Layer-by-Layer Assembly of Molecular Metal Oxides on Hematite for Visible Light Driven Water Splitting

Abstract

Hematite is one of the candidates for solar water oxidation owing to its proper band gap for water oxidation, abundance and easy synthesis. For their practical applications, however, there still remain many problems to be addressed such as a low photocurrent/stability under neutral pH condition and high onset potential for catalytic water splitting. To solve these critical issues, we developed a novel surface modification method to improve photocatalytic efficiency of hematite using layer-by-layer assembly (LbL) of cationic polyelectrolytes and anionic polyoxometalates (POMs) water oxidation catalysts. We found that the surface modification of hematite with polyelectrolytes (which is electrically and electrochemically inactive) and POMs led to the enhancement of photocurrent approximately 5 times and the cathodic shift of onset potential for water oxidation by about 400 mV. Unexpectedly, we also find that the LbL films also improve the stability of hematite films at the same time under neutral pH conditions. We believe that our findings can be further applied for assembly of various functional materials with different size and shape on virtually any kinds of photoelectrodes, providing a general and simple method to fabricate novel photoelectrochemical devices.