Underpotential Photoelectrooxidation of Water by SnS 2 −Laccase Co‐catalysts on Nanostructured Electrodes with Only Visible‐Light Irradiation

Photobio-electrocatalytic production of H2 using fluorine-doped tin oxide (FTO) electrodes covered with a NiO-In2S3 p-n junction and NiFeSe hydrogenase

Clean energy vectors are needed towards a fossil fuel-free society, diminishing both greenhouse effect and pollution. Electrochemical water splitting is a clean route to obtain green hydrogen, the cleanest fuel; although efficient electrocatalysts are required to avoid high overpotentials in this process. The combination of inorganic semiconductors with biocatalysts for photoelectrochemical H₂ production is an alternative approach to overcome this challenge. N-type semiconductors can be coupled to a co-catalyst for H₂ production in the presence of a sacrificial electron donor in solution, but the replacement of the latter with an electrode is a challenge. In this work we attach a NiFeSe-hydrogenase with high activity for H₂ production with the n-type semiconductor indium sulfide, which upon visible irradiation is able to transfer its excited electrons to the enzyme. In order to enhance the transfer of the generated holes towards the electrode for their replenishment, we have explored the inclusion of a p-type material, NiO, to induce a p-n junction for H₂ production in a photoelectrochemical biocatalytic system in absence of sacrificial reagents.

Sulfide-Based Photocatalysts Using Visible Light, with Special Focus on In2S3, SnS2 and ZnIn2S4

Sulfides are frequently used as photocatalysts, since they absorb visible light better than many oxides. They have the disadvantage of being more easily photocorroded. This occurs mostly in oxidizing conditions; therefore, they are commonly used instead in reduction processes, such as CO2 reduction to fuels or H2 production. Here a summary will be presented of a number of sulfides used in several photocatalytic processes; where appropriate, some recent reviews will be presented of their behaviour. Results obtained in recent years by our group using some octahedral sulfides will be shown, showing how to determine their wavelength-dependent photocatalytic activities, checking their mechanisms in some cases, and verifying how they can be modified to extend their wavelength range of activity. It will be shown here as well how using photocatalytic or photoelectrochemical setups, by combining some enzymes with these sulfides, allows achieving the photo-splitting of water into H2 and O2, thus constituting a scheme of artificial photosynthesis.

Intervening Bismuth Tungstate with DNA Chain Assemblies: A Perception toward Feedstock Conversion via Photoelectrocatalytic Water Splitting

An advanced approach with DNA-mediated bismuth tungstate (Bi₂WO₆) one-dimensional (1-D) nanochain assemblies for hydrogen production with 5-fold enhanced photoelectrochemical (PEC) water splitting reaction is presented. The creation of new surface states upon DNA modification mediates the electron transfer in a facile manner for a better PEC process. The UV-Vis-DRS analysis results a red shift in the optical absorption phenomenon with the interference of DNA modification on Bi₂WO₆, and, thus, the band gap was tuned from 3.05 eV to 2.71 eV. The applied bias photon-to-current efficiency (ABPE) was calculated and shows a maximum for the Bi₂WO₆@DNA-2 (25.22 × 10^-4%), compared to pristine Bi₂WO₆ (7.76 × 10^-4%). Furthermore, the idea of practical utility of produced hydrogen from PEC is established for the first time with photocatalytic feedstock conversion to platform chemicals using cinnamaldehyde, 2-hydroxy-1-phenylethanone, and 2-(3-methoxyphenoxy)-1-phenylethanone in large scale by hydrogenation and/or hydrogenolysis reactions under eco-friendly green conditions with external hydrogen pressure in an aqueous mixture. Also, the recyclability experiment delivered good yields, which further confirm the robustness of the developed catalyst.

Enhancement of Biosensors by Implementing Photoelectrochemical Processes

Research on biosensors is growing in relevance, taking benefit from groundbreaking knowledge that allows for new biosensing strategies. Electrochemical biosensors can benefit from research on semiconducting materials for energy applications. This research seeks the optimization of the semiconductor-electrode interfaces including light-harvesting materials, among other improvements. Once that knowledge is acquired, it can be implemented with biological recognition elements, which are able to transfer a chemical signal to the photoelectrochemical system, yielding photo-biosensors. This has been a matter of research as it allows both a superior suppression of background electrochemical signals and the switching ON and OFF upon illumination. Effective electrode-semiconductor interfaces and their coupling with biorecognition units are reviewed in this work.

Production of SnS2 Nanostructure as Improved Light-Assisted Electrochemical Water Splitting

Tin disulfide (SnS₂) has gained a lot of interest in the field of converting solar energy into chemical fuels in light-assisted electrochemical water splitting due to its visible-light band gap and high electronic mobility. However, further decreasing the recombination rate of electron-hole pairs and increasing the density of active states at the valence band edge of the photoelectrodes were a critical problem. Here, we were successful in fabricating the super-thin SnS₂ nanostructure by a hydrothermal and solution etching method. The super-thin SnS₂ nanostructure as a photo-electrocatalytic material exhibited low overpotential of 0.25 V at the current density of −10 mA·cm⁻² and the potential remained basically unchanged after 1000 cycles in an H₂SO₄ electrolyte solution, which was better than that of the SnS₂ nanosheet and SnS/SnS₂ heterojunction nanosheet. These results show the potential application of super-thin SnS₂ nanostructure in electrochemical/photo-electrocatalytic field.