C=C π Bond Modified Graphitic Carbon Nitride Films for Enhanced Photoelectrochemical Cell Performance

Abstract

Applications of graphitic carbon nitride (g-CN) in photoelectrochemical and optoelectronic devices are still hindered due to the difficulties in synthesis of g-CN films with tunable chemical, physical and catalytic properties. Herein we present a general method to alter the electronic and photoelectrochemical properties of g-CN films by annealing. We found that N atoms can be removed from the g-CN networks after annealing treatment. Assisted by theoretical calculations, we confirm that upon appropriate N removal, the adjacent C atoms will form new C=C π bonds. Detailed calculations demonstrate that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are located at the structure unit with C=C π bonds and the electrons are more delocalized. Valence band X-ray photoelectron spectroscopy spectra together with optical absorption spectra unveil that the structure changes result in the alteration of the g-CN energy levels and position of band edges. Our results show that the photocurrent density of the annealed g-CN film is doubled compared with the pristine one, thanks to the better charge separation and transport within the film induced by the new C=C π bonds. An ultrathin TiO film (2.2 nm) is further deposited on the g-CN film as stabilizer and the photocurrent density is kept at 0.05 mA cm at 1.23 V versus reversible hydrogen electrode after two-cycle stability assessment. This work enables the applications of g-CN films in many electronic and optoelectronic devices.

Phosphorus‐doped Isotype g‐C3N4/g‐C3N4: An Efficient Charge Transfer System for Photoelectrochemical Water Oxidation

“…The facilitated charge separation occurring for the samples with higher carrier density is then supported by EIS Nyquist plots obtained under illumination. Normally, the smaller diameter of semicircle in Nyquist plots signifies the lower charge transfer impedance . In Figure f, the smaller semicircle for P‐g‐C 3 N is observed, suggesting more efficient charge transfer.…”

“…Normally, the smaller diameter of semicircle in Nyquist plots signifies the lower charge transfer impedance. [39] In Figure 5f, the smaller semicircle for P-g-C 3 N is observed, suggesting more efficient charge transfer. Accordingly, the relatively large semicircle radius of pristine g-C 3 N 4 means fast charge recombination, probably caused by poor electronic conductivity.…”

Kohlenstoffnitridmaterialien für photochemische Zellen zur Wasserspaltung

“…[85] Der In-situ-Gastransportmechanismus erlaubt eine vollständige Beschichtung des mesoporçsen TiO 2 -Films durch Erhitzen von pulverfçrmigen Vorstufen, die nur mit der Oberfläche des Films in Kontakt stehen. [53,86,87] Die Kondensation eines supramolekularen Komplexes wurde auch zwischen zwei Elektroden unter einer inerten Atmosphäre durchgeführt. B. Fehlen von sogenannten Pinholes,d.h.…”

“…Niu et al zeigten, dass durch die Kontrolle der Kondensationstemperatur der CN-Vorstufen Stickstoff-Leerstellen induziert werden konnten, was zu zusätzlichen Absorptionsbanden von 450 bis 600 nm führte. [87] Ein weiteres Verfahren zur Beeinflussung der elektronischen Eigenschaften von CN-Filmen ist ein maßgeschneidertes Monomer-Design, um so das optische Absorptionsfenster einzustellen, damit ein hçherer Anteil des Solarspektrums genutzt wird. [87] Ein weiteres Verfahren zur Beeinflussung der elektronischen Eigenschaften von CN-Filmen ist ein maßgeschneidertes Monomer-Design, um so das optische Absorptionsfenster einzustellen, damit ein hçherer Anteil des Solarspektrums genutzt wird.…”

Dual Protection Layer Strategy to Increase Photoelectrode–Catalyst Interfacial Stability: A Case Study on Black Silicon Photoelectrodes

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sunlight is sufficient to supply the ≈18 TW of energy required to meet our current global energy needs [2] and sustain our soci ety's projected energy demands (≈80 TW to carry society through the end of this century). Numerous strategies to harvest solar energy have been proposed and studied, such as photovoltaics, [5] water splitting, [6][7][8][9] and artificial photosynthesis of organic molecules. Numerous strategies to harvest solar energy have been proposed and studied, such as photovoltaics, [5] water splitting, [6][7][8][9] and artificial photosynthesis of organic molecules.

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