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Tutorial EC4: Advanced Characterization of (Photo) Electrochemical Energy Materials

Sunday, November 27, 2016
8:30 AM - 5:00 PM
Hynes, Level 2, Room 203

Instructors

  • Ethan J. Crumlin, Lawrence Berkeley National Laboratory
  • Heinz Frei, Lawrence Berkeley National Laboratory
  • Dino Klotz, Israel Institute of Technology

8:30 am — 10:00 am

Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) for Catalysis and Electrochemistry

Ethan J. Crumlin  

X-ray Photoelectron Spectroscopy (XPS) is a surface sensitive technique that can provide surface elemental, chemical, and potential information. This technique has traditionally been used to study sample surface chemistry in ex situ ultra-high vacuum (UHV) conditions.  However, environmental, biological, and energy materials involve interactions with gases, liquids and/or solids which requires a technique capable of probing these interfaces under operating and realistic conditions. This motivated the development of ambient pressure XPS (APXPS) which provides the ability to obtain information from chemical species to potential information such as work functions, applied potentials, and the electrochemical double layer. This segment of the tutorial will introduce APXPS as a technique for observing interface phenomena with a focus on energy sciences, using successful studies to demonstrate the practical aspects and powerful features of this technique. The emphasis is on the practical considerations ranging from sample configurations, data collection strategies, and instrument operation, to scientific questions that can be probed.

  1. Basics of XPS and APXPS  
    a. Technique
    b. Instrumentation
    c. Synchrotron-based Systems
    d. Emergence of Lab-based Systems
    e. Spectroscopy and Microscopy
     
  2. Solid/Gas Interface
    a. Surface Chemistry/Catalysis
        1. Surface Chemistry
        2. Work Function
    b. Solid-State Electrochemistry
        1. Solid Oxide Electrochemical Cells
        2. Lithium Air Battery 
    1. Solid/Liquid Interface
      a. Interface Chemistry
      b. Semiconductors
      c. Electrochemical Double Layer
       
    2. Solid/Solid Interface
      a. Batteries 

    10:30 am — 12:00 pm

    Time-Resolved Fourier-Transform Infrared Spectroscopy of Catalysis for Energy Under Reaction Conditions

    Heinz Frei

    Time resolved monitoring of thermal or photo-induced catalysis under reaction conditions with a structure-specific spectroscopy such as FT-IR provides critical mechanistic insights for guiding design improvements of catalysts. This holds in particular for the field of materials for the conversion of carbon dioxide and water to fuels and chemicals, which is very challenging given the stringent materials requirements of robustness, efficiency and scalability. The tutorial will introduce the spectroscopic methods and experimental techniques for monitoring photo-driven and thermally driven catalysis of carbon dioxide reduction, water oxidation and hydrocarbon conversion at metal oxide, metal particle and semiconductor catalysts on time scales ranging from milliseconds to nanoseconds. The emphasis will be on experimental techniques, spectroscopic analysis and determination of mechanisms using latest research on catalytic systems for sunlight to fuel as examples.

    1. Basics of Rapid-Scan FT-IR Spectroscopy

    2. Time-Resolved FT-IR Spectroscopy on the Millisecond Time Scale
      a. Under Reaction Conditions
      b. Photocatalysis at the Liquid-Solid Interface
      c. Molecular Catalysts in Solution
      d. Thermal Catalysis at the Gas-Solid Interface

    3. Basics of Step-Scan FT-IR Spectroscopy
      a. Time-Resolved FT-IR Spectroscopy on the Nano- and Microsecond Time Scale under Reaction Conditions
      b. Dynamics of Small Radicals in Nanostructured Environments
      c. Photocatalysis on Semiconductor Surfaces 

    1:30 pm — 5:00 pm

    Photoelectrochemical Impedance Techniques

    Dino Klotz

    Electrochemical Impedance Spectroscopy (EIS) is a powerful tool to characterize electrochemical systems by probing the dynamics of the relevant charge carriers. In the field of photoelectrochemistry, photoelectrochemical impedance spectroscopy (PEIS: EIS conducted while illuminating the sample statically) is becoming a method of strong interest. Intensity modulated photocurrent /photovoltage spectroscopy (IMPS/IMVS) are relatively new and powerful techniques but only few results have been published using them.

    The tutorial will provide a general introduction into EIS and the basic concept of impedance analysis will be explained, thereby demonstrating the capacity of this analysis method. This includes measurement, data analysis, modeling and interpretation. Further, the distribution of relaxation times (DRT) will be introduced as a valuable tool for the empirical analysis of impedance data.

    The main focus of this segment will be dedicated to the trio of PEIS, IMPS and IMVS. Starting from scratch, a comprehensive empirical analysis approach for photoelectrochemical (PEC) cells will be presented. It will be demonstrated with measurements on hematite photoanodes that PEIS, IMPS and IMVS are able to provide new insights into the rate-limiting processes in PEC cells and are well-suited to probe the charge carrier dynamics of complex photoelectrochemical reactions.

    1. Electrochemical Impedance Spectroscopy (EIS)
      a. Measurements
      b. Data Analysis
      c. Modeling 
      d. Interpretation of Model Results
      e. Analysis by the Distribution of Relaxation Times (DRT) 
      1. Photoelectrochemical Impedance Spectroscopy (PEIS) 
          
      2. Intensity Modulated Photocurrent Spectroscopy (IMPS) 
          
      3. Intensity Modulated Photovoltage Spectroscopy (IMVS) 
          
      4. Comprehensive Analysis of PEIS, IMPS and IMVS
        a. Relationship between PEIS, IMPS and IMVS
        b. General IMPS Analysis
             i. Comparison to Chopped Light Measurements
             ii. Analysis Approach to Extract Positive and Negative Components in the Photocurrent
        c. Observations gained from Measurement Results on Hematite Photoanodes
        d. Examples for Advanced Cell Characterization
        e. DRT Analysis of PEIS and IMVS Measurements