Further, research has shown that without the direct presence of a solid-supported electrolyte, CO2 reduction selectivity can be heavily penalized. The two cathode variations shown in Fig. and then similarly involve the diffusion of CO2 across a gas-liquid interface and through a thin electrolyte to a porous catalyst layer (Fig. ), where evidence suggests that the reaction occurs primarily in the aqueous phase rather than at a three-phase solid-liquid-gas interface. Water management is essential to maintain a stable gas-liquid equilibrium as both flooding of the gas-diffusion layer and evaporation of the catholyte will impact CO2 transport to the catalyst layer. A catalyst can be applied to the gas-diffusion layer via drop-casting, airbrushing, electrodeposition, compression, or incorporation into the porous layer itself.