UC San Diego

For the proposed solar sulfur-ammonia thermochemical water-splitting cycle, cobalt ferrite nanoparticles have potential use as an electrocatalyst, for the anodic reaction step of ammonium sulfite oxidizing to ammonium sulfate for the production of hydrogen. Electrophoretic deposition (EPD) of cobalt ferrite nanoparticles was investigated as a method of coating three-dimensional graphite electrodes to provide a high surface area and perhaps enhance the electrocatalytic activity. EPD was performed from 5 different bath compositions into several different substrates including aluminum, graphite paper, 3 mm carbon felt, and 6 mm graphite felt. The bath compositions were 2 g/L of cobalt ferrite nanoparticles in 100 % acetylacetone, 100 % acetylacetone with 0.2 wt. % polyethylenimine (PEI), in 100 % ethanol, and in 90/10 vol. % water/isopropanol with 1 mM or 0.05 mM of hexadecyltrimethlyammonium bromide (CTAB). The deposit morphologies were studied using a scanning electron microscope (SEM). The SEM showed full penetration and coating of the felt in 100 % ethanol bath into both 3 mm carbon felt and 6 mm graphite felt. Linear sweep voltammetry in 2 M ammonium sulfite was used to test the electrocatalytic activity of the EPD deposits. The highest electrochemical activity for cobalt ferrite on 3 mm carbon felt was deposits from 100 % acetylacetone with 0.2 wt. % polyethylenimine. The highest electrochemical activity for cobalt ferrite on 6 mm graphite felt was found in deposits from 90/10 vol. % water/isopropanol with 0.05 mM CTAB, followed by deposits from 100 % acetylacetone with 0.2 wt. % polyethylenimine.