title: Monolayer-precision synthesis of molybdenum sulfide nanoparticles and their nanoscale size effects in the hydrogen evolution reaction.
abstract: Metal sulfide-based nanostructured materials have emerged as promising catalysts for hydrogen evolution reaction (HER), and significant progress has been achieved in enhancing their activity and durability for the HER. The understanding of nanoscale size-dependent catalytic activities can suggest critical information regarding catalytic reactivity, providing the scientific basis for the design of advanced catalysts. However, nanoscale size effects in metal sulfide-based HER catalysts have not yet been established fully, due to the synthetic difficulty in precisely size-controlled metal sulfide nanoparticles. Here we report the preparation of molybdenum sulfide (MoS2) nanoparticles with monolayer precision from one to four layers with the nearly constant basal plane size of 5 nm, and their size-dependent catalytic activity in the HER. Using density functional theory (DFT) calculations, we identified the most favorable single-, double-, and triple-layer MoS2 model structures for the HER, and calculated elementary step energetics of the HER over these three model structures. Combining HER activity measurements and the DFT calculation results, we establish that the turnover frequency of MoS2 nanoparticles in the HER increases in a quasi-linear manner with decreased layer numbers. Cobalt-promoted MoS2 nanoparticles also exhibited similar HER activity trend. We attribute the higher HER activity of smaller metal sulfide nanoparticles to the higher degree of oxidation, higher Mo-S coordination number, formation of the 1T phase, and lower activation energy required to overcome transition state. This insight into the nanoscale size-dependent HER activity trend will facilitate the design of advanced HER catalysts as well as other hydrotreating catalysts.
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Bora
authors: B
authors: Seo
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Gwan Yeong
authors: GY
authors: Jung
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Young Jin
authors: YJ
authors: Sa
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Hu Young
authors: HY
authors: Jeong
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Jae Yeong
authors: JY
authors: Cheon
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Jeong Hyeon
authors: JH
authors: Lee
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Ho Young
authors: HY
authors: Kim
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Jin Chul
authors: JC
authors: Kim
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Hyeon Suk
authors: HS
authors: Shin
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Sang Kyu
authors: SK
authors: Kwak
authors: †Department of Chemistry, ‡School of Energy and Chemical Engineering, and §UNIST Central Research Facilities (UCRF), Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 689-798, Republic of Korea.
authors: Sang Hoon
authors: SH
authors: Joo
keywords: MoS2; catalyst; hydrogen evolution reaction; monolayer-precision synthesis; nanoscale size effect