Hydrofluoric acid-free etched MAX on 3D-printed nanocarbon electrode for photoelectrochemical hydrogen production

MXenes have emerged as a promising material for a disparate range of photo-electrochemical conversion and energy storage devices. However, most reported synthesis process involves hydrofluoric acid (HF) and fluoride-based compounds. HF severe toxicity persists impediment to the scalable production and fabrication of MXenes. Thus, fluoride-free protocols are currently being explored. Here, we demonstrate a novel fluoride-free protocol for the etching of the MAX phase (Ti3AlC2) utilizing an acidic mixture of nitric acid, phosphoric acid, and acetic acid. Such acidic etching modulated the electronic structure and chemical composition of the MAX surface converting it into MAX-derived flower-like titanium phosphate and titanium oxide which boosts its photo-electrochemical properties. The photo-electrochemical hydrogen evolution reaction is evaluated using 3D-printed and screen-printed carbon electrodes exposing under visible light illumination with 365 and 460 nm wavelengths. Such HF-free etched Ti3AlC2 MAX and the MAX-derived flower-like titanium phosphate and titanium oxide coated 3D-printed nanocarbon and screen-printed carbon electrodes demonstrate a novel process to be applied for an energy conversion application. This work will pave the way to etch other MAX phases through an environment-friendly and easy-handling technique that is to be used beyond photo-electrochemical applications.