Borocarbonitride Layers on Titanium Dioxide Nanoribbons for Efficient Photoelectrocatalytic Water Splitting.

Nuria Jiménez-Arévalo,Marco Sbroscia,Carlo Mariani,Isabel J Ferrer,Alessio Giampietri,Eduardo Flores,Fabrice Leardini,José R Ares,Maria Grazia Betti

doi:10.3390/ma14195490

Abstract

Heterostructures formed by ultrathin borocarbonitride (BCN) layers grown on TiO2 nanoribbons were investigated as photoanodes for photoelectrochemical water splitting. TiO2 nanoribbons were obtained by thermal oxidation of TiS3 samples. Then, BCN layers were successfully grown by plasma enhanced chemical vapour deposition. The structure and the chemical composition of the starting TiS3, the TiO2 nanoribbons and the TiO2-BCN heterostructures were investigated by Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Diffuse reflectance measurements showed a change in the gap from 0.94 eV (TiS3) to 3.3 eV (TiO2) after the thermal annealing of the starting material. Morphological characterizations, such as scanning electron microscopy and optical microscopy, show that the morphology of the samples was not affected by the change in the structure and composition. The obtained TiO2-BCN heterostructures were measured in a photoelectrochemical cell, showing an enhanced density of current under dark conditions and higher photocurrents when compared with TiO2. Finally, using electrochemical impedance spectroscopy, the flat band potential was determined to be equal in both TiO2 and TiO2-BCN samples, whereas the product of the dielectric constant and the density of donors was higher for TiO2-BCN.

Highlights

The current energetic model based on fossil fuels is unsustainable from an environmental perspective, as it is one of the leading causes of global warming and climate change [1,2,3]
It is clear from the scanning electron microscopy (SEM) measurements, that there was no significant change in the morphology, apart from a slight increase of the roughness on the TiO2
We acquired optical microscopy images to have a deeper understanding of the change on the surface of these nanoribbons (Figure 1b), which allowed us to determine that the material became more transparent to the optical microscope, in good agreement with the results reported by Ghasemi et al [17] and with our optical characterizations shown below

Summary

Introduction

The current energetic model based on fossil fuels is unsustainable from an environmental perspective, as it is one of the leading causes of global warming and climate change [1,2,3]. Hydrogen has been reported to be a suitable energy vector and a clean energy fuel if its production comes from renewable sources [2,4]. In 1972, Honda and Fujishima reported a way to obtain hydrogen by carrying out a photoassisted water splitting reaction using TiO2 as the photoanode [5]. Since this effect has been considered one of the cleanest methods to obtain green hydrogen and a promising strategy to overcome the environmental and energy crises [6,7]. The OER is the rate-determining step as it involves the transfer of four electrons [8], and this is the reaction we will tackle in this paper

Methods

Results

Conclusion