Precisely controlled synthesis of reduced graphene oxide supported electrocatalysts for PEM fuel cells by pulsed photocatalytic deposition

Official URL: https://risc01.sabanciuniv.edu/record=b2711493_(Table of contents)

It has almost been a decade that scientists have been trying to address the shortcomings of batteries and polymer electrolyte membrane (PEM) fuel cells in production cost. One of the most important parts of the PEM fuel cells is its catalyst layer, CL. The CL of PEM fuel cells consists of Pt-based particles deposited on a carbon support. Although carbon black (CB)/Pt shows a promising electrochemical performance for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR), its vulnerability to the PEM fuel cells’ harsh environment has made this carbon-based electrocatalysts very sensitive to corrosion, and performance loss. One of the promising candidates to replace carbon black in CL preparation seemed to be graphene-based support. This study demonstrated the capability of a novel method in controlling the structural and electrochemical properties of electrocatalysts deposited on graphene-based supports, utilizing a pulsed-UV setup for the synthesis procedure. In the second chapter, the variation of UVon and UVoff periods resulted in samples with a range of different structures, compositions, and activities. The results revealed a dominant growth and agglomeration phase of Pt particles, mostly with metallic states, by increasing both UVon and Uoff time spontaneously. Further chemical reduction by highly concentrated ascorbic acid was used to confirm proposed mechanisms, which lead to samples even with more metallic Pt (Pt0) and higher electrochemical activities. The rest of the second chapter focused on utilizing a series of transition metal ions, Co2+, Ni2+ or Fe2+, to assist the deposition of Pt on PRGO planes that resulted in various types of Pt particles size, morphologies and distribution. Different interactions between hole scavengers and PRGO particles or water molecules, was the main parameter that modulated the Pt4+ reduction. The structural and electrochemical properties of electrocatalysts revealed that utilizing the cobalt-based hole scavenger, caused a dominant growth phase of Pt particles at preferred positions, with improved electrocatalytic activities (ECSA value of 195.91 m2.g-1 for Co2+ vs. 152.01 m2.g-1 for methanol). The third chapter includes the computational methods in evaluating the properties of the samples by modelling either the cyclic voltammetry data with a neural network algorithm or DFT calculation of H2 adsorption on graphene-based electrocatalysts. The result of the neural network modelling demonstrated the potential of the proposed method in designing a highly controllable synthesis procedure by which the electrochemical properties of the electrocatalysts could be predictable before the synthesis. The DFT calculation by the Quantum-Espresso code revealed that the existence of oxygen functional groups on graphene plane not only affects the crystal structure of deposited Pt particles, but also hinders the adsorption of H2 molecules on Pt surface.