A Highly Ordered Hydrophilic–Hydrophobic Janus Bi-Functional Layer with Ultralow Pt Loading and Fast Gas/Water Transport for Fuel Cells

One of the critical challenges that limit broad commercialization of proton exchange membrane fuel cells(PEMFC)is to reduce the usage of Pt while maintaining high power output and sufficient durability.Herein,a novel bifunctional layer consisting of vertically aligned carbon nanotubes(VACNTs)and nanoparticles of Pt-Co catalysts(Pt-Co/VACNTs)is reported for highperformance PEMFCs.Readily prepared by a two-step process,the Pt-Co/VACNTs layer with a hydrophilic catalyst-loaded side and a hydrophobic gas diffusion side enables a PTFE-free electrode structure with fully exposed catalyst active sites and superior gas–water diffusion capability.When tested in a PEMFC,the bi-functional Pt-Co/VACNTs layer with ultralow Pt loading(~65μgcathodecm-2)demonstrates a power density of 19.5 kW gPt cathode-1 at 0.6 V,more than seven times that of a cell with commercial Pt/C catalyst(2.7 kW gPt cathode-1 at 0.6 V)at a loading of 400μgcathodecm-2 tested under similar conditions.This remarkable design of VACNTs-based catalyst with dual functionalities enables much lower Pt loading,faster mass transport,and higher electrochemical performance and stability.Further,the preparation procedure can be easily scaled up for low-cost fabrication and commercialization.