A New Si/TiO2/Pt p-n Junction Semiconductor to Demonstrate Photoelectrochemical CO2 Conversion

Photoelectrocatalytic Utilization of CO2 : A Big Show of Si-based Photoelectrodes

CO2 is a greenhouse gas that contributes to environmental deterioration; however, it can also be utilized as an abundant C1 resource for the production of valuable chemicals. Solar-driven photoelectrocatalytic (PEC) CO2 utilization represents an advanced technology for the resourcing of CO2 . The key to achieving PEC CO2 utilization lies in high-performance semiconductor photoelectrodes. Si-based photoelectrodes have attracted increasing attention in the field of PEC CO2 utilization due to their suitable band gap (1.1 eV), high carrier mobility, low cost, and abundance on Earth. There are two pathways to PEC CO2 utilization using Si-based photoelectrodes: direct reduction of CO2 into small molecule fuels and chemicals, and fixation of CO2 with organic substrates to generate high-value chemicals. The efficiency and product selectivity of PEC CO2 utilization depends on the structures of the photoelectrodes as well as the composition, morphology, and size of the catalysts. In recent years, significant and influential progress has been made in utilizing Si-based photoelectrodes for PEC CO2 utilization. This review summarizes the latest research achievements in Si-based PEC CO2 utilization, with a particular emphasis on the mechanistic understanding of CO2 reduction and fixation, which will inspire future developments in this field.

CO2 Reduction of Hybrid Cu2 O-Cu/Gas Diffusion Layer Electrodes and their Integration in a Cu-based Photoelectrocatalytic Cell

Cu₂ O/gas diffusion layer (GDL) electrodes prepared by electrodeposition were studied for the electrocatalytic reduction of CO₂ . The designed electrode was also tested in solar-light-induced CO₂ conversion in combination with a CuO/NtTiO₂ photoanode using a compact photoelectrocatalytic (PEC) cell. Both PEC cell electrodes were prepared using non-critical raw materials and low cost, easily scalable procedures. In the PEC experiments, a total carbon faradaic selectivity of about 90 % to formate and about 75 % to acetate was obtained after 24 h of operations without application of potential/current or using sacrificial agents. In electrocatalytic tests of CO₂ reduction at -1.5 V, the same electrode yielded high total faradaic selectivity (>95 %) but formed selectively formate (about 80 % selectivity) rather than acetate. The in situ transformation of the Cu₂ O/GDL electrode leads to the formation of a hybrid Cu₂ O-Cu/GDL system. Cyclic voltammetry data indicate that the potential and the presence of CO₂ (not only of HCO₃ ^- species) are both important elements in this transformation. Data also indicate that the surface concentration of CO₂ (or of its products of transformation) on the electrode is an important factor to determine performance in the conversion of CO₂ .

Semiconductor-Based Photoelectrochemical Conversion of Carbon Dioxide: Stepping Towards Artificial Photosynthesis

The photoelectrochemical (PEC) carbon dioxide reduction process stands out as a promising avenue for the conversion of solar energy into chemical feedstocks, among various methods available for carbon dioxide mitigation. Semiconductors derived from cheap and abundant elements are interesting candidates for catalysis. Whether employed as intrinsic semiconductors or hybridized with metallic cocatalysts, biocatalysts, and metal molecular complexes, semiconductor photocathodes exhibit good performance and low overpotential during carbon dioxide reduction. Apart from focusing on carbon dioxide reduction materials and chemistry, PEC cells towards standalone devices that use photohybrid electrodes or solar cells have also been a hot topic in recent research. An overview of the state-of-the-art progress in PEC carbon dioxide reduction is presented and a deep understanding of the catalysts of carbon dioxide reduction is also given.

Charge Transport in Two-Photon Semiconducting Structures for Solar Fuels

Semiconducting heterostructures are emerging as promising light absorbers and offer effective electron-hole separation to drive solar chemistry. This technology relies on semiconductor composites or photoelectrodes that work in the presence of a redox mediator and that create cascade junctions to promote surface catalytic reactions. Rational tuning of their structures and compositions is crucial to fully exploit their functionality. In this review, we describe the possibilities of applying the two-photon concept to the field of solar fuels. A wide range of strategies including the indirect combination of two semiconductors by a redox couple, direct coupling of two semiconductors, multicomponent structures with a conductive mediator, related photoelectrodes, as well as two-photon cells are discussed for light energy harvesting and charge transport. Examples of charge extraction models from the literature are summarized to understand the mechanism of interfacial carrier dynamics and to rationalize experimental observations. We focus on a working principle of the constituent components and linking the photosynthetic activity with the proposed models. This work gives a new perspective on artificial photosynthesis by taking simultaneous advantages of photon absorption and charge transfer, outlining an encouraging roadmap towards solar fuels.