Earth-abundant, nonprecious, and efficient electrocatalysts for effective hydrogen evolution reaction (HER) are crucial for future large-scale green energy production. Low-cost two-dimensional MXenes have been widely studied in energy-storage devices owing to their unique chemical and physical properties and have recently attracted scientists in the electrocatalysis field. Nevertheless, their electrocatalytic activity still remains unsatisfactory. Herein, we present a facile and general strategy using ammonia heat treatment to enhance the hydrogen evolution catalysis of Ti 3 C 2 T x MXenes by modification with a nitrogen heteroatom. Importantly, our approach is focused on revealing: (1) the contribution of all possible incorporated N species including Ti−N, N−H, and N in O−Ti−N, rather than considering only that of Ti−N x motifs as previously reported for N-doped MXene electrocatalysts, and their role in inducing a change in the electronic configuration of the as-prepared catalysts, which then leads to increased electrical conductivity and improved intrinsic catalytic reactivity; and (2) the importance of controlling the proper amount of N obtained at a suitable calcined temperature to assist the shift of the Gibbs free energy for hydrogen adsorption (ΔH ad *) approaching 0 eV (ideal value), as proved by the density functional theory. Moreover, experimental findings indicate that nitrogen-doped Ti 3 C 2 T x annealed at 600 °C shows superior improved HER electrocatalytic performance compared to pristine Ti 3 C 2 T x , with an onset potential of −30 mV and an overpotential as low as 198 at 10 mA cm −2 , as well as a much smaller Tafel slope of 92 mV dec −1 .

In this work, we proposed to combine oxalic acid and ferric ions in very low concentrations to create new, economic, and effective homogeneous photo-Fenton catalytic systems for the degradation of methylene blue. The effects of ferric concentration, H2C2O4 concentration, pH, and tert-butanol on the catalytic activity were also investigated. According to the experimental results, Fe3+ ions exhibited impressive catalytic performances in the presence of H2C2O4 at concentrations below type B (5.0 mg.l–1) from the Vietnam National Technical Regulation on Industrial Wastewater. Specifically, a ferric concentration of 3.0 mg.l–1, H2C2O4 concentration of 10–3 mol.l–1, and pH value of 3 were found to be the best conditions for MB degradation under UVA light. Furthermore, owing to a very low concentration of ferric ions, iron sludge formation can be avoided after wastewater treatment, which makes the photo-Fenton process suitable for practical applications.