Room-temperature conversion of the photoelectrochemical oxidation of methane into electricity at nanostructured TiO₂

The energy potential of methane is restrained by the energy input required to break its C-H bond. Therefore, most of the energy conversion processes of methane use thermochemical activation which is highly endothermic. The present report demonstrates the effective photoelectrochemical activity of a TiO2 nanotube arrays photoanode towards methane oxidation in acidic electrolyte and ambient conditions. The examined photoanode exhibits a higher photocurrent density response in the presence of methane as compared to that obtained in its absence (0.54 vs. 0.27 mA cm-2, respectively). Products characterization reveals a relatively high faradaic efficiency towards the formation of CO2 and formic acid (72 and 16% at 0.3 V vs. RHE, respectively). These results are correlated to the role of the special surface architecture of the nanotube arrays in dictating the reaction pathways. The first time room-temperature operation of a solar driven fuel cell (photo-fuel cell), in which methane oxidation is converted to electricity, is also demonstrated. This device performing with an acidic electrolyte or as a gas phase photo-fuel cell exhibited output maximum power densities of 69 and 82 μW cm-2, respectively.