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25: Artificial Leaf

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    Artificial Leaf?

    Review batteries:

    The anode is the ________ [source of electrons / accepts electrons].

    The cathode is the ________ [source of electrons / accepts electrons].


    Dan Nocera at MIT reported on the design of an “artificial leaf” (Acc. Chem. Res. 2012,

    45, 767-776). Under natural sunlight, such a device can convert water to O2 and H2. Nocera put an Oxygen Evolving Complex (OEC) mimic at the anode.

    • Write out the reaction carried out by the OEC.

    • Is this an oxidation or a reduction?

    Nocera put in an H2 formation cell using a NiMoZn alloy at the Cathode.

    • Write out the reaction carried out by the nickel alloy to form hydrogen.

    • Is this an oxidation or a reduction?

    The battery:

    • On the following diagram, label the sites of a) oxygen production and b) hydrogen production as well as the path of c) electron flow. Show the balanced reactions.

      Screen Shot 2019-05-18 at 8.44.34 PM.png

    Reactions at the Cathode

    To form H2 gas from H+ ions.

    • Write a half-reaction for this process.

    • Using the reduction potential table, what is the reduction potential for this reaction?

    • Is nickel that would be capable of reducing H+ to form H2.

    • Propose a catalytic cycle for the formation of H2 using a NiMoZn alloy. Assume that electrons and protons are readily available.

    Reactions at the Anode

    The OEC complex mimic is a cobalt oxide complex.

    Ullman, Brodsky, Li, Zheng, and Nocera, J. Am. Chem. Soc., 2016, 138, 4229-4236.

    Screen Shot 2019-05-18 at 8.51.44 PM.png

    • Complete the proposed mechanism for the formation of oxygen at an edge site of the cobalt complex.

      Screen Shot 2019-05-18 at 8.53.03 PM.png

    • Is the formation of O2 from H2O [exothermic or endothermic] ?

    • Why is light needed to make this artificial leaf function?

    Adding in the Dark Cycle

    Nocera reported more recently that he has furthered his “artificial leaf” to include engineered dark cycle machinery from a photosynthesizing bacterium. This allows the hydrogen produced and CO2 to be utilized in the formation of biomaterials.

    Liu, Colón, Ziesack, Silver, and Nocera, Science, 2016, 352 (6290), 1210-1213.

    • Draw the balanced reaction for the dark reaction in photosynthesis.

    • How does this bioengineered system (below) differ?

      Screen Shot 2019-05-18 at 8.54.55 PM.png

      Reproduced from PNAS, 2015, 112, 2337-2342.

    • What is the source of the carbon in this system? How will this affect the carbon balance in the atmosphere?

    25: Artificial Leaf is shared under a not declared license and was authored, remixed, and/or curated by Kate Graham.

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