No abstract

Sunlight-driven CO2 hydrogenation has drawn tremendous attention. However, selective CH4 formation via CO2 photoreduction is very challenging. Herein, we report a metal oxide semiconductor heterojunction consisting of BiVO4 and WO3 as a photocatalyst for the efficient conversion of carbon dioxide (CO2) selectively to methane (105 μmol g–1 h–1) under visible light in the absence of a sacrificial agent. Wise selection of the reaction medium and the strategically tuned heterojunction upon strain relaxation suppresses the competitive hydrogen generation reaction. The detailed photophysical, photoelectrochemical, and X-ray absorption spectroscopy studies pointed to the Z-scheme mechanism of electron transfer, which favors superior electron and hole separation compared to the individual components of the composite catalyst and other well-known photocatalysts reported for CO2 reduction. The observations are further corroborated by experimental diffuse reflectance infrared Fourier transform spectroscopy and theoretical density-functional theory calculations, which reveal that the heterojunction has a lower free-energy barrier for CO2 conversion to CH4 due to the larger stabilization of the *CH2O intermediate on the strain-relaxed heterojunction surface, in comparison to the pristine BiVO4 surface. The present work provides fundamental insights for constructing high-performance heterojunction photocatalysts for the selective conversion of CO2 to desired chemicals and fuels.

A facile non-template-assisted mechanical ball milling technique was employed to generate a PdBi alloy catalyst. The induced lattice strain upon the milling time caused a shift of the d-band center, thereby enhancing the oxygen reduction reaction (ORR) catalytic activity. Additionally, the Pd–O reduction potential and adsorbed OH coverage used as descriptors stipulated the cause of the enhanced ORR activity upon the increased milling interval. Redox properties of surface Pd are directly correlated with a positive shift in the Pd–O reduction potential and OH surface coverage. Hence, by deconvoluting the lattice strain and the role of the descriptor species we achieved a catalyst system with a specific activity 5.4× higher than that of commercial Pt/C, as well as an improved durability. The experimental observation is well-corroborated by a theoretical simulation done by inducing strain to the system externally.

The development of an efficient photocatalyst for C2 product formation from CO 2 is of urgent importance toward the deployment of solar-fuel production. Here, we report a template-free, cost-effective synthetic strategy to develop a carbazole-derived porous organic polymer (POP)-based composite catalyst. The composite catalyst is comprised of In 2.77 S 4 and porous organic polymer (POP) and is held together by inducedpolarity-driven electrostatic interaction. Utilizing the synergy of the catalytically active In centers and light-harvesting POPs, the catalyst showed 98.9% selectivity toward the generation of C 2 H 4 , with a formation rate of 67.65 μmol g −1 h −1 . Two different oxidation states of the In 2.77 S 4 spinel were exploited for the C−C coupling process, and this was investigated by X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations. The role of POP was elucidated via several photophysical and photoelectrochemical studies. The electron transfer was mapped by several correlated approaches, which assisted in establishing the Z-scheme mechanism. Furthermore, the mechanism of C 2 H 4 formation was extensively investigated using density functional theory (DFT) calculations from multiple possible pathways.

Direct photocatalytic conversion of CO2 to ethanol remains a scientific challenge because of the sluggish kinetics of C-C coupling and complex multielectron transfer processes. To achieve a green transformation of...

The discovery of new materials for efficient transformation of carbon dioxide (CO 2 ) into desired fuel can revolutionize large-scale renewable energy storage and mitigate environmental damage due to carbon emissions. In this work, we discovered an operando generated stable Ni−In kinetic phase that selectively converts CO 2 to methanol (CTM) at low pressure compared to the state-of-the-art materials. The catalytic nature of a well-known methanation catalyst, nickel, has been tuned with the introduction of inactive indium, which enhances the CTM process. The remarkable change in the mechanistic pathways toward methanol production has been mapped by operando diffuse reflectance infrared Fourier transform spectroscopy analysis, corroborated by first-principles calculations. The ordered arrangement and pronounced electronegativity difference between metals are attributed to the complete shift in mechanism. The approach and findings of this work provide a unique advance toward the next-generation catalyst discovery for going beyond the state-of-the-art in CO 2 reduction technologies.

Rational design of efficient electrode materials for fuel cell, water oxidation, and the metal-air battery is now cutting–edge activity in renewable energy research. In this regard, tuning the activity at...

Porous organic polymers (POPs) continue to garner immense attention for CO 2 capture and sequestration (CCS) as well as CO 2 fixation to generate useful chemicals for alleviating global warming. Functionally engineered, visible light responsive organic photopolymers with extended π-conjugation and abundant heteroatoms enable photogenerated charge carriers, enhancement in visible light absorption, higher charge separation, and reduction in charge recombination during photocatalysis. In this work, we have explored the construction of a chemically stable, pyridine-equipped, and imine-linked porous organic polymer (Py-POP) by template-free Schiff base condensation of 1,3,5-tris(4aminophenyl) benzene (APB) and 2,6-pyridinedicarboxaldehyde (PDC). This donor−acceptor Py-POP with extensive π-conjugations enables photocatalytic fixation of CO 2 with styrene epoxide (STE) under visible light illumination. We have achieved an impressive conversion of STE to styrene carbonate (STC) (∼99%) under optimized reaction conditions using tert-butyl ammonium bromide (TBAB) as a promoter. Both the efficient CO 2 adsorption and activation for photocatalytic fixation reaction are enabled by the existence of both imine and pyridine moieties in Py-POP. The interaction between Py-POP and CO 2 is further illustrated by density functional theory (DFT) calculations that show that all the POP-CO 2 interactions are favorable and exergonic. Using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization techniques, we elucidate the mechanistic pathways of active key surface species in CO 2 photofixation with Py-POP. Our results provide mechanistic insight into the effectiveness of efficient, sustainable porous organic photocatalysts in visible light-driven CO 2 conversion for various energy applications.