Efficient solar photoelectrosynthesis of methanol from carbon dioxide using hybrid CuO–Cu2O semiconductor nanorod arrays

Solar photoelectrosynthesis of methanol was driven on hybrid CuO-Cu(2)O semiconductor nanorod arrays for the first time at potentials ~800 mV below the thermodynamic threshold value and at Faradaic efficiencies up to ~95%. The CuO-Cu(2)O nanorod arrays were prepared on Cu substrates by a two-step approach consisting of the initial thermal growth of CuO nanorods followed by controlled electrodeposition of p-type Cu(2)O crystallites on their walls. No homogeneous co-catalysts (such as pyridine, imidazole or metal cyclam complexes) were used contrasting with earlier studies on this topic using p-type semiconductor photocathodes. The roles of the core-shell nanorod electrode geometry and the copper oxide composition were established by varying the time of electrodeposition of the Cu(2)O phase on the CuO nanorod core surface.