Au Nanoparticle Decorated g-C3N4/Bi2S3 Photoanodes for Photoelectrochemical Water Splitting

To address the energy scarcity and prevailing environmental issues, renewable energy resource-based technological advances are quite vital. Solar energy harnessing for photoelectrochemical (PEC) water splitting seems to be a viable strategy for the same. The development of an efficient photoelectrode is the key task in the photoelectrochemical process. In this study, we have fabricated Au nanoparticles (NPs) decorated onto a g-C3N4/Bi2S3 heterojunction by drop-casting method. The g-C3N4/Bi2S3 heterojunction was fabricated using annealing followed by a doctor blade method, while Bi2S3 was loaded using successive ionic layer adsorption and reaction (SILAR). Although g-C3N4 is a polymeric semiconductor with unique properties, it suffers from high electro-hole recombination and low conductivity. Bi2S3 and Au NPs have been introduced to overcome these issues as they offer advantages such as high optical absorption coefficient, favorable band alignment, narrow bandgap, and improved charge carrier density. The Au NPs play a vital role in preventing charge recombination due to the surface plasmon resonance effect, resulting in good photochemical energy conversion efficiency, photostability, and interfacial charge transfer kinetics. The g-C3N4/Bi2S3/Au heterojunction exhibited a photocurrent density of 1.4 mA/cm2 at 1.23 V versus RHE and a solar-to-hydrogen efficiency (STH) of 0.72% at 0.68 V versus RHE in neutral medium. The photostability of the fabricated electrodes was ensured by scanning up to 1000 s in the neutral electrolyte (0.1 M Na2SO4). Electrode/electrolyte charge transfer kinetics was analyzed by impedance analysis, and it was found that in comparison to the individual counterparts, the g-C3N4/Bi2S3/Au photoelectrode displayed a smaller semicircle in the high-frequency region indicating better charge transfer at electrode/electrolyte surface.