Photocharging of Europium(III) Tellurium Oxide as a Photoelectrocatalyst

Abstract

This work reveals that Eu2TeO6, as a photoelectrocatalyst, exhibits a sustained photocharging effect that results in an enhanced and “sustained” dark current (subsequent to the termination of illumination), which is greater than the current obtained through applied electrical potential alone. Samples of europium tellurium oxide, prepared through the employment of a Pechini sol–gel route and calcined at 400 and 900 °C, were characterized for selective physicochemical properties and comparatively evaluated as an electrocatalyst, photoelectrocatalyst, and photocharged electrocatalyst by employing, as a suitable case study, the oxygen evolution reaction (OER) in alkaline medium. The sample calcined at 400 °C exhibited amorphous characteristics while the sample calcined at 900 °C proved to be Eu2TeO6. The evaluation was conducted in a modified electrochemical cell housing a lamp, with the material deposited onto a glassy carbon electrode support rather than on fluorine- or indium-doped tin oxide glass plates. With a band gap of 4.31 eV, Eu2TeO6 (calcined at 900 °C) exhibited improved OER activity upon continuous UV-light irradiation, with the unexpected result of sustained improved activity for up to 40 min subsequent to the termination of the UV irradiation. At 1.8 V (versus RHE, reversible hydrogen electrode), the photocurrent, after 150 min of irradiation, increased by 107% from 0.44 to 0.91 mA cm–2. Surprisingly, after 150 min of irradiation, the dark current was sustained at 0.86 mA cm–2 for 40 min (at which point measurement was terminated), which represents a sustained increase of 95% compared to the initial unirradiated sample. The phenomenon observed here could contribute toward an improved understanding of photocharging and ultimately to the exploitation of more efficient solar energy conversion and storage.

Photocharged Water Splitting Employing a Nickel(II) Tellurium Oxide (Photo)anode in Alkaline Medium

“…19 There are a few instances in which Ni-based oxides and oxyhydroxides have been used as cocatalysts to enhance the efficiency of PEC activity, namely, Ni/TiO 2 nanotubes, 20 α-Fe 2 O 3 /NiCeO x , 19 NiOOH-coated codoped (Sn, Zr) α-Fe 2 O 3 , 21 etc. Having earlier reported on the remarkable ability of europium(III) tellurium oxide to photocharge and utilize the stored charge to split water (in the dark), 22 we now report on nickel(II) tellurium oxide exhibiting the same phenomenon. As nickel tellurium oxides display outstanding optical, magnetic, and ferroelectric properties, 23,24 it was synthesized via a Pechini sol−gel route and successively sintered at different temperatures.…”

“…This is consistent with what is published in the literature for similar systems. 22,31 The overall fit (thick line) superimposes very well onto the raw experimental data (filled black circles) for all three samples. Component O1 is located on the lower BE side of the spectrum and takes up the majority of the spectral weight of this core level.…”

“…(a) Schematic diagram of the photoelectrochemical cell, reproduced with permission from Kriek et al Copyright 2019 American Chemical Society. (b) Photometric data (redrawn) of the LED lamp employed.…”

“…The activity of these samples can be further improved and more effectively compared with the benchmark photoelectrocatalysts by (i) employing more conducting support materials like fluorineor indium-doped tin oxide glasses, (ii) employing reduced graphene oxide (rGO) in the ink, and (iii) employing specific light intensities (e.g., 1 sun = 100 mW cm −2 ). To explore whether the material is able to retain some of the induced photoelectrochemical activity after termination of the light source, as was observed for europium(III) tellurium oxide, 22 LSV scans were recorded at different time intervals subsequent to the termination of the LED light source (Figure 11). Although the photocurrent density for the NTO-600 sample declined slightly, a significant amount of charge was retained (up to 40 min, subsequent to which monitoring of the sample was terminated), which is still substantially higher than the current for the non-illuminated pure EC scan.…”

Orthogonal Preparation of SrFeO3-δ Nanocomposites as Effective Oxygen Transfer Agents for Chemical-Looping Steam Methane Reforming

“…This framework is prone to collapse during drying, which reduces the uniformity of the gel. A number of studies have shown that the calcination temperature has a great influence on the nature of metal oxides. − High calcination temperatures favor the crystal growth but too high ones accelerate sintering, resulting in a sharp decrease in the specific surface area. For example, as the calcination temperature increases from 800 to 900 °C, the specific surface area of Ni 6 Mo 6 C decreases from 96 to 5 m 2 /g …”