Semiconducting Ta₃N₅-Polymer Nanohybrid that Photoelectrolyze Water

Abstract

The successful preparation of a nanohybrid electrode made from Ta 3 N 5 nanoparticle powders interlinked by Nafion is described. The basic photoelectrochemical properties as anode for water photolysis are investigated and gas evolution as well as corrosion reactions are determined by differential electrochemical mass spectroscopy (DEMS) and X-ray photoelectron spectroscopy (XPS). The sample shows oxygen evolution but also photocorrosion, oxidation of the Ta 3 N 5 nanoparticles via the O 1s line in XPS experiment. The photocorrosion reaction results in a core-shell structure consisting of a tantalum oxide shell and a tantalum nitride core as seen in XPS and x-ray diffraction.In the search for structures and devices that split water with visible light in a Z-scheme analogue of photosynthesis, photonic absorbers that have a suited energy gap and the according absolute positions of the energy bands (1) have still to be identified. More robust systems can be developed using inorganic material components for tandem devices that split water without external bias and with visible light (2). The highest theoretical efficiency is about 44% (3) and, using photocathode materials such as Si or layer transition metal dichalcogenides (4 , 5) which develop between 0.6V and 0.7V photovoltage, the energy gap of the anode material should be in the range of 1.7-1.9eV, thereby providing the additional photovoltage for water splitting (including overpotential losses) of 1.0V-1.2V. The latter assumption is based on the observation that in most semiconductor solar cell structures, the attainable photovoltage does not exceed 60%-70% of the energy gap (6, 7).In the development of photoanodes with Earth abundant materials and using scalable processes, only a few candidates have been identified and studied for the oxidative lightinduced water dissociation. They comprise WO 3 , BiVO 4 and Fe 2 O 3 , for example (8,9). Although limited by too large energy gaps or an unfavorable position of the band edges with respect to the water oxidation potential, the materials are intensively investigated (10). Their preparation is typically based on low-cost scalable processes such as electrodeposition, sol-gel synthesis, spin coating and spray pyrolysis (11). Besides combinatorial approaches to identify novel photoanode materials (10), the exploration and extension of preparation methods represents another route to develop materials and material composites.In this work, we present a method that allows the preparation of nanocomposite materials from powder samples that can be used as photoactive electrodes. The method is generally applicable for powder samples and will allow the screening of a large range of nanoparticle samples that have so far been unaccessible for inclusion in the search for 10.1149/05830.0001ecst ©The Electrochemical Society ECS Transactions, 58 (30) 1-7 (2014) 1 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 137.99.31.134 Downloaded on 2015-04-12 to IP