Insights on Carbon Neutrality by Photocatalytic Conversion of Small Molecules into Value-Added Chemicals or Fuels

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Photocatalytic conversion of small molecules (including H 2 O, CO 2 , N 2 , CH 4 , and benzene) into value-added chemicals or fuels (e.g., H 2 , NH 3 , C 2 + , etc.) is a promising strategy to cope with both the worldwide increasing energy demand and greenhouse gas emission in both energy sectors and chemical industry, thus paving an effective way to carbon neutrality. On the other hand, compared with conventionally thermo-or electrocatalytic processes, photoactivation can convert these very stable small molecules by the unexhausted solar energy, so leading to store solar energy in chemical bonds. Thus, it can effectively reduce the reliance on the nonrenewable fossil fuels and avoid the substantial emission of hazardous gases such as CO 2 , NO x , and so on while producing valued-added chemicals. For example, semiconductors can absorb solar light to split H 2 O into H 2 and O 2 or convert CO 2 to alcohols, which can then be used as zero or neutral carbon energy sources. Although many efforts have already been made on photocatalytic small molecule activation, the light−energy conversion efficiency is still rather moderate and the yield of aimed value-added chemicals cannot meet the requirement of large-scale application. The core for these artificial photocatalytic processes is to discover a novel photocatalyst with high efficiency, low cost, and excellent durability. Over the past two decades, the Tang group has discovered a few benchmark photocatalysts (such as dual-metal-loaded metal oxides, atomic photocatalysts, carbon-doped TiO 2 , and polymer heterojunctions, etc.) and investigated them for photocatalytic conversion of the above-mentioned five robust molecules into value-added chemicals or liquid fuels. Besides, advanced photocatalytic reaction systems including batch and continuous flow membrane reactors have been studied. More importantly, the underlying reaction mechanism of these processes has been thoroughly analyzed using the state-of-the-art static and time-resolved spectroscopies. In this Account, we present the group's recent research progress in search of efficient photocatalysts for these small molecules' photoactivation. First, the strategies used in the group with respect to three key factors in photocatalysis, including light harvesting, charge separation, and reactant adsorption/product desorption, are comprehensively analyzed with the aim to provide a clear strategy for efficient photocatalyst design toward small and robust molecule photoactivation under ambient conditions. The application of in situ and operando techniques on charge carrier dynamics and reaction pathway analysis used in the group are next discussed. Finally, we point out the key challenges and future research directions toward each specific small molecule's photoactivation process.

Materials Design for Photocatalytic CO2 Conversion to C2+ Products

“…These irregularities can either naturally manifest during the material growth or be intentionally introduced through post-treatment processes. 44,45 Due to their ease of introduction, defects have found extensive use in studies related to photocatalytic CO 2 conversion. Their functions, such as optimizing the separation of photogenerated charge carriers, expanding the range of light absorption, and providing abundant catalytic sites, have demonstrated their effectiveness in enhancing the process of photocatalytic CO 2 conversion.…”

“…Defects, in the context of materials, pertain to irregularities that occur within the crystal lattice of a material. These irregularities can either naturally manifest during the material growth or be intentionally introduced through post-treatment processes. , Due to their ease of introduction, defects have found extensive use in studies related to photocatalytic CO 2 conversion. Their functions, such as optimizing the separation of photogenerated charge carriers, expanding the range of light absorption, and providing abundant catalytic sites, have demonstrated their effectiveness in enhancing the process of photocatalytic CO 2 conversion. , Moreover, recent advancements have shown that defect engineering can also be employed to modulate the selectivity of products generated during photocatalytic CO 2 conversion .…”

Rational Construction and Efficient Regulation of Stable and Long-Lived Charge-Separation State in Fullerene Materials

“…They can provide more opportunities for the separated electrons/holes to engage in subsequent photoreactions (Scheme 1) and promote energy conversion. 3,6 Among them, fullerenes can act as electron acceptor candidates to achieve stable and long-lived CSs. Represented by C 60 , fullerenes are unique gifts from the cosmic nebulae known as "Nano Prince".…”

“…Currently, driven by the energy crisis and environmental pollution, high-performance photoelectronic materials with donor (D) and acceptor (A) structures are increasingly favored by researchers to utilize solar energy and facilitate energy conversion fully. These materials are widely used in organic photovoltaics, photocatalysis, mimicking photosynthesis, photoluminescence materials, and other fields. − Among these materials, the stable and long-lived charge-separation state (CSs) determines performance directly. They can provide more opportunities for the separated electrons/holes to engage in subsequent photoreactions (Scheme ) and promote energy conversion. , Among them, fullerenes can act as electron acceptor candidates to achieve stable and long-lived CSs.…”

Defect Chemistry in 2D Atomic Layers for Energy Photocatalysis

“…Photocatalysis is a promising technology to simultaneously relieve worldwide energy crisis and environmental pollution issues, supplying an effective avenue to realize carbon neutrality. , Through photocatalysis reactions, different small molecules, such as H 2 O, N 2 , and CO 2 , can be converted to high-value-added chemicals with only the consumption of sustainable solar energy. − Despite enormous prospects, current photocatalysis research faces the problem of low catalytic efficiency. During the photocatalytic reaction, the semiconductors are excited under solar irradiation to generate electron–hole pairs.…”