Solid-state transition metal dichalcogenide electrocatalysts for the hydrogen evolution reaction

QD Chemistry

McGlynn, Jessica C. ; Ganin, Alexey

University:University of Glasgow

Department:School of Chemistry

关键词: hydrogen evolution, transition metal dichalcogenides, electrocatalysts.;   

Others  :  http://theses.gla.ac.uk/81290/7/22020McGlynnPhD.pdf

来源: University of Glasgow

【 摘 要 】

This work seeks to understand the origins of catalytic behaviour in transition metal dichalcogenide electrocatalysts, which are currently convoluted by a variety of factors. To achieve this, a solid-state approach to molybdenum ditelluride (MoTe2) is investigated, which allows for the synthesis of both semiconducting 2H- and metallic 1T’-phases in the bulk form. In doing so, not only is the effect of surface area excluded as the route to advanced activity, but also the role that lithium may play in altering the elemental composition. Therefore, the only factor remaining that may affect the electrocatalytic activity of MoTe2 is the change in coordination geometry which governs the semiconducting / metallic character. As a result, one may confidently attribute the emergence of catalytic activity to the result of polymorphic transition.Continuing with the quest of understanding the origins of catalytic behaviour, the metallic 1T’-MoTe2 material is studied exclusively, with the effect of surface area now being considered. Again using a solid-state approach, thus removing external factors which may otherwise contaminate this study, a low temperature variant of 1T’-MoTe2 is synthesised in order to explore the result of introducing a degree of disorder to the crystalline material. This method will then highlight the importance of intrinsic activity measurements when comparing HER electrocatalysts. Upon fully characterising the 1T’-MoTe2 materials, the phenomenon of activation is explored. With the aim of understanding the origins of catalytic enhancement in mind, efforts are turned towards determining the primary reason of activation, and excluding changes in structure and composition as the root cause of the improvement. Following ex-situ characterisation, intrinsic activity measurements coupled with computational studies such as Density Functional Theory (DFT) explore the possibility of an electrochemical activation, which may be inherent to 1T’-MoTe2.In a final endeavour to understand the mechanism behind electrochemical activation, attempts were made to scale up the working electrode to comply with in operando electrochemical cells. Additionally, alternative activation mechanisms are considered and confirmation of the catalytic sites at which activation takes place is revealed. Thus, this thesis aims to provide a coherent explanation for the observed catalytic activity in MoTe2, which may also be applied to other members of the TMDC family.