Qingquan He

Highly Efficient Ag2O/Bi2O2CO3 p-n Heterojunction Photocatalysts with Improved Visible-Light Responsive Activity

Ag2O/Bi2O2CO3 p-n heterojunctions are prepared with commercial Bi2O2CO3 as precursor via a simple photosynthesis process. The obtained Ag2O/Bi2O2CO3 p-n heterojunctions show higher photocatalytic activity than that of pure n-Bi2O2CO3, and the obtained Ag2O/Bi2O2CO3 (AB-4) heterojunction exhibits the best photocatalytic activity under visible light (λ > 400 nm), with which Rhodamine B, methyl blue and methyl orange can be completely degraded within 12 min. Photoluminescent spectra and photoelectrochemical measurement further indicate that the Ag2O/Bi2O2CO3 p-n heterojunctions greatly enhance the charge generation and suppress the charge recombination of photogenerated electron-hole pairs, which would be beneficial to improve their photocatalytic activity.

Ultrathin FeSe2 Nanosheets: Controlled Synthesis and Application as a Heterogeneous Catalyst in Dye‐Sensitized Solar Cells

Two-dimensional (2D) semiconducting nanosheets have emerged as an important field of materials, owing to their unique properties and potential applications in areas ranging from electronics to catalysis. However, the controlled synthesis of ultrathin 2D nanosheets remains a great challenge, due to the lack of an intrinsic driving force for anisotropic growth. High-quality ultrathin 2D FeSe2 nanosheets with average thickness below 7 nm have been synthesized on large scale by a facile solution method, and a formation mechanism has been proposed. Due to their favorable structural features, the as-synthesized ultrathin FeSe2 nanosheets exhibit excellent electrocatalytic activity for the reduction of triiodide to iodide and low charge-transfer resistance at the electrolyte-electrode interface in dye-sensitized solar cells (DSSCs). The DSSCs with FeSe2 nanosheets as counter electrode material achieve a high power conversion efficiency of 7.53% under a simulated solar illumination of 100 mW cm(-2) (AM 1.5), which is comparable with that of Pt-based devices (7.47%).

Rationally Designed n–n Heterojunction with Highly Efficient Solar Hydrogen Evolution

In most of the reported n-n heterojunction photocatalysts, both the conduction and valence bands of one semiconductor are more negative than those of the other semiconductor. In this work, we designed and synthesized a novel n-n heterojunction photocatalyst, namely CdS-ZnWO4 heterojunctions, in which ZnWO4 has more negative conduction band and more positive valence band than those of CdS. The hydrogen evolution rate of CdS-30 mol %-ZnWO4 reaches 31.46 mmol h(-1)  g(-1) under visible light, which is approximately 8 and 755 times higher than that of pure CdS and ZnWO4 under similar conditions, respectively. The location of the surface active sites is researched and a plausible mechanism of performance enhancement by the tuning of the structure is proposed based on the photoelectrochemical characterization. The results illustrate that this kind of nonconventional n-n heterojunctions is also suitable and highly efficient for solar hydrogen evolution.

The role of Mott-Schottky heterojunctions in Ag-Ag8SnS6 as counter electrodes in dye-sensitized solar cells.

Well-defined uniform pyramidal Ag-Ag8SnS6 heterodimers are prepared via a one-pot method. A plausible formation mechanism for the unique structures based on a seed-growth process and an etching effect due to oleylamine is proposed. The formed metal-semiconductor Mott-Schottky heterojunction promotes electron transfer from semiconducting Ag8 SnS6 to metallic Ag, which catalyzes the reduction of I3 (-) to I(-). When used as counter electrode in dye-sensitized solar cells, the heterodimers show comparable performance to platinum.

Homogenously hexagonal prismatic AgBiS2 nanocrystals: controlled synthesis and application in quantum dot-sensitized solar cells

Homogenously hexagonal prismatic AgBiS2 nanocrystals with sizes of about 7.6 nm have been synthesized by the selective absorption of oleylamine and anisotropic growth in a mixed solvent system. Quantum dot-sensitized solar cells with the as-prepared AgBiS2 nanocrystals as counterelectrode materials showed a conversion efficiency of 2.09% compared with that of Pt (1.73%).

Efficient Counter Electrode Manufactured from Ag2S Nanocrystal Ink for Dye-Sensitized Solar Cells

It is generally believed that silver or silver-based compounds are not suitable counter electrode (CE) materials for dye-sensitized solar cells (DSSCs) due to the corrosion of the I(-) /I3 (-) redox couple in electrolytes. However, Ag2 S has potential applications in DSSCs for catalyzing I3 (-) reduction reactions because of its high carrier concentration and tiny solubility product constant. In the present work, CE manufactured from Ag2 S nanocrystals ink exhibited efficient electrocatalytic activity in the reduction of I3 (-) to I(-) in DSSCs. The DSSC consisting of Ag2 S CE displayed a higher power conversion efficiency of 8.40 % than that of Pt CE (8.11 %). Moreover, the devices also showed the characteristics of fast activity onset, high multiple start/stop capability and good irradiated stability. The simple composition, easy preparation, stable chemical property, and good catalytic performance make the developed Ag2 S CE as a promising alternative to Pt CE in DSSCs.

