Improved overall water splitting with barium tantalate mixed oxide composites

Abstract

The combination of effective charge carrier separation and improved electron transfer in highly crystalline barium tantalate composites modified with Rh-Cr 2 O 3 core-shell co-catalyst systems induces enhanced activity for overall water splitting (OWS) with stoichiometric amounts of H 2 and O 2 (2 : 1). A sol-gel route employing complexing reagents was investigated to prepare selectively defined mixed oxide materials with improved surface areas and smaller particle sizes compared to the conventional solid state reaction (SSR). The catalytic activities of the materials are investigated in photocatalytic test reactions for hydrogen production and overall water splitting. The formation of Rh-Cr 2 O 3 core-shell co-catalyst systems for water splitting is evidenced by transmission electron microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). Moreover, we developed new and highly active barium tantalate composites for hydrogen generation from aqueous methanol solutions under UV-light, which show the highest hydrogen evolution rate for a three-component composite consisting of Ba 5 Ta 4 O 15 /Ba 3 Ta 5 O 15 / BaTa 2 O 6 . Hydrogen rates of more than 6 mmol h À1 can be achieved without any co-catalyst. Using Rh-Cr 2 O 3 core-shell co-catalysts on these three-component composites simultaneous generation of H 2 and O 2 from pure water splitting reaches rates up to 70% higher than for the pure Ba 5 Ta 4 O 15 .

Oxidized Mild Steel S235: An Efficient Anode for Electrocatalytically Initiated Water Splitting

“…[18] Researchers led by Strasser and Wark reported ac ore-shell architecture based on noble-metal-containing nanoparticles, which is ap ossible route not only to reduce the price of noble-metal-containing catalysts [19] but also to enhancetheir stability and efficiency. [20] Neverthelesst here is still al ack of efficient, stable, and low-priced catalysts made from earth-abundant, affordable elements. Pioneering studies by the groups of Hoare, Bard, Bockris, and several others [21][22][23] showed that the voltage necessary to produce oxygen on am etal surfacei sr elated to the redox potential of the metal/metal oxide couple, or in other words, even in the case of noble metals no oxygen can be released from the surface if the corresponding metal oxide is not formed.…”

Heterojunctions in Composite Photocatalysts

“…Right: vectorial charge transfer over the three-component heterojunction after charge carrier excitation. Reproduced with permission from Soldat et al [2], ©2014 Royal Society of Chemistry depended on the amount of WO 3 mixed into the TiO 2 matrix; an optimum amount of 3% nominal W/Ti ratio resulted in a value of 16%, higher than measured photoanodes of Evonik-Degussa Aeroxide TiO 2 P25.…”

“…Another example of the in situ formation of photocatalyst heterojunctions using synthetic control of composition and keeping the surface area constant was recently shown in the sol-gel-induced formation of barium tantalate multicomponent heterojunctions [2]. By adjusting the barium precursor in sol-gel complexation synthesis, two-component and three-component semiconductor heterojunctions were prepared and investigated in hydrogen evolution and overall water splitting.…”

“…The absorption threshold can also be increased by combining two semiconductors with different band gaps. Moreover, vectorial charge transfer can be even optimized so that the formation of multiphase heterojunctions leads to even better charge carrier separation than achieved by co-catalyst decoration [2].…”

New insight into calcium tantalate nanocomposite photocatalysts for overall water splitting and reforming of alcohols and biomass derivatives

“…6 Briefly, the atomic ratios of Ta 2 O 5 and Ca 2 CO 3 precursors were ground with a mixture of 45:55 wt. % NaCl/KCl salts at a weight ratio of 1:2 and then calcined at 1123 K for 2 h in air using a corundum crucible.…”