Nanoplasmonic zirconium nitride photocatalyst for direct overall water splitting

The ability of plasmonic nanostructures to efficiently harvest light energy and generate energetic hot carriers makes them promising materials for utilization in photocatalytic water spitting. Apart from the traditional Au and Ag based plasmonic photocatalysts, more recently the noble–metal–free alternative plasmonic materials have attracted ever–increasing interest. Here we report the first use of plasmonic zirconium nitride (ZrN) nanoparticles as a promising photocatalyst for water splitting. Highly crystalline ZrN nanoparticles with sizes dominating at 30–50 nm were synthesized that exhibit intense visible and near–infrared absorption due to localized surface plasmon resonance (LSPR). Without utilizing any noble metal cocatalysts such as Pt, the plasmonic ZrN nanoparticles alone showed stable photocatalytic activity for H₂ evolution in aqueous solution with methanol as sacrificial electron donor. The addition of a cobalt oxide (CoO_x) cocatalyst can facilitate the separation of photogenerated charge carriers and further improve the photocatalytic activity. The optimized CoO_x modified ZrN photocatalyst was observed not only to activate the O₂ evolution reaction with presence of electron acceptor, but also to drive overall water splitting for the simultaneous H₂ and O₂ evolution in the absence of any sacrificial agents.