Solar-light driven CO₂reduction into value-added chemicals and fuels emerges as a significant approach for CO₂conversion. However, inefficient electron-hole separation and the complex multi-electrons transfer processes hamper the efficiency of CO₂photoreduction. Herein, we prepare ferroelectric Bi₃TiNbO₉nanosheets and employ corona poling to strengthen their ferroelectric polarization to facilitate the bulk charge separation within Bi₃TiNbO₉nanosheets. Furthermore, surface oxygen vacancies are introduced to extend the photo-absorption of the synthesized materials and also to promote the adsorption and activation of CO₂molecules on the catalysts’ surface. More importantly, the oxygen vacancies exert a pinning effect on ferroelectric domains that enables Bi₃TiNbO₉nanosheets to maintain superb ferroelectric polarization, tackling above-mentioned key challenges in photocatalytic CO₂reduction. This work highlights the importance of ferroelectric properties and controlled surface defect engineering, and emphasizes the key roles of tuning bulk and surface properties in enhancing the CO₂photoreduction performance.

Several application fields can benefit from solar-hydrogen technologies via specific short-term and long-term pathways.

The recent surge in investigating electrocatalysts for the H₂ evolution reaction is based on finding a cheap alternative to Pt. However platinum's excellent catalytic activity means very little catalyst needs to be used. The present study combines model experiments with numerical modeling to determine exactly how little catalyst is needed. Specifically we investigate ultra-low Pt loadings for use in photoelectrochemical H₂ evolution using TiO₂–Ti-pn⁺Si photocathodes. At a current density of 10 mA cm⁻², we photocathodically evolve H₂ at +465, +450, +350 and +270 mV vs., RHE at Pt loadings of 1000, 200, 50, and 10 ng cm⁻² corresponding to HER overpotentials of η_1000ng = 32 mV, η_200ng = 46 mV, η_50ng = 142 mV, and η_10ng = 231 mV. To put this in perspective, if 30% of the world's current annual Pt production was used for H₂ evolution catalysis, using a loading of 100 ng cm⁻² and a current of 10 mA cm⁻² would produce 1 TW_average of H₂. The photoelectrochemical data matched the modeling calculations implying that we were near the fundamental maximum in performance for our system. Furthermore modeling indicated that the overpotentials were dominated by mass transfer effects, rather than catalysis unless catalyst loadings were less than 1000 ng cm⁻².

Large amounts of carbon monoxide are produced by industrial processes such as biomass gasification and steel manufacturing. The CO present in vent streams is often burnt, this produces a large amount of CO₂, e.g., oxidation of CO from metallurgic flue gasses is solely responsible for 2.7% of manmade CO₂ emissions. The separation of N₂ from CO due to their very similar physical properties is very challenging, meaning that numerous energy-intensive steps are required for CO separation, making the CO separation from many process streams uneconomical in spite of CO being a valuable building block in the production of major chemicals through C1 chemistry and the production of linear hydrocarbons by the Fischer–Tropsch process. The development of suitable processes for the separation of carbon monoxide has both industrial and environmental significance. Especially since CO is a main product of electrocatalytic CO₂ reduction, an emerging sustainable technology to enable carbon neutrality. This technology also requires an energy-efficient separation process. Therefore, there is a great need to develop energy efficient CO separation processes adequate for these different process streams. As such the urgency of separating carbon monoxide is gaining greater recognition, with research in the field becoming more and more crucial. This review details the principles on which CO separation is based and provides an overview of currently commercialised CO separation processes and their limitations. Adsorption is identified as a technology with the potential for CO separation with high selectivity and energy efficiency. We review the research efforts, mainly seen in the last decades, in developing new materials for CO separation via ad/bsorption and membrane technology. We have geared our review to both traditional CO sources and emerging CO sources, including CO production from CO₂ conversion. To that end, a variety of emerging processes as potential CO₂-to-CO technologies are discussed and, specifically, the need for CO capture after electrochemical CO₂ reduction is highlighted, which is still underexposed in the available literature. Altogether, we aim to highlight the knowledge gaps that could guide future research to improve CO separation performance for industrial implementation.

Materials used for photocatalytic overall water splitting (POWS) are typically composed of light-absorbing semiconductor crystals, functionalized with so-called co-catalytic nanoparticles to improve the kinetics of the hydrogen and/or oxygen evolution reactions. While function, quantity, and protection of such metal(oxide) nanoparticles has been addressed in the literature of photocatalysis, the stability and transients in the active oxidation-state upon illumination have received rela-tively little attention. In this perspective the latest insights in the active state of frequently applied co-catalysts systems, in-cluding Pt, Rh/Cr2O3 or Ni/NiOx, will be presented. While the initial morphology and oxidation state of such nanoparticles is a strong function of the applied preparation procedure, significant changes in these properties can occur during water splitting. We discuss these changes in relation to the nature of the cocatalyst/semiconductor interface. We also show how know-how of other disciplines such as heterogeneous catalysis or electro-catalysis, and recent advances in analytical methodology, can help to determine the active state of co-catalytic nanoparticles in photocatalytic applications.