Metal-organic framework-based materials for photoelectrochemical water-splitting

Abstract

The increasing demand for energy coupled with environmental issues, encourages researchers to look out for renewable and particularly green alternatives to traditional fossil fuels. Photoelectrochemical (PEC) water-splitting demonstrates a promising route to produce hydrogen as a zero-emission energy carrier in a green manner [1]. In this regard, the exploration of proper photo-active materials to construct PEC cells, as well as finding suitable co-catalysts, is of great interest. Among potential materials for PEC water-splitting applications, p-type cuprous oxide (Cu2O) has been intensively studied due to its suitable band energy position, earth abundance, and low toxicity [2]. However, established techniques such as atomic layer deposition (ALD) to produce highly efficient Cu2O-based PEC cells are costly and not commercially applicable[3]. Therefore, more commercially viable Cu2O preparation methods need to be studied, for instance, the electrochemical deposition technique. Furthermore, metal-organic frameworks (MOFs) - a unique class of crystalline, porous materials recognized for their enhanced specific surface area and catalytic abilities - are investigated for their application in PEC watersplitting[2, 4].The aim of this thesis is to explore the photo-cathodic behavior of cuprous oxide (Cu2O),its enhancement in PEC performance using additional overlayers (metal oxides and polymerbased),and particularly to create a unique combination with a copper-based metal-organicframework, namely Cu-BDCNH2. Cuprous oxide was deposited on glass/Au and ITO via ECD(electrochemical deposition) in a common three-electrode set-up to yield cuprous oxide-basedphoto-cathodes. As the synthesis of this MOF has not been implemented yet to the best of our knowledge, various settings and conditions have been tested to allow the growth of a continuousMOF layer onto the Cu2O substrate film. To do so, other works of literature were used asstarting points and adapted accordingly. Afterward, the obtained Cu2O/MOF system wastested and analyzed through various methods (XRD, FTIR, XPS, SEM, EDS) and comparedto existing literature. By combining MOF and Cu2O, it was ultimately possible to achieve aphoto-current density of 1.5 mA/cm2 without the need for an additional co-catalyst.