Bridging the Gap Between Bulk and Nanostructured Photoelectrodes: The Impact of Surface States on the Electrocatalytic and Photoelectrochemical Properties of MoS2

Molybdenite (MoS2) is a material that has been previously studied for its photoelectrochemical properties in bulk form and, more recently, for its electrocatalytic hydrogen evolution properties in various nanostructured forms. Herein, we aim to address the properties of bulk and nanostructured MoS2 in order to assess the future potential of harnessing nanostructured MoS2 as a more efficient photocathode for photoelectrochemical hydrogen production. Using an in-situ method to progressively create defects at the surface of bulk MoS2, we show that losses due to recombination of photogenerated charge carriers at surface states occur concurrently with an enhancement in catalytic activity for hydrogen evolution. We further explore how these surface defects affect the measured flat-band potential, and we discuss the consequences of the distinct electronic properties of bulk versus nanostructured MoS2. Our results for MoS2 show that differences in morphological length scales (bulk vs nanoscale) give rise to unique surface properties that can greatly impact material performance and the represent key differences that researchers can leverage in order to develop more efficient nanoscaled photoelectrodes.