A nanowire photoanode SrTaO 2 N, a semiconductor suitable for overall water-splitting with a band gap of 2.3 eV, was coated with functional overlayers to yield a core−shell structure while maintaining its one-dimensional morphology. The nanowires were grown hydrothermally on tantalum, and the perovskite-related oxynitride structure was obtained by nitridation. Three functional overlayers have been deposited on the nanowires to enhance the efficiency of photoelectrochemical (PEC) water oxidation. The deposition of TiO x protects the oxynitride from photocorrosion and suppresses charge-carrier recombination at the surface. Ni(OH) x acts a hole-storage layer and decreases the dark-current contribution. This leads to a significantly improved extraction of photogenerated holes to the electrode−electrolyte surface. The photocurrents can be increased by the deposition of a cobalt phosphate (CoP i ) layer as a cocatalyst. The heterojunction nanowire photoanode generates a current density of 0.27 mA cm −2 at 1.23 V vs the reversible hydrogen electrode (RHE) under simulated sunlight (AM 1.5G). Simultaneously, the dark-current contribution, a common problem for oxynitride photoanodes grown on metallic substrates, is almost completely minimized. This is the first report of a quaternary oxynitride nanowire photoanode in core− shell geometry containing functional overlayers for synergetic hole extraction and an electrocatalyst.

Sn2O(CN2) was obtained from a solid-state metathesis. Its crystal structure incorporates a Sn2+ ion with a 5s2 lone pair and was analyzed in relation to that of SnO by electronicstructure calculations and a COHP bonding analysis.

We propose a semi-quantitative quantum-chemical model correctly ranking the ubiquitous carbon allotropes diamond and graphite in terms of energy despite their drastic structural differences.