Edge selenium-doped graphene nanoplatelets as durable metal-free cathodes for iodine reduction reaction in dye-sensitized solar cells

Metal-free carbon-based electrocatalysts for dye-sensitized solar cells (DSSCs) are sufficiently active in Co(II)/Co(III) electrolytes, but are not satisfactory in the traditional iodide/triiodide (I-/I3-) electrolyte. Thus, the active and stable metal-free carbon-based catalysts in both electrolytes are highly needed. Here, we report the synthesis of edge-selenated graphene nanoplatelets (SeGnPs) and its electrocatalytic activities in both Co(II)/Co(III) and I-/I3- electrolytes for DSSCs. The SeGnPs can be prepared by a simple mechanochemical reaction between graphite and Se powders, and the edge-selective doping and preservation of the pristine graphene basal plane in the SeGnPs were confirmed by various analytical techniques, including atomic-resolution transmission electron microscopy (AR-TEM). Tested as counter electrode (CE) for DSSCs in both Co(bpy)32+/3+ (bpy=2,2'-bipyridine) and I-/I3- electrolytes, the SeGnP-CEs exhibited outstanding electrocatalytic activity with an ultimately high stability. Furthermore, the I3- reduction mechanism, which has not been fully understood on carbon-based CE materials to date, was clarified by an electrochemical kinetics study combined with density functional theory (DFT) and non-equilibrium Green???s function (NEGF) calculations