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The common solution for protecting p‐type semiconductors against photocorrosion in a photo‐electrochemical (PEC) cell is by applying a TiO2 over‐layer via atomic layer deposition (ALD). However, for the case of CuBi2O4 (CBO), this approach leads to a significant decline in electrode performance, despite the small conduction band offset between CBO and TiO2. Here, electrochemical impedance spectroscopy (EIS) under light illumination is used to study how to enhance charge transport in CuBi2O4/TiO2 photocathodes. A 15 nm TiO2 overlayer enables a small charge transfer resistance to the electrolyte while preserving the performance and stability of the CBO film. When increasing the TiO2 thickness from 15 to 20 nm, the photogenerated currents decrease by 74%. The EIS data are fit with an equivalent circuit model that enabled to extract the charge transfer resistances, capacitances, and time constants that influence the PEC performance of the electrode as a function of the TiO2 layer thickness, together with the flat‐band potentials and doping densities of both the CBO and TiO2 layers under light illumination. The decline in performance is attributed to accumulation and recombination of photogenerated carriers at the CBO‐TiO2 interface, due to a band mismatch between the two semiconductors. [ABSTRACT FROM AUTHOR]

Abstract The common solution for protecting p‐type semiconductors against photocorrosion in a photo‐electrochemical (PEC) cell is by applying a TiO2 over‐layer via atomic layer deposition (ALD). However, for the case of CuBi2O4 (CBO), this approach leads to a significant decline in electrode performance, despite the small conduction band offset between CBO and TiO2. Here, electrochemical impedance spectroscopy (EIS) under light illumination is used to study how to enhance charge transport in CuBi2O4/TiO2 photocathodes. A 15 nm TiO2 overlayer enables a small charge transfer resistance to the electrolyte while preserving the performance and stability of the CBO film. When increasing the TiO2 thickness from 15 to 20 nm, the photogenerated currents decrease by 74%. The EIS data are fit with an equivalent circuit model that enabled to extract the charge transfer resistances, capacitances, and time constants that influence the PEC performance of the electrode as a function of the TiO2 layer thickness, together with the flat‐band potentials and doping densities of both the CBO and TiO2 layers under light illumination. The decline in performance is attributed to accumulation and recombination of photogenerated carriers at the CBO‐TiO2 interface, due to a band mismatch between the two semiconductors.

The photoelectrochemical properties of titanium dioxide (TiO2) nanoparticles are directly related to the presence of certain facets. The synthesis of such particles is challenged using volatile and sensitive precursors utilizing shape capping agents. In this study, an easier two‐step synthesis technique for the preparation of well‐specified morphology TiO2 nanocrystals from TiO2 powder is demonstrated. The facet‐dependent Fermi level and flat band potential of the prepared particles are calculated and their photoelectrochemical properties are investigated by Cu2+ and Pb2+ photo/electrodeposition. From Cu2+ electrodeposition, it is shown that the presence of {100} and {001} facets in cubic morphology facilitates the electrodeposition with progressive nucleation mechanisms, while the presence of {101} facet in octahedral geometry follows instantaneous nucleation mechanisms. The activity of electroreduction is also related to the flat‐band potential which shows the highest activity in Pb2+ electrodeposition for octahedron nanostructure due to the alignment of the reduction potential to the edge of the flat band. Photodeposition of Cu2+ and Pb2+ ions shows identical trends to electrodeposition indicating the facets influence in ion adsorption and structure of the bandgap of morphological TiO2. The findings emphasize the importance of facet‐dependent surface adsorption and bandgap structure designing faceted TiO2 nanoparticles for tailored applications. [ABSTRACT FROM AUTHOR]

Abstract The photoelectrochemical properties of titanium dioxide (TiO2) nanoparticles are directly related to the presence of certain facets. The synthesis of such particles is challenged using volatile and sensitive precursors utilizing shape capping agents. In this study, an easier two‐step synthesis technique for the preparation of well‐specified morphology TiO2 nanocrystals from TiO2 powder is demonstrated. The facet‐dependent Fermi level and flat band potential of the prepared particles are calculated and their photoelectrochemical properties are investigated by Cu2+ and Pb2+ photo/electrodeposition. From Cu2+ electrodeposition, it is shown that the presence of {100} and {001} facets in cubic morphology facilitates the electrodeposition with progressive nucleation mechanisms, while the presence of {101} facet in octahedral geometry follows instantaneous nucleation mechanisms. The activity of electroreduction is also related to the flat‐band potential which shows the highest activity in Pb2+ electrodeposition for octahedron nanostructure due to the alignment of the reduction potential to the edge of the flat band. Photodeposition of Cu2+ and Pb2+ ions shows identical trends to electrodeposition indicating the facets influence in ion adsorption and structure of the bandgap of morphological TiO2. The findings emphasize the importance of facet‐dependent surface adsorption and bandgap structure designing faceted TiO2 nanoparticles for tailored applications.

