Carbon Nitride/Reduced Graphene Oxide Film with Enhanced Electron Diffusion Length: An Efficient Photo‐Electrochemical Cell for Hydrogen Generation

Abstract

robust, and highly efficient semiconductors; the latter should have good conductivity, be able to transfer charges rapidly at the semiconductor/liquid electrolyte interface, display long-term stability, possess good light-harvesting properties, and have a suitable energy band position for the desired reaction. [6,7] Despite significant progress in this field, [3,[10][11][12][13][14][15][16][17] semiconductors that fulfill all these requirements rarely exist today, and the production of such semiconductors is still much sought after.Over the past few years, polymeric graphitic carbon nitride (CN) has attracted widespread attention due to its outstanding electronic properties, which have been exploited in various applications, including photo-and electrocatalysis, [18][19][20][21][22][23][24] heterogeneous catalysis, [25][26][27][28] CO 2 reduction, [29][30][31] water splitting, [32][33][34][35][36][37][38][39][40] light-emitting diodes, [41] photovoltaics, [42][43][44] and sensing. [45][46][47] Its unique and tunable optical, chemical, and catalytic properties, alongside its low price and remarkably high stability to oxidation, make it a very attractive material for PEC applications. [11,48,49] However, despite the great progress in utilizing CN materials in PECs, several factors still hinder the cell activity, such as poor electron-hole separation efficiency, short electron diffusion length owing to the poor electronic conductivity of CN materials, deficient hole transfer from the CN surface to solution, and low absorption coefficient. [25] We envision that the improvement of the electron diffusion length would result in significant enhancement of the electron and hole lifetimes and would increase their probability to reach the conductive substrate and the electrolyte, respectively, prior to their recombination. Moreover, a longer diffusion length allows the construction of a thicker absorber layer, thus increasing the surface density of accessible photoactive sites. One way to improve both charge separation and electron diffusion length is by compositing CN with conductive carbon materials, such as graphene and carbon nanotubes. [11,18,19] Upon illumination, excited electrons can be promptly injected into the conductive graphene, while the holes remain in the CN matrix. Consequently, the lifetime of the excitons is prolonged, enhancing their probability for further reaction. To date, various CN/graphene composites have been introduced, mainly as powders, and have demonstrated good photoactivity. [11,18,19] However, the poor dispersibility of CN/graphene composites in most solvents Polymeric carbon nitride (CN) has emerged as a promising semiconductor for energy-related applications. However, its utilization in photo-electrochemical cells is still very limited owing to poor electron-hole separation efficiency, short electron diffusion length, and low absorption coefficient. Here the synthesis of a highly porous carbon nitride/reduced graphene oxide (CN-rGO) film with good photo-electrochemical properties is repor...

Carbon Nitride Materials for Water Splitting Photoelectrochemical Cells

“…Chemie increased PEC performance from 70 to 150 mAcm À2 . [85] In this study,the CN layer acted as an efficient hole extraction layer rather than as an absorber.Carbon-based nanostructures such as reduced graphene oxide (rGO), [75,120,121] carbon nanotubes (CNT), [66,122,123] and others [97] can also serve as electron conduction paths.…”

A Water‐Splitting Carbon Nitride Photoelectrochemical Cell with Efficient Charge Separation and Remarkably Low Onset Potential

“…We assume that the photocurrent in presence of TEOArepresents the maximum current that can be obtained without any hole-transfer limitations. [13] TheC N electrode exhibits adouble photocurrent at 245 mAcm À2 after addition of 10 %T EOAi nto the 0.1m KOHs olution (Supporting Information, Figure S26a). In good agreement with this observation, the IPCE value at 400 nm is improved to 19 %( Supporting Information, Figure S26b).…”

Kohlenstoffnitridmaterialien für photochemische Zellen zur Wasserspaltung

“…Tang et al zeigten, dass die Konstruktion eines bordotierten CN/CN-Heteroübergangs zu einer signifikanten Verbesserung des Photostroms führen kann, was einer verbesserten Ladungstrennung und einem verbesserten Ladungsübergang innerhalb der Elektrode zu verdanken ist. [121] Zur Verbesserung der Lichtsammeleigenschaften und der Ladungstrennung von angeregten Ladungen kann auch eine porçse Elektronenstruktur verwendet werden. Diese führt zu einer hohen Ladungsrekombinationsrate und einer sehr geringen Diffusionslänge.L etztere beschränkt die Dicke der aktiven Lichtsammelschicht und beschränkt dadurch die Lichtabsorption.…”

“…[119] CN auf der Oberfläche von ZnO-Nanodrähten erhçhte die PEC-Leistung von 70 auf 150 mAcm À2 . [85] In dieser Studie wirkte die CN-Schicht eher wie eine effiziente Lochextraktionsschicht als wie ein Absorber.K ohlenstoffbasierte Nanostrukturen wie etwa reduziertes Graphenoxid (rGO), [75,120,121] Kohlenstoffnanorçhren (CNT) [66,122,123] und andere [97] kçnnen ebenfalls als Elektronenleitungswege dienen.…”

“…Bis heute betragen die hçchsten berichteten Photostromdichten fürd ie Wasseroxidation in alkalischer und neutraler Umgebung rund 0.1 mA cm À2 bei Beleuchtung mit 1Sun bei 1.23 V RHE .D ie Verwendung eines effizienten Lochfängers wie etwa Tr iethanolamin kann den Photostrom drastisch auf bis zu 0.66 mA cm À2 erhçhen. [121] Die üblichen PEC-Messungen sind in Abbildung 5g ezeigt. Die erste Untersuchung einer PEC besteht in der Messung der Photostromdichte als Funktion der angelegten Spannung.D as Anfangspotential ist das Potential, bei dem die Zunahme des Photostroms beginnt (Abbildung 5c [39] Das Einfügen von CN in verschiedene Bulk-Heterojunctions (BJH) verbesserte die Effizienz, [40,136] und CN/PBT zeigten PV-Eigenschaften, wobei CN als Elektronenakzeptor wirkte,w ährend PBT der Donor war.D ies wurde der Bildung eines BJH an der CN-PBT-Grenzfläche zugeschrieben.…”