The present study emphasizes the enhancement in catalytic activity due to the formation of vacancies using dispersion corrected density functional theory. We observed that without vacancy formation, in general the edge site is an active site for hydrogen adsorption, while the lowest Gibbs free energy (ΔGH) is found to be for Janus HfSSe at the S-edge site. Furthermore, interestingly, due to the hindrance of the edge site, it facilitates only the Volmer-Heyrovsky reaction rather than the Volmer-Tafel. Among the mono vacancies, the Hafnium mono vacancy shows the lowest adsorption energy.We observed a competition between the evolution of H2S and H2 gas in the case of HfS2-VHf, whereas in the case of defected Janus and HfSe2, due to the presence of Se layers, we observed no competitiveness with H2S or H2Se gas with hydrogen gas. These defected materials exhibit lower reactional Gibbs free energy than a pristine monolayer due to its metallic nature. We observed that Hafnium vacancy enhances the HER activity, and pave the way for dominating Volmer-Heyrovsky reaction.