LAUSR

Large scale development of the 2D transition metal di-chalcogenides (TMDC) relies on landmark improvement in performances which could emerge from nanostructuration. Using p-WS 2 nanoflakes with different degrees of exfoliation and fracturing, we provide here perspectives to develop high surface area 2D p-WS 2 films for the photocatalytic hydrogen generation. We first demonstrate the critical role of inter-nanoflakes contacts within high surface area 2D films highlighting the benefit of plane/plane vs edge/plane contacts. We provide evidence of the high density of surface states displayed by these 2D films from electrochemical measurements. In addition to operate as recombination centres, the surface states were shown to give rise to deleterious Fermi level pinning (FLP) which dramatically decreases the efficiency of charge carrier separation. Lastly, promising strategies yielding FLP suppression via surface states modification are 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 are fabricated with the above pre-requisites, i.e. a high proportion of plane/plane contacts and a successful surface states chemical modification, a photocurrent up to 4.5 mA cm -2 was achieved for the first time on 2D p-WS 2 photocathodes for hydrogen generation.