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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.

3D Fe3O4/NiO was grafted on to the 2D rGO/h‐BN by electro‐precipitation method. Nitrogen of h‐BN moiety and oxygen functional groups of rGO played the role of negative active site to trap the metallic cations. Electrochemical charge storage mechanism was optimized by controlling the stoichiometry and defect contents of Fe3O4/NiO@rGO/h‐BN. Stoichiometry of the electro‐precipitated samples was tailored in presence of negative active sites of rGO/h‐BN and applied D.C. bias of the electrochemical bath. In addition, the nucleation and growth of metal oxides were influenced by the stacking and vacancy defects of rGO/h‐BN sheets. High specific capacitance (1328 F g−1) of Fe3O4/NiO@rGO/h‐BN was attributed to the synergistic effect of electrochemical double layer capacitance of rGO, chemi‐adsorption of –OH ions on Lewis acid (boron of h‐BN moiety) and redox capacitance of Fe3O4/NiO in alkaline medium. In addition, the presence of pyrrolic defect at the rGO/h‐BN stacking region acted as the nucleation site and provided additional redox capacitance by shifting the Fermi level towards the valance band. An asymmetric supercapacitor (ASC) was constructed using Fe3O4/NiO@rGO/h‐BN and thermally reduced GO as positive and negative electrode, respectively. ASC showed high energy (82 W h Kg−1) and power density (5600 W Kg−1) along with low relaxation time constant (2.2 ms) and high stability (79%) after 10,000 charge discharge cycles. Electrochemical charge storage mechanism was optimized by controlling the stoichiometry and defect contents of Fe3O4/NiO@rGO/h‐BN. 3D Fe3O4/NiO was grafted on to the 2D rGO/h‐BN by electro‐precipitation method. The stoichiometry of the electro‐precipitated samples was tailored in presence of negative active sites of rGO/h‐BN and applied D.C. bias of the electrochemical bath. [ABSTRACT FROM AUTHOR]

In order to analyze the correlation between the optoelectronic properties and chalcogen present in the conjugated side chain of benzodithiophene (BDT) based 2D π-conjugated polymers, we synthesized a new series of 2D π-conjugated polymers P1 (S), P2 (Se), and P3 (O), in which alkoxyphenyl-thiophene, alkoxyphenyl-selenophene and alkoxyphenyl-furan substituted BDT as an electron rich donor unit and thieno[3,4 -c ]pyrrole-4,6-dione as an electron deficient acceptor unit, respectively. The P1 - P3 showed varied optoelectronic properties with respect to the chalcogen present in the conjugated side chains of donor unit. The bulk heterojunction (BHJ) polymer solar cells (PSCs) based on P1 - P3 showed maximum power conversion efficiency of 3.37, 3.53 and 1.54%, respectively. In particular, open-circuit voltages ( V oc ) of P1 - P3 based PSCs were (0.92, 0.96 and 0.80 V) significantly affected upon chalcogen exchange, which was further analyzed by Mott-Schottky analysis and, the obtained flat-band potential values are well matched with the V oc of P1 - P3 based devices. [ABSTRACT FROM AUTHOR]

Capacitance-voltage ( C-V) and modulated light-induced current-voltage measurements were employed to investigate the Cu2O/electrolyte junction of electrodeposited n-Cu2O thin films. The Mott-Schottky plots resulting from the C-V measurements revealed that the extrapolated flat-band potential of n-Cu2O films was strongly influenced by the pH of the bath where the films were grown. The flat-band potential change was 300 mV for a pH difference of 0.8 and showed that the surface chemistry at an n-Cu2O/aqueous electrolyte interface was strongly affected by the pH of the film deposition bath. In addition, current-potential measurements revealed that at the measured flat-band potential the photocurrent did not vanish for n-Cu2O films and the Fermi level at the interface was pinned due to the presence of electrically active surface states. Information on the presence of electrically active surface states and the shift in flat-band potential will be very useful for applications of n-Cu2O films in various devices. [ABSTRACT FROM AUTHOR]

Boron doped diamond (BDD) shows high chemical stability in contact with a liquid phase even under extreme pH conditions, high electrochemical activity, and allows very stable covalent functionalization on O- or N-terminated surfaces. It is therefore an excellent electrode material for many applications such as analytics, biosensors, and purification. Furthermore, the electrodes can be covalently functionalized with photo-sensitive dyes to generate photo currents. However, the energetic conditions and charge transfer mechanisms are not fully known and therefore have been investigated in this work. The focus was set on the energy band diagrams of nanocrystalline diamond (NCD) layers, especially on the flat-band potential VF and the band-bending ϕB in the space charge layer, for both O- and N-terminated surfaces, and the charge transfer mechanisms at the semiconductor/electrolyte phase-boundary, with or without electro-active organic dyes, such as manganese phthalocyanine. For this study NCD samples were grown by hot filament chemical vapor deposition (HFCVD) with a boron doping density NA ranging between 5.8 and 9.6 × 1020 cm−3. The pristine surface was then processed by oxygen or ammonia plasma to modify the termination to O and NH2, respectively. After that a series of Mott-Schottky plots was measured for both terminations at several frequencies spanning from 3 Hz to 10 kHz and in two different electrolytes, namely 0.1 M H2SO4 and 0.1 M KCl. The results showed nearly the same flat-band potential for both surface terminations, but a remarkable difference in the band-bending. The latter is most probably responsible for the better photoelectrical conversion observed in N-terminated NCD samples. The open-circuit potential (OCP) and chronoamperometric measurements performed after covalent functionalization of the samples with the color dyes revealed that only the N-terminated material delivered a measurable photocurrent. Although the global efficiency of the photoelectric conversion was low, these initial results show that by optimized selection of materials and modification technologies providing a proper match of the energy levels at all charge transfer steps, a higher energy output could be achieved. [ABSTRACT FROM AUTHOR]

