Photoelectrochemical Carbon Dioxide Reduction Using a Nanoporous Ag Cathode

Solar fuel production from abundant sources using photoelectrochemical (PEC) systems is an attractive approach to address the challenges associated with the intermittence of solar energy. In comparison to electrochemical systems, PEC cells directly utilize solar energy as the energy input, and if necessary, then an additional external bias can be applied to drive the desired reaction. In this work, a PEC cell composing of a Ni-coated Si photoanode and a nanoporous Ag cathode was developed for CO₂ conversion to CO. The thin Ni layer not only protected the Si wafer from photocorrosion but also served as the oxygen evolution catalyst. At an external bias of 2.0 V, the PEC cell delivered a current density of 10 mA cm^-2 with a CO Faradaic efficiency of ∼70%. More importantly, a stable performance up to 3 h was achieved under photoelectrolysis conditions, which is among the best literature-reported performances for PEC CO₂ reduction cells. The photovoltage of the PEC cell was estimated to be ∼0.4 V, which corresponded to a 17% energy saving by solar energy utilization. Postreaction structural analysis showed the corrosion of the Ni layer at the Si photoanode/catalyst interface, which caused performance degradation under prolonged operations. A stable oxygen evolution catalyst with a robust interface is crucial to the long-term stability of PEC CO₂ reduction cells.