Au@SiO2@Au core-shell-shell nanoparticles for enhancing photocatalytic activity of hematite

Photoelectrochemical (PEC) water splitting for hydrogen generation using abundantly available solar energy is a promising strategy toward developing a carbon-neutral society. Here, we demonstrate the first use of Au@SiO2@Au core-shell-shell (CSS) plasmonic nanoparticles (NPs) for improvement of the photocatalytic performance in PEC photoanodes using hematite as a testing system. Using rigorous calculations based on the Mie scattering theory on CSS NPs, we have designed and optimized the dimensions of each layer in the CSS NPs for the double resonance peaks of the CSS NPs with maximal contribution to the enhancement of the hematite PEC activity. Two different NP/hematite architectures on synthesized Sn-doped hematite nanocoral films have been studied – a top-deposited configuration with the optimized CSS NPs on the surface of the hematite, and an embedded configuration with the hematite nanocorals grown over the optimized CSS NPs. Compared with the bare hematite, the average photocurrent density, as a measure of the PEC activity, was found to be improved by 0.6 mA/cm2 and 1.45 mA/cm2 for the top-deposited and embedded CSS NP/hematite configurations, respectively. In particular, the best embedded sample showed an improvement in the photocurrent density from 0.82 mA/cm2 for the bare hematite to 3.0 mA/cm2. This improvement of 2.18 mA/cm2 is one of the highest improvements gained from a plasmonic enhancement strategy for a hematite photoelectrocatalytic system. In addition, the CSS NPs outperformed Au NPs by 1.67 times in the top-deposited configuration and up to 8 times in the embedded configuration. Our simulation and experiment results showed the following key features of CSS NPs which are critical for improving the photocurrent of hematite: (1) a double resonance peak, each of which can contribute separately to the photocurrent, (2) easy tunability of the peaks by varying the dimensions of the CSS NPs and subsequently making the plasmonic peaks strongly scattering or strongly absorbing, thereby optimizing the contributions to the PEC activity of hematite, and (3) spatially uniform electric field distributions which extend 20–25 nm from the outer surface and hence offer potential of increasing carrier generation. Our results show CSS NPs as new and improved plasmonic systems for enhancing PEC performance.