Highlights: [•] A Y2O3:Dy3+ nanophosphor was used as luminescence medium in DSSC. [•] Both the open-circuit voltage and the short-circuit current density increased. [•] The light-to-electric conversion efficiency increased from 6.077 to 7.521%. [ABSTRACT FROM AUTHOR]

The semiconductor properties of nitrogenated nanocrystalline diamond electrodes and their corrosion transformations caused by electrochemical experiment in indifferent electrolyte (1 M KSO) were studied by the electrochemical impedance spectroscopy method. It was shown that after electrochemical measurements a narrow diamond peak at 1335.7 cm appears in the Raman spectrum; formerly the peak was hidden at a background of the intense signal inherent to graphite-like carbon. It was suggested that the corrosion damage caused by the exposure to electrochemical experiment resulted in a decrease of relative amount of nondiamond (graphite-like) carbon in the subsurface layer in the nanocrystalline diamond. By using Mott-Schottky plots, the nanocrystalline diamond was shown having n-type conductance. Within the bounds of the 'effective medium' approach, the nanocrystalline diamond's flat-band potential in aqueous solution and the noncompensated donor apparent concentration were estimated. [ABSTRACT FROM AUTHOR]

Abstract: Different amounts of Co-doped TiO2 powders and thin films were prepared by following a conventional co-precipitation and sol–gel dip coating technique, respectively. The synthesized powders and thin films were subjected to thermal treatments from 400 to 800 °C and were thoroughly investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive analysis with X-rays, FT-infrared, FT-Raman, diffuse reflectance spectroscopy, ultraviolet–visible spectroscopy, BET surface area, zeta potential, flat band potential measurements, band-gap energy, etc. The photocatalytic ability of the powders was evaluated by methylene blue (MB) degradation studies. The thin films were characterized by photocurrent and ultraviolet–visible (UV–Vis) spectroscopy techniques. The characterization results suggest that the Co-doped TiO2 powders synthesized in this study consist mainly anatase phase, and possess reasonably high specific surface area, low band gap energy and flat band potentials amenable to water oxidation in photoelectrochemical (PEC) cells. The photocatalytic degradation of MB over Co-doped TiO2 powders followed the Langmuir–Hinshelwood first order reaction rate relationship. The 0.1 wt.% Co-doped TiO2 composition provided the higher photocurrent, n-type semi-conducting behavior and higher photocatalytic activity among various Co-doped TiO2 compositions and pure TiO2 investigated. [Copyright &y& Elsevier]

Abstract: Suitable morphology for fast electron transportation is a crucial requirement for photoelectrochemical (PEC) solar cells. Highly oriented and well defined zinc oxide (ZnO) nano/micro-scale structures were grown on the glass and FTO coated glass substrates. The grown nanostructures have been characterized by X-ray diffraction pattern (XRD), scanning electron microscope (SEM) and optical absorption techniques. XRD patterns confirm high crystalline quality of ZnO with hexagonal wurtzite structure. SEM micrographs show the formation of disk, rod, spindle and flower-like morphologies at different pH values ranging from 5 to 10. The PEC solar cell configuration of ZnO/0.5M Na2SO4/graphite has been used to record the current voltage (I–V) and capacitance voltage (C–V) characteristics of the films. The junction ideality factor (nl ), series and shunt resistance (Rs and Rsh ), flat-band-potential (V fb), donor concentration (ND ), fill factor (FF) and efficiency (η) have been estimated. Energy band diagram of ZnO and Na2SO4 electrolyte has been constructed. [Copyright &y& Elsevier]

[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]

Abstract: The interfacial kinetics of charge transfer at n-GaAs/liquid junctions were controlled by anchoring positively charged species, such as tetra(-4-pyridyl)porphyrinatomanganese(III), with the semiconductor surface. Unlike earlier adsorption techniques, the charges have been chemically anchored to the semiconductor surface, in this work, via a ligand. The number of charges per site (attached molecule) ranged from +1 to +5. The positive charges shifted the band-edges towards more positive potential values. The degree of shift increased with surface charge density. In the dark, the flat band potential (measured by Mott–Schottky technique) and the onset potential were shifted by up to 300mV depending on surface charge density. Relatively less of a shift was observed during illumination of the system. Other surface characteristics, such as conversion efficiency and photoluminescence intensity, have been enhanced. The basis for these shifts and their implications with respect to control of interfacial processes are discussed. [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]

Exfoliated nanosheets derived from Dion-Jacobson phase layer perovskites (TBAxH1-xA2B3O10, A = Sr, Ca, B = Nb, Ta) were grown layer-by-layer on fluorine-doped tin oxide and gold electrode surfaces. Electrochemical impedance spectra (EIS) of the five-layer nanosheet films in contact with aqueous electrolyte solutions were analyzed by the Mott-Schottky method to obtain flat-band potentials (VFB) of the oxide semiconductors as a function of pH. Despite capacitive contributions from the electrode-solution interface, reliable values could be obtained from capacitance measurements over a limited potential range near VFB. The measured values of VFB shifted -59 mV/pH over the pH range of 4-8 and were in close agreement with the empirical correlation between conduction band-edge potentials and optical band gaps proposed by Matsumoto ( J. Solid State Chem. 1996, 126 (2), 227-234 ). Density functional theory calculations showed that A-site substitution influenced band energies by modulating the strength of A-O bonding, and that subsitution of Ta for Nb on B-sites resulted in a negative shift of the conduction band-edge potential.