Ultrathin Ti-doped WO3 nanosheets realizing selective photoreduction of CO2 to CH3OH.

Arduous CO2 activation and sluggish charge transfer retard the photoreduction of CO2 to CH3OH with high efficiency and selectivity. Here, we fabricate ultrathin Ti-doped WO3 nanosheets possessing approving active sites and optimized carrier dynamics as a promising catalyst. Quasi in situ X-ray photoelectron spectroscopy and synchrotron-radiation X-ray absorption near-edge spectroscopy firmly confirm that the true active sites for CO2 reduction are the W sites rather the Ti sites, while the Ti dopants can facilitate charge transfer, which accelerates the generation of crucial COOH* intermediates as revealed by in situ Fourier-transform infrared spectroscopy and density functional theory calculations. Besides, the Gibbs free energy calculations also validate that Ti doping can lower the energy barrier of CO2 activation and CH3OH desorption by 0.22 eV and 0.42 eV, respectively, thus promoting the formation of CH3OH. In consequence, the Ti-doped WO3 ultrathin nanosheets show a superior CH3OH selectivity of 88.9% and reach a CH3OH evolution rate of 16.8 µmol g-1 h-1, about 3.3 times higher than that on WO3 nanosheets. This work sheds light on promoting CO2 photoreduction to CH3OH by rational elemental doping.

Selective CO2 Photoreduction to CH4 via Pdδ+ -Assisted Hydrodeoxygenation over CeO2 Nanosheets.

Here, noble-metal-doped two-dimensional metal oxide nanosheets are designed to realize selective CO2 photoreduction to CH4 . As a prototype, Pd-doped CeO2 nanosheets are fabricated, where the active sites of Pdδ+ (2<δ<4) and Ce3+ -Ov are revealed by quasi in situ X-ray photoelectron spectra and in situ electron paramagnetic resonance spectra. Moreover, in situ Fourier-transform infrared spectra of D2 O photodissociation and desorption verify the existence of the Pd-OD bond, implying that Pdδ+ sites can participate in water oxidation to deliver H* species for facilitating the protonation of the intermediates. Furthermore, theoretical calculations suggest the Pd doping could regulate the formation energy barrier of the key intermediates CO* and CH3 O*, thus making CO2 reduction to CH4 become the favorable process. Accordingly, Pd-doped CeO2 nanosheets achieve nearly 100 % CH4 selectivity of CO2 photoreduction, with the raising CH4 evolution rate of 41.6 µmol g-1 h-1 .

Surface Engineering on Commercial Cu Foil for Steering C2H4/CH4 Ratio in CO2 Electroreduction.

Designing catalysts with high selectivity toward C2 products in CO2 electroreduction is crucial to energy storage and sustainable development. Here, we propose a Cu foil kinetic model with abundant nanocavities possessing higher reaction rate constant k to steer the ratio of C2H4 to the competing CH4 during CO2 electroreduction. Chemical kinetic simulation demonstrates that the nanocavities could enrich the adsorbed CO surface concentration (θCOad), while the higher k helps to lower the C-C coupling barrier for CO intermediates, thus favoring the formation of C2H4. The commercial Cu foil treated with cyclic voltammetry is used to match this model, displaying a remarkable C2H4/CH4 ratio of 4.11, which is 18 times larger than that on the pristine Cu foil. This work offers a handy strategy for surface modification and provides new insights into the C-C coupling and the C2H4 selectivity in terms of mass transfer flux and energy barrier.

Efficient Visible-Light-Driven CO2 Reduction Mediated by Defect-Engineered BiOBr Atomic Layers.

Solar CO2 reduction efficiency is largely limited by poor photoabsorption, sluggish electron-hole separation, and a high CO2 activation barrier. Defect engineering was employed to optimize these crucial processes. As a prototype, BiOBr atomic layers were fabricated and abundant oxygen vacancies were deliberately created on their surfaces. X-ray absorption near-edge structure and electron paramagnetic resonance spectra confirm the formation of oxygen vacancies. Theoretical calculations reveal the creation of new defect levels resulting from the oxygen vacancies, which extends the photoresponse into the visible-light region. The charge delocalization around the oxygen vacancies contributes to CO2 conversion into COOH* intermediate, which was confirmed by in situ Fourier-transform infrared spectroscopy. Surface photovoltage spectra and time-resolved fluorescence emission decay spectra indicate that the introduced oxygen vacancies promote the separation of carriers. As a result, the oxygen-deficient BiOBr atomic layers achieve visible-light-driven CO2 reduction with a CO formation rate of 87.4 µmol g-1 h-1 , which was not only 20 and 24 times higher than that of BiOBr atomic layers and bulk BiOBr, respectively, but also outperformed most previously reported single photocatalysts under comparable conditions.