Effect of bandgap alignment on the photoreduction of CO₂ into methane based on Cu₂O-decorated CuO microspheres

Semiconductors' band gap alignment is important for the photoreduction of CO₂ to methane. In the paper, two kinds of Cu₂O-decorated CuO microspheres composed with nanoflakes were prepared by using two different methods. Their electron behaviors were studied from the XPS spectra and photoelectrochemical measurements. Both samples are p-type CuO covered with an amount of Cu₂O nanoparticles on their surface. Combined with their bandgaps and flat band potentials, CuO-Mic has a well-matched bandgap alignment between Cu₂O and CuO, which is favorable for the separation of photogenerated electron-hole pairs. Those photogenerated carriers are beneficial for the conversion of CO₂ to CH₄, as an 8-electron process for the conversion of CO₂ to CH₄ will consume more photogenerated electrons for the chemical reactions than that of the 2-electron process for CO₂ reduction to CO. Therefore, CuO-Mic has much better photocatalytic activity for CO₂ reduction to CH₄ with a CH₄ yield ten times higher than that of CuO-Hyd under a visible light irradiation, the CO yields of the CO₂ reduction are identical. (paper)