Considering Nafion's  capacity for absorbing water, we find that porosity of the CL is significantly influenced by water absorption after swelling of the CL due to the presence of Nafion  , leading to a significant reduction in porosity as shown in Fig. . With increased water absorption the ionic pathways within the CL agglomerates are wetted and enhanced, while CO2 gas transport within the CL becomes more obstructed, which influences the overall efficiency of the reaction. Apart from obstruction of CO2(g) transport, the active surface area is drastically reduced, represented by the steep decline in the active surface after water saturation, as shown in Fig. .