The manufacturer impregnates the porous layer with an acidic electrolyte solution, and applies platinum wire electrical connections to the platinum black surfaces. The manufacturer mounts the entire assembly in a plastic case, which also includes a gas inlet that allows a breath sample to be introduced. Various manufacturers employ numerous proprietary nuances in their construction. The basic configuration, however, follows that described above and illustrated in Figure 1. The exact chemistry of the reaction that takes place in an alcohol fuel cell is open to some conjecture.
Researchers assume that the reaction converts alcohol to acetic acid.
In the process, this conversion produces two free electrons per molecule of alcohol. This reaction takes place on the upper surface of the fuel cell. Thus, the upper surface has an excess of electrons, and the lower surface has a corresponding deficiency of electrons. If you connect the two surfaces electrically, a current flows through this external circuit to neutralize the charge. This current is a direct indication of the amount of alcohol consumed by the fuel cell.