A photograph of the scanning droplet cell suspended over a composition library. The drop of solution at the bottom of the cell contacts a 2.5 mm-diameter region of the working electrode containing a single 1 mm square sample. Nine ports (labeled A through I) are used for the solution flow and insertion of electrodes and fiber optic. The 385 nm light from an internal fiber optic illuminates the working electrode and produces a visible purple glow in the port A PTFE tube.
(a) The photoelectrochemical characterization of a Fe0.6Co0.26Ni0.07Ti0.07Ox sample in 0.1 M NaOH. The current (black) at a fixed potential was measured during 2 Hz cycling of illumination. The measured current after each illumination transition (blue, dashed) was analyzed and indicated a 70 nA photocurrent (red, right vertical axis). (b) CVs for characterization of a Fe0.57Co0.23Ni0.1Ti0.1Ox (blue) and a Co0.94Ni0.03Ti0.03Ox (green) sample for OER electrocatalysis in 0.1 M NaOH. The forward (solid) and reverse (dashed) sweeps are shown along with the residual current for the forward sweep (dotted). The FOM of catalytic current at 0.5 V is labeled on the blue trace.
Mapping of the OER catalytic current at 0.5 V overpotential in 0.1 M NaOH. This FOM for each sample of a metal oxide composition library plate (photograph in (a)) is shown in (b) using the false color scale at the bottom right. Combined with two additional plates, the quaternary composition map is shown in (c), where the horizontal planes of data points correspond to 3.3 at. % intervals of Ti concentration. Sets of three planes are plotted together in each of 10 ternary composition plots shown in (d).
The mapping shown in Fig. 3 is repeated by rastering the droplet cell over the (Fe-Co-Ni)Ox ternary compositions in three separate screens. The results from each of the three screenings demonstrated that the FOM is well repeated for most compositions but increases with repeated testing for Ni-rich compositions due to an aging phenomenon of Ni-rich electrocatalysts.
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