From which kind of process you want to determine the efficiency?
In electrodeposition the efficiency could be determined by the relationship of mass difference before and after deposition and the applied electrical charge.
Efficiency of a modified electrode can be determined by comparing its response (towards the oxidation or reduction of an electroactive spicies) with the response of unmodified electrode submited to the same experimental conditions.
I think that your purpose is the study of catalysts. Right?
I am not the most expertise on it. However, I agree with Charif Dehchar.
You should made the same experiments with and without the catalyst. The comparison of the kinetical parameters with commercial catalysts should give you the efficiency of the material.