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.