Electrocatalysis for Membrane Fuel Cells

Preface xv Part I Overview of Systems 1 1 System-level Constraints on Fuel Cell Materials and Electrocatalysts 3 Elliot Padgett and Dimitrios Papageorgopoulos 1.1 Overview of Fuel Cell Applications and System Designs 3 1.1.1 System-level Fuel Cell Metrics 3 1.1.2 Fuel Cell Subsystems and Balance of Plant (BOP) Components 5 1.1.3 Comparison of Fuel Cell Systems for Different Applications 9 1.2 Application-derived Requirements and Constraints 10 1.2.1 Fuel Cell Performance and the Heat Rejection Constraint 10 1.2.2 Startup, Flexibility, and Robustness 13 1.2.3 Fuel Cell Durability 14 1.2.4 Cost 16 1.3 Material Pathways to Improved Fuel Cells 18 1.4 Note 19 Acronyms 20 Symbols 20 References 20 2 PEM Fuel Cell Design from the Atom to the Automobile 23 Andrew Haug and Michael Yandrasits 2.1 Introduction 23 2.2 The PEMFC Catalyst 27 2.3 The Electrode 32 2.4 Membrane 38 2.5 The GDL 42 2.6 CCM and MEA 46 2.7 Flowfield and Single Fuel Cell 50 2.8 Stack and System 55 Acronyms 57 References 58 Part II Basics – Fundamentals 69 3 Electrochemical Fundamentals 71 Vito Di Noto, Gioele Pagot, Keti Vezzù, Enrico Negro, and Paolo Sgarbossa 3.1 Principles of Electrochemistry 71 3.2 The Role of the First Faraday Law 71 3.3 Electric Double Layer and the Formation of a Potential Difference at the Interface 73 3.4 The Cell 74 3.5 The Spontaneous Processes and the Nernst Equation 75 3.6 Representation of an Electrochemical Cell and the Nernst Equation 77 3.7 The Electrochemical Series 79 3.8 Dependence of the E cell on Temperature and Pressure 82 3.9 Thermodynamic Efficiencies 83 3.10 Case Study – The Impact of Thermodynamics on the Corrosion of Low-T FC Electrodes 85 3.11 Reaction Kinetics and Fuel Cells 88 3.11.1 Correlation Between Current and Reaction Kinetics 88 3.11.2 The Concept of Exchange Current 89 3.12 Charge Transfer Theory Based on Distribution of Energy States 89 3.12.1 The Butler–Volmer Equation 96 3.12.2 The Tafel Equation 100 3.12.3 Interplay Between Exchange Current and Electrocatalyst Activity 101 3.13 Conclusions 103 Acronyms 104 Symbols 104 References 107 4 Quantifying the Kinetic Parameters of Fuel Cell Reactions 111 Viktoriia A. Saveleva, Juan Herranz, and Thomas J. Schmidt 4.1 Introduction 111 4.2 Electrochemical Active Surface Area (ECSA) Determination 114 4.2.1 ECSA Determination Using Underpotential Deposition 115 4.2.1.1 Hydrogen Underpotential Deposition (H UPD) 116 4.2.1.2 Copper Underpotential Deposition (Cu UPD) 117 4.2.2 ECSA Quantification Based on the Adsorption of Probe Molecules 118 4.2.2.1 CO Stripping 118 4.2.2.2 No –2 ∕NO Sorption 119 4.2.3 Double-layer Capacitance Measurements and Other Methods 120 4.2.4 ECSA Measurements in a PEFC: Which Method to Choose? 120 4.3 H 2 -Oxidation and Electrochemical Setups for the Quantification of Kinetic Parameters 121 4.3.1 Rotating Disc Electrodes (RDEs) 122 4.3.2 Hydrogen Pump (PEFC) Approach 124 4.3.3 Ultramicroelectrode Approach 125 4.3.4 Scanning Electrochemical Microscopy (SECM) Approach 125 4.3.5 Floating Electrode Method 127 4.3.6 Methods Summary 128 4.4 ORR Kinetics 129 4.4.1 ORR Mechanism Studies with RRDE Setups 129 4.4.2 ORR Pathway on Me/N/C ORR Catalysts 130 4.4.3 ORR Kinetics: Methods 132 4.4.3.1 Pt-based Electrodes 132 4.4.3.2 Pt-free Catalysts: RDE vs. PEFC Kinetic Studies 133 4.5 Concluding Remarks 133 Acronyms 134 Symbols 134 References 135 5 Adverse and Beneficial Functions of Surface Layers Formed on Fuel Cell Electrocatalysts 149 Shimshon Gottesfeld 5.1 Introduction 149 5.2 Catalyst Capping in Heterogeneous Catalysis and in Electrocatalysis 151 5.3 