Abstract
Dissipation of phosphoric acid from fuel cells operating for 2 years is found to cause an increase of gas permeability between the fuel electrode and air electrode and a rapid decrease of the cell voltage. After phosphoric acid is replenished in the cells, gas permeability decreases and the cell voltage is recovered.
Characteristics of cells before acid replenishment are as follows.
(1) Low open circuit voltage.
(2) High temperature rise due to reactive gas supply for the open circuit condition. The temperature rise is in proportion to the conductance of gas permeability between the fuel electrode and air electrode.
(3) Temperature rise depends mostly on the flow rate of fuel gas. Heat of direct combustion can be separated from the heat of the electro-chemical reaction by the measured temperature rise. The ratio of direct combusion to the electro-chemical reaction decreases by increasing fuel utilization.
(4) Air utilization, fuel utilization or pressure difference dependency of the cell voltage have hardly any change due to acid replenishment.
