Photocatalytic Overall Water Splitting: Observing H2 and O2 Transients with Ni/NiOx-Modified Mg:SrTiO3

Abstract

SrTiO3 is a promising semiconductor driving photocatalytic overall water splitting (POWS) under UV light illumination. Improving the performance of SrTiO3 in decomposing water into H2 and O2 can be achieved by introducing feasible co-catalyst, such as Pt or Ni/NiOx. Though co-catalysts are employed in heterogeneous photocatalysis engineering of semiconductor/co-catalysts interfaces is rarely reported in literature [1]. In addition, limited attention has been paid to structural/electronic changes of co-catalysts during illumination/reaction and transients occurring in hydrogen and/or oxygen evolution are barely discussed. In this contribution the photocatalytic performance of SrTiO3-based systems will be analyzed using a Continuously Stirred Tank Reactor (CSTR) connected to a micro GC-PDD (Pulsed Discharge Detector). Due to the favorable time-resolution of the GC-PDD transients in the evolution of H2 and O2, especially in the initial stages of testing, can be easily revealed. We will highlight the following recent observations: For Ni/NiOx-modified SrTiO3, severe changes in the oxidation state of NiOx assigned to the transformation of Ni(OH)2 to NiOOH leading to an active photocatalyst/co-catalyst material in agreement with transient H2 evolution will be discussed [2];Electronic modification of SrTiO3 by Mg incorporation into the perovskite structure can be obtained by a simple solid-state preparation [3]. While significant improvements in the steady state photocatalytic efficiency are obtained (Fig. 1), we also observed drastic changes in the initial transients caused by the interaction of Mg and Ni/NiOx;Finally, it will be highlighted that stabilization of the Ni/NiOx-modified Mg:SrTiO3 photocatalyst is obtained by photodeposition of CrOx from Cr(VI) containing solutions [4]. Enhanced stability is probably caused by electronic modification of Ni/NiOx as a severe influence of the back reaction of H2 and O2 was not observed for the process conditions used.Finally, the general stability of SrTiO3 in aqueous environment will be discussed. Thus, using state-of-the-art micro-GC analysis we were able to design a stable composite photocatalyst and improve the efficiency of the system (AQE) from 0.6% to >40%.