Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Full Length Article Thermodynamic driven phase engineering in VMo 2 S 4 nanosheets for superior water splitting Songge Zhang a,1 , Jiace Hao a,1 , Han Zhu a, ⁎ , Xiaodi Jiang b , Xinxin Sang a , Guohua Gao b , Haiyan Zhu a , Shuanglong Lu a , Mingliang Du a, ⁎ a Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China b Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, Key Laboratory of Road and Traffic Engineering of the Ministry of Education, Tongji University, Shanghai 200092, People's Republic of China ARTICLE INFO Keywords: Phase engineering VMo 2 S 4 Overall water splitting ABSTRACT A concept of experiment to tune the two-dimensional MoS 2 into VMo 2 S 4 via thermodynamic driven phase en- gineering by combining the facile electrospinning technology and S-vapor assisted graphitization process has been demonstrated. Compared to V doped MoS 2 nanosheets, the VMo 2 S 4 nanosheets show a superior oxygen evolution reaction (OER) activity in alkaline electrolyte, reaching a current density of 10 mA cm -2 at over- potential of 295 mV with Tafel slope of 97 mV dec -1 . The VMo 2 S 4 nanosheets also show superior water splitting activity with 10 mA cm -2 at a cell voltage of 1.65 V. The theoretical and experimental results reveal that the V introduction into interplane of MoS 2 leads to the significant decrease in the energy barrier for *OOH formation (0.99 eV), thus suggesting the improved transformation from *OOH to O 2 . 1. Introduction Electrocatalytic overall water splitting (OWS) to produce hydrogen and oxygen has become an efficient way to solve the energy crisis and ecological issues in society, especially for automotive industries [1–4]. It involves an anodic oxygen evolution reaction (OER) and a cathode hydrogen evolution reaction (HER), both of which involves OH* or H* during the reaction [5–7]. Too strong OH* or H* adsorption towards the active sites of electrocatalysts would result in catalyst poisoning while too weak OH* or H* adsorption towards the active sites would require a large overpotential to overcome energy barriers [8,9]. Hence, the rational modulation for balancing the absorption of OH* and H* is critical to achieve the high-performance electrocatalysts for water splitting. Due to the sluggish kinetics and four-electron transfer, the OER is the bottleneck of the OWS [10,11]. Therefore, designing effec- tive OER catalysts is prerequisite for outstanding OWS electrocatalysts MoS 2 -based materials have been reported for many times as a pro- mising electrocatalyst. [12–15] Most of these reports focus on the HER performance of MoS 2 , while it is rarely reported for OER and OWS performance [16–18]. This is because of the OER inertness of MoS 2 . Coupling with transition-metal oxide, carbide, sulfide for a compound catalysts, such as Co 9 S 8 @MoS 2 , MoS 2 /Ni 3 S 2 and Mo-N/C@MoS 2 , to modulate the electronic structure of MoS 2 is an effective method to endow MoS 2 OER and OWS performance [19–21].These electro- catalysts show enhanced electrical conductivity and decreased H* ad- sorption energy, indicating the outstanding OWS activities. However, these added compounds are limited to first row transition metal (Fe, Co and Ni) and the OER active compounds are not originated from the basal plane of MoS 2 itself but the new added components, such as Co 9 S 8 , Ni 3 S 2 and Mo-N/C. Hence, developing a facile strategy to tune the basal plane of MoS 2 into active site for OER and OWS is challenging and attractive. Here, we reported a concept of experiment to tune the MoS 2 into VMo 2 S 4 via phase engineering by combining the facile electrospinning technology and S-vapor assisted graphitization process. The experi- mental results demonstrate that the VMo 2 S 4 /CNFs show superior OER and OWS performance with an overpotential of 295 mV at 10 mA cm -2 and a cell voltage of 1.65 V at 10 mA cm -2 . Theoretical results indicate that the OOH* intermediates in OER process could be easily stabilized by the sulphur and surface metals (V and Mo), exhibiting a lower en- ergy barrier of 0.99 eV when compared with the V-MoS 2 (2.84 eV), thus showing outstanding OWS activity. https://doi.org/10.1016/j.apsusc.2020.146755 Received 18 March 2020; Received in revised form 7 May 2020; Accepted 21 May 2020 ⁎ Corresponding authors. E-mail addresses: zhysw@jiangnan.edu.cn (H. Zhu), du@jiangnan.edu.cn (M. Du). 1 These authors contributed equally to this work. Applied Surface Science 527 (2020) 146755 Available online 25 May 2020 0169-4332/ © 2020 Elsevier B.V. All rights reserved. T