Hydrogen production via bacterial fermentation is currently limited to a maximum of 4 moles of hydrogen per mole of glucose, and under these conditions results in a fermentation end product (acetate; 2 mol/mol glucose) that bacteria are unable to further convert to hydrogen. It is shown here that this biochemical barrier can be circumvented by generating hydrogen gas from acetate using a completely anaerobic microbial fuel cell (MFC). By augmenting the electrochemical potential achieved by bacteria in this MFC with an additional voltage of 250 mV or more, it was possible to produce hydrogen at the cathode directly from the oxidized organic matter. More than 90% of the protons and electrons produced by the bacteria from the oxidation of acetate were recovered as hydrogen gas, with an overall Coulombic efficiency (total recovery of electrons from acetate) of 60-78%. This is equivalent to an overall yield of 2.9 mol H2/mol acetate (assuming 78% Coulombic efficiency and 92% recovery of electrons as hydrogen). This bio-electrochemically assisted microbial system, if combined with hydrogen fermentation that produces 2-3 mol H2/mol glucose, has the potential to produce ca. 8-9 mol H2/mol glucose at an energy cost equivalent to 1.2 mol H2/mol glucose. Production of hydrogen by this anaerobic MFC process is not limited to carbohydrates, as in a fermentation process, as any biodegradable dissolved organic matter can theoretically be used in this process to generate hydrogen from the complete oxidation of organic matter.

Several poly(perfluorosulfonic acid) membranes (NAFION, EW ) 1100) with the same sulfonic acid content were systematically investigated with SANS under in-situ water vapor sorption and/or with bulk water to quantify the effects of relative humidity (RH), membrane processing (melt-extruded and solution-casting), prehistory (pretreated at 80°C and as-received), and thickness on the nanoscale structure at room temperature. The sorption isotherm (water uptake vs RH) of the membranes showed a strong correlation between the interionic domain distance (L ion ) and RH. The melt-extruded membranes showed evidence of partial alignment of better organized ionic domains than those solution-cast. Pretreating the membranes resulted in a larger L ion and a broader scattering over the entire range of RH. The ionic peak of the melt-extruded membranes (as-received and pretreated) became more symmetric and narrower with sorption time. Diffusion coefficients of water vapor, based on structural evolution and Fick's second law, are in the range of 1 × 10 -7 -3 × 10 -7 cm 2 /s for both extruded (pretreated and as-received) membranes. A thickness-dependent crystalline feature around Q ≈ 0.03 Å -1 was also observed.

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