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 MoS2, amorphous
MoSx, 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.