Semiconductor‐Based, Solar‐Driven Photochemical Cells for Fuel Generation from Carbon Dioxide in Aqueous Solutions

There has been active interest to identify new methods to reduce CO 2 into usable fuel sources. In this work, we demonstrate two types of photo‐electrochemical cells (PECs) that photoreduce CO 2 directly to formate in aqueous solutions both in the presence and absence of external bias or additional electron sources. The photocathodes were either a CuFeO 2 /CuO electrode or a bilayer of CdTe on NiO, whereas the photoanode was a bilayer of NiO x on CdS. The PECs were characterized by using both electrochemistry and spectroscopy, and the products formed from CO 2 reduction were characterized and quantified by using 1 H NMR spectroscopy and ESI‐MS. In addition, an organohydride catalyst was tested in conjunction with the PECs, which not only showed a significant gain of 85 times in CO 2 reduction (27 μ m formate without the catalyst, 2.3 m m formate with it) compared to the NiO/CdTe photocathode system but could also generate methanol under an external bias (10 μ m ).