Fabricating a Au@TiO2 Plasmonic System To Elucidate Alkali-Induced Enhancement of Photocatalytic H2 Evolution: Surface Potential Shift or Methanol Oxidation Acceleration?

Ming Zhao, Hua Xu, Shuxin Ouyang, Hua Tong, Huayu Chen, Yunxiang Li, Lizhu Song, Jinhua Ye

Index: 10.1021/acscatal.8b00317

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Abstract

Enhancement in photocatalytic H2 evolution induced by an alkaline reaction environment has been experimentally recognized, but there is not yet a consensus regarding the promotion mechanism (surface potential shift (SPS) or methanol oxidation (MO)). Herein, we construct a Au@TiO2 plasmonic system, since this architecture can easily separate the proton reduction process (only related to SPS) and the electron donor oxidation process (only related to MO) in physical space. The H2 evolution rate over the Au@TiO2 system in a strongly basic environment is exponentially greater (by approximately 2 orders of magnitude) than that of the same reaction in a neutral environment. To explore which of these two processes is the dominant factor for the enhancement of the H2 evolution, two investigation schemes are proposed. For Au@ST01 (ST01, a commercial anatase TiO2), the decisive role of the SPS on the enhancement of H2 evolution is semiquantitatively deduced from the open-circuit potential (OCP) test (exceeds 80% at pH <13.5 and more than 50% at pH ≥13.5) and is further confirmed by electrochemical impedance spectroscopy (EIS) and photoresponse current tests. For Au@T100 and Au@T101 (T100 and T101, facet-controlled anatase TiO2), the irregular fluctuation of the ratio of H2 evolution rates (rH2(Au@T100)/rH2(Au@T101)) suggests a secondary role of MO. This study clarifies the mechanism of the alkali-induced enhancement of H2 evolution and provides a perspective for the modulation of reaction environments.