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Direct conversion of carbon dioxide (CO2) to high-value chemicals or fuels would provide new energy sources and environmental remediation. The conversion process however involves complex reaction pathways with multiple competing products, strongly depending on catalysts and applied potential; conventional computational models fail to accurately predict the process and products. Herein, we have created a computational approach, based on the density functional theory (DFT) and electrical double-layer interface models with explicit hydrogen bonding, to accurately predict potential-dependent reaction pathways, catalytic activity, and product selectivity of electrochemical CO2 reduction. The onset potentials and the potential to achieve maximum faradaic efficiency of CO2 reduction were calculated, which agree well with the experimental results for single-atom catalysts. This work provides a fundamental understanding of the complex potential-dependent catalytic behavior, and new approaches for screening of catalysts for not only CO2 reduction but also more complex reaction systems, such as nitrogen reduction and urea oxidation. [ABSTRACT FROM AUTHOR]

The development of nanomaterials with multifunctional properties presents a viable business case for potential scale-up of nanomaterial fabrication. Hence, the design and engineering of structures as well as tuning of active sites are crucial in generating multifunctional properties in nanomaterials. In this regard, we demonstrate a three-dimensional (3D) fractal structure of Au–Bi2O3 with a fractal dimension (Df) of ≈ 1.80, which is obtained from the small-angle X-ray scattering (SAXS) measurement and through the box counting algorithm. The fractal structures, fabricated via a one-step direct synthesis, gives a homogeneous distribution of catalytically active nanocrystals Au and Bi2O3 on a 3D platform with a large active surface area, resulting in a strong enhancement of its localized electric field. Therefore, when applied as a catalyst for electrochemical CO2 reduction reactions (CO2RR) and optical gas sensing, the material displays an excellent performance. Specifically, the fractal structure exhibits a high selectivity towards the formation of formate, achieving a very high faradaic efficiency of 97% and high mass-specific formate current density of −54 mA mg−1 at −1.1 V vs. a reversible hydrogen electrode (RHE). Similarly, this structure displayed a plasmonic shift as high as ∼5 nm for 4 vol% acetone sensing with a detection limit of 100 ppm towards different volatile organic compounds (VOCs). [ABSTRACT FROM AUTHOR]

Surface coating of a protective layer can prevent the corrosion of Cu2O at electrode liquid junctions (ELJs) in photoelectrochemical water splitting. However, a facile methodology for the deposition of a conformal protective layer is still a challenge. Here, an ultrathin layer of amorphous ZnO is introduced on Cu2O by pulsed electrodeposition, to construct a "sandwich" structure of a composite photoelectrode of TiO2/ZnO/Cu2O on an FTO substrate. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) visualises the spatial distribution of Ti, Zn, Cu, and Sn elements of the composite. Benefiting from the homogeneous coating of a ZnO layer, visible cracks in TiO2 coating are significantly reduced, thus preventing the direct contact between the electrolyte and Cu2O. Moreover, due to the ultrathin property of the amorphous ZnO layer, the energetic electrons from the excited Cu2O can be injected via the ZnO layer into TiO2, as elucidated by time-resolved photoluminescence (TRPL) results. The resulting composite photoelectrode shows enhanced photoelectrochemical activity and stability, compared to the bare Cu2O, as well as the TiO2/Cu2O photoelectrode. This study offers a versatile and effective method for improving the stability and charge separation efficiency of Cu2O, which is useful in guiding the surface coating of other nanostructured materials for solar energy conversion. [ABSTRACT FROM AUTHOR]

The research interest on bismuth vanadate (BiVO4) has heightened over the past decade due to its proven high activity for water oxidation and organic degradations under visible light. Although metal doping and water-oxidation cocatalyst loading have been widely demonstrated to be useful to overcome the poor electron transport and slow water oxidation kinetics of BiVO4, the efficiency of this material is still greatly limited by poor charge separation. Various efforts directed at modifying the surface and bulk properties to improve the performance of BiVO4-based materials have therefore been developed, including crystal facet engineering, coupling with graphitic carbon material, annealing treatment, and nanoscaling. This review aims to provide insights into the most recent progress in these strategies in regard to their influences on the charge separation, transport, and transfer aspects of BiVO4, all of which are crucial to govern photochemical conversion efficiency. Understanding of these charge kinetics in relation to the properties of BiVO4 is of fundamental importance for rational design of BiVO4 with optimum structures, which may serve as a general guideline for the fabrication of metal oxide photocatalysts. [ABSTRACT FROM AUTHOR]

