,E_1/2 and Tafel slope are 0.91 V?0.84 V and 59 m Vdec^-1,respectively.The overpotential is400 m V for OER and-220 m V for HER at a current density of 10 m A cm^-2,respectively.Co@NCL-based Zn-air battery reaches a maximum power density of 170 m W cm^-2 and energy density of 934.93 Wh kg_Zn^-1.The voltage gap of charge-dischare at a current density of 10 m A cm^-2 shows no significant change after 140 cycles.Moreover,the as-assembled overall water-splitting electrolyzer delivers a current density of 10 m A cm^-2 at 1.70 V.The performances of Zn-air battery and water-splitting cells based on Co@NCL catalyst are better than most of reported non-noble carbon based trifunctional catalysts.(4)Inspired by the protection effect caused by core-shell structure and the synergistic effect between different active species within a multi-compounds,the FeCo/Co₂P@NPCF composite trifunctional catalyst has been developed through a liquid pre-growth process and a subsequent pyrolysis process.On the basis of synergistic effects of FeCo nanoparitcles encapsuled in graphitic carbon film,Co₂P nanoparticles and N,P-codoped carbon nanofiber networks,the as-fabricated catalyst exhibits excellent electrocatalytic activites and stabilities toward ORR,OER and HER.The as-constructed Zn-air battery exhibits a low charge-discharge voltage gap of 0.80 V(at 10 m A cm^-2)after 624 cycles(107 h).Moreover,the as-assembled overall water-splitting electrolyzer delivers a current density of 10 m A cm^-2 at 1.68 V,which is better than most of reported trifunctional catalysts.Furthermore,two FeCo/Co₂P@NPCF-based Zn-air batteries in series can drive the overall water-splitting,which evidences their bright prospect to be practically applied in metal-air batteries,water-splitting cells and other energy conversion devices.