Enhanced low-humidity performance in a proton exchange membrane fuel cell by the insertion of microcrystalline cellulose between the gas diffusion layer and the anode catalyst layer

Abstract

A high-performance self-humidifying membrane electrode assembly (MEA) was prepared by inserting hygroscopic microcrystalline cellulose (MCC) between the gas diffusion layer (GDL) and the catalyst layer (CL). At low humidity, the MEA exhibited good self-humidification, including high output and good stability. With our optimal MEA, in which the MCC loading was ca. 0.5 mg cm−2, the current density at 0.6 V reached 1100 mA cm−2 and the maximum power density was 751 mW cm−2, at a relative humidity (RH) of 30% for both anode and cathode gases and a cell temperature of 70 °C; the performance was comparable to that of a MEA prepared without added MCC and operated at 100% RH. Further, after 24 h of operation at low humidity and 0.6 V, the MEA's current density decreased by only 9.1%, compared with the 60% decline experienced by the MEA without MCC after 3 h under the same conditions, demonstrating the former's good self-humidification stability. When we attempted to insert the MCC layer elsewhere, including between the membrane and the anode CL, we found that inserting it between the GDL and the anode CL yielded the best performance. The high self-humidification performance of this MEA is attributable to the strong wettability and water-retention capacity of MCC. The MCC layer between the GDL and the anode CL ensured the latter would remain sufficiently wet and accelerated hydrogen activation and proton transfer, resulting in the MEA having high self-humidification under conditions of low humidity and high cell temperature.