An effective Mo-based ternary oxide Bi2MoO6/MoO3 thin film for photoelectrochemical (PEC) water oxidation was prepared via a simple and direct thin film synthesis route. The synthesis strategy involved subjecting a MoO3 thin film, prepared by anodising a Mo foil, to hydrothermal treatment in the presence of a bismuth salt solution. The new approach removes the need for preformed particles to prepare the film, in turn providing a robust and stable anode for PEC water splitting. X-ray diffraction of the Bi2MoO6/MoO3 thin film revealed the film possessed two photocatalytically active phases of Bi2MoO6: (i) a low temperature phase (γ(L)-Bi2MoO6), and (ii) a high temperature phase (γ(H)-Bi2MoO6). UV-vis spectroscopy showed the optical band gaps of γ(L)-Bi2MoO6 and γ(H)-Bi2MoO6 were 2.75 eV and 3.1 eV, respectively. In contrast, the neat MoO3 thin film had a wider band gap of 3.4 eV. Transforming the surface MoO3 into Bi2MoO6 to construct the Bi2MoO6/MoO3 composite electrode leads to an improvement in photoelectrochemical (PEC) performance. The Bi2MoO6/MoO3 electrode exhibited a 79% enhancement in anodic photocurrent density compared to the unmodified MoO3 thin film under a positive bias of 0.4 V vs. Ag/AgCl. The better performance was attributed to: (i) the narrow optical band gap of Bi2MoO6, which extended the absorption of light by the film into the visible range and (ii) the well-aligned band structure of MoO3 and Bi2MoO6. The Bi2MoO6/MoO3 thin film electrode was subsequently utilised as a photoanode for PEC water splitting. The Bi2MoO6/MoO3 thin film electrode provided close to 100% faradic photocurrent-to-O2 conversion efficiency for PEC water splitting under UV illumination and, importantly, exhibited excellent photostability as a consequence of the unique synthesis method. [ABSTRACT FROM AUTHOR]

Vertically aligned ZnO nanorod arrays on a fluorine doped tin oxide (FTO) substrate were uniformly coated with visible light active CuInS2 nanoparticles using electrodeposition regulated by using an optimized frequency. As the diffusion of the fresh metallic precursor to the bottom of the one-dimensional nanostructure is the major challenge during electrodeposition, frequency tuning has demonstrated its effectiveness in balancing the diffusion and deposition of the secondary component (CuInS2) on the one-dimensional substrate (ZnO). The high quality of the heterojunction between CuInS2 and ZnO together with their intimate interaction facilitated efficient charge shuttling from CuInS2 to ZnO to yield a four-fold visible light response compared with traditionally synthesized CuInS2–ZnO nanostructures. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) porous polyurethane sponge serves as the sacrificial scaffold for the hydrothermally-synthesized anatase TiO2-reduced graphene oxide (RGO) composites. The internal channel of the 3D polyurethane structure provides larger exposed TiO2 seeding and crystal growth area on the pre-adsorbed graphene oxide during the synthesis. The uniform pore size within the polyurethane also prevents severe aggregation of TiO2 nanoparticles. As a result, TiO2 nanoparticles are finely dispersed on the RGO sheets. In addition to the general advantages of introducing graphitic carbon to TiO2 (i.e. hydrophobic carbon for preferential organic adsorption and excellent electron transport of RGO), the presence of polyurethane sponge during the synthesis offers larger contact area between TiO2 and RGO which is facilitated by the excellent dispersion of TiO2. Besides, formation of Ti–O–C species is found at the interface and it extends the light absorption of the composite into visible light region. Combining the localized organic adsorption adjacent to TiO2, efficient charge transfer from large contact area of TiO2–RGO and the extended light response of the composite, this material demonstrates enhanced photoelectrochemical oxidation of ethanol. [ABSTRACT FROM AUTHOR]