Platinum nanoparticle-polyoxometalate based bimetallic catalyst for proton exchange membrane fuel cell and bipolar electrodeposition based combinatorial material library applied in sensors and energy systems

Abstract

The first part of chapter 1 summarizes the reports on the improved oxygen reduction reaction (ORR) kinetics on Pt-bimetallic catalysts used in proton exchange membrane fuel cell (PEMFC). An account on the significance of polyoxometalate (POM), an inorganic ligand system to stabilize the base metal component of a multimetallic ORR catalyst, is given in addressing the issue associated with the instability of bimetallic Pt alloy surface under PEMFC cathode operating condition. The second part of chapter 1 deals with the significance of combinatorial material library and various methods including bipolar electrochemistry to synthesize the material library. Chapter 2 deals with a bimetallic ORR catalyst system composed of Pt nanoparticle (PtNP) and Co-substituted Dawson type polyoxometalate (Co-POM). The fabricated electrocatalysts films (POM-stabilized PtNP, cysteamine- or poly (diallyl dimethyl ammonium chloride) (PDDA)-stabilized PtNP/POM layer-by-layer (LBL) assembly) were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The ORR kinetics of the electrocatalysts were studied using the rotating disc electrode (RDE) experiment. We confirmed our hypothesis that Co center in Co-POM helps promote O=O bond splitting and transfer the split O atom to the PtNP surface from the ORR kinetics using the PDDA-stabilized PtNP/POM LBL assembly. In chapter 3, we report the synthesis of Ag-Au alloy gradients on stainless steel substrates using bipolar electrodeposition (BP-ED). The alloy gradient was characterized using SEM/EDX. Confocal Raman microscopy was employed to determine the optimum alloy composition of 70 atomic% Ag/30 atomic% Au that resulted in the maximum surface enhanced Raman scattering (SERS) intensity and the optimum composition is explained on the basis of composition-dependent changes in the local surface plasmon resonance (LSPR) of the electrodeposited Ag-Au alloy. Chapter 4 deals with the Pd-Au alloy gradient generated by bipolar electrodeposition on a gold bipolar electrode, its characterization using SEM/EDX and its screening for the electrocatalytic activity towards formate oxidation using Raman spectroelectrochemistry. The optimum composition, 70 atomic% Pd/ 30 atomic% Au, is explained based on the band theory model applied to alloys between metals from group VIII and IB. Chapter 5 summarizes my research work and provides the directions for future studies.