Aluminum and copper plasmonics for enhancing internal quantum efficiency of core-shell and core-multishell nanowire photoelectrodes

One of the critical challenges for achieving solar-to-hydrogen efficiency greater than 10% (100 W/m2), especially in metal oxide photoelectrodes, is the poor internal quantum efficiency arising from high, bulk and surface, recombination and insufficient light absorption. Plasmonic light harvesting has emerged as a promising strategy to address this challenge. However, most designs are photocatalyst specific and employ precious metals, making large scale applications infeasible. We present metal-photocatalyst core-shell and semiconductor-metal-photocatalyst coremultishell nanowires as a novel class of multi-functional plasmonic photoelectrodes. By combining the optical resonances with the localized surface plasmon resonance within the proposed structures, we achieve extreme light absorption in the visible range within ultrathin photocatalyst layers. Such enhanced absorption ensures that the photocharges are preferentially generated very close to the photocatalyst-electrolyte interface and can effectively drive the reaction forward, thereby improving the internal quantum efficiency. Specifically, for nanowires in an aqueous electrolyte, we demonstrate the effectiveness of aluminum and copper to confine light and establish them as plasmonic alternatives to precious metal counterparts such as silver and gold therefore enabling cheap and scalable plasmonics. Further, we probe the absorption as a function of the permittivity of the electrolyte and show that the absorption in such nanowires is large even for high permittivity electrolytes. Hematite and copper(I) oxide have been chosen as the test materials to validate the generality of this approach. Notably, for hematite, we show that aluminum is more effective than copper, while for a broadband absorber such as copper(I) oxide, we show that both aluminum and copper are equally effective for plasmonic light harvesting.