Improved performance of the direct methanol redox fuel cell

Advancements in the performance of the direct methanol redox fuel cell (DMRFC) were made through anolyte/catholyte composition and cell temperature studies. Catholytes prepared with different iron salts were considered for use in the DMRFC in order to improve the catholyte charge density (i.e., iron salt solubility) and fuel cell performance. Following an initial screening of different iron salts, catholytes prepared with FeNH4(SO4)2, Fe(ClO4)3 or Fe(NO3)3 were selected and evaluated using electrolyte conductivity measurements, cyclic voltammetry and fuel cell testing. Solubility limits at 25 °C were observed to be much higher for the Fe(ClO4)3 (>2.5 M) and Fe(NO3)3 (>3 M) salts than FeNH4(SO4)2 (~1 M). The Fe(ClO4)3 catholyte was identified as a suitable candidate due to its high electrochemical activity, electrochemical reversibility, observed half-cell potential (0.83 V vs. SHE at 90 °C) and solubility. DMRFC testing at 90 °C demonstrated a substantial improvement in the non-optimized power density for the perchlorate system (79 mW cm−2) relative to that obtained for the sulfate system (25 mW cm−2). Separate fuel cell tests showed that increasing the cell temperature to 90 °C and increasing the methanol concentration in the anolyte to 16.7 M (i.e., equimolar H2O/CH3OH) yield significant DMRFC performance improvements. Stable DMRFC performance was demonstrated in short-term durability tests.