Non-precious metal catalysts prepared by chemical functionalization of carbon surfaces.
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New sources of power are of great interest as attempts to make smaller, more convenient and environmentally friendly sources are being investigated. Hydrogen fuel cells are a way to combine both an effective method of power supply, converting chemical energy into electrical energy directly, and a way to employ clean energy. Fuel cells involve the use of platinum (Pt) as a catalyst, for both the oxygen reduction and hydrogen oxidation reactions, which is both rare and expensive. As such, there is significant ongoing research towards the discovery of non-precious metal catalysts (NPMC) with activity comparable to that of Pt. The Fe-N/C catalyst system is a promising alternative, though the exact structure of the active catalytic site is still debated. Active catalysts are typically formed by high temperature (600 – 1000°C) pyrolysis in an ammonia atmosphere of a carbon with adsorbed iron on the surface. Our approach to these catalysts employs surface chemical methods to more systematically synthesize the active site in order to better relate structure and activity. The current nitrogen compound of interest is 5,6-diamino-1,10-phenanthroline (aphen) which was attached to a carbon support (Black Pearls 2000 or Ketjen Black EC600JD) using a diazonium coupling reaction. This a chemisorption process, as opposed to physisorption one, that allows for a clearer model of attachment of the aphen molecule. In order to understand the effects of the precursor and the metal on active site density and activity many synthetic parameters were varied and measurements were taken at each step of the process. Aphen loading was investigated by preparing a series of samples with increasing ratios of aphen to Black Pearls 2000 and Ketjen Black EC600JD. Iron uptake was also explored by using two different iron salts; iron(III) chloride and iron(II) acetate. An alternate carbon support and synthetic route was also explored using graphene oxide in a glycerol reflux to mimic reactions commonly used to make organometallic compounds. Overall it was found that the Black Pearls 2000 outperformed the Ketjen Black EC600JD samples at all ratios. An optimal heat treatment, ink loading and ratio of aphen to carbon black pearls was determined for these catalyst materials. It was also observed that using iron(III) chloride for the iron uptake step produced the most active catalyst. Electrochemical and structural measurements indicate that the success of the diazonium coupling reaction and graphitization during heat treatment are essential to the synthesis of active materials.