Seebeck-voltage-triggered self-biased photoelectrochemical water splitting using HfOx/SiOx bi-layer protected Si photocathodes

Abstract

The use of a photoelectrochemical device is an efficient method of converting solar energy into hydrogen fuel via water splitting reactions. One of the best photoelectrode materials is Si, which absorbs a broad wavelength range of incident light and produces a high photocurrent level (~44 mA·cm −2 ). However, the maximum photovoltage that can be generated in single-junction Si devices (~0.75 V) is much lower than the voltage required for a water splitting reaction (>1.6 V). In addition, the Si surface is electrochemically oxidized or reduced when it comes into direct contact with the aqueous electrolyte. Here, we propose the hybridization of the photoelectrochemical device with a thermoelectric device, where the Seebeck voltage generated by the thermal energy triggers the self-biased water splitting reaction without compromising the photocurrent level at 42 mA cm −2 . In this hybrid device p-Si, where the surface is protected by HfO x /SiO x bilayers, is used as a photocathode. The HfO x exhibits high corrosion resistance and protection ability, thereby ensuring stability. On applying the Seebeck voltage, the tunneling barrier of HfO x is placed at a negligible energy level in the electron transfer from Si to the electrolyte, showing charge transfer kinetics independent of the HfO x thickness. These findings serve as a proof-of-concept of the stable and high-efficiency production of hydrogen fuel by the photoelectrochemical-thermoelectric hybrid devices.

Water Splitting: From Electrode to Green Energy System

“…Considering these factors, the energy conversion efficiency of TE device (5–10%) is low, compared to PVs (up to 46%) [ 159 ]. Therefore, several researches have demonstrated that by combing TE and PEC reaction, the utilization efficiency for both solar energy harvest and water splitting can reach a high content [ 160 ]. The first proposed the combination of PEC and photothermal-electrochemical cycles for H 2 production by solar energy was by Nikola Getoff in 1984 [ 161 ], which was in acid aqueous solution using I 2 and I 3 − acting as a sensitizer with the existence of ferrous ions.…”

Emerging Chalcogenide Thin Films for Solar Energy Harvesting Devices

“…Many of these layers also provide an additional band bending and hence enhance the photocurrent and onset potential of the whole photocathode stack, increasing the attractiveness of using such a layer. Overlayers such as TiO 2 , − In 2 S 3 , ZnS, HfO 2 , , and Al 2 O 3 , have demonstrated almost no degradation in the various testing durations mentioned in the many works cited. On the other hand, due to the inherent stability of metal oxides in water, most photoanodes do not require complex protection and have high stabilities in most electrolytes. , …”

Green Hydrogen Generation: Recent Advances and Challenges

“…The sunlight is used to separate water by using specialized semiconductors knows as photoelectrochemical materials in PEC reaction. The use of TEC with PEC leads to maximize the solar energy harvest and enhance the performance of electrolysis process [18].…”