Thin-film catalysts for proton exchange membrane water electrolyzers and unitized regenerative ... fuel cells

This work revolves around the hydrogen economy and energy-storage electrochemical systems. More specifically, it investigates the possibility of using magnetron sputtering for deposition of efficient thin-film anode catalysts with low noble metal content for proton exchange membrane water electrolyzers (PEM-WEs) and unitized regenerative fuel cells (PEM-URFCs). The motivation for this research derives from the urgent need to minimize the price of such electrochemical devices should they enter the mass production. Numerous experiments were carried out, correlating the actual in-cell performance with the varying position of thin-film catalyst within the membrane electrode assembly, with the composition of high-surface support sublayer and with the chemical structure of the catalyst itself. The wide arsenal of analytical methods ranging from electrochemical impedance spectroscopy through electrochemical atomic force microscopy to photoelectron spectroscopy allowed the description of the complex phenomena behind different obtained efficiencies. Systematic optimizations led to the design of a novel PEM-WE anode thin-film iridium catalyst which performs similarly to the standard counterparts despite using just a fraction of their noble metal content. Moreover, the layer-by-layer approach resulted in the design of a Ir/TiC/Pt bi-functional anode for PEM-URFC which is able to operate in both the fuel cell and electrolyzer regime and thus helps to cut the cost of the whole conversion system even further. Supervisor’s Foreword 6 Abstract 8 Acknowledgements 9 Contents 10 Abbreviations 12 1 Introduction 14 1.1 Hydrogen Economy 15 1.2 Proton Exchange Membrane Fuel Cell (PEM-FC) 18 1.3 Proton Exchange Membrane Water Electrolyzer (PEM-WE) 23 1.4 Proton Exchange Membrane Unitized Regenerative Fuel Cell (PEM-URFC) 26 1.5 Performance and Efficiency of PEM-FC, PEM-WE and PEM-URFC 29 1.6 Thesis Motivation and Targets 32 References 32 2 Experimental 38 2.1 Magnetron Sputtering 38 2.2 Scanning Electron Microscopy (SEM) 40 2.3 Atomic Force Microscopy (AFM) 42 2.4 Photoelectron Spectroscopy (PES) 44 2.5 Electrochemical Measurements and Characterizations 46 References 48 3 Results 49 3.1 PEM-WE Testing Cell Setup 49 3.2 Thin-Film Catalyst Deposition and Noble Metal Loading Determination 52 3.3 Thin-Film Magnetron Sputtered Anode Catalyst for PEM-WE 53 3.3.1 Ir Thin-Film Catalyst Sputtered Directly on Membrane 54 3.3.2 Ir Thin-Film Catalyst Sputtered on Ti Mesh GDL 56 3.3.3 Ir Thin-Film Catalyst Sputtered on Ti-Coated Carbon Paper GDL 58 3.3.4 Ir Supported on TiC Nanoparticles 61 3.3.5 Further Optimization of Experimental PEM-WE MEA with Ir Thin-Film Catalyst Supported on TiC Particles (PEM and Anode GDL) 77 3.4 Thin-Film Magnetron Sputtered Catalyst for PEM-URFC 83 3.4.1 Reference Performances of Dedicated PEM-WE and PEM-FC Cells 84 3.4.2 Thin-Film Bifunctional Anode Catalyst for PEM-URFC (Pt–Ir Co-sputtering) 86 3.4.3 Thin-Film Bifunctional Anode Catalyst for PEM-URFC (Pt, Ir Sandwich Sputtering) 96 3.5 Round-Trip Efficiency of PEM-URFC with Thin-Film Bifunctional Anode Catalyst 101 References 102 4 Summary and Conclusions 105 Author’s CV 109 Front Matter ....Pages i-xiv Introduction (Peter Kúš)....Pages 1-24 Experimental (Peter Kúš)....Pages 25-35 Results (Peter Kúš)....Pages 37-92 Summary and Conclusions (Peter Kúš)....Pages 93-96 Back Matter ....Pages 97-101