Integrated molten and vapor condensation of polymeric carbon nitride photoelectrode towards efficient water splitting

Abstract

Polymeric carbon nitride (PCN) has received extensive attention in suspension photocatalysis, whereas the preparation of high-quality PCN film is still at an initial stage, limiting its practical application in photoelectrochemical (PEC) systems. Herein, an integrated molten and vapor condensation route is realized using small molecule precursors dicyandiamide (DCDA) and thiourea (TU) to form PCN film photoelectrode with high performance. The in-situ deposition route endows the PCN film with a composite structure including a thick porous zone with suitable thickness for light absorption and thin compact zone with a higher C/N ratio for better charge transportations. The growth of the specific film and the functions of precursors DCDA and TU are investigated in detail. Owing to the unique condensation route and film structure, this PCN film exhibits excellent performance in PEC water splitting with a photocurrent density of ca. 140 μA cm −2 in 0.1 mol L −1 NaOH electrolyte at 1.23V RHE , which is competitive or higher than the results of the reported PCN photoanodes prepared by the molten-mediated method and thermal vapor condensation. The integrated molten and vapor condensation strategy is enlightening for comprehending the growth of PCN photoelectrodes.

Recent progress of graphitic carbon nitride films and their application in photoelectrochemical water splitting

“…117 Integrating molten and vapor condensation of a mixture of dicyandiamide and thiourea on FTO resulted in a composite CN structure, where a thick porous zone is suitable for light absorption, and a thin compact zone with a higher C/N ratio showed better charge transportation. 118 Plasma heating was adopted by Guo and Huang et al to transform a mixture of melamine–cyanuric acid supramolecular complexes and KMnO 4 on FTO into a CN/Mn 2 O 3 /FTO p–n heterojunction photoanode. 119 Direct pyrolysis of a supramolecular hydrogel formed by hydrogen bonding between melamine and 4-cyanobenzoic acid leads to a free-standing CN film, which showed good adsorption and photocatalytic degradation ability of organic dyes.…”

Robust Carbon Nitride Homojunction Photoelectrode for Solar-Driven Water Splitting

“…32−34 In addition, the molten DCDA can be converted into melamine at 234 °C followed by the formation of melem at higher temperatures, 9,26,35 which could be in situ coated on substrates and further condensed into CN. 36 The molten-generated CN should have high roughness and thickness, contributing to a higher electrochemical surface areas and enhanced light absorption.…”

“…Apart from TCY, sulfur-free, small-molecule precursor dicyandiamide (DCDA) also has low melting (203 °C) and boiling points (229 °C), which can also offer vapor molecules at lower temperatures compared to melamine . More importantly, the vaporized TCY and DCDA molecules could react with each other to form melem. − In addition, the molten DCDA can be converted into melamine at 234 °C followed by the formation of melem at higher temperatures, ,, which could be in situ coated on substrates and further condensed into CN . The molten-generated CN should have high roughness and thickness, contributing to a higher electrochemical surface areas and enhanced light absorption.…”