Discussion Forum

Hello,

I'm doing a stationary study on a 1D photoelectrochemistry model and I want to account for charge transfer at the semiconductor - electrolyte interface. There is no coupling between the Semiconductor module and Electrochemistry module in COMSOL 5.4, so I have to make my own. For the semiconductor electrode I'm using the Semiconductor Interface and for the electrolyte I'm using Electrostatics coupled with Transport of Diluted Species.

Here is how I tried to model it:

1. I started by defining the boundary conditions of the electrode as Metal Contact, with the Workfunction in the metal being the redox potential in the electrolyte.

2. To get rid of the thermionic currents at the Metal Contact, I replaced the default Richardson's coefficients to a very small value (1e-100 ).

3. I defined a reaction rate R at the semiconductor-electrolyte boundary, calculated from variables on both sides of the interface. I created a Surface Reaction condition in the electrolyte phase and used the calculated rate R. On the Semiconductor side, I defined a User-Defined Recombination with recombination rate for the entire electrode. Then I created a Pointwise Constraint at the boundary where I constrained the expression .

Since both the consumed charges in the electrolyte and the recombined carriers in the semiconductor are controlled by R, I thought this would be a good way to account for interfacial charge transfer. However, I used probes to check the values of the surface reaction rate and recombination rate, and it turns out the recombination rate in the semiconductor is always 0.

Does anyone have any idea why is this? How else can I control for the charge transfer across semiconductor interfaces? And another issue is how can I define the current at the opposite semiconductor boundary to be the same as the current from charge transfer to the electrolyte? Since R is defined only for one boundary, I can't use it at the other one.