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      On the Role of Metals in Nitrogen-Doped Carbon Electrocatalysts for Oxygen Reduction

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      Angewandte Chemie International Edition

      Wiley-Blackwell

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          High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt.

          The prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of polymer electrolyte fuel cells. We describe a family of non-precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power. The approach uses polyaniline as a precursor to a carbon-nitrogen template for high-temperature synthesis of catalysts incorporating iron and cobalt. The most active materials in the group catalyze the ORR at potentials within ~60 millivolts of that delivered by state-of-the-art carbon-supported platinum, combining their high activity with remarkable performance stability for non-precious metal catalysts (700 hours at a fuel cell voltage of 0.4 volts) as well as excellent four-electron selectivity (hydrogen peroxide yield <1.0%).
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            Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs

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              Nickel-iron oxyhydroxide oxygen-evolution electrocatalysts: the role of intentional and incidental iron incorporation.

              Fe plays a critical, but not yet understood, role in enhancing the activity of the Ni-based oxygen evolution reaction (OER) electrocatalysts. We report electrochemical, in situ electrical, photoelectron spectroscopy, and X-ray diffraction measurements on Ni(1-x)Fe(x)(OH)2/Ni(1-x)Fe(x)OOH thin films to investigate the changes in electronic properties, OER activity, and structure as a result of Fe inclusion. We developed a simple method for purification of KOH electrolyte that uses precipitated bulk Ni(OH)2 to absorb Fe impurities. Cyclic voltammetry on rigorously Fe-free Ni(OH)2/NiOOH reveals new Ni redox features and no significant OER current until >400 mV overpotential, different from previous reports which were likely affected by Fe impurities. We show through controlled crystallization that β-NiOOH is less active for OER than the disordered γ-NiOOH starting material and that previous reports of increased activity for β-NiOOH are due to incorporation of Fe-impurities during the crystallization process. Through-film in situ conductivity measurements show a >30-fold increase in film conductivity with Fe addition, but this change in conductivity is not sufficient to explain the observed changes in activity. Measurements of activity as a function of film thickness on Au and glassy carbon substrates are consistent with the hypothesis that Fe exerts a partial-charge-transfer activation effect on Ni, similar to that observed for noble-metal electrode surfaces. These results have significant implications for the design and study of Ni(1-x)Fe(x)OOH OER electrocatalysts, which are the fastest measured OER catalysts under basic conditions.
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                Author and article information

                Journal
                Angewandte Chemie International Edition
                Angew. Chem. Int. Ed.
                Wiley-Blackwell
                14337851
                August 24 2015
                August 24 2015
                : 54
                : 35
                : 10102-10120
                Article
                10.1002/anie.201500569
                © 2015
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