FeOx Hy and Fe-containing Ni/Co oxyhydroxides are the most-active catalysts for the oxygen evolution reaction (OER) in alkaline media. However, the activity of Fe sites appears strongly dependent on the electrode-substrate material and/or the elemental composition of the matrix in which it is embedded. A fundamental understanding of these interactions that modulate the OER activity of FeOx Hy is lacking. We report the use of cyclic voltammetry and chronopotentiometry to assess the substrate-dependent activity of FeOx Hy on a number of commonly used electrode substrates, including Au, Pt, Pd, Cu, and C. We also evaluate the OER activity and Tafel behavior of these metallic substrates in 1 M KOH aqueous solution with Fe3+ and other electrolyte impurities. We find that the OER activity of FeOx Hy varies by substrate in the order Au>Pd≈Pt≈Cu>C. The trend may be caused by differences in the adsorption strength of the Fe oxo ion on the substrate, where a stronger adhesion results in more adsorbed Fe at the interface during steady-state OER and possibly a decreased charge-transfer resistance at the FeOx Hy -substrate interface. These results suggest that the local atomic and electronic structure of [FeO6 ] units play an important role in catalysis of the OER as the activity can be tuned substantially by substrate interactions.
Keywords: electrochemistry; heterogeneous catalysis; iron oxyhydroxide; oxygen evolution; water electrolysis.
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