Spatial charge separation achieved on the anisotropic facets of high symmetry SrTiO3 nanocrystals for highly efficient photocatalytic overall water splitting.

Plasmonic photocatalysis, stemming from the effective light absorbance and confinement of surface plasmons, provides a pathway to enhance solar energy conversion. Although the plasmonic hot electrons in water reduction have been extensively studied, exactly how the plasmonic hot holes participate in the water splitting reaction has not yet been well understood. In particular, where the plasmonic hot holes participate in water oxidation is still illusive. Herein, taking Au/TiO as a plasmonic photocatalyst prototype, we investigated the plasmonic hot holes involved in water oxidation. The reaction sites are positioned by photodeposition together with element mapping by electron microscopy, while the distribution of holes is probed by surface photovoltage imaging with Kelvin probe force microscopy. We demonstrated that the plasmonic holes are mainly concentrated near the gold-semiconductor interface, which is further identified as the reaction site for plasmonic water oxidation. Density functional theory also corroborates these findings by revealing the promotion role of interfacial structure (Ti-O-Au) for oxygen evolution. Furthermore, the interfacial effect on plasmonic water oxidation is validated by other Au-semiconductor photocatalytic systems (Au/SrTiO, Au/BaTiO, etc.).

Charge separation among different crystal facets of a semiconductor has been observed experimentally, but the underlying reasons behind this phenomenon are unknown. In this work, the activation energies of carrier hopping and the mobility of electron/hole transport along seven low-index crystal orientations of bulk BiVO4 have been calculated using a small polaron model. The calculated mobility and our previous experimental results reveal that there is a parallel relationship between the carrier mobility along the crystal axis and the carrier preferred accumulation on the corresponding crystal facets. It is proposed that the mobility of electrons (or holes) along the crystal axis [hkl] might be essentially related to the charge separation among the indices of corresponding facets (hkl); namely, the mobility of electrons (or holes) along the crystal axis [hkl] is the largest among all possible crystal axes, and the photogenerated electrons (or holes) tend to be accumulated on the indices of the corresponding facet (hkl) when the surface factors like surface band bending, surface energetic differences, etc. are not considered.

The 0D/1D graphitic carbon nitride (g-C3N4)/TiO2 heterostructures containing an interfacial oxygen vacancy layer were sequentially constructed by anodic oxidation, NaBH4 reduction, and vapor deposition methods. Visible light absorption was significantly improved via construction of the interfacial oxygen vacancy layer and coupling with g-C3N4. Thus, 0D/1D g-C3N4/OV-TiO2 showed an optimal photocurrent density as high as 0.72 mA/cm2 at 1.23 V versus reversible hydrogen electrode under visible light irradiation, 8-fold higher than the data of g-C3N4/TiO2 without interfacial oxygen vacancy layer. Electrochemical impedance spectroscopy (EIS) revealed the 0D/1D g-C3N4/OV-TiO2 heterostructured photoanode showed the lowest charge transfer resistance among all the prepared photoanodes. This improved photoelectrochemical (PEC) performance could be attributed to the generation of Z-scheme heterostructure via construction of an interfacial oxygen vacancy layer between TiO2 and g-C3N4. This interfacial layer can promote charge carrier separation and transportation processes. The formation of this Z-scheme heterostructure was confirmed by hydroxyl fluorescence capture characterization and spin-polarized density functional theory calculations. We believe that our work can help rationally design and construct highly efficient heterostructured photoanodes for PEC water splitting applications.

Electron transfer processes from semiconductor to molecular catalysts was studied in a model hybrid photocatalytic hydrogen evolution system composed of [Co((III))(dmgH)2PyCl] (CoPy) and CdS under different pH conditions. Thermodynamic and kinetic studies revealed that photocatalytic H2 evolution under high pH conditions (pH 13.5) can only account for the thermodynamically more favorable single-step simultaneous two-electron transfer from photoirradiated CdS to Co(III)Py to produce unavoidable intermediate Co(I)Py, rather than a two-step successive one-electron transfer process. This finding not only provides new insight into the charge transfer processes between semiconductors and molecular catalysts but also opens up a new avenue for the assembly and optimization of semiconductor-molecular catalyst hybrid systems processed through multielectron transfer processes.

First principles-based mesoscale characterization of electron transport in W/Mo-doped BiVO4 reveals the existence of “stabilization” regions around dopant sites. The stabilization regions decrease slightly the electron polaron mobility, albeit the overall electrode conductivity increases.

Neutral oxygen vacancies (Ovʼs) in semiconductor oxides give rise to excess electrons that have the potential to affect the binding of adsorbates to the surface through surface-to-adsorbate charge transfer, and, as a result, to alter the overpotential (OP) of reactions on oxygen-deficient materials compared to stoichiometric materials. We report a systematic computational investigation of the effects of Ovʼs on the oxygen evolution reaction (OER) overpotential for β-Ga2O3, a d 10 semiconductor that has been shown to exhibit high activity for water splitting. We investigated 18 β-Ga2O3 surfaces/slabs, with and without Ovʼs and observed a clear dependence of OER activity on Ovʼs. A general finding emerged that the excess electrons associated with Ovʼs are found to participate in charge transfer to OER intermediates, making their bonds to the surface more ionic and stronger, depending on the amount of charge transfer. The OER reaction step free energies are significantly affected and the ensuing overpotentials are altered. The amount of charge transfer varies with the types of intermediates (OH*, dangling O*, surface-bound peroxo O*, and dangling OOH*), their open valencies, and their electronegativity. The work function and the position of the gap states of the excess electrons in the band gap are found to be useful descriptors of whether and how much Ov-induced charge transfer may occur and affect the overpotential. However, it was also found that the chemical environment of the O atom where the vacancy was created, may have a negating effect on the general observation. Specifically some Ov structures underwent a strong relaxation to form Ga–Ga bonds, trapping the vacancy electrons, and preventing them to engage in charge transfer. Oxygen vacancies are common defects in photocatalyst materials so that our investigation can provide guiding principles for designing efficient photocatalysts.

Nin and (NiO)n clusters located on different β-Ga2O3(100) surface sites participate in photocatalytic proton reduction and water oxidation reactions, respectively.