Valentina Gacha, Carles Ros, Xènia Garcia, Jordi Llorca, Jordi Martorell, Dimitrios Raptis (2024), Enhancing charge extraction in BiVO4 photoanodes by ZrCl4 treatment of SnO2 hole-blocking layers. Energy Environ. Mater. e12809. https://doi.org/10.1002/eem2.12809

Abstract

In the search for more efficient and sustainable photoelectrochemical devices, BiVO₄ is nowadays one of the best-performing photoanode material, with favourable band structure for water oxidation. However, BiVO₄ photoanodes face challenges such as poor charge transport and slow kinetics. To address these issues, SnO₂ films are commonly used as hole blocking layers, reducing recombination rate and enhancing charge lifespan and overall productivity. Yet, this method encounters problems like high defect concentrations at the SnO₂/BiVO₄ interface and pinholes in the SnO₂ layer, which lead to charge recombination. In this study, we explore a ZrCl₄ treatment to improve the effectiveness of SnO₂ as a hole-blocking layer in BiVO₄ photoanodes. Our findings, supported by detailed optoelectronic characterization and continuous and modulated electrochemical analysis, reveal that ZrCl₄ treatment significantly enhances the hole-blocking properties of SnO₂. This treatment results in a 37 % increase in photocurrent density at 1.23 VRHE and a 40 mV shift in the onset voltage, demonstrating a substantial improvement in overall photoanode efficiency..

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Yudania Sánchez, Maxim Guc, Sara Martí-Sánchez, Maykel Jiménez-Guerra, Shadai Lugo-Loredo, Jordi Arbiol, Alejandro Perez-Rodriguez, Jordi Martorell, Carles Ros. (2024). 2D nanosheet SnS₂ solution-processed photoanodes: Unveiling enhanced visible light absorption for solar fuels applications. International Journal of Hydrogen Energy, 77, 193–202. DOI: https://doi.org/https://doi.org/10.1016/j.ijhydene.2024.06.160

Abstract

The excessive band gap of metal oxide photoanodes currently poses a significant challenge to scaling up photoelectrochemical water splitting and CO2 reduction processes. However, metal sulfides with a 2D nanostructured morphology present a promising alternative, offering improved optoelectronic properties and catalytic capabilities in the oxygen evolution reaction (OER). Furthermore, this study breaks new ground by demonstrating, for the first time, the visible spectra absorption capabilities of SnxSy photoanodes. These photoanodes were fabricated using facile non-vacuum techniques and subsequently post-annealed in a sulfur atmosphere. This process yielded SnS2 multilayer nanosheets exhibiting remarkable visible-light absorption down to 900 nm wavelengths.

Annealing at an optimal temperature of 500 °C led to remarkable results, including photovoltages exceeding 1 V and photocurrents surpassing 1.6 mA/cm2 at 1.23VRHE. Moreover, we observed an impressive incident photon-to-current conversion efficiency (IPCE) of 75% at 330 nm. Notably, photon conversion within the 500–900 nm range (down to 1.37 eV) associates with a phase transformation from orthorhombic α-SnS to Sn2S3, and subsequently to hexagonal SnS2. Furthermore, IPCE plays a crucial role in elucidating effective phase transformation and photon conversion at wavelengths below the dominant direct band gap for SnS2. This observation suggests the potential existence of indirect transitions or confinement effects within the low-dimensional nanosheets. In conclusion, SnS2 nanosheets, fabricated through solution-processed methods, hold immense promise for the development of large-scale, cost-effective, and efficient photoelectrochemical devices.

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