Comparison of Different Synthetic Routes of Hybrid Hematite-TiO2 Nanotubes-Based Electrodes.

Ana Luiza Fornazari,Judith Castillo-Rodriguez,Daniel Correa-Encalada,Samuel A Hevia,Rodrigo Del Río,Enrique A Dalchiele

doi:10.3390/ma14164501

Abstract

Nowadays, green hydrogen is an important niche of interest in which the search for a suitable composite material is indispensable. In this sense, titanium oxide nanotubes (TiO2 nanotube, TNTs) were prepared from double anodic oxidation of Ti foil in ethylene glycol electrolyte. The morphology of the nanotubes was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Once characterized, nanotubes were used as templates for the deposition of hematite. The use of three synthetic procedures was assayed: Chemical Vapor Deposition (CVD), Successive Ionic Layer Adsorption and Reaction (SILAR), and electrochemical synthesis. In the first case, CVD, the deposition of hematite onto TiO2 yielded an uncovered substrate with the oxide and a negative shift of the flat band potential. On the other hand, the SILAR method yielded a considerable amount of hematite on the surface of nanotubes, leading to an obstruction of the tubes in most cases. Finally, with the electrochemical synthesis, the composite material obtained showed great control of the deposition, including the inner surface of the TNT. In addition, the impedance characterization showed a negative shift, indicating the changes of the interface electrode–electrolyte due to the modification with hematite. Finally, the screening of the methods showed the electrochemical synthesis as the best protocol for the desired material.

Highlights

Nowadays, nanoscience and nanotechnology are widely used due to their high potential to benefit several areas such as energy production, water decontamination, development of medicines, information and communication technologies, construction of more resistant materials, and light generation [1].After discovering carbon nanotubes (CNTs) in the 1990s, other nanotubular shapes became of great interest to researchers due to their properties and excellent performances in various applications [2,3,4,5]
Chemical Vapor Deposition (CVD) method, method, it surface, the Firstly, it allows allowsaahomogenous homogenousdeposition depositionofofthe the surface, electrochemistry of the interface indicated the contribution of different surfaces
The electrochemistry of the interface indicated the contribution of different surfaces

Summary

Introduction

After discovering carbon nanotubes (CNTs) in the 1990s, other nanotubular shapes became of great interest to researchers due to their properties and excellent performances in various applications [2,3,4,5]. In this sense, the TiO2 nanotube (TNTs) and nanopore arrays are among the most favorable nanomaterials for research because they can be fabricated and exploited due to their large surface area. TiO2 and iron oxide (hematite, α-Fe2 O3 ) are two of the most studied materials for constructing photoanodes due to their resistance to photocorrosion, non-toxicity, natural abundance, and low-cost production [13]. Some disadvantages, like their inherently low electrical conductivity and free limited medium path for the carriers’

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