MXene Anion Engineering for Efficient Hydrogen Evolution
Anand P. Tiwari, Shay McBride, Andrew B. Hamlin, Md. Saifur Rahman, Julia E. Huddy, Geoffroy Hautier, William J. Scheideler
Abstract
MXenes have attracted attention as promising electrocatalysts for performing the hydrogen evolution reaction (HER). However, the poor intrinsic kinetics and inadequate density of active sites restrict MXenes as viable electrocatalysts for efficient hydrogen production. Herein, these hindrances are overcome via tunable doping of anion atoms as electron donors in titanium carbide (Ti 3 C 2 T X ) MXenes. By engineering the co-doping of nitrogen and sulfur anions, we achieve efficient electrocatalytic activity through synergistic chemical and structural changes. The modified MXene offers an optimal concentration of Ti–S and Ti–N bonds at the surface of hexagonal nanoplate-decorated nanosheets, resulting in a low overpotential of 260 mV and a Tafel slope of 85 mV/dec in an acidic medium, which is improved 3× over that of the pristine MXene (overpotential of 770 mV). This modified Ti 3 C 2 T X catalyst also displays superior durability compared with other earth-abundant catalysts, showing an operation for 60 h of continuous hydrogen evolution without any decay in its performance. The enhanced electrocatalytic activity of anion-co-doped Ti 3 C 2 T X MXene is attributed to manipulation of the electronic structure through synergistic N and S bonding, which promotes balanced adsorption/desorption of the intermediate hydrogen H* by lowering the Gibbs free energy (Δ G H* = −0.07 eV). Our strategy to improve the electrocatalytic activity of Ti 3 C 2 T X by anion engineering has the potential to enhance the electrocatalytic activity of numerous MXenes as well as other high surface area 2D materials.