A Proton Selective Carbon Nitride Layer for High Durability Fuel Cells

Abstract To achieve a balance between performance and durability in electrochemical energy conversion systems, such as fuel cells (FC) and water electrolyzers (WE), proton exchange membranes (PEMs) must be optimized for minimal thickness and resistance while maximizing gas rejection and durability. 2D materials, with Angstrom‐scale pores, hold the potential to revolutionize these devices by enabling highly selective proton transport and mitigating degradation pathways. However, to date no material has been implemented that can prevent gas crossover and extend the device lifetime without compromising initial performance. In this study, it is demonstrated that polytriazine imide (PTI), a 2D graphitic carbon nitride with optimally sized and functionalized lattice pores, facilitates unimpeded proton transport. By engineering a centimeter‐scale monolayer film composed of tessellated PTI nanosheets and placing it at the cathode‐PEM interface, significant gains in performance, efficiency, and durability ‐are achieved. These results in PEMFCs show halved hydrogen crossover and over a threefold increase in lifetime. This approach promises to accelerate the adoption of economically viable FCs and WEs with enhanced output and extended service lifetimes, essential for achieving a decarbonized society.