Mitigation of Edge and Surface States Effects in Two‐Dimensional WS₂ for Photocatalytic H₂ Generation

Abstract

Large scale development of the 2D transition metal dichalcogenides (TMDC) relies on landmark improvement in performance, which could emerge from nanostructuration. Using p-WS 2 nanoflakes with different degrees of exfoliation and fracturing, perspectives were provided to develop highsurface-area 2D p-WS 2 films for the photocatalytic hydrogen generation. The critical role of inter-nanoflakes contacts within high-surface-area 2D films was demonstrated, highlighting the benefit of plane/plane versus edge/plane contacts. Evidence of the high density of surface states displayed by these 2D films was provided through electrochemical measurements. In addition to operating as recombination centers, the surface states were shown to give rise to deleterious Fermi-level pinning (FLP), which dramatically decreased the efficiency of charge carrier separation. Lastly, promising strategies yielding FLP suppression via surface states modification were proposed. In particular, use of a multifunctional ultrathin film displaying healing, catalytic, and n-type semiconduction properties was shown to greatly enhance charge carrier separation and transport to the photo-electrode/electrolyte interface. When the 2D photoelectrodes were fabricated with the above prerequisites (i. e., a high proportion of plane/plane contacts and a successful surface states chemical modification), a photocurrent up to 4.5 mA cm À 2 was achieved for the first time on 2D p-WS 2 photocathodes for hydrogen generation.

Molybdenum sulfo-selenide nanocomposites with carbon nanotubes and reduced graphene oxide for photocatalytic hydrogen evolution reaction

“…Since the discovery of graphene with novel properties, 24,25 two-dimensional (2D) transition metal dichalcogenides (TMDCs) have gained more importance due to their wide range of applications ranging from electronics 26,27 to catalysis. 28,29 The library of 2D TMDCs, including MoS 2 , 30 MoSe 2 , 31 WS 2 , 32 WSe 2 , 33 and MoTe 2 , 34 has been utilized in various photocatalytic/electrocatalytic applications due to their suitable physicochemical characteristics including large surface area, earth-abundant characteristics, and chemical inertness. 35 Normally, three processes are involved in photocatalytic water splitting: (1) light absorption by a catalyst, (2) charge-carrier generation/separation, and lastly (3) redox reactions at the catalyst's surface.…”