Controlled chemical etching leads to efficient silicon–bismuth interface for photoelectrochemical CO2 reduction to formate

Abstract

Photoelectrochemical (PEC) reduction of CO2 to useful chemical feedstocks or fuels is desirable but challenging. Its performance improvement requires not only the development of suitable semiconductors and cocatalysts but also the design of efficient semiconductor–cocatalyst interface to facilitate the rapid charge transfer. Many efforts have been undertaken on the former aspect, whereas less attention is paid on the latter. In this study, we report that Bi3+-assisted chemical etching of Si wafers affords efficient and robust Si–Bi interface for high-performance PEC CO2 reduction. Thus-formed Si/Bi photocathodes exhibit positive onset potential, large photocurrent density (∼10 mA/cm2 under 0.5 sun), and high formate Faradaic efficiency (up to 90%). In addition, we demonstrate that the photocurrent density can be further enhanced to ∼12 mA/cm2 by patterning the photocathode using photolithography to expose one-third of the Si surface without noticeably compromising the formate selectivity.