Layered Noble Metal Dichalcogenides: Tailoring Electrochemical and Catalytic Properties.

Owing to the anisotropic nature, layered transition metal dichalcogenides (TMDs) have captured tremendous attention for their promising uses in a plethora of applications. Currently, bulk of the research is centered on Group 6 TMDs. Layered noble metal dichalcogenides, in particular the noble metal tellurides, belong to a subset of Group 10 TMDs, wherein the transition metal is a noble metal of either palladium or platinum. We address here a lack of contemporary knowledge on these compounds by providing a comprehensive study on the electrochemistry of layered noble metal tellurides, PdTe2 and PtTe2 , and their efficiency as electrocatalysts toward the hydrogen evolution reaction (HER). Observed parallels in the electrochemical peaks of the noble metal tellurides are traced to the tellurium electrochemistry. PdTe2 and PtTe2 can be discriminated by their distinct reduction peaks in the first cathodic scans. Considering the influence of the metal component, PtTe2 outperforms PdTe2 in aspects of charge transfer and electrocatalysis. The heterogeneous electron transfer (HET) rate of PtTe2 is an order of magnitude faster than PdTe2 , and a lower HER overpotential of 0.54 V versus reversible hydrogen electrode (RHE) at a current density of -10 mA cm-2 is evident in PtTe2 . On PdTe2 and PtTe2 surfaces, adsorption via the Volmer process has been identified as the limiting step for HER. A general phenomenon for the noble metal tellurides is that faster HET rates are observed upon electrochemical reductive pretreatment, whereas slower HET rates occur when the noble metal tellurides are oxidized during pretreatment. PtTe2 becomes successfully activated for HER when subject to oxidative treatment, whereas oxidized or reduced PdTe2 shows a deactivated HER performance. These findings provide fundamental insights that are pivotal to advancing the field of the underemphasized TMDs. Furthermore, electrochemical tuning as a means to tailor specific properties of the TMDs is advantageous for the development of their future applications.