Catalysts for the hydrogen evolution reaction in alkaline medium: Configuring a cooperative mechanism at the Ag-Ag$_2$S-MoS$_2$ interface

TL;DR

This paper reports a novel Ag@MoS2 core-shell catalyst that enhances hydrogen evolution in alkaline media by leveraging interface cooperativity and defect engineering, advancing catalyst design for the hydrogen economy.

Contribution

It introduces a hybrid Ag@MoS2 structure with engineered interfaces and defects that significantly improves HER activity in alkaline conditions.

Findings

Enhanced HER activity in alkaline media due to interface cooperativity.

Charge transfer between core and shell facilitates water dissociation.

Defective MoS2 shell promotes hydrogen recombination.

Abstract

Designing electrocatalysts for HER in alkaline conditions to overcome the sluggish kinetics associated with the additional water dissociation step is a recognized challenge in promoting the hydrogen economy. To this end, delicately tuning the atomic-scale structure and surface composition of nanoparticles is a common strategy and, specifically, making use of hybrid structures, can produce synergistic effects that lead to highly active catalysts. Here, we present a core-shell catalyst of Ag@MoS$_2$ that shows promising results towards the hydrogen evolution reaction (HER) in both 0.5 M H2SO4 and 0.5 M KOH. In this hybrid structure, the MoS$_2$ shell is strained and defective, and charge transfer occurs between the conductive core and the shell, contributing to the electrocatalytic activity. The shelling process results in a large fraction of Ag$_2$S in the cores, and adjusting the relative fractions of Ag, Ag$_2$S, and MoS$_2$ leads to improved catalytic activity and fast charge-transfer kinetics. We suggest that the enhancement of alkaline HER is associated with a cooperative effect of the interfaces, where the Ag(I) sites in Ag$_2$S drive the water dissociation step, and the formed hydrogen subsequently recombines on the defective MoS$_2$ shell. This study demonstrates the benefits of hybrid structures as functional nanomaterials and provides a scheme to activate MoS$_2$ for HER in alkaline conditions.