Photocatalytic CO2 conversion to value-added chemicals is a promising solution to mitigate the current energy and environmental issues but is a challenging process. The main obstacles include the inertness of CO2 molecule, the sluggish multi-electron process, the unfavorable thermodynamics, and the selectivity control to preferable products. Furthermore, the lack of fundamental understanding of the reaction pathways accounts for the very moderate performance in the field. Therefore, in this Perspective, we attempt to discuss the possible reaction mechanisms toward all C1 and C2 value-added products, taking into account the experimental evidence and theoretical calculation on the surface adsorption, proton and electron transfer, and products desorption. Finally, the remaining challenges in the field, including mechanistic understanding, reactor design, economic consideration, and potential solutions, are critically discussed by us.

https://pubs.acs.org/doi/pdf/10.1021/acscatal.2c01012

Insight on Reaction Pathways of Photocatalytic CO2 Conversion

Sparked by natural photosynthesis, solar photocatalysis using metal‐free graphitic carbon nitride (g‐C3N4) with appealing electronic structure has turned up as the most captivating technique to the quest for sustainable energy generation and pollution‐free environment. Nonetheless, low‐dimensional g‐C3N4 is thwarted from sluggish kinetics and rapid recombination of photogenerated carriers upon light irradiation. Among multifarious modification strategies, engineering 2D cocatalysts is anticipated to accelerate redox kinetics, augment active sites and ameliorate electron–hole separation of 2D g‐C3N4 for boosted activity thanks to its face‐to‐face contact surface. It is of timely and technological significance to review the 2D/2D interfaces with state‐of‐the‐art 2D cocatalysts, spanning from carbon‐containing to phosphorus‐containing, metal dichalcogenide, and other cocatalysts. Fundamental principles for each photocatalytic application will be introduced. Thereafter, the recent advances of 2D/2D cocatalyst‐mediated g‐C3N4 systems will be critically evaluated based on their interfacial engineering, emerging roles, and impacts toward stability and catalytic efficiency. Importantly, mechanistic insights into the charge dynamics and structure–performance relationship will be deciphered. Last, noteworthy research directions are prospected to deliver insightful ideas for future development of g‐C3N4. Overall, this review is anticipated to serve as a scaffold and cornerstone in designing dimensionality‐dependent 2D cocatalyst‐assisted g‐C3N4 toward renewable energy and ecologically green environment.

Tailor‐Engineered 2D Cocatalysts: Harnessing Electron–Hole Redox Center of 2D g‐C3N4 Photocatalysts toward Solar‐to‐Chemical Conversion and Environmental Purification

Abstract Photochemical conversion of CO 2 into high-value C 2+ products is difficult to achieve due to the energetic and mechanistic challenges in forming multiple C-C bonds. Herein, an efficient photocatalyst for the conversion of CO 2 into C 3 H 8 is prepared by implanting Cu single atoms on Ti 0.91 O 2 atomically-thin single layers. Cu single atoms promote the formation of neighbouring oxygen vacancies (V O s) in Ti 0.91 O 2 matrix. These oxygen vacancies modulate the electronic coupling interaction between Cu atoms and adjacent Ti atoms to form a unique Cu-Ti-V O unit in Ti 0.91 O 2 matrix. A high electron-based selectivity of 64.8% for C 3 H 8 (product-based selectivity of 32.4%), and 86.2% for total C 2+ hydrocarbons (product-based selectivity of 50.2%) are achieved. Theoretical calculations suggest that Cu-Ti-V O unit may stabilize the key *CHOCO and *CH 2 OCOCO intermediates and reduce their energy levels, tuning both C 1 -C 1 and C 1 -C 2 couplings into thermodynamically-favourable exothermal processes. Tandem catalysis mechanism and potential reaction pathway are tentatively proposed for C 3 H 8 formation, involving an overall ( 20 e − – 20 H + ) reduction and coupling of three CO 2 molecules at room temperature. 

/pdf/room-temperature-photosynthesis-of-propane-from-co2-with-cu-1tvsmp8g.pdf

Room-temperature photosynthesis of propane from CO2 with Cu single atoms on vacancy-rich TiO2