A series of tin oxides were synthesized with polystyrene microspheres (250 nm) as the template. It was shown that an increase in the template content led to increasing specific pore volume and to the formation of bimodal pore structure with pores of 9 and 70 nm in diameter. Addition of cetyltrimethylammonium bromide (CTAB) during synthesis led to the formation of friable structures (SEM data), to an increase in the average pore diameter from 19 to 111 nm, and to the formation of macropores of 80–400 nm in size. All materials had similar surface properties and cassiterite structure with 5.9–10.8 nm coherent scattering region (XRD data). Flat-band potentials of the samples were determined and their photoelectrocatalytic properties to oxidation of water and methanol were studied in the potential range of 0.4–1.6 V RHE. It was shown that the sample obtained using CTAB was characterized by lower flat-band potential value, but appeared significantly higher photocurrent in methanol oxidation, which resulted from enhanced macro-meso-porous structure to facilitate methanol pore diffusion. [ABSTRACT FROM AUTHOR]

In this work, the morphological and electrical properties of the composite nanoporous carbon material/thermally expanded graphite or acetylene black have been investigated. Nanoporous carbon material was obtained from plant materials by its thermochemical activation based on potassium hydroxide. The dependence of the specific capacity of the nanoporous carbon/electrolyte electrochemical system on the applied potential was determined by the impedance spectroscopy method. Furthermore, the concentration of charge transfer and the density of states, as well as the flat-band potential of the system under research, were determined based on the Mott-Schottky model.

[Display omitted] • Synthesis of Co, Ni and Mn based bimetallic and trimetallic oxide-hydroxide porous nanosheets via simple hydrothermal route. • Probe -electronic modulation via -X-Ray photoelectron spectroscopy and Mott-Schottky Analysis. • High flat-band and low activation energy for improved OER kinetics. • Establish the energy band diagram. • Importance of intrinsic activity. Multimetallic systems have been the subject of intensive research for their promising electrocatalytic activities. Herein, we describe the synthesis of bimetallic and trimetallic (Ni, Co and Mn) oxide-hydroxide nanosheets and evaluate their catalytic activity toward water oxidation. The catalytic activity of porous trimetallic nanosheets was found to be higher than that of bimetallic hybrids. In addition, the trimetallic systems also possess excellent stability. A current density of 10 mA/cm2 is achieved for an overpotential of 287 mV and ∼0% loss even after 8000 cycles. The enhanced performance by the trimetallic system can be attributed to the large electrochemical surface area and better intrinsic activity. The electronic modulation in this three-element system is evident from the X-Ray Photoelectron Spectroscopy (XPS) study and Mott-Schottky analysis. The position of flat-band potential plays a significant role in determining the charge transfer kinetics, thereby affecting the water oxidation activity in the semiconductor-electrolyte system. Trimetallic system also offers better oxygen evolution reaction kinetics as evident from the least activation energy compared to the bimetallic counterparts. The local structure system is realized with the X-ray absorption spectroscopy (XAS) analysis. The present study highlights the importance of intrinsic activity in designing efficient non-noble metal electrocatalysts. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with a study about the position of the flat-band potential and the surface chemistry of boron-doped diamond electrodes. Successive and mild anodic treatments have been performed on as-deposited electrodes, in H2SO4. From Mott–Schottky plots, flat-band potential (V FB) evolution has been monitored, exhibiting successively negative then positive shifts during surface oxidation, depending on the anodic coulometric charge. Thanks to surface characterization by X-ray Photoelectron Spectroscopy (XPS), this particular evolution of V FB has been related to the evolution of specific oxygen functionalities at the surface. While the general trends in the literature is to associate the V FB displacement with the generation of oxygenated terminations, the results presented in this study exhibit the high sensitivity of V FB to hydroxyl or ether groups. [Copyright &y& Elsevier]

A study was made of the interfacial properties of Poly(pyrrole) (PP) deposited electrochemically onto single crystal p-Si surfaces. The interfacial properties are dependent upon the counterions. The formation of 'Quasi-Ohmic' and 'non-Ohmic' contacts, respectively, of PP(C1O) and PP films doped with other counterions (BF and para-toluene sulfonate) with p-Si, are explained in-terms of the conductivity of these films and the flat band potential, V , of PP relative to that of p-Si. The PP film seems to passivate or block intrinsic surface states present on the p-Si surface. The differences in the impedance behavior of para-toluene sulfonate doped and C1O doped PP are compared. [ABSTRACT FROM AUTHOR]

Here we describe the production features of a porous layer on the surface of n-type single-crystalline zinc selenide. The surface structure is investigated and the photomicrographs of porous layers of the treated ZnSe crystal are represented. Process of the mosaic structure formation depending on the etching time is considered. The value of the flat-band potential with respect to the used electrolyte is calculated. [ABSTRACT FROM AUTHOR]