Methyl phosphate formation as a major degradation mode of direct methanol fuel cells with phosphoric acid based electrolytes

Durability and degradation of vapor-fed direct dimethyl ether high temperature polymer electrolyte membrane fuel cells

“…The 1 H NMR spectra of the MEA extracts of the cells that had been operated at 160 and 200 °C, are shown in show in Figure 6a and 6b, respectively. In addition to signals corresponding to H3PO4, DME and methanol characteristic signals from methyl phosphates (methyl phosphoric acid esters) were observed in the spectra [24], although at relatively low contents (<1 mol% for at both 160 and 200 °C). Further steps towards assessing the chemical compatibility between phosphoric acid and DME were therefore taken.…”

“…Formation of methyl phosphates as a result of a chemical reaction between methanol and phosphoric acid at high temperatures was recently described as a major degradation mode of HT-PEM fuel cells operated on methanol [24]. In order to investigate if a similar degradation mode could be involved with DME as a fuel as well, the MEAs were rapidly taken out after the durability tests and small pieces were cut off and placed in DMSO-d6.…”

“…While degradation rates as low as 0.5 μV h -1 have been achieved for PBI/phosphoric acidbased cells at 160 °C and 200 mA cm 2 with hydrogen and air over 9200 h [23], cells fed directly with methanol/water vapor mixtures [12,13,15] or reformates with high methanol residual contents [18] degrade at a much faster rate. This is, at least partly, due to the severe chemical incompatibility between the methanol fed to the anode and the phosphoric acid within the polymer membrane and electrode structures, resulting in formation of methyl phosphates with lower proton conductivity and higher volatility than phosphoric acid [24]. A similar mechanism may also be part of the explanation of the fast degradation observed for cells with phosphoric acid-based electrolytes fed with ethanol [25,26].…”

Transport properties of blended sulfonated poly(styrene‐isobutylene‐styrene) and isopropyl phosphate membranes

“…Phosphoric acid is the material with the highest intrinsic proton conductivity (i.e. , 85 wt % H 3 PO 4 has a conductivity of 70 mS/cm); however, direct esterification of phosphoric acid during DMFC operation produces methyl phosphates, which degrade the doped PEMs . Organophosphates are known for their antioxidative and flame retardant abilities .…”

Understanding ternary poly(potassium benzimidazolide)-based polymer electrolytes

“…During the last two decades this electrolyte system has been thoroughly characterized with respect to e.g. the chemistry of acid uptake and proton transport [8][9][10][11][12][13][14], thermal [15] and chemical stability [16,17], nanostructure [18] as well as gas permeability [19].…”