Research On Properties Of Porous Nano-Carbon Catalyst For Oxygen Reduction Reaction Derived From F127

Oxygen reduction reaction(ORR)catalyst is one of the key materials of Anion Exchange Membrane Fuel Cell(AEMFC).The development of new catalysts with high activity,good stability and low cost,especially metal-free ORR catalyst has become one of the key technologies to accelerate the development of AEMFC.In this paper,the amphiphilicity of block copolymer F127 was used to assemble into micelles and then pyrolyzed at high temperature to fabricate hollow porous nano-carbon ORR catalysts with different morphologies and nitrogen doping.During self-assembly,ZnCl2 and PVP were introduced into the aqueous solution to control the shape of micelles.At last,the electrochemical characteristic of the obtained nano-carbon for ORR was evaluated in O2 saturated 0.1M KOH solution.The main conclusions are as follows:Firstly,F127 as precursor was assembled in aqueous solution having ZnCl2.And then hexamethylenetetramine(HMT)was added into the solution to form transparent film,which was pyrolyzed at 700? in inert atmosphere.The even hollow nanocarbon ball(C-700)was obtained,which was about 50 nm in diameter,thickness of 5 nm-7 nm.In O2 saturation 0.1 M KOH solution,its onset potential and half-wave potential of ORR and limit current density were 0.89 V to 0.71 V and 5.12 mA/cm2@0.45 V,closing to that of the commercialized 20wt%Pt/C.The onset potential and half-wave potential of C-700 changed little after 2000 cyclic voltammetiy cycles while the limit current density attenuated by 12.2%.Secondly,PEO-PPO-PEO three block copolymer with different molecular weight(2900,8400,12600 and 14600 g/mol)were also used to fabricate the nanocarbon materials according the above mentioned method(pyrolyzed at 700?).At 700?,the four block copolymers could be pyrolyzed into nano-carbon materials.As the molecular weight of block copolymers increases,the derived nano-carbon particles gradually increase from 20 nm to 50 nm.When the molecular weight is increased to 12600 g/mol,the even,hollow nano carbon spheres was obtained(C-12600).When the molecular weight was further increased,the derived hollow nanospheres collapsed.The above derived carbon spheres can catalyze ORR in alkaline environment,but the electrochemical performance of C-12600 was the best.Finally,in order to further improve the electrochemical performance of derived carbon material,nitrogen was doped in the nanocarbon materials by introducing PVP into the self-assembly of F127.When adding 10%PVP and pyrolysis in 800?,the uniform,hollow capsule nano-carbon(C-N-800)was gotten,which was about 50 nm in width,100 nm long,thickness of 5 nm.In O2 saturated 0.1M KOH solution,the onset potential,half-wave potential and limit current density for C-N-800 were 0.91 V to 0.77 V and 5.45 mA/cm2@0.45 V,respectively,which were comparable to that of commercial 20wt%Pt/C.After 5000 cyclic voltammetry tests,its onset potential and half-wave potential was little changed,and the limit current density attenuated by only 11.7%,showing a good application prospect.