Electrocatalysts Derived From Polydopamine-transition Metal Complexes: Synthesis And Electrocatalytic Performance

Water electrolyzer and hydrogen-oxygen fuel cell are two decisive devices to form a clean energy cycle mode in the blueprint of hydrogen energy.Oxygen evolution reaction?OER?,hydrogen evolution reaction?HER?and oxygen reduction reaction?ORR?are important half reactions in these two kinds of energy devices.Unfortunately,all three reactions heavily rely on expensive precious metal catalyst such as Pt/C,IrO₂and RuO₂ due to their sluggish dynamics.The limited resources and high cost of these precious metals,however limit their large-scale applications.In order to address this dilemma,intensive in-depth research has been carried out to,on the one hand,reduce the noble metal loading while improving the catalytic activity and stability.Meanwhile,alternative catalysts based on non-noble metals have been developed.In this thesis,a simple and effective synthetic method was developed to synthesize several efficient transition metal-carbon composite catalysts by using polydopamine?PDA?as a universal precursor to chelate transition metal ions.As-prepared catalysts were systematically investigated.The main contents are as follows:?1?Mesoporous Fe/Mn-N-C hollow nanospheres were synthesized as an excellent Janus electrocatalyst for ORR and OER.Fe/Mn ion-incorporated PDA?Fe/Mn-PDA?precursor was prepared via a simple one-pot reaction in an aqueous solution at room temperature,followed by therm annealing in Argon?Ar?atmosphere.This Fe/Mn-N-C catalyst contains spinel MnFe₂O₄/metallic Fe hybrid nanoparticles encapsulated in N-doped hollow carbon spheres and demonstrates a synergistically improved ORR/OER activity.In alkaline environment,Fe/Mn-N-C shows the ORR activity comparable to that of commercial Pt/C catalyst and superb OER activity close to commercial RuO₂catalyst.When tested in a Zn-air battery,it demonstrates excellent performance including power density,durability,and cycling.?2?Ultrasmall Ir nanoparticles supported on N-doped graphene?Ir@N-G-750?was synthesized as an efficient bifunctional OER/HER electrocatalyst.This Ir@N-G-750was derived from Ir ion-incorporated PDA modified graphene oxide?Ir-PDA-GO?precursor by thermal annealing in Ar atmosphere.Ir@N-G-750 shows excellent electrocatalytic activity and durability toward both HER and OER in both acidic and alkaline electrolytes.Further studies show that there are abundant Ir-N coordination in Ir@N-G-750,which enhances the electron density in Ir atoms,changes the electronic structure of Ir nanoparticles and improves their electrochemical catalytic activity and stability.?3?Rh₂P nanoparticles decorated N-doped carbon cloth was synthesized as a bifunctional HER/OER electrocatalyst.The carbon cloth is firstly modified by PDA to adsorb precious metal Rh³⁺,and then the phytic acid is chelated by hydrothermal method to form Rh/P-PDA-CC precursor,which is then converted into Rh₂P@N/P-CC by pyrolysis in an inert atmosphere.Electrochemical evaluation shows that Rh₂P@N/P-CC is a bifunctional electrocatalyst with impressive OER and HER activity.It shows excellent HER activity and stability in acidic environment,and OER activity and stability in alkaline electrolyte.In summary,a simple and unique PDA-based method was developed to synthesize three highly efficient catalysts.Their catalytic performance and nanostrucutres and compositions were systematically investigated to discover the active sites and catalytic mechanism,which may contribute to building of rational structure-activity relationship in this area.