  Ammonium tetrathiomolybdate (ATM) spontaneously self assembles on Au
electrodes forming a hydrophilic, air stable, pH (3-11) tolerant multilayer
that is stable over a reasonably large potential window. The ATM functionalized
Au electrodes can adsorb iron porphyrin catalysts and act as O2 reducing
electrodes. These electrodes are stable enough to perform rotating disk
electrochemistry (RDE) as well as rotating ring disk electrochemistry (RRDE)
experiments. The X-ray photoelectron spectroscopy (XPS) data indicate that the
sulphide atoms of ATM anchors a single ATM layer on to Au and the subsequent
layers grow vertically due to the presence of hydrogen bonding NH4+
counter-ions. The formation and growth of these ATM adlayers is investigated
using atomic force microscopy (AFM), scanning electron microscopy (SEM) and a
series of electrochemical data. The ATM functionalized Au electrodes have
double layer capacitance comparable to those reported for Au electrode bearing
short chain alkyl thiol self assembled monolayer (SAM). Importantly, the rate
of interfacial charge transfer (CT) can be tuned by controlling the thickness
of the adlayers by simply adjusting the deposition time. Importantly the
kinetics of a catalyst adsorbed on this ATM adlayer can be switched from mass
transfer limited to CT limited regime by adjusting the deposition time.
