Optical, Electrochemical, and Photoelectrochemical Behavior of Copper Pyrovanadate: A Unified Theoretical and Experimental Study

Abstract

Copper vanadates have been important to the development of new-generation photoelectrodes for solar water splitting and hydrogen generation. Of these, copper pyrovanadate (β-Cu2V2O7), the 2:1 ternary compound derived from CuO and V2O5, has been of particular interest to the solar fuel community. This n-type semiconductor has shown the highest photocurrent for water oxidation at 1.23 V versus reversible hydrogen electrode and exhibits good photostability in aqueous media of pH 9.2. However, further successful application of this material in photoelectrochemical (PEC) devices hinges on a comprehensive understanding of its optical, electrochemical, and optoelectronic attributes. This was done in this study by a combination of density-functional theory (for the structural, magnetic, and optical characterization) and experiments, with the latter using both small-signal (intensity-modulated photocurrent spectroscopy, IMPS) and large-signal, transient photocurrent (TP) analyses. Both IMPS and TP measurements yielded complementary and self-consistent insights into the rate constants for hole transfer and carrier recombination at the irradiated β-Cu2V2O7/electrolyte interface, specifically their dependence on the applied bias potential. The information from PEC data analyses was also self-consistent with that garnered from the optical (diffuse reflectance spectroscopy) data.

Pressure-Induced Phase Transition and Band Gap Decrease in Semiconducting β-Cu2V2O7

“…The band gap energies of β- and γ-Cu 2 V 2 O 7 were experimentally determined to be 1.91 and 1.73 eV, respectively, thereby corresponding to a band gap collapse of 0.18 eV (∼9%) across the β → γ phase transition (as shown by arrow 1 in Figure ). The β-phase band gap energy of 1.91 eV is in good agreement with the previously reported experimental values of 1.78 eV (ref ), 1.91 eV (ref ), and 2.21 eV (ref ) and the theoretically calculated value of 2.00 eV . The band gap of γ-Cu 2 V 2 O 7 has not previously been reported.…”

Pressure-induced phase transitions and electronic properties of Cd2V2O7

“…Because of their band gap, appropriate photostability, luminescence, photocatalytic activity, ability to accept dopants, hydrophilicity, crystalline quality, thermal stability, and ability to absorb gases, 1 pyrovanadates are used in a wide range of applications. 1 Among them, cadmium pyrovanadate (Cd 2 V 2 O 7 ) has received remarkable attention because of its multiple possible technological uses. They include photocatalysis, 2,3 photoluminescence, 4 gas sensing, 5 among many others.…”

Solution Combustion Synthesis and Characterization of Magnesium Copper Vanadates

“…Kelvin probe force microscopy (KPFM) was performed on an instrument equipped with a 2 mm diameter gold alloy-coated tip (KP Technology, APS04). Surface photovoltage spectroscopy (SPS) and ambient-pressure photoemission spectroscopy (APES) employed instrumentation and measurement protocols given elsewhere Figure S2 shows a block diagram of the integrated setup for KPFM, SPS, and APES.…”

“…Surface photovoltage spectroscopy (SPS) and ambient-pressure photoemission spectroscopy (APES) employed instrumentation and measurement protocols given elsewhere. 11 Figure S2 shows a block diagram of the integrated setup for KPFM, SPS, and APES. X-ray photoelectron spectroscopy (XPS) was carried out on a Thermo XPS NEXSA instrument using an Al K α X-ray source.…”

“…After all, many of these compounds (e.g., Fe 2 O 3 ) occur in nature as minerals attesting to their robustness. Thus, phase spaces encompassing binary metal oxides as the end members (e.g., Cu x O, Bi 2 O 3 , V 2 O 3 ) and a multitude of stable (ternary) compounds have attracted much recent interest. − ,− Corresponding studies on phase spaces involving ternary oxides as end members, however, are much less commonplace, hence one of the motivations for this study. Examples of prior research on ternary oxide solid solutions include (Ba 1– x Sn x )­ZrO 3 , M 2 V 2 O 7 (M = Mn, Cu), Eu 1– x Ca x TiO 3 , (Cu 1– x Li x )­GaO 2 , (Bi 1– x Fe x )­VO 4, (Li 1– x Cu x )­Nb 3 O 8 , M x Bi 2– x Ti 2 O 7 (M = Fe, Mn), BiZn 2 VO 6 , BiCu 2 VO 6 , and Cu 5 (Ta 1– x Nb x ) 11 O 30 .…”