2 Jul 2015

A discussion on "Electrochemical formation of a surface-adsorbed hydrogen-evolving species"

Literature Discussion

Submitted by Kevin Hoke, Berry College
Categories
Description: 
The paper entitled “Electrochemical hydrogenation of a homogeneous nickel complex to form a surface adsorbed hydrogen-evolving species” explores the discovery, characterization and catalytic activity of a film that deposited on the electrode while studying a nickel complex under electrocatalytic conditions.
 
This literature discussion includes several sets of questions that address different aspects of the paper, as described in the implementation notes. Discussion questions cover the structure and electron configuration of the compounds used to form catalysts, their synthesis and reactivity, the formation and activity of the catalytic film, electrocatalysis using cyclic voltammetry, and the characterization of the catalytic film.  The list of questions is extensive, but we encourage you to review them and select the ones that will best fit the goals of your lesson. 
 
This learning object was developed at the 2015 NSF sponsored cCWCS VIPEr workshop at University of Washington where we were fortunate to hear Prof. Jillian Dempsey present this research. It is worth mentioning that the first author of this paper was an undergraduate student at UNC-CH. The Dempsey’s research lab focuses on developing new technology to support a solar energy economy through catalysis. 
 
Reference: Chem. Commun., 201551, 5290-5293 DOI: 10.1039/c4cc08662g
 
Several questions of the discussion focus on data found in the supporting information. 
Learning Goals: 
By completing this activity, the student will be able to:
  • Identify the difference between facial and meridional geometries.
  • Apply 18 electron counting rules to a transition metal complex.
  • Apply electrochemical concepts to describe qualitative features of a cyclic voltammogram trace.
  • Apply knowledge of redox chemistry to understand electrocatalysis.
  • Demonstrate an understanding of reduction and oxidation reactions as they relate to transition metal complexes.
  • Use retrosynthetic analysis to determine which starting materials are needed for a Schiff base product.
  • Understand what a hydrogenation reaction is and show what happens to a double bond when it is hydrogenated.
  • Understand the use of SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) images to characterize a film. 
  • Understand the use of XPS (X-ray Photoelectron Spectroscopy) and EDS (Electron Dispersion Spectroscopy) to elucidate the elemental composition of a film.
Implementation Notes: 
It may help to split this activity and assign portions to groups of students. Or it may be better to spread the questions out over several weeks of the course, as relevant topics present themselves in the course content. For reference, the questions are split into groups below. You may also choose to eliminate certain groups of questions if they do not align with the covered content of your course. Also, a suggested exam question is included separately.
 
Questions 1-3. The structure and electronic configuration of two octahedral nickel(II) complexes. Includes basic concepts on coordination chemistry like isomerism, coordination geometry, oxidation state, and the 18 electron rule.
 
Questions 4-9. Synthesis and reactions of the organic ligands coordinated to nickel. Includes imine chemistry and the concepts of hydrogenation, hybridization, and aromaticity.
 
Questions 10-15. Electrochemical deposition of a film and its catalytic activity to produce hydrogen. Electrocatalysis and hydrogen evolution. Includes topics of cyclic voltammetry, overpotential, reversible and irreversible reductions. 
 
Questions 16-17. Discussion of methods used in the paper: CV, imaging (SEM and TEM) and spectroscopic techniques (XPS and EDS) and how XPS was used to characterize the film . Question 16 is particularly amenable to division among groups of students.
 
Suggestions for exam questions (faculty handout only). The provided exam question would be used to assess students after they have completed the in-class discussion. If very specific details about the mechanism behind the voltammetric response are desired then students may benefit from access to a clean version of the paper during the exam, 
 
This activity has not yet been tested. If the in-class discussion is to fit within 50 minutes, then several questions need to be left out of the discussion, though the students still need to do them to prepare for the discussion. Also, closely related questions can be addressed together. For example, questions 1, 2, and 6 are primarily intended to review concepts that the students need to answer questions 3, 4-5,  and 7-8. Question 9 deals with organic retrosynthetic analysis and is not essential for the questions that follow. Questions 10-13 deal with the heart of the paper, and questions 14-17 deal with controls and characterization of the system. The instructor's priorities should determine whether only the most critical questions (such as 3-5, 7-8, 10-13, and perhaps 14 and 15) are each briefly discussed in one fifty class period, or if at least half of two class periods are used for a more extensive discussion.
 
 
The activity uses some figures from the paper itself. The paper was published under a Creative Commons Attribution-NonCommercial 3.0 Unported (CC BY-NC 3.0) license as described below:
 
Time Required: 
Untested. A selection of key questions could be discussed in one 50 minute session (see implementation notes). Otherwise, the activity could take over 90 minutes.
Evaluation
Evaluation Methods: 
Options for assessment include: 
  • Students can complete the questions and submit their responses, which are then evaluated for clear understanding of the concepts. (Is the student able to describe clearly the chemistry in the paper?) 
  • Students can be evaluated for the quality of their contributions to in-class discussion. (Is it evident that the student has read the paper?)
  • Students can be asked follow up questions on a later exam. (Can the student recall and apply the principles discussed in the activity to a similar problem?) 
Evaluation Results: 

We have no results at this time for this newly created activity.  If you use this object in Fall 2015, please post comments to this LO so we can include your results!

Creative Commons License: 
Creative Commons Licence

Comments

In Spring 2016, I used a shortened portion of this activity at the end of the semester in a senior/junior level inorganic foundations course. I assigned Questions 1, 2, 5, 7, 16 (CV and XPS only) , 10a&b, 11, 12, and 17 (in that order). The students worked on the assignment out of class and I collected their responses and had a short in-class discussion.

6 students submitted responses. Two students did not count the 18 electron rule correctly (last part of question 1). Three had varying degrees of "wrongness" on the how complexes 1 and 2 were related (Question 5). These three students thought that they were mer/fac isomers of each other (not really, since the ligands are different) but one of these three also recognized the key part of the correct response: the second is the hydrogenated version of the first.

The other questions were answered correctly. 

At this point in the syllabus, the students had seen cyclic voltammetry in lab and were recently learning 18 electron rule and counting. Mer/fac isomerism had been covered much earlier in the course. This was their only exposure to the topic of XPS.

 

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