Particle suspension reactors (PSRs), where solar fuels are generated via a slurry of photocatalytic nanoparticles, present an advantage over traditional planar photoelectrodes due to their significantly decreased startup and maintenance costs. One promising type of low-dimensional semiconductor material that can be used in PSRs is the silicon nanowire (SiNW). SiNWs grown via the vapor-liquid-solid mechanism can be doped during growth to encode sequential p-i-n junctions. Dopant transitions are sufficiently abrupt to allow n-p units between each p-i-n junction to act as a tunnel junction, thus allowing voltage summation across the length of a single wire. This enables exceptional photovoltaic characteristics, including a photovoltage that is directly proportional to the number of junctions, generating upwards of 10 V for a single 40-junction NW, well in excess of what is needed for CO2 reduction. The use of molecular catalysts in tandem with SiNWs for CO2 reduction is of strong interest because they typically offer a narrower distribution of higher carbon products in comparison to their heterogeneous counterparts. Their properties, and hence catalytic activity, can be rationally tuned via simple synthetic modifications. To this end, we have demonstrated the efficacy of this architecture by suspending multijunction nanowires with a molecular CO2 reduction catalyst, cobalt bis(terpyridine), to create a highly selective hybrid photocatalytic system that generates exclusively formate and CO under 1-sun illumination. Current work seeks to improve the performance of PSRs by elucidating the mechanisms governing the photovoltaic and electrochemical response at the single nanowire scale, using single nanowire devices, and at the reactor scale, using finite-element modeling and operando time-resolved spectroscopy. Additionally, by integrating multiple molecular catalyst species with SiNWs, we aim to upgrade products to higher carbon fuels.

Hybrid multijunction silicon nanowires for solar driven CO2 reduction in suspension

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.