Solar H2 has shown great promise for transportation fuel and other chemical processing operations. In this paper, we examine the spatially distributed nature of both the chemical vapor deposition (CVD) process for creating semiconductor films and the photoelectrochemical (PEC) cells used to evaluate their H2-production capabilities. Our ultimate goal is to connect the two models into a complete system, whereby the process operating conditions of the CVD reactor can be explicitly connected to the spatio-temporal nature of the H2 producing films.
In this paper we consider the CVD of copper oxides, low-cost and environmentally benign semiconductors with demonstrated potential for solar hydrogen production by the PEC splitting of water -. Experiments with a hot-wall CVD reactor and a cuprous iodide/oxygen precursor system revealed unexpected film deposition spatial patterns and temperature/oxygen partial pressure dependencies these results were documented in our earlier work . In the cited study, response surface and a relatively simple physically based model were used to suggested the deposition process is largely governed by surface reactions in contrast to previously published research where gas-phase reaction and particle nucleation were considered the key deposition processes .
To further investigate the nature of the deposition process and the source of the deposition patterns observed in , a more detailed sequence of physically based models will be presented in this paper. We start with a relatively simple one-dimensional model coupling precursor transport and a combination of surface and gas phase reactions. Mode fidelity is increased by allowing for two-dimensional transport in the gas phase - solutions using a global eigenfunction expansion approach will be compared to those obtained using COMSOL. Our primary goal in this portion of the study is to evaluate the relative importance of the different reaction mechanisms and to provide a definitive answer for why the unique films compositional spatial variations are found in this reactor system.
The PEC cell modeling work begins with elementary models of the electrical characteristics of the junctions formed between the semiconductor, the conducting substrate, and the electrolyte solution of the PEC cell. Because of the time and spatially dependent nature of the solution ion distribution, and 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. With this model, the connections between the spatial nature of the CVD film and the H2 evolution of the cell will be evaluated.
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