Long-term degradation behaviors research on a direct methanol fuel cell with more than 3000h lifetime

Highlights: • Lifetime of a DMFC reaches 3135.7 h by adopting new test strategy. • Proton (H+) recovery method and increasing operation temperature recovery DMFC discharge ability. • N₂ purging worked as an effective method to eliminate cathode water flooding. • The real degradation behavior along with operation time is revealed. This paper focuses on the gradual performance and durability degradation behaviors of a direct methanol fuel cell (DMFC) with more than 3000 h lifetime. This work adopted a new DMFC test strategy and the entire lifetime test consisted of No.1-No.166 single operation. Stage-failure phenomenon occurred in the lifetime test, which indicated the existence of recoverable and non-recoverable degradations during the entire operation process. In-situ electrochemical tests were applied to the DMFC to analyse causes of durability and performance loss. When single cell came to failure, some recoverable methods were conducted to realize the recovery and improvement of DMFC performance and durability. As a result, during each single operation, continuous lifting pressure operation can realize the improvement of catalyst activity and optimization of mass transfer channel. Proton (H⁺) recovery method and increasing operation temperature can effectively solve the problem of internal resistance enlargement. According to the results of electrochemical monitoring, higher temperature results in the rapid degradation of catalytic layer activity, and lower temperature causes the increase of membrane resistance. N₂ purging works as an effective method to eliminate the concentration polarization caused by cathode "water flooding" phenomenon. Based on these results, it can be concluded that the main degradation of DMFC successively changes with operation time, which mainly comes from internal resistance enlargement, cathode concentration polarization and final deactivation of catalyst at different operation stages. This work well explains the real long-term degradation behaviors of DMFC along with operation time, and provides several practicable methods for recovering DMFC performance and durability.