Focus on photochemical and photothermal catalysts for solar fuel conversion

Solar fuel conversion holds immense promise in the quest for sustainable energy sources. As we grapple with the challenges of climate change and diminishing fossil fuel reserves, harnessing the power of sunlight to produce clean and renewable fuels has become a focal point of scientific research. Two prominent avenues within this realm are photochemical and photothermal catalysis, each with its unique strengths and applications [1–4]. Photochemical catalysts are akin to nature's photosynthesis, converting sunlight into chemical energy to drive water splitting into hydrogen, CO₂ conversion into renewable hydrocarbon fuels, and removal of environmental pollutants. Photothermal catalysts make use of a different facet of solar energy—the ability to generate heat. By utilizing light-absorbing materials, they can raise the temperature of a reaction environment, enabling thermally-driven chemical reactions. Challenges in photochemical and photothermal catalysis fields include optimization of the efficiency of conversion processes and development of cost-effective catalysts. This collection aims to shed light on recent achievement of taking advantage of photochemical and photothermal catalysis for solar fuel conversion.

Photochemical conversion of CO₂ into solar fuels is one of the prospective strategies to reduce the CO₂ emission and develop a sustainable carbon economy [5]. Ye et al synthesized Ni-doped Bi₄O₅I₂ photocatalyst, exhibiting a remarkably CO₂ conversion into CO and CH₄. Ni doping, which are used as springboards for electrons transition, promotes photoexcited electrons and holes separation. Oxygen-doped 2D g-C₃N₄ by Xu et al proves to effectively enhance the yield of photocatalytic CO₂ production of CH₄. O element doping introduces new impurity energy levels, which making electrons easier to be excited. In addition, benefitting from the ultrathin structure of g-C₃N₄, the larger surface area and shorter electrons migration distance effectively improve the CO₂ reduction efficiency. Ouyang et al reported the synergetic modulation of oxygen vacancy and surface alkali over SrTiO₃ for enhancement of CO₂ photoconversion. Oxygen vacancy extends the light absorption and promotes the CO₂ adsorption over SrTiO₃. The surface alkali OH connected with Sr sites of SrTiO₃ could weaken the Sr–O bonding thus facilitate the regeneration of surface oxygen vacancy under the light illumination.

Hydrogen is considered as one of potential energy carriers to store solar energy [6]. Peng et al introduced a unique 2D/2D nanocomposite consisting of heterometallic Zn-/Co-porphyrin conjugated polymer coupling with graphite carbon nitride, efficiently converting solar radiation and water into H₂. Strong π–π stacking interaction between two components facilitates the fast charge transfer from the conjugated polymer to carbon nitride. Zulfequar et al reported incorporation of graphene and Cu₂ZnSnS₄ quantum dots into hematite thin films for a photoelectrochemical cell to realize water splitting into H₂ efficiently. The presence of Cu₂ZnSnS₄ quantum dots enhances the absorption properties of composite along with creating the p–n junction heterostructure which aids the transportation of the charge carriers. Zhang et al synthesized a series of transition metal catalysts based on layered double hydroxide precursors for photothermal nonoxidative coupling reactions of methane, providing novel strategies to convert methane into high-value chemicals. Flower-like hierarchical ZnO microspheres display great photocatalytic performance in H₂O₂ production under simulated sunlight irradiation. The remarkable photocatalytic activity is attributed to enhanced light utilization, large surface area, abundant exposed active sites, improved separation efficiency, and prolonged carrier lifespan. The random disposal and immature recycling of post-consumer polyethylene terephthalate (PET) packages lead to a severe threaten to the ecological system. Qiu et al summarized the latest advances on photoreforming of PET plastics into value-added chemicals, involving the advantages of photocatalytic PET plastics conversion.

In summary, this Collection is dedicated to the promising directions in photochemical and photothermal catalysis of solar fuels, focusing on developing efficient and cost-effective catalysts with the ultimate goal of creating a sustainable and scalable energy solution. We are pleased to see booming publication in this area discussing the relationships between, structures, surface states and defects of catalysts, and their solar fuel production activity/selectivity/stability. Finally, we would like to take this opportunity to sincerely thank all the authors and reviewers for their great contributions to the issue.

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