Passivation of PGM/TM and Non-PGM HOR Catalysts and Its Possible Prevention 156 5.4 Literature Reports on Fuel Cell Catalyst Protection by Capping 161 5.4.1 Protection of ORR Pt catalysts Against Agglomeration by an Ultrathin Overlayer of Mesoporous SiO 2 or Me–SiO 2 161 5.4.2 Protection by Carbon Caps Against Catalyst Detachment and Catalyst Passivation Under Ambient Conditions 162 5.5 Other Means for Improving the Performance Stability of Supported Electrocatalysts 166 5.5.1 Replacement of Carbon Supports by Ceramic Supports 166 5.5.2 Protection of Pt Catalysts by Enclosure in Mesopores 167 5.6 Conclusions 170 Abbreviations 171 References 171 Part III State of the Art 175 6 Design of PGM-free ORR Catalysts: From Molecular to the State of the Art 177 Naomi Levy and Lior Elbaz 6.1 Introduction 177 6.2 The Influence of Molecular Changes Within the Complex 179 6.2.1 The Role of the Metal Center 179 6.2.2 Addition of Substituents to MCs 183 6.2.2.1 Beta-substituents 184 6.2.3 Meso-substituents 186 6.2.4 Axial Ligands 187 6.3 Cooperative Effects Between Neighboring MCs 190 6.3.1 Bimetallic Cofacial Complexes – “Packman” Complexes 191 6.3.2 MC Polymers 191 6.4 The Physical and/or Chemical Interactions Between the Catalyst and Its Support Material 193 6.5 Effect of Pyrolysis 194 Acronyms 196 References 196 7 Recent Advances in Electrocatalysts for Hydrogen Oxidation Reaction in Alkaline Electrolytes 205 Indra N. Pulidindi and Meital Shviro 7.1 Introduction 205 7.2 Mechanism of the HOR in Alkaline Media 206 7.3 Electrocatalysts for Alkaline HOR 212 7.3.1 Platinum Group Metal HOR Electrocatalysts 212 7.3.2 Non-platinum Group Metal-based HOR Electrocatalysts 214 7.4 Conclusions 220 Acronyms 221 References 221 8 Membranes for Fuel Cells 227 Paolo Sgarbossa, Giovanni Crivellaro, Francesco Lanero, Gioele Pagot, Afaaf R. Alvi, Enrico Negro, Keti Vezzù, and Vito Di Noto 8.1 Introduction 227 8.2 Properties of the PE separators 228 8.2.1 Benchmarking of IEMs 229 8.2.2 Ion-exchange Capacity (IEC) 229 8.2.3 Water Uptake (WU), Swelling Ratio (SR), and Water Transport 231 8.2.4 Ionic Conductivity (σ) 233 8.2.5 Gas Permeability 234 8.2.6 Chemical Stability 235 8.2.7 Thermal and Mechanical Stability 237 8.2.8 Cost of the IEMs 239 8.3 Classification of Ion-exchange Membranes 240 8.3.1 Cation-exchange Membranes (CEMs) 240 8.3.1.1 Perfluorinated Membranes 240 8.3.1.2 Nonperfluorinated Membranes 245 8.3.2 Anion-exchange Membranes (AEMs) 246 8.3.2.1 Functionalized Polyketones 247 8.3.2.2 Poly(Vinyl Benzyl Trimethyl Ammonium) (PVBTMA) Polymers 248 8.3.2.3 Poly(sulfones) (PS) 249 8.3.3 Hybrid Ion-exchange Membranes 249 8.3.3.1 Hybrid Membranes with Single Ceramic Oxoclusters [P/(M X O Y) n ] 250 8.3.3.2 Hybrid Membranes Comprising Surface-functionalized Nanofillers 254 8.3.3.3 Hybrid Membranes Doped with hierarchical “Core–Shell” Nanofillers 254 8.3.4 Porous Membranes 257 8.3.4.1 Porous Membranes as Host Material 257 8.3.4.2 Porous Membranes as Support Layer 258 8.3.4.3 Porous Membranes as Unconventional Separators 259 8.4 Mechanism of Ion Conduction 259 8.5 Summary and Perspectives 268 Acronyms 271 Symbols 272 References 272 9 Supports for Oxygen Reduction Catalysts: Understanding and Improving Structure, Stability, and Activity 287 Iwona A. Rutkowska, Sylwia Zoladek, and Pawel J. Kulesza 9.1 Introduction 287 9.2 Carbon Black Supports 288 9.3 Decoration and Modification with Metal Oxide Nanostructures 289 9.4 Carbon Nanotube as Carriers 291 9.5 Doping, Modification, and Other Carbon Supports 293 9.6 Graphene as Catalytic Component 293 9.7 Metal Oxide-containing ORR Catalysts 296 9.8 Photodeposition