Evaluating the Hydrogen Evolution Reaction Activity of Colloidally Prepared PtSe₂ and PtTe₂ Catalysts in an Alkaline Medium

Abstract

The hydrogen evolution reaction (HER) in alkaline electrolytes using transition metal dichalcogenides is a research area that is not tapped into. Alkaline HER ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow> <mml:msub><mml:mrow><mml:mn>2</mml:mn> <mml:mi>H</mml:mi></mml:mrow> <mml:mn>2</mml:mn></mml:msub> <mml:mi>O</mml:mi> <mml:mo>+</mml:mo> <mml:mn>2</mml:mn> <mml:msup><mml:mrow><mml:mi>e</mml:mi> <mml:mspace></mml:mspace></mml:mrow> <mml:mo>-</mml:mo></mml:msup> <mml:mo>→</mml:mo> <mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mo>+</mml:mo> <mml:msup><mml:mrow><mml:mi>O</mml:mi> <mml:mi>H</mml:mi></mml:mrow> <mml:mo>-</mml:mo></mml:msup> <mml:mspace></mml:mspace></mml:mrow> <mml:annotation>${{2H}_{2}O+2{e\ }^{-}\to {H}_{2}+{OH}^{-}{\rm \ }}$</mml:annotation> </mml:semantics> </mml:math> ) is harder to achieve relative to acidic HER ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow> <mml:msup><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mo>+</mml:mo></mml:msup> <mml:mo>+</mml:mo> <mml:mn>2</mml:mn> <mml:msup><mml:mrow><mml:mi>e</mml:mi> <mml:mspace></mml:mspace></mml:mrow> <mml:mo>-</mml:mo></mml:msup> <mml:mo>→</mml:mo> <mml:mspace></mml:mspace> <mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> <mml:annotation>${{H}^{+}+2{e\ }^{-}\to \ {H}_{2}}$</mml:annotation> </mml:semantics> </mml:math> ), this is attributed to the additional water dissociation step that occurs in basic HER to generate H⁺ ions. In fact, for most catalysts, their HER activity decreases tremendously when the electrolyte is changed from acidic to basic conditions. Platinum dichalcogenides, PtX₂ (X=S, Se, Te), are an interesting member of transition metal dichalcogenides (TMDs) as these show an immense hybridization of the Pt d orbitals and chalcogen p orbitals because of closely correlated orbital energies. The trend in electronic properties of these materials changes drastically as the chalcogen is changed, with PtS₂ reported to exhibit semi-conductor properties, PtSe₂ is semi-metallic or semi-conductive, depending on the number of layers, while PtTe₂ is metallic. The effect of varying the chalcogen atom on the HER activity of Pt dichalcogenides will be studied. Pt dichalcogenides have previously been prepared by direct high-temperature chalcogen deposition of Pt substrate and evaluated as electrocatalysts for HER in H₂SO₄. The previously employed synthesis procedures for PtX₂ limit these compounds' mass production and post-synthesis treatment. In this study, we demonstrated, for the first time the preparation of PtSe₂ and PtTe₂ by colloidal synthesis. Colloidal synthesis offers the possibility of large-scale synthesis of materials and affords the employment of the colloids at various concentrations in ink formulation. The electrochemical HER results acquired in 1 M KOH indicate that PtTe₂ has a superior HER catalytic activity to PtSe₂. A potential of 108 mV for PtTe₂ and 161 mV for PtSe₂ is required to produce a current density of -10 mA cm^-2 from these catalysts. PtTe₂ has a low Tafel slope of 79 mVdec^-1, indicating faster HER kinetics on PtTe₂. Nonetheless, the stability of these catalysts in an alkaline medium needs to be improved to render them excellent HER electrocatalysts.