The chemical and thermal stability of several solid acid compounds under fuel cell operating conditions has been investigated, primarily by thermogravimetric methods. Thermal decomposition of CsHSO4, a material which has shown promise as an alternative electrolyte for proton exchange membrane (PEM) fuel cells, initiates at ∼175°C under inert conditions. The overall decomposition process can be expressed as 2CsHSO4 → Cs2SO4 + H2O + SO3 with Cs2S2O7 appearing as an intermediate byproduct at slow heating rates. Under reducing conditions, chemical decomposition can occur via reaction with hydrogen according to 2CsHSO4 + 4H2 → Cs2SO4 + 4H2O + H2S. In the absence of fuel cell catalysts, this reduction reaction is slow; however, materials such as Pt, Pd, and WC are highly effective in catalyzing the reduction of sulfur and the generation of H2S. In the case of M3H(XO4)2 compounds, where M = Cs, NH4, or Rb and X = S or Se, a similar reduction reaction occurs: 2M3H(XO4)2 + 4H2 → 3M2XO4 + 4H2O + H2X. In an operational fuel cell based on CsHSO4, performance degraded with time, presumably as a result of H2S poisoning of the anode catalyst. The performance loss was recoverable by exposure of the fuel cell to air at 160°C.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Energy Engineering and Power Technology
- Fuel Technology