Improving the Efficiency of Gallium Telluride through Defects Engineering and Interfacing with its Native Oxide

The formation of a nanoscale sub-stoichiometric wide-band-gap Ga2O3 skin over narrow-band-gap gallium telluride upon air exposure  is beneficial for electrocatalysis, photocatalysis, and gas sensing. 
Adv. Funct. Mat. (2022)

Gallium telluride (GaTe) is a van der Waals semiconductora showing a direct band gap already in the bulk, but also in-plane anisotropy, mirrored in its anisotropic optical properties. However, the rapid degradation of GaTe in air, promoted by Te vacancies, is detrimental for device applications. Here, we radically change the perspective, by demonstrating that the surface oxidation of GaTe could be unexpectedly exploited for expanding the breadth of applications of GaTe.

At the BACH beamline of IOM-CNR, we measured the core-level spectra to assess chemical stability in the ambient atmosphere. We measured both the defect-free and defective GaTe samples  after keeping the clean surface in ambient air for a different amount of time (Figure) and after exposing the samples to different gases (namely oxygen and water). Changes were evident already after 1 min in air, with the formation of components (GaTe*) at low BE associated with intercalation of ambient gases under the first layer and the concomitant decreased interaction with the underlying layer. At the same time, the Ga2Te3/Te(0) component is present at ≈0.3–0.5 eV higher BE in both Te-3d and Ga-3d with respect to the core levels of pristine GaTe. After 2 h in air, the GaTe surface exhibited a sub-monolayer gallium-oxide phase (with thickness <0.2 ML, with ML standing for monolayer), as well as an increased intensity for the Ga2Te3/Te(0) spectral component. According to theoretical results, the oxidation process starts at Te vacancies or from Ga2Te3 formed after the decomposition of water-intercalated GaTe. After 21 h in air, the surface is passivated with an outermost oxide skin with GaTeO, Ga2O3, Ga2O3, Te, and Te oxides (TeOx, TeO2, TeO3). These oxides further evolved to oxy-hydroxide species, as a consequence of favorable water dissociation at defects on the oxidized surface. 

Density functional theory calculations demonstate, that the Ga2O3/GaTe heterostructure has drastically different performance with respect to GaTe in i) electrocatalysis (namely, hydrogen evolution reaction, HER), ii) photocatalysis, iii) and gas sensing. In particular, the Heyrovsky step (Hads + H+ + e− → H2) of HER in an acidic medium is barrier-free for the sub-stoichiometric gallium-oxide/gallium-telluride heterostructure, which also enables a significant reduction of costs by 160 times with respect to state-of-the-art Pt/C electrodes.

Moreover, in photocatalytic processes, the generation of electron-hole pairs occurs at the underlying GaTe bulk, whereas catalytic reactions occur at active sites of the Ga2O3 skin. Thus, the natural interaction of metal chalcogenides toward the ambient gases could be exploited in photocatalysis, where the underlying vdW semiconductor (GaTe) provides electron-hole pair, while O-vacancy sites of the Ga2O3 skin formed upon oxidation represent the active sites for catalytic reactions. Finally, we prove that the Ga2O3/GaTe heterostructure is a suitable platform for sensing of water(H2O), ammonia (NH3), and nitrogen dioxide (NO2) at operational temperatures extended up to 600 °C (useful for identification and detection of gaseous species in combustion processes), mainly due to the increased area of charge redistribution after adsorption achieved upon surface oxidation of GaTe.
These findings pave the way for a novel generation of efficient and cheap (photo-) electrocatalysts and gas sensors, based on self-assembled heterostructures produced by exploiting the natural interaction with the ambient atmosphere.

We acknowledge support from MUR (Eurofel project, FOE progetti internazionali).


Improving the Efficiency of Gallium Telluride for Photocatalysis, Electrocatalysis, and Chemical Sensing through Defects Engineering and Interfacing with its Native Oxide

Federica Bondino,Songül Duman,Silvia Nappini,Gianluca D'Olimpio,Corneliu Ghica,Tevfik Onur Menteş,Federico Mazzola,Marian Cosmin Istrate,Matteo Jugovac,Mykhailo Vorokhta,Sergio Santoro,Bekir Gürbulak,Andrea Locatelli,Danil W. Boukhvalov,Antonio Politano 

Advanced Functional Materials (2022)

Last Updated on Tuesday, 13 September 2022 14:39