Semiconductor nanowires are considered a promising candidate for solar-to-fuel conversion applications because of their unique properties, such as the high surface area and strong light trapping effect. Nanowires made of silicon, one of the most abundant semiconducting materials, have been widely investigated for photoelectrochemical H2 evolution and CO2 reduction. Recently, Yang and co-workers interfaced silicon nanowires with the biological CO2-reducing catalyst and realized solar-powered CO2 reduction to acetate. However, the mechanism of the electron transfer from solid-state materials to bacterium is still elusive. Here, we use electrochemical methods to probe the extracellular electron transfer from silicon nanowire to bacterium, S. Ovata. Specifically, with the help of Tafel plot and electrochemical impedance spectroscopy, we found that the kinetics of the heterogeneous electron transfer would switch at a certain overpotential, providing insight into the competition between the direct and indirect electron transfer pathways. Moreover, although considerable research effort has focused on studying wire arrays, the inhomogeneity in the geometry, doping, defects and catalyst loading present in such arrays can obscure the link between these properties and the photoelectrochemical performance of the wires, and correlating performance with the specific properties of individual wires is difficult because of ensemble averaging. Recently, we developed a single-nanowire-based photoelectrode platform that can be used to reliably probe the current–voltage (I–V) characteristics of individual nanowires. We find that the photovoltage output of ensemble array samples can be limited by poorly performing individual wires, which highlights the importance of improving nanowire homogeneity within an array. Furthermore, the platform allows the flux of photogenerated electrons to be quantified as a function of the lengths and diameters of individual nanowires. Such characterization of the photogenerated carrier flux at the semiconductor/electrolyte interface is essential for designing nanowire photoelectrodes that match the activity of their loaded electrocatalysts.

Silicon nanowires for solar-to-fuel conversion

253rd National Meeting (2017)

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