Doping engineering in S-scheme composite for Regulating the selectivity of photocatalytic CO2 reduction

Regulating product selectivity in photocatalytic CO2 reduction to enhance the yield of valuable hydrocarbons remains a formidable challenge because of the diversity of reduction products and the competitive reduction of H2O. Herein, ultrathin Bi2O3/ Co-doped SrBi4Ti4O15 S-scheme photocatalysts (Co-BS) were synthesized using a hydrothermal method. The Bi2O3/Co-doped SrBi4Ti4O15 photocatalyst exhibited significantly higher selectivity for CH4 (62.3 μmolg-1) and CH3OH (54.1 μmolg-1) in CO2 reduction compared with pure SrBi4Ti4O15 (27.2 and 0.8 μmolg-1) and the Bi2O3/SrBi4Ti4O15 S-scheme without Co (30.2 and 0 μmolg-1). The experimental results demonstrated that the inclusion of Co into SrBi4Ti4O15 expanded the range of light absorption and generated an internal electric field between Co-doped SrBi4Ti4O15 and Bi2O3. Density functional theory calculations and other experimental findings confirmed the formation of a new doping energy level in the Bi2O3/SrBi4Ti4O15 S-scheme heterojunction after Co doping. The valence band electrons of Bi2O3/SrBi4Ti4O15 transitioned to the Co-doped level because of the interconversion between Co3+ and Co2+ under the action of the internal electric field. Furthermore, the corresponding characterizations revealed that the adsorption and electron transfer rates of the surface active sites were accelerated after Co doping, enhancing electron involvement in the photocatalytic reaction process. This study presented a metal-doped S-scheme heterojunction approach for CO2 reduction to produce high-value products, enhancing the conversion of solar energy into energy resources.

In situ addition of Ni salt onto a skeletal Cu7S4 integrated CdS nanorod photocatalyst for efficient production of H2 under solar light irradiation

Development of earth-abundant, low cost, skeletal-type copper sulfide superstructures and in situ addition of Ni salts plays a prominent role to enhance the activity of CdS semiconductor nanostructures for photocatalytic H₂ production.

1D WO3 Nanorods/2D WO3-x Nanoflakes Homojunction Structure for Enhanced Charge Separation and Transfer towards Efficient Photoelectrochemical Performance

Designing and fabricating photoelectrodes with low carrier recombination, high carrier transfer, and high light-capture capability is of great significance for achieving effective photoelectrochemical (PEC) water splitting. Herein, for the first time, 2D nonstoichiometric WO_3-x nanoflakes (NFs) were vertically grown by hydrothermal synthesis on 1D WO₃ nanorods (NRs) obtained by a hydrothermal method and high-temperature annealing (HTA). In this 1D HTA-WO₃ /2D WO_3-x photoanode, the 2D WO_3-x NFs with active areas could maximize light harvesting, and the unique 1D/2D homojunction structure could improve the carrier-separation efficiency. At the same time, the 1D WO₃ NRs with high aspect ratio were more beneficial to charge transfer after HTA. As expected, the 1D HTA-WO₃ /2D WO_3-x photoanode yielded an enhanced photocurrent density of 0.98 mA cm^-2 at 1.23 V versus reversible hydrogen electrode, which is approximately 3.16 times that of pristine WO₃ . The improvement could be attributed to the synergistic effect of HTA and the homojunction structure in the 1D HTA-WO₃ /2D WO_3-x photoanode, which could effectively improve carrier separation and transfer. Furthermore, this work may provide a promising strategy for the design and fabrication of semiconductor-based photoelectrodes.

Oxygen deficiency introduced to Z-scheme CdS/WO3-x nanomaterials with MoS2 as the cocatalyst towards enhancing visible-light-driven hydrogen evolution

An oxygen deficiency modified Z-scheme CdS/WO3-x nanohybrid with MoS2 as the cocatalyst was synthesized by a microwave hydrothermal method and was used for photocatalytic hydrogen production under visible light irradiation. Loadings of WO3-x and MoS2 as well as the synthesis time of the microwave-assisted hydrothermal process were optimized, and the physicochemical and optical properties of the as-prepared photocatalysts were characterized by various techniques. Results showed that the material with 30 wt% of WO3-x, 0.1 wt% of MoS2 and a preparation time of 120 minutes exhibited the most desirable morphology and structure for hydrogen production. The maximum hydrogen production of 2852.5 μmol g-1 h-1 was achieved, which was 5.5 times that of pure CdS (519.1 μmol g-1 h-1) and 1.5 times that of CdS/30 wt% WO3-x (1879.0 μmol g-1 h-1), and the external quantum efficiency (EQE) reached 10.0% at 420 nm. The improvement of photocatalytic performance could be attributed to the Z-scheme formed between CdS and WO3-x and MoS2 as an electron trap. It is worth mentioning that the size of the composite had a negative correlation with the H2 production rate.