Concurrent Vacancy and Adatom Defects of Mo_1-xNb_xSe₂ Alloy Nanosheets Enhance Electochemical Performance of Hydrogen Evolution Reaction

Ik Seon Kwon 권익선 (제1저자, 박사과정), In Hye Kwak, Ju Yeon Kim, Tekalign Terfa Debela, Yun Chang Park, Jeunghee Park (박정희 교수님),* Hong Seok Kang

 

ACS Nano 2021, ASAP (Impact factor: 14.588)

 

Abstract: Earth-abundant transition metal dichalcogenide nanosheets have emerged as an excellent catalyst for electrochemical water splitting to generate H₂. Alloying the nanosheets with heteroatoms is a promising strategy to enhance their catalytic performance. Herein, we synthesized hexagonal (2H) phase Mo_1-xNb_xSe₂ nanosheets over the whole composition range using a solvothermal reaction. Alloying results in a variety of atomic-scale crystal defects such as Se vacancies, metal vacancies, and adatoms. The defect content is maximized when x approaches 0.5. Detailed structure analysis revealed that the NbSe₂ bonding structures in the alloy phase are more disordered than the MoSe₂ ones. Compared to MoSe₂ and NbSe₂, Mo_0.5Nb_0.5Se₂ exhibits much higher electrocatalytic performance for hydrogen evolution reaction. First-principles calculation was performed for the formation energy in the models for vacancies and adatoms, supporting that the alloy phase has more defects than either NbSe₂ or MoSe₂. The calculation predicted that the separated NbSe₂ domain at x = 0.5 favors the concurrent formation of Nb/Se vacancies and adatoms in a highly cooperative way. Moreover, the Gibbs free energy along the reaction path suggests that the enhanced HER performance of alloy nanosheets originates from the higher concentration of defects that favor H atom adsorption.