TiO<sub>2</sub> Nanotube Arrays Decorated with Reduced Graphene Oxide and Cu–Tetracyanoquinodimethane as Anode Materials for Photoelectrochemical Water Oxidation
Ramesh Poonchi Sivasankaran, Pran Krisna Das, Maheswari Arunachalam, Rohini Subhash Kanase, Yong Il Park, Jeongsuk Seo, Soon Hyung Kang
Abstract
While the ever-increasing energy crisis for sustainable and renewable energy sources has prompted the development of innovative materials for photoelectrochemical water oxidation, the techniques to enhance solar-to-hydrogen efficiency and provide long-term stability remain significant challenges. In this work, we report a ternary material system based on reduced graphene oxide (r-GO) and copper–tetracyanoquinodimethane (Cu–TCNQ) decorated on anodically aligned TiO2 nanotubes (TONTs), which simultaneously improve the charge separation and water oxidation kinetics. r-GO and Cu–TCNQ were sequentially decorated on the surface of TONTs by a facile electrophoretic deposition method and marked in brief as TONTs/r-GO/Cu–TCNQ. The fabricated TONT/r-GO/Cu–TCNQ photoanode film was systematically characterized by various techniques, namely, X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy, field emission-scanning electron microscopy, field emission-transmission electron microscopy, and X-ray photoelectron spectroscopy. Photoelectrochemical water oxidation was evaluated in 1 M NaOH as an electrolyte, and the TONT/r-GO/Cu–TCNQ photoanode film exhibited a considerably improved JSC (photocurrent density) value of 0.72 mA/cm2 at 1.23 V versus VRHE (reversible hydrogen electrode) compared to the JSC value (0.30 mA/cm2) of bare TONTs. The obtained experimental results demonstrated that r-GO with a high work function and higher electron mobility accepts photogenerated electrons from the conduction band of TONTs and leads to suppressed charge recombination and favorable charge separation/transfer events, whereas Cu–TCNQ acts as an oxygen evolution reaction co-catalyst, which accepts photogenerated holes from the valence band of TONTs, accelerating the surface water oxidation reaction. Additionally, photoluminescence spectroscopy, incident photon-to-current efficiency, Mott–Schottky plot, and electrochemical impedance spectroscopy confirmed that the r-GO and Cu–TCNQ complexes boost the charge separation/transfer events.