where FE s,c,t denotes the Faraday efficiency toward component c of stack s, j s,t the current density of stack s, A Cell the active electrode area, N Cell the number of cells per stack, ∆t the length of time step, F the Faraday constant, and z c the number of electrons transferred. Note that FE s,c,t of CO 2 -electrolyzers often sharply varies with respect to j s,t . For example, when a silver catalyst is applied to the cathode, the CO 2 reduction reaction that generates CO is superior at low current density due to its low onset potential while the hydrogen evolution reaction becomes dominant at high current density . Therefore, this dependency should be properly represented by exploiting either experiment or simulation data.