of Pt on Various Oxide–Carbon Composites 299 9.9 Other Supports 301 9.10 Alkaline Medium 302 9.11 Toward More Complex Hybrid Systems 303 9.12 Stabilization Approaches 306 9.13 Conclusions and Perspectives 307 Acknowledgment 308 Acronyms 308 References 308 Part IV Physical–Chemical Characterization 319 10 Understanding the Electrocatalytic Reaction in the Fuel Cell by Tracking the Dynamics of the Catalyst by X-ray Absorption Spectroscopy 321 Ditty Dixon, Aiswarya Bhaskar, and Aswathi Thottungal 10.1 Introduction 321 10.2 A Short Introduction to XAS 323 10.3 Application of XAS in Electrocatalysis 325 10.3.1 Ex Situ Characterization of Electrocatalyst 325 10.3.2 Operando XAS Studies 330 10.4 Δμ XANES Analysis to Track Adsorbate 334 10.5 Time-resolved Operando XAS Measurements in Fuel Cells 338 10.6 Fourth-generation Synchrotron Facilities and Advanced Characterization Techniques 340 10.6.1 Total-reflection Fluorescence X-ray Absorption Spectroscopy 341 10.6.2 Resonant X-ray Emission Spectroscopy (RXES) 341 10.6.3 Combined XRD and XAS 342 10.7 Conclusions 342 Acronyms 343 References 344 Part V Modeling 349 11 Unraveling Local Electrocatalytic Conditions with Theory and Computation 351 Jun Huang, Mohammad J. Eslamibidgoli, and Michael H. Eikerling 11.1 Local Reaction Conditions: Why Bother? 351 11.2 From Electrochemical Cells to Interfaces: Basic Concepts 352 11.3 Characteristics of Electrocatalytic Interfaces 355 11.4 Multifaceted Effects of Surface Charging on the Local Reaction Conditions 356 11.5 The Challenges in Modeling Electrified Interfaces using First-principles Methods 358 11.5.1 Computational Hydrogen Electrode 359 11.5.2 Unit-cell Extrapolation, Explicit Solvated Protons, and Excess Electrons 360 11.5.3 Counter Charge and Reference Electrode 361 11.5.4 Effective Screening Medium and mPB Theory 361 11.5.5 Grand-canonical DFT 362 11.6 A Concerted Theoretical–Computational Framework 362 11.7 Case Study: Oxygen Reduction at Pt(111) 364 11.8 Outlook 367 Acronyms 367 Symbols 368 References 368 Part VI Protocols 375 12 Quantifying the Activity of Electrocatalysts 377 Karla Vega-Granados and Nicolas Alonso-Vante 12.1 Introduction: Toward a Systematic Protocol for Activity Measurements 377 12.2 Materials Consideration 378 12.2.1 PGM Group 378 12.2.2 Low PGM and PGM-free Approaches 379 12.2.3 Impact of Support Effects on Catalytic Sites 381 12.3 Electrochemical Cell Considerations 382 12.3.1 Cell Configuration and Material 382 12.3.2 Electrolyte 385 12.3.2.1 Purity 385 12.3.2.2 Protons vs. Hydroxide Ions 386 12.3.2.3 Influence of Counterions 388 12.3.3 Electrode Potential Measurements 388 12.3.4 Preparation of Electrodes 391 12.3.5 Well-defined and Nanoparticulated Objects 395 12.4 Parameters Diagnostic of Electrochemical Performance 396 12.4.1 Surface Area 396 12.4.2 Hydrogen Underpotential Deposition Integration 397 12.4.2.1 Surface Oxide Reduction 398 12.4.2.2 CO Monolayer Oxidation (CO Stripping) 400 12.4.2.3 Underpotential Deposition of Metals 401 12.4.2.4 Double-layer Capacitance 402 12.4.3 Electrocatalysts Site Density 402 12.4.4 Data Evaluation (Half-Cell Reactions) 404 12.4.5 The E 1/2 and E (j Pt (5%)) Parameters 405 12.5 Stability Tests 407 12.6 Data Evaluation (Auxiliary Techniques) 409 12.6.1 Surface Atoms vs. Bulk 410 12.7 Conclusions 411 Acknowledgments 412 Acronyms 412 Symbols 413 References 414 13 Durability of Fuel Cell Electrocatalysts and Methods for Performance Assessment 429 Bianca M. Ceballos and Piotr Zelenay 13.1 Introduction 429 13.2 Fuel Cell PGM-free Electrocatalysts for Low-temperature Applications 431 13.3 PGM-free Electrocatalyst Degradation