Revealing the Contribution of Individual Factors to Hydrogen Evolution Reaction Catalytic Activity

Abstract

For the electrochemical hydrogen evolution reaction (HER), the electrical properties of catalysts can play an important role in influencing the overall catalytic activity. This is particularly important for semiconducting HER catalysts such as MoS , which has been extensively studied over the last decade. Herein, on-chip microreactors on two model catalysts, semiconducting MoS and semimetallic WTe , are employed to extract the effects of individual factors and study their relations with the HER catalytic activity. It is shown that electron injection at the catalyst/current collector interface and intralayer and interlayer charge transport within the catalyst can be more important than thermodynamic energy considerations. For WTe , the site-dependent activities and the relations of the pure thermodynamics to the overall activity are measured and established, as the microreactors allow precise measurements of the type and area of the catalytic sites. The approach presents opportunities to study electrochemical reactions systematically to help establish rational design principles for future electrocatalysts.

Unveiling the Interfacial Effects for Enhanced Hydrogen Evolution Reaction on MoS2/WTe2 Hybrid Structures

“…Indeed, several studies have shown varying HER activities by interfacing MoS 2 flakes with different supports . Our previous results also showed that a graphene heterostructured contact (MoS 2 /graphene heterostructure) yielded a 100 mV decrease in overpotential at 10 mA cm −2 as compared to graphene edge contacts . Thus, establishing a clear understanding of precisely what effects the interface has on modulating the HER activities of MoS 2 is critical …”

“…The relatively close Fermi level alignment between MoS 2 and WTe 2 leads to a lower Schottky barrier at the MoS 2 ‐WTe 2 interface, compared to an interface between MoS 2 and common metal electrodes . A lower Schottky barrier can improve HER activity by promoting efficient electron injection at the interface . Figure b illustrates the microreactor fabricated for HER measurements.…”

“…The MoS 2 ‐WTe 2 heterostructure was constructed by stacking a chemical vapor deposited (CVD) monolayer MoS 2 flake on a mechanically exfoliated WTe 2 flake. Since we previously report that WTe 2 is catalytically active for the HER, we ensured that only MoS 2 was exposed to the electrolyte during the measurement of the heterostructured devices. Comparison between the devices allows us to isolate the effect of the interface from the effect of the Schottky barrier.…”

“…However, Δ G H alone does not determine the overall HER activity; charge injection into MoS 2 has a large effect on catalytic efficiency . Our previous work demonstrated that a Schottky barrier, a tunnel barrier for an electron at the interface between semiconducting MoS 2 and its conducting support, can suppress MoS 2 catalytic activity due to inefficient charge injection . Additionally, for monolayer TMDs, the local environment can significantly modulate the electronic band structure and electron transport dynamics .…”

“…Additionally, for monolayer TMDs, the local environment can significantly modulate the electronic band structure and electron transport dynamics . For monolayer MoS 2 , the immediately adjacent support can change multiple factors that affect HER, such as Δ G H , the doping level of MoS 2 , and the Schottky barrier height . Indeed, several studies have shown varying HER activities by interfacing MoS 2 flakes with different supports .…”