Efficient Ag8GeS6 counter electrode prepared from nanocrystal ink for dye-sensitized solar cells

Ternary metal sulfides could provide more alternatives and tune physicochemical properties due to the presence of two cations. However, only Co/Ni-based ternary sulfides have been explored as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). Herein, CEs fabricated using Ag8GeS6 nanocrystal ink exhibited efficient electrocatalytic activity in the reduction of I3− to I− in DSSCs. The DSSC with the Ag8GeS6 CE displayed a higher power conversion efficiency of 8.10% than that with the Pt CE (8.02%). Moreover, the devices also showed the characteristics of fast activity onset, high multiple start/stop capability and good irradiation stability. The results indicated that the developed Ag8GeS6 CE could be a promising alternative to Pt CEs in DSSCs.

AgInxGa1−xS2 solid solution nanocrystals: synthesis, band gap tuning and photocatalytic activity

AgInxGa1−xS2 (x = 0, 0.3, 0.5, 0.7 and 1) solid solutions with a size of 25–100 nm have been synthesized in a mixed solvent system via a solvothermal process. The crystal structure of the solid solutions gradually transforms from tetragonal to orthorhombic, along with the chemical composition (x value changes from 0 to 1), and the band gap of the solid solutions can be tuned from 2.37 eV to 1.62 eV. Further studies revealed that the obtained AgInxGa1−xS2 solid solutions show improved photocatalytic activities under visible light irradiation compared with AgGaS2 and AgInS2, and the AgIn0.3Ga0.7S2 solid solution exhibits the best photocatalytic performance for its optimized band gap and energy structure.

Hierarchical Cu2−XSe nanotubes constructed by two-unit-cell-thick nanosheets: room-temperature synthesis and promoted electrocatalytic activity towards polysulfides

Hierarchical Cu2−XSe nanotubes, constructed by nanosheets with a thickness of two unit cells (1.2 nm), have been fabricated with Cu(OH)2 nanorod arrays as self-sacrificial templates at room temperature, with a high surface area of 72.3 m2 g−1. The unique structure of the Cu2−XSe nanotubes leads to high electrocatalytic activity towards the reduction of polysulfides, given their enlarged active surface area, rapid transportation of electrons and mass. As a result, quantum dot-sensitized solar cells (QDSSCs) with the obtained Cu2−XSe nanotubes as the counter electrode material exhibit long-term stability and a high power conversion efficiency of 5.14% (1 sun irradiation simulation), better than those of the commonly-used Cu2S/brass (3.38%) and reference Pt (1.78%) electrodes.

Synergistically Enhanced Electrochemical Performance of Ni3S4–PtX (X = Fe, Ni) Heteronanorods as Heterogeneous Catalysts in Dye-Sensitized Solar Cells

Platinum (Pt)-based alloys are considerably promising electrocatalysts for the reduction of I-/I3- and Co2+/Co3+ redox couples in dye-sensitized solar cells (DSSCs). However, it is still challenging to minimize the dosage of Pt to achieve comparable or even higher catalytic efficiency. Here, by taking full advantages of the Mott-Schottky (M-S) effect at the metal-semiconductor interface, we successfully strategize a low-Pt-based M-S catalyst with enhanced electrocatalytic performance and stability for the large-scale application of DSSCs. The optimized M-S electrocatalyst of Ni3S4-Pt2X1 (X = Fe, Ni) heteronanorods is constructed by rationally controlling the ratio of Pt to transition metal in the hybrids. It was found that the electrons transferred from Ni3S4 to Pt2X1 at their interface under the Mott-Schottky effect result in the concentration of electrons onto Pt2X1 domains, which subsequently accelerates the regeneration of both I-/I3- and Co2+/Co3+ redox shuttles in DSSCs. As a result, the DSSC with Ni3S4-Pt2Fe1 manifests an impressive power conversion efficiency (PCE) of 8.79% and 5.56% for iodine and cobalt-based electrolyte under AM1.5G illumination, respectively. These PCEs are obviously superior over those with Ni3S4-Pt, PtFe, Ni3S4, and pristine Pt electrodes. The strategy reported here is able to be further expanded to fabricate other low-Pt-alloyed M-S catalysts for wider applications in the fields of photocatalysis, water splitting, and heterojunction solar cells.