Controlling photo-activity of solution-processed hematite electrodes for solar water splitting

TLDR: In this article, a strategy to control the two kinetic processes occurring during sintering (particle size increase and dopant diffusion/activation) by incorporating Ti dopant directly into the colloid solution and reducing the annealing time was investigated.

Abstract: Hematite is a promising material for solar energy conversion via photo-electrochemical water splitting. However, the precise control of substitutional doping and nanometer feature size is important for high photon harvesting efficiency. Doped and nanostructured hematite electrodes can be prepared by a simple solution-based colloidal approach however, a high temperature (800 degrees C) annealing is required to activate the dopant atoms. This high temperature annealing step also increases the particle size above the dimension necessary for high photon harvesting efficiencies. Here we investigate a strategy to control the two kinetic processes occurring during sintering (particle size increase and dopant diffusion/activation) by incorporating Ti dopant directly into the colloid solution and reducing the annealing time. We find that this strategy leads to porous, high-surface area hematite electrodes giving a solar photocurrent density of 1.1 mA cm(-2) at 1.23 V vs. the reversible hydrogen electrode (RHE) under standard testing conditions where only 0.56 mA cm(-2) was observed at 1.23 V vs. RHE with our previous work. In addition, scanning electron micrographs examining the morphology of the electrodes suggests that our kinetic strategy is indeed effective and that further optimization may result in higher photocurrents.