Solar hydrogen evolution using metal-free photocatalytic polymeric carbon nitride/CuInS2 composites as photocathodes

Abstract

a Polymeric carbon nitride (g-C 3 N 4 ) films were synthesized on polycrystalline semiconductor CuInS 2 chalcopyrite thin film electrodes by thermal polycondensation and were investigated as photocathodes for the hydrogen evolution reaction (HER) under photoelectrochemical conditions. The composite photocathode materials were compared to g-C 3 N 4 powders and were characterized with grazing incidence X-ray diffraction and X-ray photoemission spectroscopy as well as Fourier transform infrared and Raman spectroscopies. Surface modification of polycrystalline CuInS 2 semiconducting thin films with photocatalytically active g-C 3 N 4 films revealed structural and chemical properties corresponding to the properties of g-C 3 N 4 powders. The g-C 3 N 4 /CuInS 2 composite photocathode material generates a cathodic photocurrent at potentials up to +0.36 V vs. RHE in 0.1 M H 2 SO 4 aqueous solution (pH 1), which corresponds to a +0.15 V higher onset potential of cathodic photocurrent than the unmodified CuInS 2 semiconducting thin film photocathodes. The cathodic photocurrent for the modified composite photocathode materials was reduced by almost 60% at the hydrogen redox potential. However, the photocurrent generated from the g-C 3 N 4 /CuInS 2 composite electrode was stable for 22 h. Therefore, the presence of the polymeric g-C 3 N 4 films composed of a network of nanoporous crystallites strongly protects the CuInS 2 semiconducting substrate from degradation and photocorrosion under acidic conditions. Conversion of visible light to hydrogen by photoelectrochemical water splitting can thus be successfully achieved by g-C 3 N 4 films synthesized on polycrystalline CuInS 2 chalcopyrite electrodes.

Graphitic carbon nitride nano-emitters on silicon: a photoelectrochemical heterojunction composed of earth-abundant materials for enhanced evolution of hydrogen

“…14, 15 Huda and Turner also concluded that light-induced electron-hole pairs may remain conned within the heptazine subunits 16 which could be later, to some extent, substantiated by analysis of time-resolved photoluminescence spectra. 17 Modication of the g-C 3 N 4 bulk geometry toward the nano-scale is therefore required to remedy these limitations.…”

“…To overcome this limitation, the fabrication of macroscopic solid state (photo-) electrodes with compact g-C 3 N 4 lms was soon suggested. 14,15 In this latter approach, overall water splitting is realized under sustained operation in a photoelectrochemical cell, coupling an oxygen evolving anode via external circuitry to the carbon nitride cathode. Electrons consumed at the g-C 3 N 4 electrode are thereby relled by the counter reaction at the anode according to:…”

“…There is, however, a large difference of the respective conduction band edges of about 1.4 eV (E C of Si is located at 4.05 eV, while E C of g-C 3 N 4 is located between 2.6 and 3.0 eV). 8,14,15,17 Such a band discontinuity represents an additional energy barrier which can necessitate a corresponding high overpotential unless there is an interfacial dipole that lowers this barrier. In fact, the band alignment between silicon and the g-C 3 N 4 nanostructures appears to occur without pronounced discontinuity at the conduction band edges.…”

“…Polymeric carbon nitride was deposited by polycondensation of dicyandiamide precursors under nitrogen atmosphere at 550 C. 14,15 The temperature in the preparation chamber was continuously increased at a rate of 20 C per minute and held constant for further 30 minutes at 550 C (preparation route 1). The thickness of the resulting surface lms reached typically some 10 mm.…”

Towards efficient solar-to-hydrogen conversion: Fundamentals and recent progress in copper-based chalcogenide photocathodes

“…The photocurrent of g-C 3 N 4 /CuInS 2 composite electrode was stable for 22 h in 0.1 M H 2 SO 4 aqueous solution. It was considered that the network of nanoporous g-C 3 N 4 crystallites could strongly protect the CuInS 2 substrate from degradation and photocorrosion under acidic conditions [79].…”