Single-step growth of carbon and potassium-embedded TiO2 nanotube arrays for efficient photoelectrochemical hydrogen generation

Carbon and potassium-embedded TiO2 nanotube arrays were rapidly formed via anodic oxidation of the Ti metal in ethylene glycol (EG) containing potassium hydroxide (KOH). The incorporation of KOH allowed the simultaneous control of electrochemical oxidation and chemical dissolution, resulting in the equilibrium growth of nanotube arrays with a maximum growth rate of ∼353 nm min−1. The anodic growth of nanotube arrays in the hydroxyl (OH)-rich environment induced the formation of anatase crystallites by bridging between the dissociated H2O molecules and OH group of octahedra in TiO2. High aspect ratio nanotube arrays with a large pore size formed in EG electrolyte containing KOH could efficiently harvest the light energy, thereby enhancing the photocatalytic efficiency. High reaction sites of nanotube arrays with high surface area promoted the diffusion of charge carriers to the electrolyte. Furthermore, the strong e− donation nature of adsorbed-potassium species on nanotubes facilitated the photoelectrochemical properties. Nanotube arrays formed in EG electrolyte containing 1 wt% of 1.0 M KOH exhibited a remarkable capability to generate hydrogen at an evolution rate up to ∼658.3 μL min−1 cm−2 and the photoconversion efficiency of ∼2.5%.

► C and K-embedded TiO2 nanotubes were anodically formed in EG electrolyte containing KOH.
► The anodic growth in OH-rich environment induced the formation of anatase crystallites.
► The e− donation nature of K contributes to the greater photoelectrochemical efficiency.
► A maximum H2 evolution rate up to ∼658.3 μL min−1 cm−2 with 2.5% efficiency was achieved.