fig4

Figure 4. Three major approaches for the catalyst layer fabrication. This figure is quoted with permission from Zhao et al.^[44]. CCM: The catalyst layer loaded on the proton exchange membrane; CCS: the catalyst layer loaded on the gas diffusion layer; CL: catalyst layer; DTM: the catalyst layer loaded on the proton exchange membrane through transfer; GDL: gas diffusion layer; MEA: membrane electrode assembly.