Photoelectrochemical CO sub(2) reduction by a p-type boron-doped g-C sub(3)N sub(4) electrode under visible light

• Published in: Applied catalysis. B, Environmental Environmental, 2016-09, Vol.192, p.193-198
• Main Authors: Sagaraa, Nobuhiro, Kamimuraa, Sunao, Tsubotaa, Toshiki, Ohnoa, Teruhisa
• Format: Article
• Language: English
• Subjects: Atomic beam spectroscopy; Carbon; Carbon nitride; Electrodes; Photocurrent; Photoelectric effect; Reduction; Semiconductors
• ISSN: 0926-3373
• DOI: 10.1016/j.apcatb.2016.03.055

Graphitic carbon nitride (g-C sub(3)N sub(4)) has attracted much attention as a metal-free semiconductor having visible light absorption and relatively high chemical stability under visible light irradiation. Graphitic carbon nitride (g-C sub(3)N sub(4)) and boron-doped g-C sub(3)N sub(4) (B-doped g-C sub(3)N sub(4), BCNx) were prepared by heating melamine and a mixture of dicyanodiamide and BH sub(3)NH sub(3), respectively. X-ray diffraction, a Brunauer, Emmett and Teller (BET) apparatus, and UV-vis spectra were used to analyze the physical properties of the prepared samples. Electrodes of these samples were prepared by using the electrophoresis method. X-ray photoelectron spectroscopy analyses confirmed the incorporation of boron atoms in the g-C sub(3)N sub(4) framework as well as the amount of boron atoms. Au, Ag or Rh as a co-catalyst was coated on the surface of g-C sub(3)N sub(4) and B-doped g-C sub(3)N sub(4) by using the magnetron sputtering method. The photocurrent response was observed using a solar simulator as a light source. The photocurrent response of B-doped g-C sub(3)N sub(4) was about 5-times larger than that of pure g-C sub(3)N sub(4). B-doped g-C sub(3)N sub(4) coated with Rh as a co-catalyst showed the highest photocurrent response under solar light irradiation, its photocurrent being about 10-times larger than that of original g-C sub(3)N sub(4). Under photoelectrochemical conditions, we also observed the products in gas phase and aqueous phase. C sub(2)H sub(5)OH was observed as a main product, while small amounts of CO and H sub(2) were observed in gas phase. We also discuss the relationship between co-catalysts and photocurrent responses and the carbon source of C sub(2)H sub(5)OH as a main product. The source of carbon of C sub(2)H sub(5)OH obtained by CO sub(2) reduction is discussed on the basis of results of a labeling experiment using super(13)CO sub(2).