Facile Synthesis of Boron-doped Graphitic Materials for Oxygen Reduction Purpose in Fuel Cell

Abstract

Modern civilization is blamed for aggravating climate change as well as global warming by pumping millions of tonnes of greenhouse gases into the atmosphere. In addition to environmental concerns, the ever-increasing energy demand calls for new generations of power technologies to supply such a rapid rise in energy market. Fuel cells show to be placed at the cornerstone of technology development for the current century, since they could mitigate the environmental concern and meet the escalation in energy need. However, transforming to a future sustainable energy with zero to low CO2 emission needs the development of cheap fuel cells on top of a sustainable hydrogen supply. The current scientists’ and engineers’ challenge is the fabrication of cheap, durable and reliable catalyst materials for electrochemical reduction of oxygen in cathode which is a crucial factor in determining cell’s efficiency. We also looked into this area to find new cathodic materials and compared their performance against commonly mentioned materials in literature. The focus of this contribution is to compare the Oxygen Reduction Reaction (ORR) performance of widely literature cited boron-doped graphene materials with the new type of boron-doped samples known as Graphene Organic Framework (GOF). The first chapter deals with the commercialization problem by discussing cell’s internal design, classification and its operation. Subsequently, new alternative suggested substitutes such as metallic nano catalyst, metallic-graphene hybrids, polymeric and new non-metallic graphitic electrocatalysts. The chapter will continue subsequently by introducing GOF material, which are able to form the similar CBO2 structure as the previously literature cited substitutionally boron-doped graphene (BGs) formed, as a novel catalyst for ORR. The second chapter examines the material synthesis and characterization. Three samples of substitutionally boron-doped graphene, identified as BG1, BG2 and BG3, and two types of new porous GOFs materials are synthesised under various preparation strategies. In order to confirm the integration and presence of boron in synthesised samples, variety of characterization and spectroscopic analysis are performed. XRD, TGA and FTIR are exclusively applied to GOF materials since their applications to BG samples will not provide any valuable information. However Raman and XPS characterizations are executed for all samples to determine the degree of G-band shifts (i.e. the extent of doping) and corresponding surface concentration of doped boron. The third chapter provides electrochemical results of prepared materials using conventional CV and RDE techniques in electrochemistry. To complete the discussion, subsequently, the incompetency of Koutchy-Levich (K-L) method and Rotating Disk Electrode (RDE) for determining the true ORR path is explained by reviewing Koutchy-Levich (K-L) method fundamentals. Instead Rotating Ring Disk Electrode (RRDE) technique is considered to estimate the true ORR efficiency of literature materials (BGs) versus introduced GOF substances. Finally Table 3.3 provides a comprehensive review on the results achieved during my electrochemistry analysis including testing the materials in two different laboratory facilities. The fourth chapter investigates the understanding of kinetic reaction of oxygen reduction for synthesised electrode catalysts. This is a work which barely has been considered by previous studies and could be beneficial to find the right application for materials. Based on the corresponding analysis in this chapter, except for commercial 20% Pt/C and Glassy Carbon (GC) electrodes, all materials are leading the ORR through multiple parallel-series steps with reaction constants of k1, k2 and k3 >0. However for cases like BG1 and BG2, the k3 value might be very small and close to zero that we can consider two simultaneous parallel 4e- and 2e- ORR. Finally the fifth chapter gives a summary of all thesis contents including future guides for completing this research study.