In this paper we develop mathematical and physics-based models to understand the chemical vapor deposition of copper oxide electrodes and their performance in a photo-electrochemical cell(PEC).
We consider the CVD of copper oxide, because of its demonstrated potential for solar hydrogen production by the PEC splitting of water and its low cost and practically null toxicity. Extensive experiments with a hot-wall CVD reactor and a cuprous iodide/oxygen precursor system are conducted, revealing unexpected film deposition patterns and temperature/oxygen partial pressure dependencies.
An evolutionary sequence of mathematical models is developed to understand the observed behavior, starting with an empirical response surface model (RSM) to rigorously determine the trends indicated in the data. Then, a series of physics-based models are developed to gain a theoretical understanding of the thermodynamic, reaction, and chemical species transport mechanisms at work in this reactor. In contrast to previously published research where gas-phase reaction and particle nucleation were identified as the key processes, our model predictions suggest the deposition process is largely governed by surface reactions. To study the electrodes performance in the PEC, a PDE model of the cell's equivalent electrical circuit is developed to evaluate the current-vs-voltage characteristics of the cell, under dark and illuminated conditions.
Our ultimate goal is to connect the two models, the one for the CVD and the one for the PEC, into a complete system, so that the operating conditions of the CVD reactor can be explicitly linked to the hydrogen producing performance of the deposited electrodes.