Fabrication,Characterization And Performance Investigation Of Nanoporous Core-shell Electrocatalysts For Oxygen Reduction Reaction

Among various green energy technologies,proton exchange membrane fuel cells?PEMFCs?allow highly efficient direct conversion of chemical energies in chemical fuels to electricity.With low or even zero emissions,fuel cells have been attracting worldwide attention for decades.However,the commercialization of fuel cell technologies has been hampered mainly by the heavy demand on Pt electrocatalysts,which are not only expensive,but resource limited as well.Dealloyed nanoporous metals with the unique structure and electrochemical properties have potential value for fuel cell applications.This material itself is catalytically active for a series of electrode reactions,and upon further surface functionalization,NPG leaf-based electrocatalysts can demonstrate unique structural advantages that are crucial to fuel cell electrodes,such as high surface area,high electric conductivity,high durability,and high precious metal utilization.?1?Through the method of Cu underpotential deposition – replacement reaction in situ,we construct an unsupported nanoporous cathode with a sub-nanometer-thick PtPd shell on Au,which demonstrates an initial ORR activity of 1.140 A mgPt^-1 at 0.9 V.The activity increases to 1.471 A mgPt^-1 after 30,000 potential cycles and stabilizes until 100,000 cycles.Using CO stripping and formic acid electrooxidation experiments,the origin of the activity change is revealed to be an evolution of the surface structure from an initial PtPd alloy into a bilayer structure with a Pt-rich trimetallic surface and finally into a uniform and stable PtPdAu alloy.?2?The NPG-Pt electrocatalysts with the thin Pt shell was successfully preparedby chemical deposition.The catalysts of NPG-Pt exhibits outstanding oxygen reduction reaction?ORR?activity in acidic electrolyte.Compared with the Pt/C catalyst,it reaches a Pt mass activity with 0.44 A mgPt^-1 at 0.9V?vs RHE?,which points to a two point eight folds enhancement.In addition,the material also shows surprisingly excellent stability,and after 30000 potential cycling,only 17 mV negative shift in half-wave potential was observed.Finally,the NPG-Pt catalyst materials was utilized in direct methanol fuel cell and hydrogen fuel cell and the results showed that this type of catalyst has significant advantages in increasing Pt utilization and decreasing Pt load.maximum power density,which normalized Pt mass,of fuel cell with NPG-Pt catalyst exhibits nearly 20-fold and 1.7-fold higher than the Pt/C,respectively.