Elucidating the Sole Contribution from Electromagnetic Near-Fields in Plasmon-Enhanced Cu2O Photocathodes

Despite many promising reports of plasmon-enhanced photocatalysis, the inability to identify the individual contributions from multiple enhancement mechanisms has delayed the development of general design rules for engineering efficient plasmonic photocatalysts. Herein, a plasmonic photocathode comprised of Au@SiO2 (core@shell) nanoparticles embedded within a Cu2O nanowire network is constructed to exclusively examine the contribution from one such mechanism: electromagnetic near-field enhancement. The influence of the local electromagnetic field intensity is correlated with the overall lightharvesting efficiency of the device through variation of the SiO2 shell thickness (5-22 nm) to systematically tailor the distance between the plasmonic Au nanoparticles and the Cu2O nanowires. A threefold increase in device photocurrent is achieved upon integrating the Au@SiO2 nanoparticles into the Cu2O nanowire network, further enabling a 40% reduction in semiconductor film thickness while maintaining photocathode performance. Photoelectrochemical results are further correlated with photoluminescence studies and optical simulations to confirm that the near-field enhancement is the sole mechanism responsible for increased light absorption in the plasmonic photocathode.