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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]

[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]

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.