Hydrophobicity Graded Gas Diffusion Layer for Stable Electrochemical Reduction of CO 2 .

To mitigate flooding associated with the gas diffusion layer (GDL) during electroreduction of CO 2 , we report a hydrophobicity-graded hydrophobic GDL (HGGDL). Coating uniformly dispersed polytetrafluoroethylene (PTFE) binders on the carbon fiber skeleton of a hydrophilic GDL uniformizes the hydrophobicity of the GDL and also alleviates the gas blockage of pore channels. Further adherence of the PTFE macroporous layer (PMPL) to one side of the hydrophobic carbon fiber skeleton was aided by sintering. The introduced PMPL shows an appropriate pore size and enhanced hydrophobicity. As a result, the HGGDL offers spatial control of the hydrophobicity and hence water and gas transport over the GDL. Using a nickel-single-atom catalyst, the resulting HGGDL electrode provided a CO faradaic efficiency of over 83 % at a constant current density of 75 mA cm -2 for 103 h operation in a membrane electrode assembly, which is more than 16 times that achieved with a commercial GDL.