Approximate energy band diagram and charge transfer mechanism for the Fe₂O₃–TiO₂ photoanode (left) and Fe₂O₃–H:TiO₂ photoanode (right) with external applied anodic potential under illumination.

This study evaluates the techno-economic feasibility of five solar-powered concepts for the production of autotrophic microorganisms for food and feed production; the main focus is on three concepts based on hydrogen-oxidizing bacteria (HOB), which are further compared to two microalgae-related concepts. Two locations with markedly different solar conditions are considered (Finland and Morocco), in which Morocco was found to be the most economically competitive for the cultivation of microalgae in open ponds and closed systems (1.4 and 1.9 € kg^–1, respectively). Biomass production by combined water electrolysis and HOB cultivation results in higher costs for all three considered concepts. Among these, the lowest production cost of 5.3 € kg^–1 is associated with grid-assisted electricity use in Finland, while the highest production cost of >9.1 € kg^–1 is determined for concepts using solely photovoltaics and/or photoelectrochemical technology for on-site electricity production and solar-energy conversion to H₂ by water electrolysis. All assessed concepts are capital intensive. Furthermore, a sensitivity analysis suggests that the production costs of HOB biomass can be lowered down to 2.1 € kg^–1 by optimization of the process parameters among which volumetric productivity, electricity strategy, and electricity costs have the highest cost-saving potentials. The study reveals that continuously available electricity and H₂ supply are essential for the development of a viable HOB concept due to the capital intensity of the needed technologies. In addition, volumetric productivity is the key parameter that needs to be optimized to increase the economic competitiveness of HOB production.

Solar energy induced water splitting in photoelectrochemical (PEC) cells is one of the most sustainable ways of hydrogen production. In this work, hematite (α-Fe₂O₃) thin film were modified by In³⁺ and Ti⁴⁺ co-doping for enhanced PEC performance.

Photodeposition has been demonstrated to be a reliable tool for the growth of co-catalyst nanoparticles on titanium dioxide. The current state of investigation on the technique, however, lacks a comprehensive study on the collective influence of different process parameters, preferring to confront the effect of a single parameter at a time. This paper presents a parametric study on photodeposition of platinum nanoparticles from liquid precursors on ALD-grown titanium dioxide, applicable to the fabrication of photocatalytic composite materials. In the described process, a systematic and rigorous statistical analysis of the photodeposition parameters is conducted, assessing the influential parameters that control and predict the size, density and loading of the deposited nanoparticles. The results are assessed by scanning electron microscopy, statistical analysis of micrographs, and X-ray photoelectron spectroscopy. This confirms the simplicity and the viability of photodeposition as a method for the self-assembly of metal nanoparticles from liquid precursors and provides all-round insight on the role of parameters such as the concentration of sacrificial reagents, the presence of H₂SO₄, and the concentration of the precursor solution, in the chemical and structural properties of the deposited nanoparticles.