Facet-specific heterojunction in gold-decorated pyramidal silicon for electrochemical hydrogen peroxide sensing

Abstract

Nanoscale heterojunction of asymmetrical band structures and electron distributions at the interfaces is critical for activity enhancement in various catalytic applications. However, realization of facet-specific heterojunction remains challenging; yet it has been rarely studied in electrocatalysis. In this work, we first report the enhanced electrocatalytic performance of monolith Au/Si (111) heterojunction on Si micron-scale pyramids, prepared by alkaline Si-wafer etching with surface decoration of isolated gold nanoparticles (5–15 nm). The Au/Si (111) heterojunction exhibits the facet-dependent electrochemical activities superior to Au/Si (100). Varied Si etching levels enable the mixed exposure of Si (111) and Si (100); and the results further support the facet-dependent electrochemical enhancement. By excluding the effects of surface areas and defects, studies on the role of Si (111) reveal that the Au/Si (111) interface is very essential in improving the sensitivity and the detection limit at the heterojunction. This means that usage of well-controlled facets instead of merely facilitating electron transport can be considered in heterojunction electrocatalyst design. The H2O2 sensing performance of Au/Si (111) is synergistically enhanced achieving 194 times greater sensitivity than the Au/Si (100) with a wide linear range from 0.01 to 55.55 mM, high sensitivity (171 μA mM−1 cm−2), and low detection limit of 1.24 μM.