Abstract
Proton exchange membrane fuel cells are likely to encounter voltage reversal under hydrogen starvation conditions during real-life operations.However, it is still not fully resolved which side experiences faster or more severe degradation. Different operating conditions can further complicate this issue. In this study, we investigate the degradations on the anode and cathode sides separately after voltage reversal under different humidity conditions. The experimental results show that the anode side experiences faster and more severe degradations, but the cathode side has more pronounced effects on cell performances due to the sluggish nature of oxygen reduction reaction (ORR). Our experimental results also show measuring oxygen transport resistance can be a diagnostic tool to monitor the degree of fuel cell degradation before observable significant cell performance declines.
Fabrication of thick (900-1500 µm), crack-free lithium manganese oxide (LMO) electrodes was reproducible by using an innovated slurry casting method. The selectivity and intercalation capacity of the thick electrodes were evaluated in chloride solutions with main cations in brines and in synthetic Salar de Atacama brine using cyclic voltammetry (CV) measurements. Analyses of the CV data indicated an excellent Li+ selectivity of Li+/Na+=152.7 was achievable under voltage-controlled conditions. The mass specific intercalation capacity of the thick electrodes was 6.2-11.3 mg per gram of LMO whereas an area specific capacity of 0.282 mg/cm2 was achieved with the thickest electrode, which was 3-11 folds of that for the thin electrodes reported in literature. In addition, 82% of capacity was retained over 30 intercalation/deintercalation cycles. XRD measurements revealed that both Faradaic diffusion-controlled or battery-like intercalation and pseudocapacitive reaction contributed to the selectivity. This work establishes practical technology for thick electrode fabrication that promises reduction of the manufacturing and operational cost.