Biosynthesis Of Transition Metal Catalysts Supported On Carbon Materials And Oxygen Reduction Performance

Oxygen reduction reaction?ORR?is very important for fuel cells and metal-air batteries.However,the ORR kinetic process is slow and catalysts are required to accelerate the reaction rate.Noble metal catalysts such as Pt are currently still the most efficient oxygen reduction catalysts,and non-noble metal catalysts supported on carbon materials also show good application prospects due to their low price and excellent performance.At present,commonly used oxygen reduction catalyst synthesis methods such as mechanical ball milling method,sol-gel method,hydrothermal method,electrolysis method and gas-phase reduction method are complicated,expensive,and unfriendly to the environment,often requiring the use of toxic chemical reagents.The biosynthesis method has the advantages of mild conditions,environmental friendliness,being non-toxic and harmless,etc.,which has attracted more and more attention.In this paper,using cheap bacteria as a natural reducing agents for transition metals,we successfully synthesized the hybrids of noble metals Pd/reduced graphene oxide?rGO?and bacteria,and the hybrids of non-precious metals?Co,Fe?and bacteria.After the high-temperature carbonization treatment,different transition metal element catalysts supported by carbon materials were obtained,and their composition,morphology and ORR catalytic activity were systematically studied.The main research content and results of the paper are as follows:?1?Pd/rGO and bacteria hybrids were prepared using the bacteria Shewanella oneidensis MR-1.After high-temperature carbonization,the effects of its chemical composition and microstructure on the ORR performance of the catalyst were studied.The results show that Shewanella oneidensis MR-1 could efficiently reduced Pd and GO and synthesize Pd/rGO and bacteria hybrids.Strikingly,the addition of GO greatly increases the recovery rate of Pd and reduces the particle size of Pd in the catalyst.It exhibits the promising ORR performance after calcination at 800?.It has an onset potential of 0.92 V?vs.RHE?,the half-wave potential of 0.81 V?vs.RHE?,and the limiting current density of 5.2 mA cm^-2 in 0.1 M KOH electrolyte.The yield of hydrogen peroxide is below 5%,and it has good durability and methanol tolerance.?2?In order to further reduce the cost of the catalyst,we used recombinant E.coli to prepare cobalt-containing biological hybrids,and calcined at different temperatures to obtain biochar-supported cobalt catalysts.Through XRD,SEM,HRTEM,XPS and electrochemical performance testing methods,the catalyst phase,morphology,valence bond and catalytic activity were analyzed,and the effect of different heat treatment temperature on the ORR performance was studied.The results show that the catalyst exhibits good oxygen reduction activity when pyrolyzed at 900?with the onset potential of 0.94 V?vs.RHE?,the half-wave potential of 0.76 V?vs.RHE?and limiting current density of 3.92 mA cm^-2 in 0.1 M KOH electrolyte.At the same time,it has good durability and methanol tolerance.?3?Similarly,iron-containing biohybrids were prepared using recombinant E.coli.The XRD,SEM,TEM and XPS characterization methods were used to analyze the composition,microstructure and valence bond of biosynthetic hybrids,and study the effect of different heat treatment temperatures?700,800,900 and 1000??on the catalyst ORR performance.The results show that the pyrolysis temperature has little effect on the catalytic activity of the catalyst.The catalyst exhibits the best oxygen reduction activity when pyrolyzed at 900°C.The onset potential is 0.90 V?vs.RHE?,the half-wave potential is 0.67 V?vs.RHE?,and the limiting current density is 4.32 mA cm^-2 in 0.1 M KOH electrolyte.