Among various hydrogen production methods, water electrolysis using renewable energy is an eco-friendly and sustainable technology. Especially, alkaline water electrolysis has been regarded as the most mature and reliable technology owing to its low operating temperature and long-life span. In addition, non-noble metal can be adopted as the electrode materials since it uses an alkaline electrolyte. However, one shortcoming of the alkaline electrolysis is that current density is lower than other electrolysis technologies. Therefore, many projects have been still ongoing to improve the current density, such as developing high performance catalysts.

 Raney nickel, a Ni-based solid catalyst with a porous structure, has been widely utilized as hydrogen evolution reaction (HER) electrode materials. Raney nickel is mainly derived through the selective leaching process from Ni-Al alloy leading to the enlarged surface area, which is known to be the origin of high catalytic activity of Raney nickel. Recently, our experimental investigation revealed that the catalytic activity of Raney nickel can be optimized by controlling the heat treatment time at the stage of Ni-Al alloy preparation. Interestingly, one sample comprising the largest amount of Ni₂Al₃ on the surface exhibits a remarkable current density normalized by electrochemical surface area, which indicates that the large surface area is not the only reason for the high catalytic activity of Raney nickel. Herein, density functional theory (DFT) calculations were performed to figure out if another origin of high electrocatalytic performance of Raney nickel other than the surface area exists. The HER activities on various Ni surfaces including different phases and atomic defects which can be possibly formed during the leaching, electrochemical reduction and HER processes were thoroughly investigated. Our DFT results showed that the phase transition from metallic Ni to Ni(OH)₂ can degrade the HER performance, but the atomic defects can contribute to the improvement of overall HER activity by activating the water splitting and hydrogen evolution.