Preparation And Electrocatalytic Performances Of Ag Modified Co/Fe Based Composite Catalysts

Electrolytic water technology is one of the most environmentally friendly and efficient technologies for hydrogen production.Rechargeable zinc-air battery is considered as a promising electrochemical energy storage technology due to their high energy density,high power density,high safety and low cost.These two technologies involve three electrochemical reactions:hydrogen precipitation reaction（HER）,oxygen precipitation reaction（OER）and oxygen reduction reaction（ORR）.In order to reduce the overpotential of these three reactions and increase the reaction rate,highly efficient electrocatalysts need to be developed.Currently,the noble metal-based catalyst Pt/C is considered to be the best catalyst for HER and ORR,while the highly active commercial catalysts for catalyzing OER are Ru O₂ and Ir O₂.However,the high cost and low stability seriously hinder their wide application.Therefore,it is of great importance to develop non-precious metal catalysts with high activity,high stability and low cost.Among them,non-Pt-based metal Ag is reported to have excellent catalytic ORR activity and stability in alkaline environment and excellent electrical conductivity,which has the potential to replace Pt.Moreover,among many non-precious metal materials,transition metal Co and Fe-based catalysts have shown excellent HER and OER performance.Based on this paper,non-Pt-based metal Ag with excellent electrical conductivity is compounded with transition metal Co and Fe compounds to prepare composite catalysts with catalytic HER/OER/ORR and electrocatalytic hydrolysis and zinc air battery applications.The research is as follows:1.Two-dimensional（2D）porous Co O/Co P/Co₂P nanosheets modified with highly dispersed Ag nanoparticles were prepared by hydrothermal and partial phosphorylation methods.Due to the high electrical conductivity of Ag,the synergistic effect of the composites and the higher number of active sites exposed by the 2D nanosheets,the prepared optimal catalyst showed excellent catalytic activity as cathodic and anodic catalysts in monolithic electrolytic water.The overpotentials of the optimal catalyst for catalytic HER and OER were 167 and 266 m V,respectively,when reaching a current density of 10 m A cm^-2 in 1 M KOH,and the decomposition voltage required for electrolysis of water was only 1.58 V.2.Ag/Co Fe/Co₂P/NC composite catalysts were prepared by doping Ag into Co Fe Prussian blue analogs,followed by one-step pyrolysis and phosphorylation,and a series of catalysts were obtained by optimizing the amount of phosphorus source.Due to the excellent electrical conductivity and stability of Ag,while the synergistic effect of the multi-component makes the catalysts exhibit good electrocatalytic activity and stability.Electrochemical correlation tests showed that the optimum catalyst was prepared with the overpotentiasl of 200 and 293 m V for HER and OER,respectively,at a current density of 10 m A cm^-2,and a half-wave potential of 0.759 V for ORR.The decomposition voltage was only 1.54 V at a current density of 10 m A cm^-2 when the catalyst was used to assemble an electrolytic water device.In addition,the open-circuit voltage was 1.394 V,and the maximum power density could reach 159 m W cm^-2 with a specific capacity of 808 m Ah g _Zn^-1.3.Ag/Co Fe/Fe₂O₃/NC composite catalysts were produced by first carbonizing Ag-doped Co Fe Prussian blue analogs followed by sequential low-temperature oxidation and Na BH₄ reduction.The obtained catalysts exhibited excellent catalytic OER activity and stability in alkaline media.It is worth mentioning that the optimized catalyst had overpotentials of 260 and 354 m V at current densities of 10 m A cm^-2 and200 m A cm^-2,respectively,and the catalyst was basically stable after 20 h of stability testing,which indicated their excellent stability.The above studies suggest that the catalytic performance can be enhanced by modifying the catalyst with Ag,controlling the catalyst morphology,and complementing the advantages of the multi-component composites by changing the electronic structure of the catalyst or exposing more catalytic active sites.