Solar CO2 Conversion Research Articles

Atomically precise metal nanoclusters combine with MXene towards solar CO2 conversion.

Atomically precise metal nanoclusters (NCs) have been deemed a new generation of photosensitizers for light harvesting on account of their quantum confinement effect, peculiar atom-stacking mode, and enriched catalytic active sites. Nonetheless, to date, precise charge modulation over metal NCs has still been challenging considering their ultra-short carrier lifetime and poor stability. In this work, we conceptually demonstrate the integration of metal NCs with MXene in transition metal chalcogenide (TMC) photosystems via a progressive, exquisite, and elegant interface design to trigger tunable, precise and high-efficiency charge motion over metal NCs, stimulating a directional carrier transport pathway. In this customized ternary heterostructured photosystem, metal NCs function as light-harvesting antennas, MXene serves as a terminal electron reservoir, and the TMC substrate provides suitable energy level alignment for retracting photocarriers of metal NCs, giving rise to a spatial cascade charge transport route and markedly boosting charge separation efficiency. The interface configuration and energy level alignment engineering synergistically contribute to the considerably enhanced visible-light-driven photocatalytic CO2-to-CO reduction performance of the metal NCs/TMCs/MXene heterostructure. The intermediate active species during the photocatalytic CO2 reduction are unambiguously determined, based on which the photocatalytic mechanism is elucidated. Our work will provide an inspiring idea to bridge the gap between atomically precise metal NCs and MXene in terms of controllable charge migration for solar-to-fuel conversion.

Single-atom Pt supported on non-metal doped WS2 for photocatalytic CO2 reduction: A first-principles study

Solar conversion of CO2 into energy-rich products a sustainable solution to mitigate the global energy shortage and environmental crisis. Herein, the photocatalytic CO2 reduction of WS2-based single-atom catalysts was investigated using density functional theory. The results indicated that non-metals represented by B, C, and N doped WS2 (X-WS2) could significantly enhance the photocatalytic performance of CO2 reduction. Compare with Pt@WS2, Pt@B-WS2 could reduce the Gibbs free energy from 1.41 to 1.01 eV. The comprehensive results reveal that the introduction of the B atom endowed WS2 with improved metal-support interaction to stabilize the Pt single-atom and effectively promoted charge separation and transfer, leading to higher photocatalytic performance for converting CO2 to CH4. This study provides a strategy to design superior single-atom catalysts for photocatalytic conversion CO2 to carbon–neutral fuels.

(Invited) Solar CO2 Conversion into Liquid Fuels By Photoelectrochemical Approaches

