Cobalt ferrite nanoparticles (20 nm) were synthesized and electrophoretically deposited onto aluminum foil, graphite paper, and carbon felt (3 mm thickness) from a 100% ethanol bath.  Linear sweep voltammetry was used to test the electrocatalytic activity of the deposits relative to blank substrates for the oxidation of ammonium sulfite to ammonium sulfate in a proposed sulfur ammonia (SA) water-splitting solar thermochemical cycle.  Subsequently, scanning electron microscopy (SEM) was used to study the morphology of the cobalt ferrite films.

The effects of electrophoretic deposition conditions on deposit morphology and the effects of deposit morphology on electrochemical activity in 2 M ammonium sulfite were investigated.  EPD on aluminum and graphite paper was performed such that particles were deposited on only one side of the substrate.  For the 3 mm thick carbon felt, particles were deposited on both sides of the substrate to improve deposit uniformity throughout the sample.  Both deposition time (0-10 minutes) and deposition current (0-16 mA) were varied to analyze their effects on the resulting deposit films for all substrates.

For the EPD conditions studied, a critical deposit thickness was found for graphite paper and carbon felt for maximum electrochemical current density, where additional deposited particles reduced the electrocatalytic activity of the deposits.  This thickness was estimated to be 3 particle layers for the graphite paper substrate.  At this thickness, the deposit had a 5.5 fold increase in activity relative to a blank graphite paper substrate.  SEM micrographs showed that the deposit uniformly covered the substrate and had noticeable cracking.  For the carbon felt, the critical deposit thickness was observed to be approximately 1-2 particle layers via SEM analysis.  Moreover, SEM images showed that the deposit was a uniform film with no cracking.  At this thickness, the deposit had a 4.3 fold increase in activity compared to a blank carbon felt substrate.