Overall water splitting by Pt/g-C3N4 photocatalysts without using sacrificial agents

Abstract

We report the direct splitting of pure water by light-excited graphitic carbon nitride (g-C₃N₄) modified with Pt, PtO _x , and CoO _x as redox cocatalysts, while pure g-C₃N₄ is virtually inactive for overall water splitting by photocatalysis. The novelty is in the selective creation of both H₂ and O₂ cocatalysts on surface active sites of g-C₃N₄via photodeposition triggering the splitting of water for the simultaneous evolution of H₂ and O₂ gases in a stoichiometric ratio of 2 : 1, irradiated with light, without using any sacrificial reagents. The photocatalyst was stable for 510 hours of reaction.

Fig. 1. (a) UV-vis DRS spectrum of g-C₃N₄ polymers; inset: the corresponding Tauc plot. (b) Mott–Schottky plots of the g-C₃N₄ electrode in 0.2 M Na₂SO₄, pH = 7. (c) Band structure diagram of g-C₃N₄ polymers calculated by optical absorption and typical electrochemical Mott–Schottky methods.

Fig. 2. (a) AFM image of the g-C₃N₄ polymers with Pt deposited in situ. (b) TEM image of the g-C₃N₄ polymers with Pt deposited in situ. (c) HR-TEM image of the g-C₃N₄ polymers with Pt deposited in situ. (d) STEM images of the g-C₃N₄ polymers with Pt deposited in situ. Scale bar for a, b, c and d is 50 nm, 100 nm, 2 nm and 50 nm, respectively.

Fig. 3. (a) EELS of the g-C₃N₄ polymers with Pt deposited in situ. (b) XRD of the g-C₃N₄ polymers with Pt deposited in situ. (c) High resolution of XPS analysis of Pt_4f. (d) PL spectra of the g-C₃N₄ polymers with Pt deposited in situ.

Fig. 4. Time course of water splitting activities of 3 wt% Pt, PtO_x and 1 wt% CoO_x Co-modified g-C₃N₄ polymers under (a) UV-vis (λ > 300 nm) irradiation and (b) visible light (λ > 420 nm) irradiation.