Catalyzing the Hydrogen Evolution Reaction (HER) with Molybdenum Sulfide Nanomaterials

Abstract

We discuss recent developments in nanostructured molybdenum sulfide catalysts for the electrochemical hydrogen evolution reaction. To develop a framework for performing consistent and meaningful comparisons between catalysts, we review standard experimental methodologies for measuring catalyst performance and define two metrics used in this perspective for comparing catalyst activity: the turnover frequency, an intrinsic activity metric, and the total electrode activity, a device-oriented activity metric. We discuss general strategies for synthesizing catalysts with improved activity, namely, increasing the number of electrically accessible active sites or increasing the turnover frequency of each site. Then we consider a number of state-of-the-art molybdenum sulfide catalysts, including crystalline MoS 2 , amorphous MoS x , and molecular cluster materials, to highlight these strategies in practice. Comparing these catalysts reveals that most of the molybdenum sulfide catalysts have similar active site turnover frequencies, so the total electrode activity is primarily determined by the number of accessible active sites per geometric electrode area. Emerging strategies to overcome current catalyst limitations and potential applications for molybdenum sulfide catalysts including photoelectrochemical water splitting devices and electrolyzers are also considered.

Standards and Protocols for Data Acquisition and Reporting for Studies of the Electrochemical Reduction of Carbon Dioxide

“…However, normalizing the measured activity by the electrochemically active surface area is a straightforward way to normalize catalytic activity that is meaningful and applicable to a wide variety of different electrocatalysts. 55 The electrochemically active surface area (ECSA) of a electrocatalytic material can be estimated by measuring the double-layer capacitance of the electrode-electrolyte interface. 56 The double layer capacitance can be measured by conducting cyclic voltammetry (CV) in a potential range where no Faradaic processes occur, typically a 100 mV window centered at the opencircuit potential (OCP).…”

Recent Advances in Transition-Metal-Mediated Electrocatalytic CO2 Reduction: From Homogeneous to Heterogeneous Systems

“…Due to the metallic character and a high d-electron density, the Mo-terminated edges are the main characteristic related to its catalytic performance (Figure 4e-g). A thorough review on this material family was conducted by Jaramillo et al, so this review does not go into any details [43]. …”

Hydrogen evolution activity of individual mono-, bi-, and few-layer MoS 2 towards photocatalysis

“…across heterojunctions (2), the transport of charge carriers to active sites (3) and the catalytic activity (4). Parameters (1)(2)(3) are reasonably well fulfilled in TMDs and their heterostructures.…”

“…One route to fulfill these challenges is the combination of an efficient solar energy conversion and the storage in chemical energy e.g. in hydrogen gas produced by the catalytic splitting of water [3,4]. The most efficient catalysts for the electrochemical hydrogen evolution reaction (HER) are rare and expensive noble metals such as Pt, with the electricity optionally delivered from solar cells [5].…”

“…The most efficient catalysts for the electrochemical hydrogen evolution reaction (HER) are rare and expensive noble metals such as Pt, with the electricity optionally delivered from solar cells [5]. In contrast, atomically thin, two-dimensional semiconducting transition metal dichalcogenides (TMDs), such as MoS 2 , offer the unique combination of a band gap in the visible range of about 1.9 eV for monolayers [6][7][8], high sunlight absorption of up to 15% [9][10][11], catalytically active sites for HER [4,[12][13][14][15][16] or CO 2 -reduction [17] and photocatalytic stability under harsh reaction conditions [18]. Moreover, semiconducting TMDs are earth abundant, inexpensive, and sustainable (photo-)catalysts which can be combined in lateral or vertical heterostructures [19][20][21][22].…”