Anchoring single Ni atoms on defected 2D MXene nanosheets as an efficient electrocatalyst for enhanced hydrogen evolution reaction

Abstract Electrochemical hydrogen evolution from water splitting with the help of electrocatalysts is a clean and sustainable way to produce hydrogen fuel. In this study, Mo vacancies are intentionally created on Mo2TiC2 nanosheets (D-Mo2TiC2), which provide active sites to load Ni single-atom catalysts for hydrogen evolution reaction (HER). The anchored Ni single atoms are observed to occupy the Mo vacancy sites under TEM. The crystallinity of Mo2TiC2 stays unchanged in creating Mo vacancies and loading Ni single atoms, as confirmed by XRD. The as-prepared D-Mo2TiC2/Ni catalyst exhibits a lower overpotential for HER, superior HER kinetics, larger effective surface area, and lower charge transfer resistance than the intact and defective Mo2TiC2 catalysts without Ni. The overpotential for HER at 10 mA/cm2 and the Tafel slope of the D-Mo2TiC2/Ni catalyst are −0.078 V and 56.7 mV/dec, respectively, which are approaching the best performance obtained on the Pt/C electrode. The enhanced catalytic activity of the D-Mo2TiC2/Ni has been proved to persist for 10,000 cycles of electrochemical reaction, which confirms the stability of the synthesized D-Mo2TiC2/Ni catalyst. The enhanced catalytic activity of the D-Mo2TiC2/Ni is attributed to the better conductivity resulted from Mo vacancies and the excellent catalytic activity of the anchored Ni single atoms.