27 Mar 2017

Nanomaterials for Carbon Dioxide Reduction

Literature Discussion

Submitted by Anne Bentley, Lewis & Clark College
Categories
Description: 

This literature discussion is based on an article describing the use of copper nanoparticles on an N-doped textured graphene material to carry out the highly selective reduction of CO2 to ethanol (Yang Song et al., “High-Selectivity Electrochemical Conversion of CO2 to Ethanol using a Copper Nanoparticle / N-Doped Graphene Electrode” ChemistrySelect 2016, 1, 6055-6061.  DOI: 10.1002/slct.201601169). The article provides a good introduction to the concepts of electrochemical reduction, selectivity and recycling of fossil fuels. The literature discussion assignment shared here was used as half of the final exam in a half-credit nanomaterials chemistry course, but could be adapted for use as a take-home or in-class assignment.

AttachmentSize
File CNS ethanol.docx1.99 MB
Learning Goals: 

After reading this paper and working through the problems, a student will be able to:

  • assign oxidation states to carbon and trace the oxidation and reduction of carbon through fossil fuel combustion and CO2 conversion
  • describe the role of control experiments in studying the CO2 conversion presented in the article
  • define the word “selective” in the context of this research
  • use the proposed mechanism to explain why the electrode studied produces ethanol in such a high proportion
  • identify the primary reaction competing with CO2 reduction for available electrons
Implementation Notes: 

These questions comprised half of the final exam for my half-credit nanomaterials chemistry course in the fall of 2016.  I gave the article to the students one week ahead of time. They were encouraged to read the article, make any small notes they liked, and meet with me in office hours with questions. At the final exam they were allowed to use their copy of the article, but they were also required to hand in their copy with their exam so that I could make sure they hadn't written lots of extraneous information on the exam copy.

The nanomaterials course features near-weekly homework assignments centered around articles from the literature. Because I used this article at the end of the course, students were already familiar with nanomaterials synthesis and characterization techniques. Thus, some of the questions I asked relied on previous knowledge. 

Please feel free to adapt these questions and add some of your own. Leave comments describing any new questions you’ve added.

Time Required: 
one hour
Evaluation
Evaluation Methods: 

The problems presented here represented half the points on the final exam – I have included point totals to give an idea of the weight assigned to each problem.

Evaluation Results: 

Twelve students were enrolled in my course in the fall 2016. The average overall score for these problems was 78%.

For problem 1b, I calculated the oxidation numbers using the familiar general chemistry method of assigning oxygen as –2 and hydrogen as +1. Students recently coming through organic may have some other way to do it, and you may need to provide directions for your students about your preferred method.  I think I could have worded part (c) better to try to emphasize the redox processes involved. I wanted them to think of combustion, but I think they needed to be specifically prompted, such as "Give an example of the combustion processes that generate CO2 and trace the oxidation state of carbon through the reaction." Overall my students scored 86% on problem 1.

The second problem (about another method that could be used to measure d-spacing) was fairly hit or miss.  Five students got full credit, six students got 3 points, and one got zero. Eleven out of twelve did answer part (a) correctly.  I realized as I made this LO that the article says the carbon-based material doesn’t diffract X-rays, but doesn’t actually directly explain whether or not the Cu nanoparticles diffracted X-rays, so you may need to adjust the question to be technically accurate.

Question three (re: surfactants in nanoparticle synthesis) referred back to knowledge from earlier in the course. The overall score was 61%.

Question 4 (define and describe electrodes) was fairly straightforward, and students scored 85%.

Question 5 caused some confusion, as some students missed that I was looking for “carbon-containing” products only. I didn’t count off for that mistake, but it made the problem harder for students who included hydrogen in each box.  Overall, students did very well on this problem (89% correct).

Question 6 – again, not too much trouble here (84% correct).

Question 7 – I was surprised that students didn’t do better on this question, as I thought that water reduction was mentioned often in the article.  Only three (of 12) students scored 5 points on this problem, and the average score was 53%.  This was probably my favorite question, as it foreshadows electrochemistry topics I cover in my inorganic course.

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