In situ construction of hierarchical graphitic carbon nitride homojunction as robust bifunctional photoelectrocatalyst for overall water splitting

Abstract

BACKGROUND: Sustainable production of oxygen and hydrogen via catalyst-aided water splitting utilizing solar energy has attracted increasing interest. The primary issue in this field is the development of earth-abundant and active photoelectrocatalytic materials. Herein, a novel hierarchical g-C 3 N 4 /g-C 3 N 4 metal-free homojunction catalyst is synthesized through partial hydrolysis of melamine in alkali and subsequent thermal treatment.RESULTS: The hierarchical g-C 3 N 4 /g-C 3 N 4 metal-free homojunction composed of lamellas features large exposed surface area, abundant interface contact and more channels for mass transfer, making it highly effective for water splitting with a small overpotential of 500 mV at 10 mA cm −2 and low Tafel slope of 93.1 mV dec −1 for oxygen evolution reaction (OER) in 1.0 mol L −1 potassium hydroxide (KOH) solution, as well as 259 mV at 10 mA cm −2 and 109.33 mV dec −1 for hydrogen evolution reaction (HER) in 0.5 mol L −1 sulfuric acid (H 2 SO 4 ) solution. Furthermore, the overpotential and Tafel slope further decrease to 383.4 mV and 69.52 mV dec −1 for OER, 150.1 mV and 67.93 mV dec −1 for HER upon visible light irradiation, demonstrating the exceptional photo-responsive catalytic performance, which can be attributed to the direct Z-scheme homojunction resulting in effective charge transfer and •OH and superoxide free radicals produced under visible light irradiation.CONCLUSION: This work provides a facile but effective approach for the construction of metal-free OER/HER bifunctional catalyst with high photo-responsive performance, achieving higher activity for catalyst-assisted water splitting.

Solar light‐induced photocatalytic degradation of methylparaben by g‐C3N4 in different water matrices

“…During photocatalysis, organic molecules can react either directly, by the photogenerated holes (h + ) on the surface of photocatalysts, or indirectly, through the intermediate formation of several kinds of active oxygen species by h + and e − redox reactions. [27][28][29][30][31][32] In recent years, researchers seem to agree that in order to increase the practical application of the photocatalytic process, major efforts need to be focused on the development of visible lightresponsive photocatalytic materials. Recently, graphitic carbon nitride (g-C 3 N 4 ) has received much attention because it absorbs a significant portion of visible light, due to its medium band gap of ∼2.7 eV, and because it is easy to fabricate, economic, nontoxic, and chemically and thermally stable for photocatalytic and photoelectrochemical applications.…”

“…This process uses photocatalysts, which are semiconductor materials, and artificial or solar light energy to decompose organic and hazardous pollutants, and changing them into harmless products. During photocatalysis, organic molecules can react either directly, by the photogenerated holes (h + ) on the surface of photocatalysts, or indirectly, through the intermediate formation of several kinds of active oxygen species by h + and e − redox reactions 27–32 . In recent years, researchers seem to agree that in order to increase the practical application of the photocatalytic process, major efforts need to be focused on the development of visible light‐responsive photocatalytic materials.…”