Yolanda Alvarez-Gallego

Enzymatic Electrosynthesis of Formic Acid through Carbon Dioxide Reduction in a Bioelectrochemical System: Effect of Immobilization and Carbonic Anhydrase Addition

The enzymatic electrosynthesis of formic acid from the reduction of carbon dioxide (CO2 ) by using formate dehydrogenase (FDH) as a catalyst at the cathode in both its free and immobilized forms was studied in detail in a bioelectrochemical system (BES). The essential role of solubilizing CO2 for its conversion was also studied by adding carbonic anhydrase (CA) to the FDH enzyme in both its free and immobilized forms. FDH alone in the free form showed large variation in the reduction current [(-6.2±3.9) A m-2 ], whereas the immobilized form showed less variation [(-3.8±0.5) A m-2 ] due to increased enzyme stability. The addition of CA with FDH increased the consumption of the current in both forms due to the fact that it allowed rapid dissolution of CO2 , which made it available for the catalytic reaction with FDH. Remarkably, stable consumption of the current was observed throughout the operation if both CA and FDH were immobilized onto the electrode [(-3.9±0.2) A m-2 ]. Product formation by the immobilized enzyme was also continued for three repetitive cycles, which revealed the longevity of the enzyme after immobilization. The recyclability of NADH (NAD=nicotinamide adenine dinucleotide) was also clearly evidenced on the derivative voltammetric signature. Extension of this study for continuous and long-term operation may reveal more possibilities for the rapid capture and conversion of CO2 .

Iron-containing N-doped carbon electrocatalysts for the cogeneration of hydroxylamine and electricity in a H2–NO fuel cell

Iron-containing N-doped carbon materials were investigated as electrocatalysts for the cogeneration of hydroxylamine (NH2OH) and electricity in a H2–NO fuel cell. This electrochemical route for the production of hydroxylamine is a greener alternative to the present industrial synthesis, because it allows converting the energy released during the reaction into electricity. The studied electrocatalysts were prepared by pyrolysis of composites of activated carbon and polyaniline (PANI) incorporating Fe sites (Fe-PANI-AC). Characterisation with a combination of techniques (FT-IR and Raman spectroscopy, XRD, N2-physisorption, XPS and ToF-SIMS) showed that the materials exhibit promising features as electrocatalysts for the NO reduction reaction, as they contain the desired isolated FeNxCy sites and have a relatively high degree of graphitisation, which grants good electrical conductivity. The performance of the Fe-PANI-AC electrocatalysts was investigated by means of linear sweep voltammetry (LSV) in a half cell setup and by chronoamperometry in a H2–NO fuel cell setup and compared to that of a reference electrocatalyst consisting of iron phthalocyanine supported on activated carbon (FePc/AC). The Fe-PANI-AC electrocatalysts led to higher current density than FePc/AC under all studied conditions. At low NO concentration in the feed, FePc/AC displayed higher selectivity towards hydroxylamine, whereas the Fe-PANI-AC electrocatalysts were superior at higher NO concentration (i.e. at the industrially more relevant conditions), both in terms of production rate and of selectivity towards hydroxylamine. Moreover, the Fe-PANI-AC electrocatalysts exhibited high stability under the fuel cell operating conditions. In summary, Fe-PANI-ACs displayed very promising electrocatalytic performance in the reduction of NO to hydroxylamine and offered the additional advantage of being less expensive compared to the reference FePc/AC electrocatalyst or to a benchmark noble-metal-based electrocatalyst as Pt/AC.

Gas Diffusion Electrodes Manufactured by Casting Evaluation as Air Cathodes for Microbial Fuel Cells (MFC)

One of the most intriguing renewable energy production methods being explored currently is electrical power generation by microbial fuel cells (MFCs). However, to make MFC technology economically feasible, cost efficient electrode manufacturing processes need to be proposed and demonstrated. In this context, VITO has developed an innovative electrode manufacturing process based on film casting and phase inversion. The screening and selection process of electrode compositions was done based on physicochemical properties of the active layer, which in turn maintained a close relation with their composition A dual hydrophilic-hydrophobic character in the active layer was achieved with values of εhydrophilic up to 10% while εTOTAL remained in the range 65 wt % to 75 wt %. Eventually, selected electrodes were tested as air cathodes for MFC in half cell and full cell modes. Reduction currents, up to −0.14 mA·cm2− at −100 mV (vs. Ag/AgCl) were reached in long term experiments in the cathode half-cell. In full MFC, a maximum power density of 380 mW·m−2 was observed at 100 Ω external load.