Carbon black (CB) has long been considered an inert conductive additive and support in the electrochemical CO₂ reduction reaction (CO₂RR). A growing body of evidence, however, demonstrates that CB assumes considerably more complex and active functions. This review critically re-evaluates the multifaceted roles of CB in CO₂RR, moving beyond its conventional function as a mere substrate. We first summarize the structural and physicochemical properties of different CB types and their established performance as conductive supports that facilitate three-phase interfaces and stabilize catalytic sites. We then highlight recently uncovered contributions of CB, including (1) the modulation of the reaction microenvironment, such as local pH, ion enrichment, and hydrophobicity, (2) the reconstruction of catalyst via electrochemical, confinement, and surface-chemistry pathways, (3) the enhancement of mass transport and reaction kinetics, and (4) the direct participation of CB as an active component via crystal-phase control, heteroatom doping, and active-site construction. Furthermore, CB enables several emerging functionalities, including defect-driven catalysis, universal synthesis of single-atom catalysts, and surface organometallic chemistry (SOMC). Finally, we discuss future directions, emphasizing precise catalyst design, the seamless integration of in situ characterization with theoretical modelling, and device engineering toward industrial application. This review aims to reshape the perception of CB from an inert scaffold to a versatile functional material, thereby providing a foundation for the rational design of high-performance and cost-effective CO₂RR catalysts.

Heterogeneous photosynthesis is a promising route for sustainable ammonia production, which can utilize renewable energy and water as the hydrogen source under ambient condition. In this study, a series of Bi₅O₇I (BOI) nanosheets and nanotubes are synthesized, and the surface tensile strain is formed by curling the nanosheets into nanotubes to tune the concentration and location of dynamic vacancies. Scanning transmission electron microscopy (STEM) with spherical aberration correction confirms the presence of intrinsic areal defects on the surface of the BOI nanotube resulted from surface tensile strain. The presence of areal defects lowers the formation energy of I vacancies (IV) at step edge site, thus the IV with higher concentration would be favorably generated under visible light. Rapid scan in situ Fourier transform infrared (FT-IR) analysis in the aqueous media reveals that the IV promotes photocatalytic N₂ activation and reduction, and proceeds through an associative alternating mechanism. Specially, after turning off the light, the surface vacancy sites can be reoccupied by I⁻ ions, which enables the protection and regeneration of photocatalyst surface in an aerobic and dark environment. This work provides an innovative strategy to tune concentration and location of dynamic surface vacancies on photocatalysts by building surface tensile strain for advancing sustainable ammonia production.

Photocatalytic CO₂ reduction is mainly inspired by natural photosynthesis, which could convert CO₂ into high value-added fuels or chemicals through the role of catalysts. However, the photocatalysis efficiency of the currently developed catalysts is far from meeting the actual needs due to the low efficiency of charge separation and energy transfer, and the poor adsorption and activation of CO₂ by catalyst surface. Single-atom catalysts (SACS) show an excellent activity, selectivity and stability in many important reactions, and exhibit great potential in photocatalytic reduction of CO₂ owing to their high atomic utilization and controllability of active sites. In the current review, recent progresses and challenges on SACs for photocatalytic CO₂ conversion systems are presented. The key fundamental principles and reaction mechanisms focusing on charge separation/transfer and molecular adsorption/activation on single-atom photocatalysts for CO₂ reduction are systemically explored. We outlined how single-atom active sites promote the photogenerated carriers separation/transfer and enhance molecular photoactivation. Besides, we put forward some challenges and prospects for the future development of single-atom photocatalysts in CO₂ reduction.

Photoinduced reactive oxygen species (ROS)-based pollutant removal is one of the ideal solutions to achieve the conversion of solar energy into chemical energy and thus to address environmental pollution. Here, earth-abundant CaCO₃-decorated g-C₃N₄ (g-C₃N₄ labeled as CN, CaCO₃-decorated g-C₃N₄ sample labeled as CN-CCO) has been constructed by a facile thermal polymerization method for safe and efficient photocatalytic NO removal. The decorated CaCO₃ as “transit hub” extends the π bonds of CN to deviate from the planes and steers the random charge carriers, which thus provides extra active sites and expedites spatial charge separation to facilitate adsorption/activation of reactants and promote formation of ROS participating in the removal of pollutant. Furthermore, boosted generation of ROS regulates the photocatalytic NO oxidation pathway and thus increases the selectivity of products. NO prefers to be directly oxidized into final product (nitrate) rather than toxic intermediates (NO₂), which is well demonstrated by theoretically simulated ROS-based reaction pathways and experimental characterization. The present work promotes the degradation of pollutant and simultaneously suppresses the formation of toxic by-product, which paves the way for ROS-based pollutant removal.