The Development Of Cathodic Electrocatalysts For Fuel Cells Based On Nanoporous Gold

The new energy materials and low-carbon technologies have been caught an increasing interest by researchers in order to resolve the serious energy crisis.As one of the new renewable energy technologies,the fuel cells exhibit the high efficiency,high stability as well as the property of long time working.However,the slow kinetics of cathodic and the high dependence of electrocatalysts on the platinum group metal have seriously hindered the further development of fuel cells.In this thesis,nanoporous metal with three-dimensional bicontinuous structure were designed as electrocatalysts for the cathodic oxygen reduction reaction?ORR?and the hydrogen peroxide reduction reaction?HPRR?of polymer electrolyte membrane fuel cell?PEMFC?.The main research in this thesis includes two aspects as followed:i)The surface structure of 3D nanoporous gold was first tuned by surfactant-free electrochemical potential cycling.Slow potential scan rate increased the proportion of nanoporous gold?NPG?{111}and{100}crystal surface.Rapid scan speed significantly increased the proportion of{100}crystal surface from 15.6%to 23%.A single atomic layer of platinum?NPG-Pt?was then successfully constructed on these different textured surface of nanoporous gold.When investigating the electrocatalytic activity of ORR,the electrocatalyst of NPG-Pt with rich{111}crystal surface exhibit extremely high activity,More specifically,the area ratio activity(j_k,ECSA)and mass ratio activity(j_k,mass)are 4.1 times and 15.8 times than that of commercial carbon supported platinum catalysts,respectively.ii)We investigated the effect of the residual silver amount and the ligament sizes of dealloyed nanoporous gold on the thermodynamic and kinetic properties of HPRR.The amount of silver residue in nanoporous gold significantly affected the apparent activation energy and the reaction rate.The less amount of silver,the smaller apparent activation energy and faster reaction rate.The activation energy barrier of HPRR was decreased using the larger ligament size of nanoporous gold whereas the kinetic reaction speed increased obviously.The present approach in this thesis towards enhancing the electrocatalytic activity can be applied quite generally to other nanoporous metals of interest.