Water oxidation is a critical step in water splitting to make hydrogen fuel. We first present the solution synthesis, structural/compositional characterization, and oxygen-evolution-reaction (OER) electrocatalytic properties of ~2-3 nm-thick films of NiOx, CoOx, NiyCo1-yOx, Ni0.9Fe0.1Ox, IrOx, MnOx, and FeOx. The thin-film geometry enables the use of quartz-crystal microgravimetry, voltammetry, and steady-state Tafel measurements to study the intrinsic activity and electrochemical properties of the films. Ni0.9Fe0.1Ox was the most active catalyst which is attributed to the in-situ formation of layered Ni0.9Fe0.1OOH oxyhydroxide species with nearly every Ni atom electrochemically active. Ni0.9Fe0.1OOH appears to be the fastest known OER catalyst in basic media (Trotochaud et. al. JACS 2012).To understand the role of Fe, we further studied changes in electronic properties, OER activity, and structure of Ni1�xFex(OH)2/Ni1�xFexOOH as a function of Fe incorporation. We developed a simple method for purification of KOH electrolyte that uses precipitated bulk Ni(OH)2 to absorb all Fe impurities. Voltammetry on Fe-free Ni(OH)2/NiOOH reveals new Ni redox features and no significant OER current until ~450 mV overpotential, compared to ~250 mV for Ni1�xFexOOH. We show through controlled crystallization that ߖNiOOH is less active for OER than the disordered ?-NiOOH starting material, and that previous reports of increased activity for ߖNiOOH are due to incorporation of Fe-impurities during the crystallization process. In situ conductivity measurements show the Fe increases the conductivity of NiOOH but this 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. Measurements on Co1-xFexOOH thin films show similar trends with Fe and provide new insight into the operation of these high-activity catalysts.

Thin film Ni and Co oxide/oxyhydroxide oxygen evolution electrocatalysts: The role of intentional and incidental Fe incorporation in activity enhancement

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.