Unraveling Hydrogen Evolution in Ni-Doped SnSe: Mechanistic Insights into the Synergy of Crystal Facets, Doping, and External Stimuli Using On-Chip Microelectrochemical Cell

Understanding electrocatalytic processes at the microscale in 2D-layered architectures is crucial for catalyst design and investigating underlying mechanisms. In this study, pristine and nickel (Ni)-doped tin selenide (SnSe) flakes are analyzed using on-chip microelectrochemical measurements to explore the effects of defect and facet engineering on their hydrogen evolution reaction (HER) activity. The catalytic activity is found to be influenced by the exposed crystal facets, with the edges exhibiting higher activity than the basal planes. Deliberately exposing the (010) planes of SnSe flakes, having the highest density of dangling bonds, results in a noticeable improvement in HER performance. Additionally, Ni doping in SnSe enhances the HER performance by reducing the overpotential value required to achieve a current density of 100 mA cm⁻² from 231 ± 24 to just 89 ± 35 mV versus the reversible hydrogen electrode, which is attributed to an increased number of active sites and lower semiconductor/electrolyte barrier height. Ni doping also induces a transition in p-type SnSe to n-type by substituting Sn sites and occupying Sn vacancies, which facilitates enhanced HER kinetics with ~ three times enhancement in current density. External electric fields and photoirradiation further modulate HER kinetics, highlighting the potential for tuning SnSe and similar 2D materials for electrocatalytic applications.