It is essential to control the electronic structure of graphene in order to apply graphene films for use in electrodes. We have introduced chemical dopants that modulate the electronic properties of few-layer graphene films synthesized by chemical vapor deposition. The work function, sheet carrier density, mobility, and sheet resistance of these films were systematically modulated by the reduction potential values of dopants. We further demonstrated that the power generation of a nanogenerator was strongly influenced by the choice of a graphene electrode with a modified work function. The off-current was well quenched in graphene films with high work functions (Au-doped) due to the formation of high Schottky barrier heights, whereas leakage current was observed in graphene films with low work functions (viologen-doped), due to nearly ohmic contact.

http://ma.ecsdl.org/content/MA2011-02/40/2383.full.pdf

Control of Electronic Structure of Graphene by Various Dopants and Their Effects on a Nanogenerator

Utilizing mechanical energy to produce hydrogen is emerging as a promising way to generate renewable energy, but is challenged by low efficiency and scanty cognition. In this work, graphitic carbon nitride (g-C3 N4 ) with an atomically thin sheet-like structure is applied for prominent piezocatalytic and photo-enhanced piezocatalytic H2 production. It is revealed that the anomalous piezoelectricity in g-C3 N4 originates from the strong in-plane polarization along the a-axis, contributed by the superimposed polar tri-s-triazine units and flexoelectric effect derived from the structured triangular cavities, which provides powerful electrochemical driving force for the water reduction reaction. Furthermore, the photo-enhanced charge transfer enables g-C3 N4 nanosheets to reserve more energized polarization charges to fully participate in the reaction at the surface reactive sites enriched by strain-induced carbon vacancies. Without any cocatalysts, an exceptional photo-piezocatalytic H2 evolution rate of 12.16 mmol g-1 h-1 is delivered by the g-C3 N4 nanosheets, far exceeding that of previously reported piezocatalysts and g-C3 N4 photocatalysts. Further, high pure-water-splitting performance with production of the value-added oxidation product H2 O2 via photo-piezocatalysis is also disclosed. This work not only exposes the potential of g-C3 N4 as a piezo-semiconductor for catalytic H2 evolution, but also breaks a new ground for the conversion of solar and mechanical energy by photomediated piezocatalytic reaction.

Exceptional Cocatalyst-Free Photo-Enhanced Piezocatalytic Hydrogen Evolution of Carbon Nitride Nanosheets from Strong In-Plane Polarization.

BaTiO3 nanobelt featuring controlled oxygen vacancies, namely BTO-OV-X (X represents time (h) of vacuum heat-treatment), were prepared to systematically investigate the effect of oxygen vacancies occupancy on pizeocatalytic performance for degradation of organic pollutant. Remarkably, the creation of oxygen vacancies on BaTiO3 can mediate the piezocatalytic activity. The piezocatalytic activity exhibited a volcano-type trend with increasing oxygen vacancies. Results from first-principles density functional theoretical (DFT) calculations and O2-temperature programmed desorption (O2-TPD) measurement indicated that the presence of oxygen vacancies could efficiently adsorb and activate O2 on the surface of BaTiO3 nanobelt and consequently enhance piezocatalytic activity. Importantly, with the aid of piezoresponse force microscopy (PFM) measurement, the intrinsic reason of volcano-type trend of oxygen vacancy-activity was well unveiled. This work reveals the effect and mechanism of oxygen vacancy occupancy on enhancing piezocatalytic activity of BaTiO3 nanobelt and will shed light on design of efficient piezocatalysts in the future.

