Electronic Structures and Catalytic Activities of Niobium Oxides as Electrocatalysts in Liquid‐Junction Photovoltaic Devices

Abstract

Two types of nanosized niobium oxides and their composites, pseudohexagonal Nb2O5 (TT‐Nb2O5), monoclinic NbO2 (M‐NbO2), and the coexistence of TT‐Nb2O5 and M‐NbO2 (TT‐Nb2O5/M‐NbO2), are successfully synthesized through the urea‐metal chloride route, and they exhibit excellent catalytic activity and photovoltaic performance in dye‐sensitized solar cells (DSSCs). First‐principles density function theory (DFT) calculations show that their catalytic activity is significantly influenced by their intrinsic electronic structures and properties. The lone‐pair 4d1 electrons of Nb4+ in M‐NbO2 enhance the Nb–I interaction and promote electron transfer from the M‐NbO2 counter electrode (CE) to I, thus resulting in superior catalytic properties in M‐NbO2‐based DSSCs. In addition, the adsorption energy of I on the M‐NbO2 surface is in the optimal energy range of 0.3—1.2 eV, and the Fermi level of M‐NbO2 is 0.6 eV, which is higher than the I3− reduction reaction potential, and I3− can be spontaneously reduced to 3I−. Herein, a general strategy for understanding the electronic structures and catalytic activities of transition metal compounds as CE catalysts for DSSCs is provided.

Characterization of Nb22O54 microrods grown from niobium oxide powders recovered from mine tailings

“…In particular, non-stoichiometric phases of niobium oxide (Nb22O54, Nb12O29) have been less reported in the literature, but they have been proposed as good candidates for intercalation electrode materials in lithium-ion batteries [8][9][10]. Along with these applications that have attracted high interest, niobium oxides are also useful for photocatalysis [11,12], electrocatalysis [13][14][15], coatings or light guiding [16], due to a bandgap in the near UV range or a high refractive index, respectively. It has to be taken into account that many of the properties that make niobium oxide interesting for applications are highly dependent on the crystal structure of the material as well as on the stoichiometry [16], so deeper studies are needed to elucidate the physical phenomena behind this dependence.…”

Semiconductor Electrochemistry for Clean Energy Conversion and Storage

“…At first glance, the use of TiO 2 will cause the short-circuiting issue in fuel cell conditions. This does not happen in this fuel cell case since TiO 2 possesses a higher CB above the redox potential of H 2 / H + and a lower VB than the redox potential of O 2 /O 2− [98,105,109,110], which can help effectively block electron transport through the electrolyte. When combined with the advanced NCAL symmetric electrode for demo-SOFCs, the reduced electrode materials in the anode have a lower CB than the redox potential of H 2 /H + and a higher VB than the redox potential of O 2 /O 2− .…”

“…This is why the short-circuiting problem was observed in an SDC electrolyte fuel cell after a period of operation. In short, the energy band structure of a good SOFC should obey the following rules: (1) the CB level of the electrolyte should be higher than the redox potential of H 2 /H + , (2) the Fermi In addition to wide applications of semiconductors in fuel cells, coupling or integrating semiconductors/bands and fuel cell electrochemistry has recently emerged, involving metalair batteries, photocatalytic fuel cells, photoenhanced fuel cells and many others [110,[146][147][148][149][150][151][152]. Rechargeable Li-O 2 batteries are frequently reported to be intensified by the photoassisted process.…”

Cobalt-Based Incorporated Metals in Metal–Organic Framework-Derived Nitrogen-Doped Carbon as a Robust Catalyst for Triiodide Reduction in Photovoltaics

“…It is proven that I 3 − can be effectively adsorbed on the active centers of Co–N–C and (Nb, Bi, and Mo)/Co–N–C with an optimal range (−0.33 to −1.2 eV) , of the adsorption energy for the IRR, and the corresponding charge transfer after I 3 − adsorption is further studied by Bader analysis. According to our calculations, I species (I 1 ) gets 0.46, 0.45, 0.46, and 0.47 e from Co–N–C and (Nb, Bi, and Mo)/Co–N–C CEs, respectively, which verifies the effective transformation of electrons from the metallic and bimetallic nitrogen-doped carbon surface to I 3 – . , The calculated work functions of Co–N–C and (Nb, Bi, and Mo)/Co–N–C are 4.2, 3.8, 3.9, and 3.85 eV, respectively, as shown in Figure . The Fermi levels of Co–N–C and (Nb, Bi, and Mo)/Co–N–C are all higher than the IRR equilibrium potential (∼−5.0 eV), indicating their efficient electron-donating ability in the IRR.…”

“…1 Among these, solar energy is one of the most promising candidates for harvesting electrical power. Hence, the development of versatile materials for next-generation solar cells 2,3 such as dye-sensitized solar cells (DSSCs) 1,4 and perovskite-sensitized solar cells 5 has become an active research area. The most remarkable advantage of DSSCs is the development of inexpensive, robust, and durable non-noble electrocatalysts for counter electrodes (CEs).…”