Photoelectrochemical (PEC) system for the reduction of CO2 into liquid fuels of formaldehyde/acetaldehyde, methanol and ethanol with trace amount of hydrogen gas bubbling have been described in the aspect of thermodynamics and kinetics of the CO2 reduction reaction to have efficient method by lowering activation energy of CO2 reduction on the electron transfer reaction and to do reduction potential tuning of CO2 reduction reaction for the selective reduction products. Ca/Fe doped TiO2 photoanode oxidizes water and generates the large amount of O2, electrons and protons. On the other side, rGO(reduced graphene oxide)/PVP(poly(4-vinyl)pyridine)/Nafion multi-layers have been coated and fabricated on the surface of Cu foil cathode to reduce CO2 into formaldehyde and acetaldehyde. When solar light was irradiated on the surface of photoanode, electrons get excited to the conduction band of Ca/Fe doped TiO2 and transported to the cathode via external wire with low external bias potential. rGO on Cu foil has been used for the dual functions of reduction potential tuning and multi-electron shuttling process of CO2 reduction reaction. The multi-electron shuttling function was illuminated by larger number and longer life-time of excited electrons and generating electron cloud, which have been confirmed by time-resolved photoluminescence (TR-PL) decay curves and 2D time-resolved photoluminescence (TR-PL) mapping images of Cu/rGO electrode. This allows the sequential multi-electron transport process from Cu/rGOcathode to CO2, which was studied with time-resolved chronoamperometry. N-heterocyclic poly(4-vinyl)pyridine (PVP) helps to capture and do chemical activation of reactant CO2 molecule by complexation as [PVP-CO2*] complex via charge separation and lowering transition state energy level of the electron transfer for the formation of anion radical of carbon dioxide complex with PVP as [e- + PVP-CO2*]≠ complex via electron delocalization, which is basically possible due to high basicity of lone pair electrons of nitrogen atoms of N-heterocyclic PVP compounds. These functions result in the lowered activation energy for the CO2 reduction reaction to have faster kinetics. The decreased amount of activation energy was determined with Tafel plots by measuring the slopes of it and semicircles of the electrochemical impedance spectroscopy (EIS) Nyquist plots at different temperatures. Nafion film coated on the surface of cathode assists the faster transport of H+ ions to CO2 reduction reaction sites for the simultaneous one-pot reaction of proton coupled electron transfer reactions. In the photocataytic system with semi-conducting polymers, CO2 was conversed into liquid solar fuels like formaldehyde and alcohols with solar to fuel efficiency over 2.5% to produce liquid fuel products over mM concentration for 4 hour reaction. Chang Woo Kim, So Jin Yeob, Hui-Ming Cheng, Young Soo Kang*, Selectively Exposed Crystal Facet-Engineered TiO2 Thin Film Photoanode for the Higher Performance of Photoelectrochemical Water Splitting Reaction, Energy and Environmental Sciences. 2015, 8, 3646.Amol U.Pawar, Chang WooKim, Myung Jong Kang, Young Soo Kang*, Crystal facet engineering of ZnO photoanode for the higher water splitting efficiency with proton transferable nafion film, Nano Energy 2015, 20, 156.Chang Woo Kim, Young Seok Son, Myung Jong Kang, Do Yoon Kim, Young Soo Kang*, (040)-Crystal Facet Engineering of BiVO4 Plate Photoanode for Solar Fuel Production, Energy Mater., 2016, 6, 1501754.Jin You Zheng, Amol Uttam Pawar, Chang Woo Kim, Yong Joo Kim, Young Soo Kang*, Highly enhancing photoelectrochemical performance of facilely-fabricated Bi-induced (002)-oriented WO3 film with intermittent short-time negative polarization, Applied Catalysis B 2018, 233, 88.Chang Woo Kim, Myung Jong Kang, Sohyun Ji, and Young Soo Kang*, Artificial Photosynthesis for Formaldehyde Production with 85% of Faradaic Efficiency by Tuning the Reduction Potential, ACS Catalysis 2018, 82, 968-974.Myung Jong Kang, Chang Woo Kim, Amol U. Pawar, Hyun Gil Cha, Sohyun Ji, Wen-Bin Cai, and Young Soo Kang*, Selective Alcohol on Dark Cathode by Photoelectrochemical CO2 Valorization and Their in-situ Characterization, minor revision, ACS Energy Lett. 2019, 4, 1549.Hong Ryeol Park, Amol Uttam Pawar, Umapada Pal, Tierui Zhang, Young Soo Kang, Enhanced solar photoreduction of CO2 to liquid fuel over rGO grafted NiO-CeO2 heterostructure nanocomposite, Nano Energy, 2021, 79, 105483.Amol U. Pawar, Umapada Pal, Jin You Zheng, Chang Woo Kim and Young Soo Kang*, Dynamics controlled CO2 reduction on Cu/rGO/PVP/Nafion multi-layered cathode for selective production of Acetaldehyde and Formaldehyde, Applied Catalysis B: Environmental, 2022, 303, 120921.

Sustained CO2-photoreduction activity and high selectivity over Mn, C-codoped ZnO core-triple shell hollow spheres

Solar conversion of CO2 into energy-rich products is one of the sustainable solutions to lessen the global energy shortage and environmental crisis. Pitifully, it is still challenging to attain reliable and affordable CO2 conversion. Herein, we demonstrate a facile one-pot approach to design core-triple shell Mn, C-codoped ZnO hollow spheres as efficient photocatalysts for CO2 reduction. The Mn ions, with switchable valence states, function as “ionized cocatalyst” to promote the CO2 adsorption and light harvesting of the system. Besides, they can capture photogenerated electrons from the conduction band of ZnO and provide the electrons for CO2 reduction. This process is continuous due to the switchable valence states of Mn ions. Benefiting from such unique features, the prepared photocatalysts demonstrated fairly good CO2 conversion performance. This work is endeavoured to shed light on the role of ionized cocatalyst towards sustainable energy production.

Continuous Photocatalytic Reduction of CO₂ Using Nanoporous Reduced Graphene Oxide (RGO)/Cadmium Sulfide (CdS) as Catalyst on Porous Anodic Alumina (PAA)/Aluminum Support.

Solar conversion of CO₂, using a photocatalyst in the presence of water, has attained considerable attention due to added value of the process in terms of both reduction of an environmental pollutant and production of valuable synthetic chemicals. Room temperature fabrication of porous anodic alumina (PAA), for sufficiently low time, facilitates the synthesis of self-withstanding PAA with a middle layer of aluminum. Nanoporous reduced graphene oxide (RGO), deposited on the pore walls of PAA, with subsequent deposition of cadmium sulfide (CdS) as photocatalyst over it, and efficiently enhances the photocatalytic reduction of CO₂. Morphological, structural and optical characterizations of the catalyst are executed using field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), electron dispersive X-spectroscopy (EDX) and UV-Vis absorption spectroscopy methods. Continuous photocatalytic reduction of CO₂ was carried out using flat sheet reactors and a compound parabola as the solar reflector. Semiconducting CdS nanorods, grown over PAA support with conducting RGO, show enhanced photocatalytic reduction of CO₂ to 153.8 μmol/g/hr of CH₃OH with higher photocatalytic stability than CdS alone.

Solar Conversion of CO2 into Methanol

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