DFT Study On The Activity Of Nickel-based Alloy Catalyst For Hydrogen Evolution Reaction

Hydrogen is one of the most popular secondary energy solution worldwide nowadays, because of its property of green and efficiency. In particular, water electrolysis technique is considered the most promising. However, due to the limitation of energy and cost consuming especially from negative electrode, there is still a lot of work to be done for the large-scale commercial application. Therefore, to design and research a novel cathode with high electrocatalytic activity and long-term stability has been of important practical significance and practical value. In recent years, there are two major ways to design cathode catalysts of hydrogen evolution reaction?HER?. On one hand, scientists are looking for an efficient catalyst without noble metal, such as nickel alloy as substitute. On the other hand, reducing the ratio of noble metal but maintain the efficiency is also a reasonable approach. In this work, the first-principle calculation is applied to study the nature chemistry reason behind the improved HER activity, providing a theoretical basis for preparing more highly effective catalysts in the experiment. The work mainly includes the following two aspects:Firstly, origin of the enhanced catalytic activity of NiMoP alloy is investigated by the density functional theory?DFT?. Based on the early research of our group, the NiMoP/Ni electrode shows higher activity and stability for HER than the NiP/Ni electrode. Subsequently, the DFT is utilized to compare the geometic and electronic structure, the adsorption energy of H₂O/H/OH and ?G_H* with or without Mo. From the surface charge configuration difference, it is clear that Mo transfer electrons to the surface of Ni and P, and make the bond lengths increase. From the adsorption energy, NiMoP has stronger adsorption of H₂ O than NiP but weaker affect on H and OH. Such conclusion is further confirmed by the calculations of disassociation of water. |?G_H*| has been considered as a major descriptor of the HER activity for a wide variety of metal catalysts. The optimum value of |?G_H*| should be zero. In both direct and indirect dissociation of H₂ O, the ?G_H* of NiMoP is much closer to zero rather than NiP, confirming a higher activity of hydrogen evolution. From the electronic structure and activity, it is a synergetic effect to enhanced catalytic activity of NiMoP between Ni and Mo.Secondly, the DFT is used for the understanding of relationship between Ir and Ni in the IrNi catalyst, which benefit in the mechanism of increasing efficiency with Ir. From the very beginning, pure Ir?Ir₃Ni?Ir Ni?IrNi₃ and pure Ni are modelled, respectively. The calculations of geometic structure show that the bond length of Ir-Ir bond shrinks while the bond length of Ni-Ni bond expands.The surface charge distribution show that the electrons transfer from Ni to Ir, prompting surface Ni atoms have positive charge and Ir atoms have negative charge.When Ir/Ni =1:1, Ni atoms have the most positive charge and Ir atoms have the most negative charge. DOS and the d band center calculations show that DOS show a shrinkage trend after Ni doping. The d band center of Ir and Ni atoms have curve changes with increasing Ni content or Ir content. Comprehensive analysis of the bond length, surface charge and d band center found that the bond length?surface stress effect? and the surface charge?electrons structure effect? affect combined the d band center of IrNi catalyst. As the ratio of Ni increase, the key factor changes from the Ir-Ir bond length to the charge distribution shifting; as the ratio of Ir increase, the key factor changes from the Ni-Ni bond length to the charge distribution shifting. The adsorption of H and ?G_H* calculations show that the order of catalytic activity follows: IrNi?111?>Ir Ni₃?111?>Ir₃Ni?111?. When Ir/Ni =1:1, IrNi catalyst has the best activity. In a word, when Ir: Ni is 1: 1, Ir atoms have most negative charge, and ?G_H* of Ir atoms is most close to zero, and the activity is the best of catalyst; Ni atoms have most positive charge, and ?G_H* of Ni atoms is most close to zero, and the activity is the best of catalyst. The surface charge can be used to indicate the activity of Ir Ni catalyst.