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Photoelectrochemical (PEC) water splitting is a promising approach for renewable solar light conversion. However, surface Fermi level pinning (FLP), caused by surface trap states, severely restricts the PEC activities. Theoretical calculations indicate subsurface oxygen vacancy (sub-Ov) could release the FLP and retain the active structure. A series of metal oxide semiconductors with sub-Ov were prepared through precisely regulated spin-coating and calcination. Etching X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and electron energy loss spectra (EELS) demonstrated Ov located at sub ~2-5 nm region. Mott-Schottky and open circuit photovoltage results confirmed the surface trap states elimination and Fermi level de-pinning. Thus, superior PEC performances of 5.1, 3.4, and 2.1 mA cm-2 at 1.23 V vs. RHE were achieved on BiVO4, Bi2O3, TiO2 with outstanding stability for 72 h, outperforming most reported works under the identical conditions.

Electrocatalytic N

Electrochemical nitrogen reduction reaction (eNRR) is an alternative promising manner for sustainable N2 fixation with low-emission. The major challenge for developing an efficient electrocatalyst is the cleaving of the stable N N triple bonds. Herein, we design a new MoS2 with in-plane defect cluster through a bottom-up approach for the first time, where the defect cluster is composed of three adjacent S vacancies. The well-defined in-plane defect clusters could contribute to the strong chemical adsorption and activation towards inert nitrogen, achieving an excellent eNRR performance with an ammonia yield rate of 43.4 ± 3 μg h−1 mgcat.−1 and a Faradaic efficiency of 16.8 ± 2% at −0.3 V (vs. RHE). The performance is much higher than that of MoS2 with the edge defect. Isotopic labeling confirms that N atoms of produced NH4+ originate from N2. Furthermore, the in-plane defect clusters realized the alternate hydrogenation of nitrogen in a side-on way to synthesize ammonia. This work provides a prospecting strategy for fine-tuning in-plane defects in a catalyst, and also promotes the progress of eNRR.

The difficulty of adsorption and activation of CO2 at the catalytic site and rapid recombination of photogenerated charge carriers severely restrict the CO2 conversion efficiency. Here, we fabricate a novel alkaline Co(OH)2-decorated ultrathin 2D titanic acid nanosheet (H2Ti6O13) catalyst, which rationally couples the structural and functional merits of ultrathin 2D supports with catalytically active Co species. Alkaline Co(OH)2 beneficially binds and activates CO2 molecules, while monolayer H2Ti6O13 acts as an electron relay that bridges a photosensitizer with Co(OH)2 catalytic sites. As such, photoexcited charges can be efficiently channeled from light absorbers to activated CO2 molecules through the ultrathin hybrid Co(OH)2/H2Ti6O13 composite, thereby producing syngas (CO/H2 mixture) from photoreduction of CO2. High evolution rates of 56.5 μmol h-1 for CO and 59.3 μmol h-1 for H2 are achieved over optimal Co(OH)2/H2Ti6O13 by visible light illumination. In addition, the CO/H2 ratio can be facilely tuned from 1:1 to 1:2.4 by changing the Co(OH)2 content, thus presenting a feasible approach to controllably synthesize different H2/CO mixtures for target applications.

The difficulty of adsorption and activation of CO

Photocatalytic reduction of CO2 to solar fuels has been considered as a promising route to solve the energy crisis and environmental issues. Herein, the spatially separated CoO and Au dual cocatalysts are used as the hole and electron collectors, which are loaded on the internal and external surface of TiO2 hollow sphere (THS), respectively (denoted as Aux@THS@CoO). It is found that the Au nanoparticle and Co species are homogenous deposited on the surface of THS without doping. DRS results show that the photoabsorption performances of THS are enhanced obviously in the visible light region. XPS analysis reveals that an internal electric field is constructed, which could promote the separation of photoinduced charge carriers. Subsequently, Au2.0@THS@CoO displays the highest photocurrent density compared with the counterparts. Furthermore, the results of CO2 adsorption, ESR spectra and in-situ FTIR spectra show the high adsorption capacity of CO2 on the sample and the chemisorption of CO2 on the oxygen defects of THS conversed into the active intermediate CO2−. As a result, Au2.0@THS@CoO presents a remarkably enhanced photocatalytic activity for the reduction of CO2 with H2O in CH4. The optimal activity of the catalyst is 13.3 μmol h−1 g−1, which is 60 times higher than that of THS. In addition, in-situ FTIR spectra also suggest that H2O participates in the reaction as electron donator and hole scavenger during the photocatalysis process. Finally, a possible photocatalytic process has also been proposed.

Electrochemical nitrogen reduction is suffering from the bottleneck of poor activity and low electron selectivity. Herein, we precisely synthesize an efficient electrocatalyst using phosphotungstic acid as a platform to anchor Bi species on the four-fold hollow site and associate with Li species on the three-fold hollow site. The well-designed catalyst shows a significant eNRR performance with an ammonia yield rate of 61 ± 1 μg h-1 mgcat.-1 and a recorded Faradaic efficiency of 85 ± 2% at -0.1 V vs. RHE. Isotopic labeling verifies that N atoms of formed NH4+ originate from N2. In situ experiments and theoretical calculations reveal that the Biδ+ species could promote the effective activation and hydrogenation of dinitrogen molecules at the adjacently unsaturated W active sites, and the incorporated Li species reduce the hydrogen reduction rate in the undesirable water splitting. This synergistic functionalization of Bi and Li species contributes to the high-efficient catalyst.