Pathways 432 13.3.1 Demetallation 432 13.3.2 Carbon Oxidation 436 13.3.3 Micropore Flooding 439 13.3.4 Nitrogen Protonation and Anionic Adsorption 439 13.4 PGM-free Electrocatalyst Durability and Metrics 440 13.4.1 Performance and Durability Evaluation in Air-supplied Fuel Cell Cathode 440 13.4.2 Assessment of Carbon Corrosion in Nitrogen-purged Cathode 443 13.4.3 Determination of Performance Loss upon Cycling Cathode Catalyst in Nitrogen 443 13.4.4 Recommendations for ORR Electrocatalyst Evaluation in RRDE in O 2 and in an Inert Gas 446 13.4.5 Electrocatalyst Corrosion 447 13.5 Low-PGM Catalyst Degradation 447 13.5.1 Pt Dissolution 449 13.5.2 Carbon Support Corrosion 452 13.5.3 Pt Catalyst MEA Activity Assessment and Durability 454 13.5.4 PGM Electrocatalyst MEA Conditioning in H 2 /Air 454 13.5.5 Accelerated Stress Test of PGM Electrocatalyst Durability 456 13.6 Conclusion 457 Acronyms 459 References 460 Part VII Systems 471 14 Modeling of Polymer Electrolyte Membrane Fuel Cells 473 Andrea Baricci, Andrea Casalegno, Dario Maggiolo, Federico Moro, Matteo Zago, and Massimo Guarnieri 14.1 Introduction 473 14.2 General Equations for PEMFC Models 474 14.2.1 Analytical and Numerical Modeling 474 14.2.2 Reversible Electromotive Force 476 14.2.3 Fuel Cell Voltage 477 14.2.4 Activation Overpotential 478 14.2.5 Ohmic Overpotential – PEM Model 479 14.2.6 Concentration Overpotential 480 14.2.7 Examples of Fuel Cell Modeling 482 14.3 Multiphase Water Transport Model for PEMFCs 483 14.4 Fluid Mechanics in PEMFC Porous Media: From 3D Simulations to 1D Models 488 14.4.1 From Micro- to Macroscopic Models 490 14.4.2 Porous Medium Anisotropy 491 14.4.3 Fluid–Fluid Viscous Drag 492 14.4.4 Surface Tension and Capillary Pressure 492 14.5 Physical-based Modeling for Electrochemical Impedance Spectroscopy 496 14.5.1 Experimental Measurement and Modeling Approaches 496 14.5.2 Physical-based Modeling 497 14.5.2.1 Current Relaxation 497 14.5.2.2 Laplace Transform 498 14.5.3 Typical Impedance Features of PEMFC 498 14.5.4 Application of EIS Modeling to PEMFC Diagnostic 500 14.5.5 Approximations of 1D Approach 501 14.6 Conclusions and Perspectives 502 Acronyms 503 Symbols 504 References 507 15 Physics-based Modeling of Polymer Electrolyte Membrane Fuel Cells: From Cell to Automotive Systems 511 Andrea Baricci, Matteo Zago, Simone Buso, Marco Sorrentino, and Andrea Casalegno 15.1 Polymer Fuel Cell Model for Stack Simulation 511 15.1.1 General Characteristics of a Fuel Cell System for Automotive Applications 511 15.1.2 Analysis of the Channel Geometry for Stack Performance Modeling 514 15.1.3 Analysis of the Air and Hydrogen Utilization for Stack Performance Modeling 516 15.1.4 Introduction to Transient Stack Models 518 15.2 Auxiliary Subsystems Modeling 519 15.2.1 Air Management Subsystem 519 15.2.2 Hydrogen Management Subsystem 521 15.2.3 Thermal Management Subsystem 522 15.2.4 PEMFC System Simulation 522 15.3 Electronic Power Converters for Fuel Cell-powered Vehicles 525 15.3.1 Power Converter Architecture 527 15.3.2 Load Adaptability 527 15.3.3 Power Electronic System Components 528 15.3.3.1 Port Interface Converters 530 15.3.3.2 The PEMFC Interface Converter 530 15.3.3.3 The Motor Interface Converter 530 15.3.3.4 The Energy Storage Interface 531 15.3.3.5 Supervisory Control 531 15.4 Fuel Cell Powertrains for Mobility Use 532 15.4.1 Transport Application Scenarios 532 15.4.2 Tools for the Codesign of Transport Fuel Cell Systems and Energy Management Strategies 534 15.4.2.1 Automotive Case Study: Optimal Codesign of an LDV FCHV Powertrain 535 Acronyms 540 Symbols 541 References 541 Index 545