Significant improving g-C 3 N 4 ’s photocatalytic efficiency still remains a great challenge. In this work, we synthesized ultrathin and porous 2D g-C 3 N 4 nanosheets with a controllable concentration of carbon vacancies and oxygen doping. Water vapor opens the heptazine units, introduces carbon vacancies, and acts as an oxygen source for oxygen doping under high temperatures. The synergistic effect of controllable carbon vacancies and oxygen doping can continuously regulate band structures and significantly improves the separation efficiency of photoexcited charges. As a result, the prepared g-C 3 N 4 with vigoroso reduction potential exhibits a very high photocatalytic H 2 evolution rate of 2.414 mmol g −1 h −1 under visible light and 7.414 mmol g −1 h −1 under ultraviolet-visible light, respectively, which outperforms the majority of the previously reported g-C 3 N 4 with well-tuned band structure. This work offers a new design idea for highly active g-C 3 N 4 -based photocatalysts with a well-tuned band structure. A step-by-step synergistic etching/stripping strategy is developed for preparing ultrathin and porous 2D g-C 3 N 4 nanosheets with controllable carbon vacancies and oxygen doping with a great potential in photocatalysis. • Ultra-thin and porous 2D g-C 3 N 4 nanosheets with controllable carbon vacancies and oxygen doping are prepared. • Water vapor opens the heptazine units, introduces carbon vacancies, and acts as oxygen sources for oxygen doping under high temperatures. • Synergistic effect of controllable carbon vacancies and oxygen doping can continuously regulate band structures. • Rapid separation of photoexcited charges and up-shift of conduction band boost photocatalytic performance.. 

Ultrathin Porous Carbon Nitride Nanosheets with Well-tuned Band Structures via Carbon Vacancies and Oxygen Doping for Significantly Boosting H2 Production

Synergistic Electrocatalysts for Alkaline Hydrogen Oxidation and Evolution Reactions

Photocatalytic conversion of CO2 to CH3CHO is of increasing interest but confronts significant challenge in forming C–C bond and keeping a C=O bond intact throughout the process. Here, we report the selective photocatalytic hydrogenation of CO2 to CH3CHO using a modified polymeric carbon nitride (PCN) at mild conditions. The locally crystallized PCN offers a photocatalytic activity of 1814.7 μmolh-1g-1 with a high selectivity of 98.3% for CH3CHO production, and a quantum efficiency of 22.4 % at 385 nm, outperforming all the state-of-art CO2 photocatalysts. The promoted formation of the *OCCHO intermediate on the locally crystallized PCN is disclosed as the key factor leading to the high selective CH3CHO generation. The locally crystallized PCN favors spontaneously C-C coupling towards *OCCHO formation rather than *CHO protonation, thus preventing HCHO formation. This work provides a new strategy for designing carbon nitrides for high selective and sustainable conversion of CO2 into CH3CHO.

Regulating *OCCHO intermediate pathway towards high selective photocatalytic CO2 reduction to CH3CHO over locally crystalized carbon nitride

CoMo2S4 with Superior Conductivity for Electrocatalytic Hydrogen Evolution: Elucidating the Key Role of Co

In the present contribution, a highly crystalline nano-coral matrix on amorphous polymeric carbon nitride (PCN) nanosheets are structurally crafted and identified as an efficient photocatalyst for photocatalytic CO2 reduction reaction (CRR). The modified PCN presents a unique spatial dyadic heterostructure and favorable directional charge-transfer channel, resulting in improved charge separation for CRR. Notably, DFT calculations suggest that the modified PCN possesses reduced energy barrier for CO2 reduction into CO via facile accessible of COOH intermediate and boosted CO* desorption. The as-prepared functionalized PCN materials possess a remarkable photocatalytic CO2 reduction performance, yielding CO at a rate of 486.7 μmol h−1 g−1 (i.e. 34.0 folds’ higher than pristine PCN) with a high selectivity of 98.4 %. Our strategy of designing spatial dyadic heterostructure in polymeric carbon nitride provides new insights into the architecture engineering of CRR photocatalysts for efficient CO desorption and CO2 conversion.

Boosted CO desorption behaviors induced by spatial dyadic heterostructure in polymeric carbon nitride for efficient photocatalytic CO2 conversion

Di-nuclear metal synergistic catalysis: Ni2Mo6S6O2/MoS2 two-dimensional nanosheets for hydrogen evolution reaction

The invention discloses a method for preparing a bismuth oxide nanowire film through inverted heating. The characteristic of the low melting point of bismuth metal is innovatively utilized, a direct-current magnetron sputtering method is adopted for depositing a bismuth metal film on the conductive surface of an inverted substrate, and the bismuth metal film is in a semi-molten state by preciselycontrolling the inverted heating temperature; and the bismuth oxide film with a special nanowire structure grows from the semi-molten bismuth metal under the combined action of gravity and surface tension by adjusting and controlling the proper oxygen content, and the problems that in the prior art, a film prepared through the direct-current magnetron sputtering method is usually uniform and compact, and a surface nanostructure is difficult to construct are solved. Meanwhile, a bismuth target is innovatively bound with a copper back target to enhance heat conduction, a forced water cooling technology is used in cooperation for cooling a target head, and the technical problem that the low-melting-point bismuth target is easily subjected to overheating melting deformation in the magnetron sputtering process is successfully solved.

Method for preparing bismuth oxide nanowire film through inverted heating

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