Impact of oxygen vacancy occupancy on piezo-catalytic activity of BaTiO3 nanobelt

Herein, a g-C3N4/PDI-g-C3N4 homojunction has been fabricated for piezo-photocatalytic atrazine removal and exhibited better performance than individual photocatalysis or piezocatalysis. The introduction of PDI induces the π-π interaction facilitating electrons migration, and twists the g-C3N4 plane into a more polar porous structure with enhanced piezoelectricity. The homojunction facilitates the photoelectron transfer at the g-C3N4/PDI-g-C3N4 interfaces. The photoelectricity and the piezoelectricity of g-C3N4/PDI-g-C3N4 were assessed. The finite element simulation showed that the porous structure of the g-C3N4/PDI-g-C3N4 is essential to the enhanced piezoelectricity. Astonishingly, the piezo-photocatalytic atrazine degradation rate under an optimized condition (pH=2.97) reached 94% within 60 minutes. Moreover, the g-C3N4/PDI-g-C3N4 homojunction produced 625.54 μM H2O2 during the one-hour piezo-photocatalysis. Given the quenching experiments, reactive species detection and the electronic band of g-C3N4/PDI-g-C3N4, the piezo-photocatalytic mechanism has been proposed. In addition, the degradation pathways and the reduced intermediates toxicity intermediates of atrazine have been investigated.

Unique g-C3N4/PDI-g-C3N4 homojunction with synergistic piezo-photocatalytic effect for aquatic contaminant control and H2O2 generation under visible light

Herein, a g-C 3 N 4 /PDI-g-C 3 N 4 homojunction has been fabricated for piezo-photocatalytic atrazine removal and exhibited better performance than individual photocatalysis or piezocatalysis. The introduction of PDI induces the π-π interaction facilitating electrons migration, and twists the g-C 3 N 4 plane into a more polar porous structure with enhanced piezoelectricity. The homojunction facilitates the photoelectron transfer at the g-C 3 N 4 /PDI-g-C 3 N 4 interfaces. The photoelectricity and the piezoelectricity of g-C 3 N 4 /PDI-g-C 3 N 4 were assessed. The finite element simulation showed that the porous structure of the g-C 3 N 4 /PDI-g-C 3 N 4 is essential to the enhanced piezoelectricity. Astonishingly, the piezo-photocatalytic atrazine degradation rate under an optimized condition (pH=2.97) reached 94% within 60 min. Moreover, the g-C 3 N 4 /PDI-g-C 3 N 4 homojunction produced 625.54 μM H 2 O 2 during the one-hour piezo-photocatalysis. Given the quenching experiments, reactive species detection and the electronic band of g-C 3 N 4 /PDI-g-C 3 N 4 , the piezo-photocatalytic mechanism has been proposed. In addition, the degradation pathways and the reduced intermediates toxicity intermediates of atrazine have been investigated. • Unique g-C 3 N 4 /PDI-g-C 3 N 4 (CNPC) homojunction have been fabricated. • CNPC showed superior piezo-photocatalytic atrazine removal and H 2 O 2 generation. • The π-π stacked CNPC homojunction facilitated the charge transfer. • The enhanced polarity of CNPC is responsible for the piezoelectricity increases. • The results indicated the reduced toxicity of intermediates in the system. 

Atomically thin wurtzite ZnS nanosheets (NSs) are synthesized via photocatalytic oxidation exfoliation of ZnS(en)0.5 process in room temperature and applied in piezocatalysis for the first time. On account of the excellent flexible, high piezoelectric coefficient, large mechanical energy capture area, rich and efficient catalytic active sites, the as-prepared ZnS shows superior piezocatalytic performance for H2 production from H2O without any co-catalyst and sacrificial agent. The rate of H2 evolution is as high as 1.08 μmol h−1 mg−1. Furthermore, this work would can not only enrich the high-efficiency piezocatalytic materials system, but can also provide a new idea for the exploitation of piezocatalysts with excellent performance in piezocatalytic H2 evolution from pure water.

Atomically thin ZnS nanosheets: Facile synthesis and superior piezocatalytic H2 production from pure H2O

Piezopotential-driven simulated electrocatalytic nanosystem of ultrasmall MoC quantum dots encapsulated in ultrathin N-doped graphene vesicles for superhigh H2 production from pure water

Wenting Hu

Papers

Atomically thin ZnS nanosheets: Facile synthesis and superior piezocatalytic H2 production from pure H2O

Piezopotential-driven simulated electrocatalytic nanosystem of ultrasmall MoC quantum dots encapsulated in ultrathin N-doped graphene vesicles for superhigh H2 production from pure water