Title: Reaction Mechanism for the Hydrogen Evolution Reaction on the Basal Plane Sulfur Vacancy Site of MoS₂ Using Grand Canonical Potential Kinetics

Abstract

We develop the grand canonical potential kinetics (GCP-K) formulation based on thermodynamics from quantum mechanics calculations to provide a fundamental basis for understanding heterogeneous electrochemical reactions. Our GCP-K formulation arises naturally from minimizing the free energy using a Legendre transform relating the net charge of the system and the applied voltage. Performing this macroscopic transformation explicitly allows us to make the connection of GCP-K to the traditional Butler-Volmer kinetics. Using this GCP-K based free energy, we show how to predict both the potential and pH dependent chemistry for a specific example, the hydrogen evolution reaction (HER) at a sulfur vacancy on the basal plane of MoS2.We find that the rate-determining steps in both acidic and basic conditions are the Volmer reaction in which the second hydrogen atom is adsorbed from the solution. Using the GCP-K formulation, we show that the stretched bond distances change continuously as a function of the applied potential. This shows that the main reason for the higher activity in basic conditions is that the transition state is closer to the product, which leads to a more favorable Tafel slope of 60 mV/dec. In contrast if the transition state were closer to the reactant, where the transfermore » coefficient is less than 0.5 we would obtain a Tafel slope of almost 150 mV/dec. Based on this detailed understanding of the reaction mechanism, we conclude that the second hydrogen at the chalcogenide vacant site is the most active toward the hydrogen evolution reaction. Using this as a descriptor, we compare it to the other 2H group VI metal dichalcogenides and predict that vacancies on MoTe₂ will have the best performance toward HER.« less

Authors:

Huang, Yufeng  ^[1];

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Nielsen, Robert J. ^[1]; Goddard, William A.  ^[1]

• Search DOE PAGES for author "Goddard, William A."
• Search DOE PAGES for ORCID "0000-0003-0097-5716"
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+ Show Author Affiliations

1. California Inst. of Technology (CalTech), Pasadena, CA (United States)

Publication Date:

2018-11-08

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); California Institute of Technology (CalTech), Pasadena, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1543728

Grant/Contract Number:  

SC0004993

Resource Type:

Accepted Manuscript

Journal Name:

Journal of the American Chemical Society

Additional Journal Information:

Journal Volume: 140; Journal Issue: 48; Journal ID: ISSN 0002-7863

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Chemistry