Photoelectrocatalytic Reduction of Nitrobenzene to Azobenzene by Using Ag Nanoparticles-Decorated Si Nanocone Arrays Photocathodes

Photoelectrocatalytic (PEC) reduction of nitrobenzene (NB) is an extremely promising technology for renewable energy utilization and conversion. PEC reduction of NB to produce higher-value azobenzene (AZB) instead of aniline (AN), which is now commonly reported, is not currently achievable. In this work, we fabricated Ag nanoparticles (AgNPs)-decorated silicon nanocone (SiNC) array photocathodes with which the PEC reduction of NB to azobenzene (AZB) was realized for the first time. The SiNC array structure constructed by cryogenic dry etching greatly improved the light absorption ability of the photoelectrode. Ag was chosen as the cocatalyst because of its larger potential difference for the NB reduction reaction and the competing side reaction hydrogen evolution reaction. The Schottky junction formed by AgNPs with Si facilitates the rapid extraction of photogenerated electrons to participate in the PEC reaction. Under the optimized conditions, the PEC reduction of NB was achieved with a conversion of more than 90 %, with the reduction products being mainly AZB (9 : 1 ratio of AZB to AN) as well as excellent stability. The present work provides a photoelectrode that highly selectively PEC reduction of NB to AZB, and also provides insights into the design and preparation of high-performance silicon-based photoelectrodes.